Issuing organisatio n Thermoplastic Piping Welding Specification BES-CO-05-306-01 Rev: 1 / 27.04.2010 PA&E Sheet 1 / 19 A print of this do cument is only valid at the date of p rinting. For reference, use the actual version available on Borena. THERMOPLASTIC PIPING WELDING SPECIFICATION BES-CO-05-306 Preparer Date Name/Position 27.04.2010 Gino De Landtsheer / Piping Expert TSG - PTS Issuer Date Name/Position 27.04.2010 Gino De Landtsheer / Piping Expert TSG - PTS Process owner Date Name/Position 27.04.2010 Filip Goovaerts / Specs PA&E 1 Approved Rev. Description
Transcript
Issuing organisation
Thermoplastic PipingWelding Specification
BES-CO-05-306-01
Rev: 1 / 27.04.2010
PA&E Sheet 1 / 19
A print of this document is only valid at the date of printing. For reference, use the actual version available on Borena.
THERMOPLASTIC PIPINGWELDING SPECIFICATION
BES-CO-05-306
Preparer Date Name/Position
27.04.2010Gino De Landtsheer / Piping ExpertTSG - PTS
Issuer Date Name/Position
27.04.2010Gino De Landtsheer / Piping ExpertTSG - PTS
Process owner Date Name/Position
27.04.2010 Filip Goovaerts / Specs PA&E
1 Approved
Rev. Description
BES-CO-05-306-01 Rev: 1/ 27.04.2010 Sheet 2 / 19
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TABLE OF CONTENTS
1 GENERAL ......................................................................................................................... 3 1.1
1.2 Review Schedule ............................................................................................................... 3 1.3 Group Amendment to the Borealis Engineering Specification ............................................ 3
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1 GENERAL
1.1 ValidityThese design requirements are valid for all BOREALIS Sites.
1.2 Review ScheduleThis Engineering Specification shall be reviewed at least every three years.
1.3 Group Amendment to the Borealis Engineering SpecificationThis Borealis Engineering Specification shall consist of the ‘BES-CO-00-001; Group Amendment to the Borealis Engineering Specifications’ which are incorporated herein andmade part here of by reference.
Content for info: General Definitions, Abbreviations, Objective and Scope, Language, UnitSystem, CE-Marking, PED / ATEX / Quality Assurance / Quality Control, General BasicDesign Requirements.
1.4 Objective and ScopeThe purpose of this document is to provide general information for the welding of thermoplastic piping systems, in order to standardize welding procedures and requiredqualifications. An improved reliability and attain consistency in thermoplastic pipingwelding should be a result of these requirements.
This engineering specification shall be applied to all new process and utility pipingconstructions, where the use of thermoplastic components is part of the applicable pipingclass specification or when thermoplastic materials can be an alternative for metallicmaterials.
This Borealis Engineering Specification is providing additional information specific to thewelding of Thermoplastic Piping systems. It shall be noted that the basic piping designrequirements, specified in the document ‘BER-CO-0-001; General Design RequirementsPiping’ should be used as a minimum requirement basis.
The minimum quality and organizational requirements for welding, specified in thedocument ‘BES-CO-05-002; Piping welding, Fabrication, Installation and Inspection ’ andDVS 2210-1 ‘Industrial Pipelines of Thermoplastic Materials; planning and execution, over ground systems’, should be mandatory in case no specific requirements are mentioned inthis engineering specification.
2 APPLIED STANDARDSIt shall be CONTRACTOR’s responsibility to be, or to become, knowledgeable of therequirements of the referenced Codes and Standards.
When an edition date is not indicated for a code or standard, the latest edition in force atthe time of CONTRACTOR’s commitment shall apply.
Intermediate changes or updates/revisions of applied codes, standards, regulations or laws during the course of the project shall be brought to COMPANY’s attention. Possibleimplications for the works shall be discussed.
The design and engineering shall satisfy all laws and regulations of the national and/or local authorities of the country in which the EQUIPMENT AND MATERIALS will belocated.
