Standardization Center
Replaces NEN 3650:1992; NEN 3650:1992/C:1996; NEN 3650-1:2001 Draft; NTA 8000:2000; NEN 3652:1998, in part. Replaces NEN 3650:1992 together with
NEN 3650-2:2003 K1-6 inclusive
Netherlands Standards
NEN 3650-1 (nl)
Requirements for Pipeline Systems– Part 1:
General
Section 1: Chapters 1-7 inclusive
ICS 23.040.10
July 2003
Netherlands Standardization Institute
Standards Commission 310 004 “Transport Pipelines” Apart from exceptions provided by the law, nothing from this publication may be duplicated and/or published by means of photocopy, microfilm, storage in computer files or otherwise, which also applies to full or partial processing, without the written consent of the Netherlands Standardization Institute
Although the utmost care has been taken with this publication, errors and omissions cannot be entirely excluded. The Netherlands Standardization Institute and/or the members of the committees therefore accept no liability, not even for direct or indirect damage, occurring due to or in relation with the application of publications issued by the Netherlands Standardization Institute.
The Netherlands Standardization Institute shall, with the exclusion of any other beneficiary, collect payments owed by third parties for duplication and/or act in and out of law, where this authority is not transferred or falls by right to the Reproduction Rights Foundation
NEN © 2003 Netherlands Standardization Institute P.O. Box 5059, 2600 DB Delft Telephone: (015) 2 690 390, Fax (015) 2690 190
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NEN 3650-1:2003
Contents – NEN 3650-1 Chapter 1 Subject and Area of Application ....................................................................................... Section 1
Chapter 2 Reference Standards......................................................................................................... Section 1
Chapter 3 Terms and Definitions ....................................................................................................... Section 1
Chapter 4 Symbols............................................................................................................................. Section 1
Chapter 5 Abbreviations .................................................................................................................... Section 1
Chapter 6 Safety ............................................................................................................................... Section 1
Chapter 7 Process Safety Conditions ............................................................................................... Section 1
Chapter 8 Construction Design …… ................................................................................................. Section 2
Chapter 9 Type (land-based) ............................................................................................................ Section 2
Chapter 10 Operation and Termination of Operations ....................................................................... Section 3
Chapter 11 Offshore Pipeline ............................................................................................................ Section 3
Appendix A (standard) Groups of pipeline systems ...........................................................................Section 3
Appendix B (standard) Design aspects – Design data ........................................................................Section 3
Appendix C (standard) Design aspects – Loading .............................................................................Section 4
Appendix D (standard) Design aspects–Tension and deformation through loading........................... Section 5
Appendix E (standard) Type with HDD-calculation ............................................................................Section 5
Appendix F (standard) Offshore pipeline aspects ..............................................................................Section 6
Appendix G (standard) Grooveless Techniques .................................................................................Section 6
Appendix H (Informational) Design aspects – Pipeline land routes ....................................................Section 6
Appendix I (Informational) Design aspects – Field data .....................................................................Section 6
Appendix J (Informational) Pipeline Systems and European Machine Guidelines 98/37/EC ............ Section 6
Appendix K (Informational) Sphere of Action Pressure Apparatus .....................................................Section 6
Bibliography .......................................................................................................................................Section 6
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Contents – Section 1 Foreword........................................................................................................................................................ 4 1 Subject and area of application ................................................................................................................ 5 2 Reference standards.................................................................................................................................. 8 3 Terms and definitions ................................................................................................................................ 9 3.1 General ..................................................................................................................................................... 9 3.2 Pipeline systems ......................................................................................................................................10 3.3 Operations - Technical Definitions And Concepts ....................................................................................12 4 Symbols ....................................................................................................................................................13 4.1 Mechanical dimensional units ..................................................................................................................13 4.2 Material dimensional units........................................................................................................................13 4.3 Process dimensional units........................................................................................................................13 4.4 Stress Dimensional Units .........................................................................................................................14 4.5 Soil survey dimensional units ...................................................................................................................14 5. Abbreviations ...........................................................................................................................................15 6. Safety ........................................................................................................................................................16 6.1 General ....................................................................................................................................................16 6.1.1 Field of application ................................................................................................................................16 6.1.2 Basic principles .....................................................................................................................................16 6.1.3 Safety aspects to be considered ...........................................................................................................16 6.1.4 Hazardous substances..........................................................................................................................16 6.1.5 Safety - minimum pipeline depth ...........................................................................................................16 6.2 Required Safety Level..............................................................................................................................16 6.2.1 External safety ......................................................................................................................................16 6.2.2 Environment .........................................................................................................................................16 6.2.3 Water Management safety ...................................................................................................................17 6.3 Safety evaluation - external safety ...........................................................................................................17 6.3.1 Field of application and purpose ..........................................................................................................17 6.3.2 Content of safety evaluation..................................................................................................................17 6.3.3 Causes of failure and determining the probability of failure..................................................................18 6.3.3.1 Causes of failure ................................................................................................................................18 6.3.3.2 Quantifying the probability of failure ...................................................................................................19 6.3.4 Quantifying the effects of product loss ..................................................................................................19 6.3.4.1 General ..............................................................................................................................................19 6.3.4.2 Accident scenarios with product loss .................................................................................................19 6.3.5 Determining Risk Contours ...................................................................................................................20 6.3.6 The environment - identifying problem areas ........................................................................................20 6.3.6.1 General ..............................................................................................................................................20 6.3.7 Risk-limiting measures ..........................................................................................................................20 6.3.7.1 General ..............................................................................................................................................20 6.3.7.2 Risk reduction by limiting probability of failure....................................................................................21 6.3.7.3 Risk reduction by limiting effects ........................................................................................................22 6.4 Environmental Impact Evaluation (land) .................................................................................................22 6.4.1 Sensitive areas......................................................................................................................................22 6.4.2 Requirements for ground-water protected areas...................................................................................22 6.4.3 Designing the Route..............................................................................................................................22 6.4.4 MER………………… .............................................................................................................................22 6.5 Water Management Project Safety ..........................................................................................................23 6.5.1 Fundamentals .......................................................................................................................................23 6.5.2 NEN 3651..............................................................................................................................................23 6.5.3 Significant Water Management Project .................................................................................................23 6.5.4 Railways................................................................................................................................................23 7 Process Safety Conditions.......................................................................................................................24 7.1 General ....................................................................................................................................................24
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7.1.1 System requirements ............................................................................................................................24 7.1.2 Design conditions..................................................................................................................................24 7.1.3 Hydraulic calculations ...........................................................................................................................24 7.2 Control of process conditions ..................................................................................................................24 7.3 Pressure Control ......................................................................................................................................24 7.3.1 General .................................................................................................................................................24 7.3.2 Pressure regulating system...................................................................................................................25 7.3.3 Pressure alarm system .........................................................................................................................25 7.3.4 Pressure control system........................................................................................................................25 7.3.5 Pressure control for pipeline grid...........................................................................................................27 7.4 Pressure Control Design ..........................................................................................................................28 7.4.1 Pressure Control – Venting ...................................................................................................................28 7.4.2 Pressure Control – Non-Venting ...........................................................................................................28 7.4.3 Instrumentation .....................................................................................................................................29 7.4.4 Start-up and periodic controls ...............................................................................................................29 7.4.5 Test reporting ........................................................................................................................................30 7.4.6 Pressure Control System Documentation .............................................................................................30 7.5 Temperature control .................................................................................................................................30 7.5.1 Temperature regulation of heat transfer systems..................................................................................31 7.5.1.1 Introduction ........................................................................................................................................31 7.5.1.2 Regulation principles ..........................................................................................................................31 7.6 Medium ....................................................................................................................................................32
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Foreword This standard is a revision of NEN 3650:1992. Besides steel pipe which was the hallmark of the 1992 publication, this edition includes other pipeline materials. The standard is divided into parts. The first part includes general requirements for pipeline systems. The parts that follow include requirements specific to the pipeline material dealt with in that section, NEN 3650-2:2003 Steel, Draft NEN 3650-3:2003 Synthetics, Draft NEN 3650-4:2003 Concrete, and Draft NEN 3650-5:2003 Cast Iron. The standards series has been drawn up under the aegis of the Netherlands Standards Commission 310004 ‘Transport pipelines’. NEN 3650-1 has the status of a national standard. The section includes general guidelines from the earlier NEN 3650:1992 and NEN 3650:1998. Material-specific requirements are included in the relevant sections dealing with those materials. Additions are made to general regulations whenever the use of materials other than steel makes this necessary. Some standards have been withdrawn, as requirements have been adjusted from the standpoint of technological progress, namely, with respect to the “total life-cycle” approach to external security (risk-control during design, installment, maintenance and shut-down), design calculation and the relation to (European and international) standards and directives. New attention is now being paid to the choice of route, articulated pipelines, offshore pipelines and grooveless techniques. A probabilistic approach was applied to structural design, where assumptions are made about various loadings (internal and external) and properties of materials. Via a model calculation, the effects on the structure are determined, which must be compared with the minimal limit values and boundary conditions. Backgrounds of the new calculation methods are covered in a supplement to NPR 3659:1996/A1:2003. Appendices A,B,C,D,E,F and G are the components of which this standard consists. Appendixes H,I,J and K are informational components of this standard. Because the Figures in this standard are in large part adopted from the old standards, and the additions were made outside NEN, the standards and editing rules for technical drawings have not been completely followed – which can be seen from the captions to the Figures. In the text part of the standard, however, correct standards were utilized. Revision of Standard NEN 3650-2 is divided into Sections. There is an annual review to determine whether or not the revision of one or more Sections is necessary. The content of each Section is examined minimally once every 5 years. Proposals for revision must be submitted in writing to NEN. Purpose of the Standard The purpose of the Standard-series is to obtain underground pipeline systems safe for people, the environment and property, by making requirements for the design, installation, start-up and shut-down of pipeline operations that will guarantee a durable, effective, and efficient system. This demands safety regulations. Deviation from the (fixed) regulations of this standard is only possible, if it can be shown that the same or higher level of safety will be otherwise attained. Interface EN- and ISO standards Relative to the relevant EN standards for the pipeline-technical domain, this standard adds additional details for conditions in the Netherlands. The stipulations of this standard, including the adopted revisions according to NEN-EN 1594:2000 and ISO 13623:2000, are applicable to pipelines, in that this is also in compliance with the stipulations of NEN-EN 1594:2000 and ISO 13623:2000. Use of Standard The people applying the standard, must be familiar with the materials employed and be in possession of the relevant expertise. The designer, builder or user of the pipeline system is reminded that this standard is not a design specification nor a handbook.
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1 Subject and Area of Application This standard specifies the safety requirements related to the safety of people, the environment and property, which are requirements for the design, installation, operation, and shutdown of pipeline systems. These requirements relate to pipeline systems for transport of substances both by land and sea, and hold for newly built systems and for the modification of existing systems. All work involving design, installation, operation, and shutdown must be carried out by qualified persons. Application of the quality guarantee system, as per EN-ISO 9001 or NEN-EN-8S0 14001, is strongly recommended. The Standard is applicable to Group I and Group II pipeline systems (see Figure 1): a) The function of Group I pipeline systems is to transport hazardous substances (see A.2.1) both by land and by
sea. For Group I, the entire pipelines system as a whole must satisfy the requirements of the Standard; b) Group II pipeline systems (see A.2.2) are for transporting substances other than in a). For Group II, the application
of the standard is limited to pipeline in or near significant water management projects and pipelines located in ground-water protection areas.
COMMENT 1 Pipeline systems consist of pipelines and stations. The pipeline can be a transport pipeline, a distribution pipeline, as well as a collector pipeline. No distinction is made between them in the Standard. COMMENT 2 Stations and other pipelines or pipeline sections of a Group II system, because they are located in b), are not subject to this Standard. COMMENT 3 It is assumed that the management of Group II systems is such that the standards governing design which were in force during the installation of the pipeline, will not be modified during the pipeline life-cycle. This is already guaranteed for Group I systems by the application of the Standard as a whole. The Standard also holds for existing pipelines or systems with regard to: - management of Group I systems; - modification of design conditions (temperature, pressure, medium). The Standard has no requirements for: - pipes for installations connecting Group I systems, except for ancillary equipment which are components of the
(pressure) containment of the system. Figure 1 shows a flow chart of the Groups in relation to the standard(s). Figure 2 provides a schematic of pipeline (system)s subject to the standard.
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GROUP I Intrinsically hazardous substance (conforming with A.2.1): • oxidizing • very flammable • inflammable • (very) toxic • warm water under law governing steam
GROUP II Substance only hazardous if released (conforming with A.2.2): • natural gas (S1.6 MPa, local transport, distribution); • non-flammable gas • water, waste water; • warm water not under law governing steam
YES YES NO
Location Pipeline • In or near important water management areas YES NO
Type of Medium • Water, not a groundwater load, (drinking water, gray water, rainwater, warm water).
NO YES
Pipeline Section Location • In or near important
ground-water protected areas
YES NO
NEN 3650-series (requirements for pipeline including ancillary equipment components of containment system) NEN 3650-1 general: • safety calculations • design • installation of new pipeline • control • revision of design conditions
NO NEN 3650 pipeline sections Other options – standards for: • drinking water provision • gas distribution • heating distribution (city heating) • sewage (waste water techniques).
Specific material specifications: • steel ⇒ NEN 3650-2 • synthetic ⇒ NEN 3650-3 • concrete ⇒ NEN 3650-4 • cast iron ⇒ NEN 3650-5
Traversing significant water management projects (all media and materials): NEN 3651 • Supplementary requirements to the NEN 3650 series.
Figure 1 – Flow Chart of Standards and Group Breakdown
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Figure 2 – Areas Of Application Of The Standard
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2 Reference Standards The following standardization documents include provisions which, since they are referenced, are likewise provisions of this standard. As this standard is going to print, the cited versions were in force. All standards documents can however be modified; it is therefore recommended that parties which make agreements on the basis of this Standard, try to apply the most recent version of the standards documents cited below. NEN 1010:2000 Safety provisions for low voltage installations (complete version) NEN 1014:1992 Lightning protection NEN 1041:1982 Safety provisions for high voltage installations NEN 1059:1994 Requirements for gas pressure regulating and measuring stations with an inlet pressure lower than 100 bar, along with the page of revisions NEN 1059/A1:1999 NEN 1059:2002 Draft National explanatory note and supplement to NEN-EN 12186 and
NEN-EN 12279 – Gas provision systems – gas pressure regulating stations for transport and distribution
NPR 2760:1991 The mutual influence of pipelines and high-voltage connections NEN 3011:1986 Safety colors and symbols NEN 3650-2:2003 Requirements for pipelines systems – Part 2: Steel NEN 3650-3:2003 Draft Requirements for pipelines systems – Part 3: Synthetic NEN 3650-4:2003 Draft Requirements for pipelines systems – Part 4: Concrete NEN 3650-5:2003 Draft Requirements for pipelines systems – Part 5: Cast Iron NEN 3651:2003 Supplementary requirements for pipelines that traverse important water management projects NPR 3659:1996/A1:2003 Underground pipelines – Basis for strength calculations NEN 6740:1991 Geotechnical – TGB 1990 – Basic requirements and loading NEN-EN 1594:2000 Gas – pipeline systems for maximal operating pressure greater than 16 bar – functional requirements NVN-ENV 1991-3:1995 Eurocode 1: Design principles and loading structures – Part 3: Traffic loads on bridges NEN-EN 12186:2000 Gas provision systems – gas pressure regulating stations for gas transport and distribution – Functional requirements NEN-EN 12583:200 Gas Provision systems – Compressor Station – Functional requirements NEN 12889:2000 Outside sewage – Installation and testing of piping for grooveless techniques NEN-EN-ISO 9001:2000 Quality Control systems – requirements NEN-EN-ISO 14001:1996 Environmental Protection systems – requirements and guidelines for use NEN-EN-IEC 60079 Electrical equipment for use in areas of potential gas explosions (all sections)
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NEN-EN-IEC 61508-5:2002 Operating safety of electrically/electronically programmable electronic
systems related to safety – Section 5: Examples of methods for determining levels of safety.