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MANUFACTURER is responsible to ensure that all requirements of the regulatingauthorities are fulfilled. However, CONTRACTOR shall supply all necessarydocumentation regarding inspection, NDT, etc. to fulfil the PED requirements.
2.1 Standards and RegulationsThe international codes and standards, to the extent specified herein, form a part of thisspecification and shall be followed. Some codes or standards (e.g. Euro codes) are stillunder development and their final number and identification are given below. If thereferenced code is not yet available, it’s preceding pre -code, draft code or relevantnational codes covering the same subject shall be followed.
In case of conflict, the order of precedence shall be:
1. National and/or local Laws and Regulations applicable at the location of the site.2. European Directives3. Applicable Design Codes (ASME BVPC, ASME B31.3, AD2000, BS 5500, EN 13445,
EN 13480, etc.)4. Project specific CATALOGUE DATA SHEETS from the LICENSOR5. COMPANY specifications
Project Specification
Local Amendment
Common Engineering Specification6. Reference to international standards (API, NFPA, etc.)
The more stringent of two conflicting regulations/standards will prevail.
In all cases CONTRACTOR shall inform COMPANY of any deviation from therequirements in the specifications, which is considered to be necessary in order to complywith national and/or local laws and regulations.
Deviations from this specification are subject to written approval by COMPANY. After thisapproval these specifications are integral part of the contract.
The standards and codes as listed in 2.1.1, 2.1.2, 2.1.3 and 2.1.4 shall be followed.
2.1.1 European Directives
97/23 EC Pressure Equipment Directive (PED) for pressure containingequipment and assemblies.
2.1.2 Applicable Design Codes
ASME B31.3;Chapter VII
Code for Pressure Piping: Process Piping – Non-metallicPiping and Piping Lined with Non-metals
AD 2000 Code Technical Rules for Pressure Vessels
2.1.3 Borealis Reference Documents
2.1.4 Standards
BES-CO-00-001 Group Amendment to the Borealis Engineering Specifications
BER-CO-05-001 General Design Requirements Piping
BES-CO-05-007 Pipe classes - ASME
BER-CO-05-301 General Design Requirements for Thermoplastic Piping
DVS 2207-1 Welding of Thermoplastics -Heated Element Butt Welding of pipes, pipeline parts andsheets of PE-HD
DVS 2207-3 Welding of Thermoplastics -
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3 INTRODUCTION
Different joining techniques are available for thermoplastic piping and the development of new applications is an ongoing process.
Depending on the raw material properties and the selected welding techniques, specificinstructions and requirements will govern. Therefore a detailed evaluation of theapplicable joining process should be performed in collaboration with both thethermoplastic raw material supplier and the manufacturer of the joining equipment.
Each joint process requires the following initial steps:
Pre-inspection of the material to be joined
Cutting of the pipe material
Cleaning of pipe components and fittings
Joining/welding of piping components
Inspection and testing (NDT) of assembled pipe spools and piping assemblies
4 INSPECTION BEFORE USEBefore use of thermoplastic pipe components and fittings, all items should be inspectedfor:
flaws
deep scratches (> 10% of actual wall thickness)
excessive warping
fine cracks on or under the surface of the plastic material (‘crazing defects’)
de-lamination (separation of layers)
or any other sign of damages
Hot Gas Welding of Thermoplastics - sheets and pipes -Welding Parameters
DVS 2207-6 Welding of Thermoplastics -Contactless Heated Element Butt Welding of pipes, pipelineparts and sheets; methods – machines - parameter
DVS 2207-11 Welding of Thermoplastics -Heated Element Butt Welding of pipes, pipeline parts andsheets of PVDF
DVS 2207-15 Welding of Thermoplastics -Heated Tool Welding of pipes, piping parts and sheets of PVDF
DVS 2208-1 Machines and equipment for welding of thermoplasticmaterial; heated element welding
DVS 2208-2 Welding of thermoplastic materials; machines and equipmentfor hot-gas welding (not extrusion welding)
DVS 2209-2 Hot-gas extrusion welding; requirements to welding machinesand equipment
DVS 2210-1 Industrial pipelines of thermoplastic materials; planning andexecution, over ground pipe systems
DVS 2211 Filler materials for thermoplastics; scope, designation,requirements, tests
DVS 2212-1 Examination of welders, group 1
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In case one or a combination of these previous defects, the operating parameters(maximum operating pressure) can be severely affected.