NEN-ISO 13686-1998 Natural gas – identification of quality NPR-ISO 14004:1997 Environmental protection – General guidelines for the principles, systems and supporting techniques. ISO 2394: 1998 General principles of reliability for structures ISO 13623: 2000 Petroleum and natural gas industries – Pipeline transportation systems 3 Terms and definitions 3.1 General 3.1.1 Installation Phase Pipeline System the phase in which the delivery, transport, processing, and connection of pipes, laying down, burying, testing and bringing on line takes place 3.1.2 ALARA (As Low as Reasonably Achievable) principle Principle through which the best available technology is applied, and where all relevant (technical, economic, and social) concerns are taken into account and weighed against environmental concerns and external security 3.1.3 Pipeline Corridor A pipeline stretch which is primarily used for laying pipe, if necessary with the civil engineering work under government aegis 3.1.4 Pipeline Stretch A stretch of land reserved by plan for laying down pipelines, which is included in the regional and end-use plan COMMENT In Rotterdam, pipeline stretches are created and managed as pipeline corridors and as such are regarded as pipeline corridor subject to this standard. 3.1.5 Operational Phase of a Pipeline System The phase after completion of the installation phase, regardless of whether the system is operational or not 3.1.6 External Safety Safety of persons in areas where hazardous substances are used 3.1.7 Hazardous Substances For The Environment (Pollution) Substances which, for example, pollute a ground-water protection zone, or brings about indirect damage as a result of causing dysfunction of a water management project. 3.1.8 Substances Hazardous to People Exposure of people to the substance can lead to injury or death.
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3.1.9 Group risk (GR) The yearly probability that a sizeable group of people will die in one occurrence as a result of some unusual event relating to the pipeline. 3.1.10 Incident An unplanned, uncontrolled event which might have resulted, but did not result in fatalities, illness, wounding or other lesion. 3.1.11 Local Risk (PR) The yearly probability that a person, continuously in a certain locality, will die as a result of some unusual event relating to the pipeline. 3.1.12 Pipeline Risk The product of the cause - and the effect of escape of the substance being transported 3.1.13 Environmental Protection Minimal probability of disturbing ecosystems, plants, animals, nature zones within the environment, and agricultural areas, aquifers, surface water for drinking, etc. but also the human experience of the natural environment 3.1.14 Water Management Safety Safety of a water management zone relating to the consequences of system failure for groups of people and/or animals and damage to property 3.2 Pipeline Systems 3.2.1 Pipeline Hollow pipe for the flow of gases, liquids or capsules, whose purpose is to transport a gas, a liquid or capsules, or a liquid used as a means to transport of heat or a dissolved or pulverized substance 3.2.2 Above-Ground Pipeline Pipeline whose placement or configuration, except at a defined number of points, is not hindered by pipe or conduit and/or by structural units, or by the terrain around it. 3.2.3 Pipeline System System consisting of one or more pipelines with their concomitant stations, whose purpose is the transport of media between locations 3.2.4 Pipeline Characteristics Pipeline Rigidity Behavior - axially rigid: pipeline elements are longitudinally inflexibly connected; moment, normal force and cross-sectional
force are transferred; - articulated: elements of pipe are connected with flexible couplings which allow some translation and/or rotation; - articulated, tension-resistant: elements of pipe are connected with flexible couplings resistant to tension; normal
force is transferred;
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- tangentially rigid: elements of pipe with high tangential rigidity (the effect of the slight deflection resulting from
horizontal support pressure is negligible); - tangentially flexible: elements of pipe with low tangential rigidity (extra horizontal support pressure through
ovalization or deflection). 3.2.5 Pipeline Elements Components of a pipeline system: - straight pipe and curved elements made by cold or warm bending; - fittings (connectors, Tee’s, elbows, flanges, convex bottoms, welding studs, mechanical couplers, etc.); - ancillary equipment (valves, expansion joints, dismantling joints, isolating couplings, safety apparatus, pressure
regulators, pumps, compressors, etc.); - structures (e.g., manifolds, “fingertype” liquid traps, PIG apparatus, blocking valve stations, gas measuring
stations, control section, etc.) 3.2.6 Installation Apparatus and facilities for the extraction, production, (chemical) treatment, storage or intake of the substances to be transported 3.2.7 Pipeline Path The path the pipeline takes COMMENT The path can be both horizontal and vertical. 3.2.8 Location The area, fenced in or not fenced in, in which one or more installations or stations are located 3.2.9 Pipe Sheath Protective pipe around the pipe transporting the medium 3.2.10 Medium The substance which is transported by the pipeline 3.2.11 Underground Pipeline Pipeline surrounded by earth. 3.2.12 Platform Structure for extraction and/or processing and/or transport of minerals including hydrocarbons and other related materials at sea 3.2.13 Station Structure, possibly including housing, for management of pipeline operations, such as: - valve stations containing the valves; - compressor- or pumping station; increasing the pressure of the medium (gas or liquid) in the pipeline;
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- sending-receiving station; sending and receiving “pigs’; - measuring and/or regulating station; measuring and/or regulating the flow rate and/or the pressure in the pipeline; - mixing station; mixing the various streams of media; - reducing station; lowering the pressure of the medium in the pipeline 3.2.14 Rising Pipe Vertical section of the offshore pipeline between the section lying on the seafloor and the connection to the platform 3.2.15 Offshore Pipeline Pipeline lying in maritime waters and estuaries, seaward of the average high-water line 3.3 Operations - Technical Definitions and Concepts 3.3.1 Installation Temperature Temperature of the pipe (section) during installation, after which it can no longer be changed without stress. COMMENT The installation temperature is in some cases artificially increased (pre-stressed) for pipe that will have to operate at high temperature. 3.3.2 Operating Pressure Internal pressure in a pipeline system, in order to bring about a certain throughput or buffer, or to maintain the same. COMMENT In general, this is internal pressure, necessary for the static performance level, friction- and local losses, and eventual desired end-pressure. 3.3.3 Operating Temperature Temperature inside a pipeline system that is the result of the system’s operation 3.3.4 Test Pressure Internal pressure in a pipeline system or a part of it, during a strength test or a vacuum test 3.3.5 Pressure Unless otherwise specified, pressure means overpressure 3.3.6 Incidental Pressure Incidental increase of pressure above the design pressure, limited to the maximum allowable incidental pressure 3.3.7 Design Pressure and Design Temperature Internal pressure and temperature (high or low) which together determine the strength calculations COMMENT The design pressure must be greater than or equal to the maximum operating pressure.
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3.3.8 Temperature Trajectory Absolute value of the difference between the two temperature extremes, such as can occur during a changeover, including considerations of operating- and environmental influences. 3.3.9 Changeover Transition from an assumed initial condition via the maximal (minimal) possible condition to the minimal (maximal) possible condition, and back again to the initial condition. 4. Symbols 4.1 Mechanical dimensional units A surface area of the pipeline cross-section mm2 De outside diameter of the pipeline mm Dg average diameter of the pipeline mm Di inside diameter of the pipeline mm Do = De + 2e outside diameter, plus the thickness of any eventual sheathing mm d minimum wall thickness taking into account factory tolerances mm dn nominal thickness to be chosen or applied from the table of measurements mm e thickness of the sheathing (corrosion sheathing, concrete wrapping, eventual marine accretions mm I or I2 inertial moment with respect to the center line mm4 Ip polar inertial moment mm4 Iw inertial moment of the pipeline wall mm4/mm Ix inertial moment with respect to an arbitrary line mm4 R radius of curvature mm re outside curvature mm fg average curvature mm ri inside curvature mm W resistance moment mm3 Ww moment of resistance of the pipeline wall mm3/mm 4.2 Material dimensional units E elasticity modulus of the pipeline material (20 °C) N/mm2 E (θ) elasticity modulus of the pipeline material at θ °C N/mm2 G frictional modulus N/mm2 αg linear expansion coefficient (average over temperature range) mm/mm·K θ, θt temperature of the pipeline material ° C υ Poisson constant - - ρ density kg/m3 4.3 Process dimensional units p internal overpressure MPa pd design pressure (overpressure) MPa pdv design pressure (overpressure) upstream of the pipeline system MPa pinc internal overpressure (incidental) MPa ∆H, ∆p pressure differential MPa v rate of flow of the medium m/s K compression modulus of the medium N/m2 t temperature ° C dt, ∆t, ∆T temperature difference K ρv density of the medium kg/m3
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4.4 Stress Dimensional Units a acceleration due to wave motion m/s2 Cm, Cd, C1 inertia with respect to drag or lift coefficient - C1 (from 1 through n
incl.) stress correction factor -
f load factor - Frr reduction factor following “rerounding” (straight pipe) - g acceleration due to gravity m/s2 h flexibility characteristic - ix, ij stress increase factor - ixp, iyp stress increase factor, including internal pressure - k, kp flexibility factor - K tangential moment coefficient - K (α,β)b of Kb moment coefficient, bottom - K (α,β)t of Kt moment coefficient, top - K (α,β)s of Ks moment coefficient, side - K (α,β)y of Ky deflection coefficient, vertical - K (α,β)x deflection coefficient, horizontal M moment Nm Mw torsion moment Nm MQ tangential moment Nm/mm1 pa critical pressure MPa pe collapse pressure (limit value) with respect to the radial elastic stability MPa pu external hydrostatic pressure MPa pp collapse pressure (limit value) relative to the radial plastic stability MPa pt strength test pressure MPa pv traffic loading pressure on the crest of the pipeline N/mm2 Qdir upper loading, directly transferred N/mm1 Qeg weight of the pipeline N/mm1 Qindir upper loading, indirectly transferred N/mm1 Qop upward loading (under water) N/mm1 Qvul load of the substance carried (medium) N/mm1 Qv traffic load N/mm1 S impact coefficient (traffic loading) - v water velocity at right-angles to the pipeline, caused by waves and current. m/s α load angle degrees β support angle degrees δy vertical deflection mm σa peak stress N/mm2 σb bending stress N/mm2 σm membrane stress N/mm2 σax axial membrane stress caused by temperature change while motion is prevented N/mm2 σp tangential stress caused by internal pressure (hoop stress) N/mm2 σp(bi) hoop stress inside the curve N/mm2 σp(bu) hoop stress outside of the curve N/mm2 σpi longitudinal stress caused by internal pressure N/mm2 σQ tangential bending stress caused by loading from above N/mm2 σtang total circumferential stress N/mm2 4.5 Soil Survey Dimensional Units B bedding width of the pipeline m c cohesion N/m2 cu undrained shear strength N/m2 dp, ∆p increase in vertical granular stress by increase or decrease of the water table N/m2 fm coefficient for calculating the ground load according to Marston - fv incremental subsidence during operations mm
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H soil covering m Hj thickness of layer m Kq load coefficient - k1(kh, kv) lateral bedding constant (horizontal or vertical) N/mm3 Kw frictional bedding constant N/mm3 L radius over which the subsidence increment reaches (field reach) m Qn, qn neutral ground loading N/mm1, N/mm2 Qh, qh ground reaction horizontal N/mm1, N/mm2 Qk, qk real ground loading (during the riveting process) N/mm1 N/mm2 Qr ground reaction vertical N/m1 Qz settling load N/m1 Qp, qp passive ground loading N/mm1 N/mm2 w ground friction N/m2 W friction between the surface of the pipe and the ground (per unit of length) N/m1 x axial coordinate m y lateral coordinate (horizontal) m z lateral coordinate (vertical) m γ contact angle horizontal support pressure degrees γ mass density soil N/m3 γn mass density wet soil N/m3 γd mass density dry soil N/m3 γk effective mass density soil (corrected for water table level) N/m3 γk,j effective mass density soil covering (corrected for water table level) N/m3 δ translation due to friction mm ϕ inside angle ground friction degrees λ pipe-ground rigidity characteristic m-1 λa relative coefficient horizontal and vertical granular stress in active condition (ground moves towards the pipe) λn relative coefficient horizontal and vertical granular stress in neutral condition - λp relative coefficient horizontal and vertical granular stress in passive condition (pipe is pressed against the ground, e.g., around curves) - ρw mass density of the water surrounding the pipe, or of the suspension in which the pipe is laid kg/ m3 σh horizontal granular stress at the height of the pipe (heart of the pipe) N/m2 σk vertical granular stress at the crest of the pipe (upper part of the pipe) N/m2 5 Abbreviations ALARA “As Low as Reasonably Achievable” CPR Commission Disaster Prevention EV External Safety GFT Closed Front Technique GR Group Risk HDD Horizontal Directional Drilling HPSD High Pressure Shut Down LOC Loss of Containment MAOP Maximal Allowable Operating Pressure of a product. This is also used in ISO standards, as the maximum operating pressure of a system. MIP Maximum Incidental Pressure MOP Maximum Operating Pressure of a system OFT Open Front Technique PBT Pneumatic Drilling Technique PR Local risk ROW Right of Way SIL Safety Integrity Level
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6 Safety 6.1 General 6.1.1 Field of Application This chapter deals with the requirements that are presently in force for land. Marine requirements are dealt with in 11.2 For operational safety, see also chapter 10. 6.1.2 Basic Principles Each pipeline must be so designed, installed and used that, from the standpoint of external security, pollution of the environment and devaluation of property, and the security of water management projects, the additional risk to the environment where the pipeline is placed, is considered acceptable. The additional risk which results from the presence of the pipeline must comply with the safety level formulated in Section 6.2. 6.1.3 Safety aspects to be considered The safety aspects which must be considered are: - external safety; - not polluting the environment; - water management safety. 6.1.4 Hazardous substances Appendix A.1 treats the classification of hazardous substances. 6.1.5 Safety – minimum pipeline depth Unless this Standard stipulates otherwise, underground pipe must have a minimal soil covering of 80 cm. See also 8.1.4. If this minimal soil covering is not possible, the pipe must have additional protection against mechanical damage, e.g., by a covering structure. In the Netherlands, a soil covering of less than 80 cm can lead to a disturbance of the pipeline bed through freezing and/or thawing. 6.2 Required Safety Level 6.2.1 External safety The required safety level for external safety depends upon local acceptance relative to the standard set for the group risk. See Note on the Risk Standards - Transport of Hazardous Substances [12]. For the most recent conceptions of external safety, see the National Environmental Policy Plan [21] and the Design Conclusion Environmental Quality Requirements - External Safety, (Staatscourant, February 2002). 6.2.2 Environment Environmental protection policy has been laid down in, among other things, “Dealing with Risks’ [13] and the National Environmental Policy Plan [21]. Needless to say the environmental protection law and the land protection law, and the relevant provincial regulations must be taken into account.