Any concern related to potential defects should result in rejection of the applicablecomponent or assembled pipe spool.
5 CUTTING
5.1 Weld Preparation ToolsFabrication and installation of thermoplastic piping requires an extensive range of highquality tools and equipment, specifically designed for use with thermoplastic material.Tools should be assembled and checked prior to start any welding activity.
All necessary equipment and tools shall be available to enable safe handling of pipematerials.
Only using these tools, improved reliability and a reduction of the assembly time for making a joint will be achieved. Use of tools, not adapted to perform a high qualityassembly, is prohibited.
5.2 CuttingBefore cutting activities will take place, the thermoplastic material should be conditioned tothe ambient working temperature of the working area or the location where the installationand jointing will take place.
Thermoplastic pipe should always be cut with a tool designed for use on the thermoplasticmaterial being installed.
It is not recommended to use saws or other cutting equipment that is used for cutting of metals, as the blade construction may snag on thermoplastic or cause an unacceptablebuild up of heat.In addition, tools used previously to cut metals may contaminate the plastic joining areawith grease or oils.
It is important to ensure that the pipe is cut square.
In case of socket fitting configurations, cutting the pipe square ensures that the pipe willbottom out in the socket. This is essential in the assembly process to get the maximum joint strength.In case of butt fusion joints, a square cut minimises planning before the joint is made.
Polyethylene, Polypropylene, ABS and lighter wall PVC-U and PVC-C piping with adiameter of 2” and below shall be cut with ratchet operated cutting shears.
For pipe diameters up to 8”, a rotary quick release pipe cutter with a cutting wheel ,adapted for use with plastic pipe materials, should be used.
Pipe with diameters above 8” may be cut with large diameter wheel pipe cutters, fitted withblades adapted for use on thermoplastic materials. The cutter should be fitted withoutboard rollers to ensure that the cut remains square.
Hand saws with a tooth design, set and hardness specifically adapted for thermoplasticmaterials may be used, provided that a mitre box or jig is used. The pipe must be checkedafter this cutting action to ensure a square cut.
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Power tools may be used, provided they are fitted with suitable blades, and run at acutting speed suitable for the type of material to be cut.
After completing the cutting process, the pipe length should be checked for accuracy andany internal or external burrs shall be removed using a de-burring tool, specificallydesigned for thermoplastic material.
The maximum permissible deviations from plane-parallelism at the joining surfaces are:
Table 3; Plane-Parallelism Deviations Tolerance Range
Pipe outside diameter (mm) Deviation (mm)
< 400 ≤ 0.5
≥ 400 ≤1.0
Chips or swarf shall be removed from the inside of the pipe.
The jointing areas of the parts applicable to welding shall be free of any damage or contamination.Polyethylene and Polypropylene pipes stored as coils should be pre-treated to reduce thepossible oval distortion due to the rolling action. This can be done by means of heat inputand use of a suitable cut pressure or a round installation pressure.
5.3 Cleaning after cuttingBasically most thermoplastic joints are of a homogeneous monolithic structure. Thismeans that the joint has the same physical and chemical characteristics as the pipe andthe fittings.
To avoid any contamination before or during the process of welding and to assure thehomogeneous monolithic structure, it is important that joining surfaces should be free of:
dirt
grease
water
mould release
any other foreign substances
Joining surfaces shall be cleaned as a minimum requirement with a clean cloth. If theapplicable surfaces cannot be successfully cleaned with this method, an emery cloth or sandpaper should be used.
To remove films of oil or grease only isopropyl alcohol should be used. This solvent willpick up the grease or oil traces and will evaporate off very quickly.
Thermoplastic pipe components should be never cleaned with other solvents!
The applicable raw material SUPPLIER and welding equipment MANUF ACTURER’sinstructions should govern to determine the proper joint preparation.
6 WELDING
6.1 Applicable jointing methodsDepending on the material, size of the pipe, the intended application and serviceconditions, different joining methods for thermoplastic piping are available.
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The piping design process should include the evaluation of the application of the different jointing methods. It can be possible to have combinations of welding methods, resulting inthe most cost-effective solution for the required level of quality.
The following table lists for a variety of pipe materials the applicable welding processeswhich can be used.
Table 1; Welding Processes Overview for Thermoplastic Materials
Buttf
i
Electrof
i
Socketf
i
Hot gas IR BCF Solvent
t
PP X X X X X
PE X X X X
PB X X
PVC-U X X
PVC-C X X
PVDF X X X X
ABS X
ECTFE X X
X = welding process that can be used
In addition to fusion welding techniques, there are a number of mechanical methods thatmay be used for joining thermoplastic pipe. These include:
Compression fittings
Flange and gasket assemblies
Push-fit sockets
Grooved
Threaded
O-ring
Bell and spigot adhesive bonding (Reinforced Thermoset Resin material)
These connection methods for Thermoplastic piping are not part of this engineeringspecification.
6.1.1 Butt Fusion WeldingButt fusion welding (DVS 2207-1 / 2207-11 / 2207-15), also known as hot plate welding, isone of the main welding techniques for thermoplastic piping.
The butt fusion process can be split-up in six phases of progress:
6.1.1.1 PreparationThe pipe ends are clamped and planed to ensure that they are flat and square. Thealignment of the pipe end is checked.
Joining surface shall be free of any pigtails or shavings.
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6.1.1.2 Bead-upThe trimmed and aligned pipes are pressed against the heater plate using the 'initial'bead-up pressure to have a good thermal contact.
The pressure is maintained until the pipe starts to melt and a uniform bead is formed oneach end due to the internal pressure forces which are pushing the material outwards.The formation of these 'weld beads' will be at the outside and inside pipe surfaces.The size of the bead depends on the material and pipe diameter.
6.1.1.3 Heat soak After the initial bead-up, the pressure is reduced to a value sufficient only to maintain thepipe in contact with the hot plate. This allows the melt depth to increase without increasingthe size of the weld beads.
The pipe ends must maintain contact with the heater plate at the soak pressure for thespecified soak time, which increases with diameter and wall thickness.
6.1.1.4 Heater plate removalWhen the heat soak time is completed, the pipe ends are retracted from the heater plate,and the heater plate removed. This is sometimes known as the 'dwell time' and should beas short as possible.
The heating plate should be taken away without any sign of damage or pollution.
6.1.1.5 Fusion jointingImmediately after removing the heater plate, the hot pipe ends are pushed together at thesame pressure as used during the initial bead-up stage.
In case of large wall thicknesses, the jointing pressure is reduced after a well defined timeframe (seconds) has elapsed. Depending on the material characteristic, this time frameshall be defined after consulting the raw material supplier.
6.1.1.6 CoolingFinally, after the jointing phase, the weld is allowed to cool whilst the jointpressure/secondary pressure is maintained for a specified time, depending of the materialcharacteristics and the size.
Pressure testing of butt fusion welds can only be performed if the applicable cooling downprocess is completely finalized. As a minimum, this shall not be less than one hour after performing the last weld.
Graph 1; Butt Fusion Welding Sequence
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Advantages
Alignment between components part of the welding process is controlled
Pipe to pipe joints are possible, without having the requirement of a connecting socket.
Application rangeButt fusion welding is applicable to pipe sizes from 50mm to 2000mm.
Disadvantages
But fusion welding can only applied on piping components which have the same wallthickness.
Under no circumstances, the faced ends should be touched, during the butt fusionprocess. This to avoid contamination of the welding area and to prevent burninginjuries.
But fusion welding is the only joining technique that can be taking into consideration for directional drilling applications and close-fit lining applications in existing piping.
Equipment
Manual, automatic and semi-automatic butt fusion machines are available.