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6.2.3 Water management safety The required safety level is based upon the added probability of the dysfunction of relevant water management projects caused by the presence of the pipeline. See also 6.5. 6.3 Safety Evaluation - External Safety 6.3.1 Field of Application and Purpose It is mandatory to do a safety evaluation for external safety for Group I pipeline systems. A safety evaluation is also required for existing Group I pipelines or sections of existing Group II pipelines, if: - there are changes in the basic design; - local or regional planning changes, or will change the environment immediately contiguous to the pipeline. The safety evaluation serves as a basis for an eventual choice of the route and, if necessary, for application of additional risk-limiting measures. 6.3.2 Content of Safety Evaluation The safety evaluation for external safety consists of the following components (see also Figure 3): a) route orientation to find the safest possible route; b) determine the local iso-risk contours and the group risk curve based upon: - (an analysis of) possible causes of failure and the probability of failure of the pipeline; - (an analysis of) the effect of the escape of the medium on the surroundings where the pipe is being laid or has
been laid;
c) compare the calculated risk contours with the environment where the pipe is being laid or has been laid and testing this with PR and GR criteria;
d) if necessary, revising the route, adopting risk-limitation measures and running another test.
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Figure 3 – Content And Scope Of External Safety Evaluation 6.3.3 Causes of failure and determining the probability of failure 6.3.3.1 Causes of Failure Potential causes of failure which must be looked at, are (in arbitrary order): - structural faults (design and installation); - operator faults (exceeding design specifications for pressure, temperature, and changeover); - settling- and subsidence differences - management faults (inspection, supervision and maintenance); - damage by third parties (vandalism);
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- time-dependent degradation of the material by outside action (e.g., corrosion of metallic pipe, aging of synthetic pipe, etc.);
- material faults (pipe material, connections, fittings, sheathing). 6.3.3.2 Quantifying the Probability of Failure The analysis of the determination of the probability of failure must be based upon statistical data that is as complete as possible, regarding comparable pipes and if possible, categorized into different causes of failure. When the data is being collected, the judgment and interpretation must not merely take into consideration the incidents with product loss, but all incidents concerning the pipeline. Failure probabilities for various categories of pipe can be taken from part 1 of CPR 18E [14]. COMMENT CPR 18E distinguishes the probability of failure with respect to the following types of pipe (it is solely concerned with high-pressure steel pipe): - a pipe which is designed, installed, and managed in conformity with the requirements of NEN 3650-1:2003; - pipelines in a pipeline corridor - other pipelines. 6.3.4 Quantifying the Effects of Product Loss 6.3.4.1 General Hazards can occur from fire, explosion, poison, asphyxiation or a shock wave. The amount of substance released is dependent upon, among other things, the internal pressure, the diameter, the characteristics of the hazardous substance, and the size of the rupture; the extent of the spread also depends upon meteorological circumstances. With these parameters, the following must be taken into account (see Figure 3). The calculation must include at least the following: - accident scenarios; - escape of liquid or gas - the manner in which the released substance is spread - ignition mechanisms (direct or delayed) and probability of ignition; - the effect of digging up the pipe; - criteria relative to injury to persons. This calculation must be carried out with the help of recognized physical models, which describe and quantify, with the aid of the relevant parameters, the possible effects of the release. These models must be validated. For useful calculation methods, see also Part 1 of CPR 18E, Chapter 6. [14] 6.3.4.2 Accident Scenarios with Product Loss CPR 18E [14] cites (accident) scenarios for underground steel pipelines. COMMENT CPR 18E cites the following scenarios: - a leak from a hole with a diameter of 20 mm; - pipeline rupture
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6.3.5 Determining Risk Contours On the basis of risk probability analysis according to 6.3.3, and the calculation of the effect according to 6.3.4, local risk contours and the group risk curves must be determined, with the help of validated models. In order to calculate the Group Risk curve, the population density, expressed in persons per hectare, must be within a 1% mortality rate. 6.3.6 The environment - identifying problem areas. 6.3.6.1 General The results of the risk calculations, presented as iso-risk lines on a topographical background, must be compared with the results of the route orientation. The pipeline satisfies the requirements of external safety if throughout the chosen route it satisfies the PR and GR requirements, and (if applicable) the condition for that medium, pipe material, process conditions and diameter of the pipe, and valid safety distances are satisfied. For other conditions (group risks and/or local risks greater than the safety level established in 6.2) the route must be revised, as supplementary risk-limiting measures (regarding a pipeline which satisfies the technical requirements of this standard) must be taken in accordance with 6.3.7. These supplementary risk-limiting measures must be adopted in the design, and secured in the management- and maintenance procedures (see Chapter 10). 6.3.7 Risk-limiting measures 6.3.7.1 General A risk-limiting measure is based upon one of two aspects of risk: - the probability of failure; measures which limit the probability of pipe failure (leaks and release of the medium) ; - the result or effect; measures which limit the consequences of release subsequent to a leak; also called mitigating measures. These measures can be of a technical-structural, organizational or a planning nature. Table 1 gives an overview of measures for reducing probability and limiting the effects. The probability limiting measures, based upon the causes of failure which are applicable to every pipeline system, thus independently of the type of material, are dealt with here. Material-specific measures are dealt with in the relevant material sections.
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Risk Limitation
Probability Limitation (Preventive) Effect Limitation (repressive) planning organizational structural planning organizational structural structural
provisions quantitative limitation reduce source
strength ‘safe’ route choice distance to other pipes and objects
personnel training inspections situation-dependent maintenance stringent reporting and permit structure (e.g., lying in the pipeline corridors) To make pipeline location known via cable and pipeline information centers (KLIC)
increase in wall thickness for limiting mechanical damage by third parties make the pipe difficult to reach: - increase the depth - markers - relief plates/covering plates, concrete tiles; - screening off the sides (raised curbs, short dam wall, hedge poles at grade); - pipe sheathing application of high-strength external sheathing location in pipeline corridors advanced instrumentation, monitoring (pigging)
distance to dwellings (zoning)
alarm procedures emergency plan disaster battle plan
shatterproof glass buildings pressure resistant (shockwave resistant)
advanced instrumentation e.g., throughput or pressure measurements with fast closing valves. acoustic volumetric or optical leak detectors separation/compartmentalization (valves) thicker wall for limiting rupture formation sheathed pipes (removing, limiting or allocating)
low pressure transport
For the effect of deeper placement, see [29], [30] and [31]. 6.3.7.2 Risk reduction by limiting probability of failure Structural measures The most important structural measures to limit failure for a pipeline, are the prevention of, or limiting of the results of, mechanical damage caused by third parties (e.g., deep- plowing or drainage work) through: - making the pipe wall of sufficient thickness, so that a scratch or dent will not rupture it; - making it more difficult to reach the pipe, by burying it further down, protecting it, and/or placing warning signs. Organizational measures COMMENT 1 Regarding organizational probability-lowering measures, it has been found that within a pipeline corridor or stretch (such as the pipeline corridors South-West Netherlands and the pipeline stretches in the Rotterdam harbor district) a stringent permit system, coupled with a complex of management measures, has significantly reduced the probability of failure that was the result of mechanical damage by third parties. In this situation a point of concern is the possible negative effect from one pipeline on others in a pipeline corridor, e.g., flooding by a failed water pipe or the effect of radiant heat from an oil or gas fire on the sheathing of neighboring pipes. COMMENT 2 The notification by pipeline owners or operators, via Cables and Pipelines Information Centers, of the location of their pipelines to parties intending to dig, is another example of an organizational measure.