Automatic machines feature electro-hydraulic controlled pipe clamps, trimmer andheater plate, with full data recording of weld parameters.
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Semi-automatic machines offer some of the benefits of auto joining equipment, withoptional data logging facilities.
6.1.2 Electro Fusion WeldingElectro Fusion Welding is also known as resistive implant welding.
This technique one of the most common used for the joining of polyethylene gas andwater pipes and pressure systems.
The electro fusion welding process involves the use of a moulded socket fitting containingan electrical resistive heating coil.
The prepared pipe ends are inserted into the sockets and clamped. An internal stop at thecentre of the fitting prevents the pipe ends from meeting. An electrical current is thenpassed through the coil for a pre-set time.
Heating of the surrounding polymer and heat transfer to the pipe wall takes place.
Cold zones at the ends of the fitting contain the melt in the central section, allowing a highmelt pressure to develop and the formation of a homogeneous joint.
Fusion indicators are commonly designed into the fitting. If sufficient melt pressure hasbeen generated, the indicators will protrude, giving the operator a visual indication that thewelding process has been carried out successfully.
If the indicators fail to protrude, then the welded fitting shall be cut out from the pipeline,and a new fitting shall be welded in place.
Important pipe preparation stages:
The pipe ends must have finished squared ends. This ensures that the central coldzones function to contain the melt.
The pipe surfaces to be joined must be properly scraped to reveal uncontaminatedmaterial. The tolerances in the electro fusion joining process are narrow, resulting inlittle or no relative movement between the pipe and the coupler. Therefore, anycontamination on the pipe surface is retained at the joint interface, which cansignificantly reduce the strength of the joint.
The pipe and fitting should be clamped during welding to eliminate relative movement.This ensures that the molten polymer is contained at the fusion interface, allowing thedevelopment of a strong joint.
The electro fusion joining process can be split-up in three phases of progress:
initial heating and fitting expansion
heat soaking and creation of joint
cooling of joint
The first two points are commonly indicated as ‘fusion time’
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Advantages
electro fusion welding is suited to installations where access is difficult, such as intrenches or around other pipes.
electro fusion welding can be used to join different grades of the same material (e.g.MDPE to HDPE)
with electro fusion welding a difference in wall thickness can be accommodated.
electro fusion welding can be used to join certain types of multiple layer pipes (e.g.nylon lined polyethylene pipe)
easy to use for repairs.
Application rangeElectro fusion welding is applicable to pipe sizes from 16mm to 800mm.
RemarksOnly if the appropriate procedures are followed, contamination and disturbance effectsthat might inhibit the fusion mechanism will be minimised.
6.1.3 Socket Fusion WeldingSocket fusion welding is a widely used technique for assembling plastics piping systemsusing injection moulded fittings. No consumables are required.
The pipe ends must be calibrated in first place by means of the peeling and chamferingtool.This preparation step removes at the same time the oxidised layer on the outside surfaceof the pipe. Removing the oxidised layer before welding is essential, as this can have adetrimental effect upon the final joint strength.The chamfering process produces a bevel on the leading edge of the pipe, which aidsentry into the socket fusion fitting during the welding process.
The welding cycle consists of a heating phase and a cooling/welding phase.
A metal socket, mounted on a hot plate, heats the outside circumference of the pipe.
Figure 1; Socket Welding – Preparation of The Welding
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Heating occurs along a defined length which will vary depending on the size of pipe andfitting being welded. A metal spigot on the opposite side of the hot plate simultaneously heats the insidesurface of the injection moulded fitting. The length of the heated region is the same as thatfor the pipe.
Figure 2; Socket Welding – Alignment and Pre-Heating
Both fitting and pipe are heated for a well defined length of time after which the heatedsocket/spigot tooling is removed and the pipe is pushed into fitting. Pipe and fitting are leftfor a predetermined time to cool and form a weld.
Figure 3; Socket Welding – Joining and Cooling
Advantages
socket fusion welding is easy to use with a short learning curve.
fast joining and cooling
Application rangeDepending upon the size of the pipe, this process can either be carried out by hand (for pipe sizes up to 50mm OD) or on a manual machine, similar to a manual butt fusionwelding machine, for pipe sizes typically between 63mm and 150mm OD.