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6.3.7.3 Risk reduction by limiting effects 6.3.7.3.1 Sectioning off the pipes with valves The quantity of medium released can in some cases by limited by applying extra valves in the pipes, or by using a material (e.g., liquid nitrogen) with which the medium is driven out of the problem segment. The application of extra valves, however, also creates new sources of faults (the valves themselves). The effectiveness of sectioning off by valves has to be demonstrated in connection with the direct environmental risks. The potential effect that such valves would have on the probability of failure, as well as on the containment of the effects, must be closely examined. Valves for sectioning off the pipe will in any case be placed at the beginning and at the end of the pipe. It must be possible to bring the valves into action quickly. Moreover, for maintenance purposes they must be easily accessible. When dealing with pipelines for liquids, the susceptibility of the terrain to accidents, and also the route of the pipeline must be taken into account. Also to be taken into account is the speed of closing with respect to water shock waves. COMMENT For further information on organizational effect-containment measures, see [32]. 6.4 Environmental Impact Evaluation (land) 6.4.1 Sensitive areas When making an environmental impact evaluation, a distinction must be made in ground-water protection areas and other sensitive areas. COMMENT Other sensitive areas include, among others: protected natural heritage areas, national parks, aquatic zones of international significance, zones making up part of an ecological main structure, the “Waddengebied” area of the Netherlands, a large nature area or an area whose main function is nature, valuable water-meadows, valuable creek beds, protected zones according to the aviary guidelines or habitat guidelines. 6.4.2 Requirements for ground-water protected areas Laying down pipelines for the transport of environmentally hazardous materials in ground-water protected areas is prohibited, unless exemption has been made by the relevant authorities. COMMENT In sandy soil with great permeability, a large area can become polluted relatively rapidly by the release of a relatively small amount of hydrocarbons; here deep HDD’s should be considered. In clay soil, not very permeable, the extent of pollution is much reduced. 6.4.3 Designing the Route Research into possible routing must coincide with external safety for the environment. If the pipeline lies in a sensitive area, then supplementary measures, to be determined in consultation with the person responsible for the relevant function for that area, might be necessary. COMMENT An example of such a measure is a sheathed pipe which is capable of transporting the material outside of the area in case of a leak. Outside of sensitive areas, some pollution is acceptable, as long as the pipeline complies with the Standard (ALARA-principle). 6.4.4 MER The regulations that govern reports on environmental impact are given in the Environmental Protection Law (Chapter 7), in the Decision on Environmental Impact Reporting 1999 and in the Regulation Start-up Notice - Environmental Impact Reporting [22].
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COMMENT The cited conclusions, 1999 edition, include among other things: An environmental impact report (MER) that is mandatory if the pipeline has a nominal diameter of more than 800 mm, and a length of more than 40 km for the transport of gas, oil or chemicals. For other pipelines, a mandatory judgment must be rendered by the relevant authorities who must decide whether or not a MER is required where there might be significant negative environmental impact. Mandatory judgment must also be rendered when a pipeline is installed, modified, or expanded, in cases where the work is related to: - a pipeline for the transport of gas, oil or chemicals (except natural gas), where more than 1 km is laid or projected for a ‘sensitive area’; - a pipeline for natural gas transport with 5 km or more of its length situated in or projected for a sensitive area; - a pipeline for the transport of water, waste water or steam, with a diameter of 1 meter or more, and a length of 10 km or more. Key items to be noted in making the decision are: the nature of the project, the sensitivity of the area, the cumulative effect with other ongoing activity, and the nature of the potential effects. 6.5 Water Management Project Safety 6.5.1 Fundamentals When carrying out a risk evaluation of a water management project, risk (R) is defined as the product of the probability of failure (P) and the effects of the failure (E) where both (failure and effect) are brought linearly into the calculation (R = P x E). 6.5.2 NEN 3651 Pipelines which lie in or near significant water management projects, must satisfy the regulations which are stated in NEN 3651:2003 Supplementary requirements for pipelines crossing significant water management projects. The area where NEN 3651:2003 is to be applied, extends up to and includes the safety zones on both sides of the water management project. The safety zone consists of the water management project’s stability zone, and the zone that would be disturbed by a pipeline leak. 6.5.3 Significant Water Management Projects The following civil engineering structures are considered significant water management projects: - a primary dam (e.g. seawall, river dike); - a reservoir dam (e.g. quay reservoir, dike along a watercourse with the water table above grade); - a secondary dam (e.g. dry dike, a subsidiary dike); - a primary road (e.g., throughway) - a secondary road (e.g., a provincial road); - a federal or provincial highway. For definitions of various water works, see NEN 3651:2003. 6.5.4 Railways Pipelines that cross railway lines must satisfy the requirements stated in the so-called ‘White Book’ [23]
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7 Process Safety Conditions 7.1 General 7.1.1 System Requirements The pipeline system must be so designed, installed and managed that during its life-cycle, it will comply with the required safety standards. The system requirements must be explicit, and documented in writing. The intended life-cycle of system operation must be firmly established. 7.1.2 Design conditions When specifying design conditions, all normal and extreme process conditions and the relevant array of throughput velocities, pressures, temperatures, product composition and quality, must be identified and taken into account. 7.1.3 Hydraulic calculation When material is to be transported through the system, hydraulic calculations must be made to determine the outer limits (under and over pressure) of the design. These calculations must include both static and dynamic conditions. COMMENT All possible deviations from the normal static flow condition must be carefully considered. Examples are: wax coming loose from the pipeline wall, hydrate forming in wet gas, changes in viscosity caused by temperature changes, slugs of liquid caused by condensation in natural gas, air bubbles or air collection in a pipeline for liquids, two-phase flow etc., but also fast-closing valves, pump breakdowns, ruptures in the line, pressure shock waves and cavitation (closely contiguous vapor bubbles) for example in elevated sections of pipelines for liquids etc., In above-ground pipelines, slugs of liquid in gas lines or air collection in liquid pipelines can cause shockwave loads, and are co-factors in determining the methods used for support. 7.2 Control of Process Conditions An important component of operations is control of process conditions. The pressure and the temperature of the material to be transported must remain within design conditions. The throughput velocity, the flow and also the composition must remain within the preset limits. Specific ancillary equipment along with the relevant control apparatus (instrumentation) are necessary for monitoring. It is recommended that both the ancillary equipment to be installed and the relevant control apparatus, be subjected to a disturbance analysis during the design phase, so that the design can be revised as necessary, and the results of the analysis can be used as a baseline when the control apparatus is brought on line (see Chapter 10). 7.3 Pressure Control 7.3.1 General The internal pressure in a pipeline system must be kept within the design limits by a pressure control system. The pressure control system consists of a pressure regulating system, a pressure alarm system and a pressure safety system. For group II pipelines, it is possible to do without such a pressure control system, provided that there is no change in process conditions during operations with respect to the basics of the design when the pipeline was installed. COMMENT 1 Since the regulations of the standard for Group II pipelines are exclusively applicable within the context of water management projects and ground-water protection zones, there are no requirements imposed with respect to the method used to control process conditions in Group II. However, in order for any permit to remain valid, process conditions must not be modified. The pressure control system can be designed deterministically. Its requirements are in agreement with those which hold for natural gas transport in NEN-EN 12186:2000, NEN 1059:1994 and Draft NEN 1059:2002