6.1.4 Hot Gas WeldingHot gas welding (DVS 2207-3) is a manual process and can be applied to mostthermoplastics.
Equipment for hot gas welding is relatively simple and easy in use. In its simplest form,the main component is a hand-held welding gun consisting of an integral blower, a heatingelement with thermostat and a set of interchangeable nozzles for directing hot gas at thework piece.
Usually, the gun is fed with air, although for some applications nitrogen gas is used. Thetemperature of the hot gas stream is typically in the range 200-400°C.
Table 2; Recommended Gases and Temperatures for Hot Gas Welding
Welding temperature (°C)(hot gas stream)
Welding gas
PVC-U 330-350 Air
PVC-C 360-410 Air
PP 280-330 Air/Nitrogen
PE 300-350 Air/Nitrogen
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PVDF 350-400 AIR
ECTFE(*) 340-350 Nitrogen
(*) At ECTFE melting temperature, hydrogen chloride and hydrofluoric are released. Theworkplace must be ventilated well. Welders should wear eye and hand protection.
(**) Resin temperature to be limited to 220°C for PE and PP.
A filler rod made of the same polymer as the components to be welded should be used(DVS 2211).
Like many manual processes, its success depends greatly on operator skill.
With the heated gas directed towards the joint, local melting or softening of thecomponents and filler rod take place. A weld is formed when the joint region and filler rodfuse and then cool to ambient temperature.
For thicker sections, extrusion welding is used. Filler material is separately heated in thebarrel of a hand-held extruder. Softened or molten material is extruded through a PTFEdie into the joint which has been pre-heated using a hot gas gun mounted on the extruder barrel.
The main advantage of hot gas welding is that the equipment is portable. However, theprocess can be slow and weld quality is operator dependent.
Fabrication of containment vessels and pipe work are the main applications.
Application rangeHot gas welding is limited, due to the lower pressure sustaining capabilities (maximumoperating pressure range < 4 bar), to welding of small branches to the run pipe, such asdrain and vent connections or instrument take off points. Increasing the pressuresustaining capabilities can be achieved with application of an additional fibreglassreinforcing wrap. This method should be avoided and only be used if other solutionscannot be applied.
Hot gas welding can be used to repair small leaks at joints in solvent welded or fusionwelded thermoplastic piping systems. In case of steady stream leakages repairs are notpossible, resulting in cutting out and replacement of the failing part.
6.1.5 Infrared WeldingTwo approaches for the welding thermoplastic materials with infrared technology areused. Both are based on the principle of hot plate welding.
Non-contact hot plate (DVS 2207-6)This system uses an electrically heated metal plate which, in some cases, is coated with aceramic.
The hot plate is heated to a temperature between 310°C and 530°C, depending on thethermoplastic to be welded, and the size of the welding machine.
When the parts to be welded are brought in close proximity to the hot plate, (typically 1.5-2.0mm) but without touching, they heat up due to radiation and convection andsubsequently soften and melt.
The plate then withdraws and the parts are forced together to form a weld.
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Infrared lamp welding (DVS 2207-6)The standard heater plate is replaced with two banks of short wave infrared emittersclamped and spring-loaded on either side of a movable platen.
Input power can be higher compared with conventional hot plate welding, resulting in weldtimes that are significantly shorter.
This technique is also capable of handling large surface area products, as it is a simpleoperation to add more emitters to the heating bank.
High power short wave infrared emitters are more efficient and effective than infraredemitters. Due to high power density, developed at a lower operating temperature, theenergy transfer is more efficient than halogen emitters, while its lower mass filamentmakes it more responsive than ceramic emitters.
Advantages
Infrared fusion welding is a contact-free process, which eliminates the possibility of contamination during the melting process of the components.
Pipe faces sticking to the heater plate can be avoided.
Infrared fusion welding is resulting in a weld bead reduced in size since the area of material softened is substantially smaller. The pipe bore is kept as large as possibleand this minimises the possibility of a reduction in the flow rate of the media within inthe pipe.
The smaller weld bead reduces the probability of service-induced deposits, building-upon the surface.
Application rangeManual IR welding machines are available in the following typical sizes:
20-63mm
63-225mm
6.1.6 Bead and Crevice Free (BCF)The Bead and Crevice Free welding method is used for clean and super-clean conditionapplications (e.g. ultra pure PVDF piping systems).
In contradiction to all previous mentioned welding methods, no weld bead is produced,resulting in a full size internal pipe bore diameter for the complete piping assembly.
The pipes are placed in a clamping arrangement, which is also the heater assembly. Aninflatable insert is placed inside the pipe, so that it covers the joint area.
As the polymer around the joint melts, it cannot deform outwards because it is constrainedby the collar nor inwards because it is constrained by the insert. In addition, the thermalexpansion, caused by the heating of the joint area, cannot be accommodated bymovement of the pipes, because they are clamped.When the joint is heated, an expansion of the materials occurs, which applies axialloading to the pipes, aiding fusion and the formation of a high quality joint.
After a predetermined time period, the heat supply to the clamping equipment is switchedoff and the joint cools.
Application rangeBCF welding machines are available for pipe sizes between 20 and 63mm
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6.1.7 Solvent Cement WeldingWelding of polymers occurs when the polymer chains at the surface of one componentare mobile enough to entangle with chains in the other component.
Usually, thermal energy is applied to raise the temperature of the polymer above theappropriate transition temperature. Above these transition temperatures, polymer chainsare mobile and if two components are brought into intimate contact, polymer chainentanglement will occur, resulting in a weld.
In solvent welding, a solvent is applied which can temporarily dissolve the polymer atroom temperature.
When dissolvement occurs, the polymer chains are free to move in the liquid and canentangle with other similarly dissolved chains in the other component.
After sufficient time, the solvent will permeate through the polymer and out into theenvironment, so that the chains lose their mobility. This leaves a solid mass of entangledpolymer chains which constitutes a solvent weld.
The joint must be fully cured before pressure can applied.
The solvent cement joining process can be split-up in two phases of progress:
cleaning of parts and applying of solvent
bringing into intimate contact for a predetermined period
The cement typically contains the solvent for the polymer, together with a small quantity of the polymer to give the cement the consistency of syrup, making application easier.
Application rangeIndustrial use of organic solvents should be limited as much as possible. Thereforesolvent welding should be avoided.
Polypropylene, polyethylene, PVDF and ECTFE materials may not be joined together using solvent cements or adhesives.
6.1.8 Vibration WeldingVibration welding is a relatively new welding process, using the mechanism for generatingheat by the interaction of two rubbing surfaces.
This is produced by the linear motion of one of the parts relative to the other, whilst a forceis applied between them. Once molten material has been generated at the joint interface,the vibration is stopped and the parts are aligned. The force is maintained as the weldcools and consolidates.
Advantages
vibration welding allows the reduction of the weld/cooling phase by 95%
less effect of contamination, as the scrubbing action during vibration welding shouldtend to move any contamination away from the interface
self-regulating weld temperature, making overheating impossible
easier production of branches
lower energy consumption
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7 WELDING REQUIREMENTS
7.1 GeneralWelding shall only start after approval by COMPANY of all applicable welding procedurespecifications and procedure qualification records.
All materials to be joined must be completely clean and the surface scraped, if required, toremove any surface deterioration (e.g. UV damage). It is recommended thatpolypropylene is scraped in all circumstances.
Before starting any welding operation, all involved piping should be drained/vented anddried completely (if applicable).
All thermoplastic welding processes shall be performed in dry and clean areas, protectedfrom adverse weather conditions that may affect weld quality. Welding activities should beperformed only with an ambient temperature above 5°C.
In case welding is performed in outdoor conditions, temporary shelters or tents shall beinstalled to completely enclose the working area.
The preferred ambient working temperature is in the range of +5°C to +45°C.Temperature conditioning of a fusion welding area can be achieved by protecting theworking area by a tent or similar device.