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The pressure control system can also be designed according to the so-called SIL-methodology, from NEN-EN-IEC 61508-5:2002; a probabilistic approach. COMMENT 2 A disadvantage of the deterministic method is that there is no quality control required for the components used. SIL-methodology design has the advantage of forcing greater insight into the structure and behavior of the safety system. The SIL-methodology is a quality system which comprehends the entire life-cycle of the safety system. This system requires detailed registration of performance, which might mean that the system can be tested less frequently. COMMENT 3 SIL is an abbreviation for “Safety Integrity Level”. The SIL-methodology is especially important when designing electrical and electronic pressure control systems. Important preconditions for the application of the SIL-method are: - sufficient knowledge of the pipeline system to be safeguarded, in order to determine the right SIL; - sufficient numerical data about behavior of failed components used in the pressure control system; - ability to show by calculation that the chosen design leads to the required risk reduction with respect to the SIL
level. 7.3.2 Pressure regulating system The pressure regulating system must be calibrated for the maximum design pressure of the pipeline. The probability of undesirable excess pressure levels is primarily determined by the probability of failure of the pressure regulating system. 7.3.3 Pressure alarm system The pressure alarm system must bring attention to a hazardous situation. Timely intervention can make the intervention of the pressure control system unnecessary. A pressure alarm system is not necessary if the safety system has a maximum trigger pressure equal to the design pressure. In all other cases a pressure alarm system is required. When the safety system is triggered, a (high priority) automatic alarm must go off. The pressure alarm system must be installed in such a way, that pressure in excess of 102% of the design pressure, as well as its duration, are recorded by the safety system. In order to prevent the triggering of the pressure alarm system within the bandwidth of the pressure regulating system, the alarm pressure trigger may be a maximum of 102% of design pressure. COMMENT For natural gas transport using Group I pipelines (operating pressure > 1.6 MPa) this 102% may be revised to 102.5% (see Table 1 from NEN-EN 12186:2000 and 6.2 in NEN-EN 1594:2000). The pressure alarm signal may not be part of the pressure regulating system’s sensors (whose failure must be signaled), but must be a dedicated pressure transmitter installed for this purpose, or a pressure transmitter of the pressure control system. 7.3.4 Pressure control system The necessity and degree of pressure control is determined by the relationship of the design pressures of the upstream and the downstream pipeline system (Table 3). The pressure control system must take automatic action, so that in the system to be safeguarded, the maximum allowable incidental pressure is not exceeded with the failure of the pressure regulating system. When designing and installing the pressure control system, the dynamic of the transport system and the lack of precision in installation and the slowness of the pressure control system (for example, the intervention time of the blocking valve), must be taken into account. The safety principles as per 7.4.1 (venting), and 7.4.2 (non-venting), can be applied separately or in combination for pressure control. When the medium is a gas, the preferred choice is to protect the environment using technology to address the cause rather than trying to mitigate the effect.
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COMMENT 1 For example, incidental pressures can be caused by the following: start-up or shutdown of a pipeline system, slow response of pressure regulating system, safety system intervention, pumps or compressors switching on- or off, valves opening and closing. COMMENT 2 In principle it is possible that at the beginning of a pipeline’s life-cycle, a relatively low operating pressure will be combined with relatively greater incidental pressure changes, while in due course incidental pressure changes can be kept down by relevant adjustments making it possible to increase operating pressure. COMMENT 3 For Group II pipeline system, the pressure security system prevents exceeding the MIP (“Maximum Incidental Pressure”). The magnitude of MIP for high-pressure gas pipelines, is 110% or 115% of MOP (Maximum Operating Pressure”) when the system is strength-tested at 125% or 130% MOP. A schematic overview of the pressure levels in a pipeline is given in Figure 4. The relation between the triggering of the pressure control system components (regulating, alarming and securing) and the permissible pressure levels are given in Figure 5.
Figure 4 – Pressure levels
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a = REGULATING PLAY - PRESSURE REGULATING SYSTEM b = PRESSURE ACCUMULATION - SAFETY VENTING c = TOLERANCE/CLOSING TIME - INSTRUMENT PRESSURE CONTROL
Figure 5 – Pressure Control The degree of pressure control for the system depends upon the design chosen, with the following consequences: - deterministic design, leading to no system at all, or one or two pressure control systems (Table 2); - probabilistic design, leading to an SIL-pressure control system in accordance with NEN-EN-IEC 61508-5:2002.
Table 2 – Composition Of Deterministically Designed Pressure Control System
Pressure ratio pressure regulation
pressure alarm pressure control system
pbo ≤ pibe yes yes 0 pbo > pibe yes yes 1
pbo - pibe >1.6 MPa and pbo > ptbe
yes yes 2a
pbo is the maximum operating pressure upstream, pbe is the maximum pressure downstream, pibe is the maximum permissible incidental pressure downstream and ptbe is the strength test pressure downstream of the pressure regulator ( = the system to be safeguarded). a two pressure control systems working independently The pressure ratio of the limits are in agreement with the stipulations of 8.3.3 of NEN-EN 12186:2000 7.3.5 Pressure control for pipeline grid In the case of a meshed pipeline network fed by two or more stations, with one or two pressure control systems, a disturbance analysis must show that the structure of the pressure control system complies with the same level of safety as that for the simple system in accordance with 7.3.4.
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7.4 Pressure Control Design Each pressure control system must separately satisfy the minimum requirements stipulated in 7.4.1 and/or 7.4.2 and 7.4.3. Moreover, the periodic controls stipulated in 7.4.4 must be made to check that the system is available when needed. For gas pressure regulating stations, the stipulations of NEN-EN 12186:2000 and NEN 1059:1994 and Draft NEN 1059:2002 are in force. COMMENT Depending upon the nature of the medium in the pipeline, and the circumstances on the outside, a choice of safety principles can be made in accordance with 7.4.1 or 7.4.2. When two safety systems are required, two unlike systems are recommended, in the light of “common cause failures”. Safety systems that shut off flow to deal with the cause, are to be preferred over mitigating safety systems. 7.4.1 Pressure Control – Venting A mitigating pressure control system can be implemented as: - directly working safety valve - indirectly working safety valve, which may or may not use ancillary equipment; - indirectly working safety shut-down valve, which may or may not use an ancillary equipment; - fusible plug The maximum allowable incidental pressure in the pipeline to be safeguarded may not be exceeded. In the design of the safety system, therefore, the following must be taken into account: - the total capacity of the system - the opening pressure of the safety valves - the trigger value for the indirectly operating safety shutdown valve; - the fusible plug threshold. The kind of construction and choice of materials for the safety valve, the safety shut-down valve, or the fuse must be demonstrably suitable. The safety valves and safety shutdown valves, or fuses, must be installed in such a way, that their action cannot be hindered by the medium to be safeguarded. Escaping substances must be safely carried away via a dedicated system. 7.4.2 Pressure Control – Non-Venting The operation of a non-venting pressure control system can be based upon: - shutting a valve (blocking valve) for the pipeline to be safeguarded so that the feeder is shut down; - shutting down the apparatus for increasing pressure; The trigger value of the pressure sensor must be such that the allowable incidental pressure in the pipeline is not exceeded (see 7.3.4). The blocking valve(s) must be so installed, that when the auxiliary energy vanishes (spring-loaded, air pressure, gas pressure etc.) the system is directed to go into a safe condition.
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Safety Devices for Small Volumes If, after safety interventions, relatively small volumes are trapped, a small safety vent must be installed to prevent a further increase of pressure caused by leakage of the blocking valve. 7.4.3 Instrumentation The instrumentation used with venting- and non-venting pressure control systems must comply with the following regulations: Safety Chain The entire instrumental safety chain must work according to the stationary flow principle. The pressure sensors must operate in such a way, that when the signal vanishes, a safety intervention takes place. The switching logic and ancillary controls must be fault-tolerant. The safety chain must be installed completely independent of the regulation- and control system. Two parallel safety systems, which must ensure the safety of the same pipeline, must be installed completely independently from each other. Structure Pipeline instrumentation must be dimensioned and installed in such a manner that they are suitable for their purpose. The instrumentation of a pressure control system must be separate from other instrumentation. The pressure sensor of each pressure control system must be redundant (e.g., one out of two, or two out of three). If necessary, the trigger for the controls and technical provisions which are part of the pressure control instrumentation, must be mechanically held in place (for safety). COMMENT Two out of three, means that two of the three pressure sensors must be addressed before the safety system is activated. Shutdown or Disconnection The pressure control system’s sensor must be connected to the pipeline to be safeguarded in such a way that it cannot be shut down or disconnected. It is permissible to deviate from this if a changeover is installed, with mutually locked shutdown valves or switches where the pressure sensor systems of the required number of pressure control systems are continuously connected to the pipeline to be safeguarded. If a transmitter is disconnected from an electrical feed, or is being expanded, then it must be made to emit the ‘addressed’ signal, so that when one of the remaining sensors is addressed, the safety system will be activated. 7.4.4 Start-up and periodic controls Before pressure control systems are brought online, they must be calibrated and tested using an approved testing procedure. “In situ” testing provides the most reliable data about the actual behavior of the safety system. It is important to record the outcome of testing, because it will determine the testing intervals. COMMENT 1 It is the responsibility of the owner or manager of the safety system, to determine when certain components must be replaced or disassembled and cleaned, if necessary consulting the manufacturer or a certified maintenance firm.
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Safety systems must be tested periodically, according to the specifications for the type of safety procedure in question. If there is no data that can be used to determine the intervals between testing for the relevant type of safety in the specific location in the system, Table 3 must be used.
Table 3 – Testing intervals for different types of pressure control systems
Component Testing interval a spring driven or weight driven loaded safety valve
4 years
mitigating valve ancillary instrumentation
1 year 1 year
blocking valve (HPSD-syst.) ancillary instrumentation
1 year 0.5 years
If enough data has been gathered from a statistical standpoint, regarding a specific type of safety, the testing intervals may or must be revised. COMMENT 2 It is advisable to increase the testing interval for mechanical components in increments of no more than half a year. When components are replaced by other types, the testing interval ought to be shortened, until sufficient data has been generated from experience which might justify an increase in the interval. Changes in the safety systems must be documented in detail. COMMENT 3 In order to better predict the behavior of specific safety equipment, it is recommended that the number of variations in design and construction should be limited to a smaller number than is usual for components that do not have a safety function. Every maintenance cycle, or modification of the safety system, must end with a test to demonstrate that the start-up and shut-down devices are in good working order. The test results must be recorded. During maintenance work and testing, where the safety system is bypass, and the pipeline system to be safeguarded is in operation, pressure control must be guaranteed in some other manner. 7.4.5 Test Reporting With each periodic testing, the relevant data such as pipe element number, production year, test method applied, testing interval, time of tests, test results, as well as any measures that might have been taken in response to the test results, must be recorded. Test results must be saved for at least five years. 7.4.6 Pressure Control System Documentation Documentation of the original design fundamentals and calculations must be available for each pressure control system. Every revision in the system must be documented in detail, and will be compared to the design fundamentals. The results of the periodic tests and other relevant aspects must be entered and maintained in a logbook. Unusual events must be logged. Undesirable addresses to the pressure control system or its failure, must minimally be regarded as unusual events. 7.5 Temperature control For the transport of materials at a higher or lower than ambient temperature, provisions must be made to prevent the increase or decrease of temperature within the pipeline exceeding the design temperature trajectory envelope.
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Based on the operations plan, temperatures and temperature variations must be laid down during the operations phase. The number of changeovers, and the amplitudes must also be taken into account, when judging the safety margins on the boundary values of material fatigue. 7.5.1 Temperature regulation of heat transport systems 7.5.1.1 Introduction The pipeline system for heat transport (city heating), normally has a feed- and a return line. The (cooled) return water is warmed, in order to act once again as (warm) feed water in the system. The temperature increase is obtained by: - drawing warmth from a heat source unit via heat exchangers and/or the tapping of steam; - using gas or oil burners to heat water in a boiler. COMMENT Heat source units and the installations for extracting heat from a heat source unit, must comply completely with the guidelines for apparatus under pressure (“Pressure Equipment Directive” (PED)) and are not within the scope of this Standard. Gas-fired boilers are also outside the scope of this Standard. 7.5.1.2 Regulation Principles The temperature of the water of city heating systems for the feed line and the return line is regulated in various places. The feed line and the return line, have different design temperatures. Heat Exchanger Feed Line When heat is delivered by a heat-source unit, the baseline temperature is primarily drawn from flue gases via flue gas heat exchangers, as well as from steam and/or cool water. For attaining the desired temperature at peak conditions, tapped steam can be used. Temperature regulation consists of a thermostat which measures the temperature of the outgoing water for city-heating, and governs a control valve for the quantity of heat carried on the feed side of the heat exchanger. In this way, the temperature in the feed line of the system is kept within the specific limits of the regulator bandwidth. The maximum thermostat trigger temperature is equal to the maximum operating temperature of the remote heating system, minus the regulating tolerance. When the temperature begins to exceed the maximum allowable, the regulator valve closes. Heat Exchanger, Return Line The temperature of the warm water in the return line of the system is determined by the delivery stations at the user end. The heat transfer at the delivery stations takes place via heat exchangers and the temperature regulator. The regulator consists among other things, of a regulating valve, which reacts to the temperature of the secondary system, while the primary return water temperature is limited by a sensor in the output line to the return transport line. The limiter in the outgoing line is calibrated to the design temperature of the return line. COMMENT When a heat source produces heat, the heat production unit (e.g., An HD-steam turbine, where the steam is tapped via condensers) has its own safety system. Exceeding the maximum temperature is paired with an increase in pressure. As a result, the safety valve of the boiler of the HD-turbine kicks in to limit the maximum pressure and with it, the maximum temperature. See Figure 6 for a summary:
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a = REGULATION BANDWIDTH TEMPERATURE CONTROL SYSTEM b = DISCONNECT BANDWIDTH BURNER/REGULATOR BANDWIDTH SAFETY VALVE
Figure 6 – Temperature Control 7.6 Medium The composition of the medium must be monitored during operations. The allowable margins of deviation from the specifications for that medium must be known, as well as what must be done to prevent undesirable conditions. These procedures must be specified, and the documents made available to operations. For pipeline systems various different products must be loaded and transported, rules for monitoring and tracking the load must be laid down, as well as the time of its arrival and its location in the receiving installation. For pipeline systems with multi-phase product transport, rules for monitoring any liquid that might remain behind in the pipeline (“liquid hold-up”) and the free volume in the slugcatcher must be laid down.