A continuous temperature logging system of the enclosed working area should be in placeto check the applicable conditions.
Any indication of quality loss due to influence of external parameters should result inperforming sample welding seams under the given conditions.
7.2 Installation TeamsBefore commencing any welding activity, the CONTRACTOR must ensure that eachmember of the installation team has received training in the applicable thermoplasticwelding processes used for the materials to be installed (DVS 2212-1 or equivalent).
Where necessary, refresher training sessions should be arranged to update theknowledge of the installation team and to provide the necessary information, required bythe applicable installation material. This information process must be organized with thepiping material SUPPLIER, since application parameters can be slightly differentaccording the type of raw material.
Team members should be aware about the correct handling of the thermoplastic material.
Welding shall be done under supervision of qualified personnel and only by certifiedwelders. Each welder should make at least two test joints, before a certificate will beissued. This certificate should have a validation period limited in time.
Each approved welder shall be allocated an identification marking or number with whichhe/she should mark each pipe weld. Marking shall be of permanent, weatherproof type(e.g. painted markings, bar coding), compatible to the thermoplastic base material.
Piping lay-out drawings or the applicable isometrics shall serve as weld maps, identifyingeach required weld with a unique weld number and the welder’s number after com pletionof the applicable weld.
BES-CO-05-306-01 Rev: 1/ 27.04.2010 Sheet 18 / 19
A print of this document is only valid at the date of printing. For reference, use the actual version available on Borena.
A full weld traceability file shall be available and kept up to date in accordance with theprogress of the assembly activities. This file should include as a minimum:
Welding Procedure Specifications (WPS) of each applicable welding process
Procedure Qualification Records (PQR)
Welders Performance Qualifications (WPQ), including validation time frame.
Welding quality control sheets with identification plan of inspected welds
Applicable NDE procedures
NDE inspection reports
Hydrostatic inspection report
All procedures included in this weld traceability file must be approved and signed byCOMPANY.
7.3 Spool assemblyTo facilitate the spool assembly and assure a good alignment during the weld activities,the use of guides, pipe rollers or support is recommended. Using this kind of tools willreduce the drag forces on the involved pipe materials.
The areas to be welded should be cleaned immediately before the welding with a clean,fat-free planning tool.
Misalignment of joining areas should not exceed the range of 0.1 times the wall thicknessat the outside surface of the pipe.
7.4 Welding EquipmentFusion welding equipment (DVS 2208-1 / DVS 2208-2 / DVS 2209-2) shall be regularlyserviced and calibrated by manufactory trained technicians. This guarantees the reliabilityand reduces the down-time by faulty equipment.
At any time, each type of welding equipment shall be accompanied with an up to dateservice record, stating:
Date of last inspection
Inspection company, including name and signature of the inspector
Calibration results
Date of next scheduled inspection.
Any equipment without a services record available at the equipment location will beremoved from the job site.
To allow full welding traceability, welding equipment with storage facilities of weld recordsshould be selected in preference.
Fusion welding equipment should be assembled according the manufacturer’s instructionsand taking into account all requirements to allow safe working practices.
Fusion welding equipment shall be protected adverse weather conditions. All precautionsmentioned in ‘Section 7.1; General’ to avoid these conditions should be taken.
In order to avoid high local stresses and deformations in the pipe applicable to the weldingprocess, the clamping devices should surround the pipe outer surface as parallel aspossible to the welding plane.
BES-CO-05-306-01 Rev: 1/ 27.04.2010 Sheet 19 / 19
A print of this document is only valid at the date of printing. For reference, use the actual version available on Borena.
Care shall be take that a clamping action should not result in any change to the circular geometry of the pipe.
Special clamping devices should be used in case of fusion butt welding of fittings (e.g.welding neck flanges, stub flanges, etc.). This is to prevent any possible deformation of the pipe.
Guide elements should be used to ensure, together with the clamping devices, the gapwidth requirements (measured on cold jointing surfaces).The sliding surfaces of guide elements should be protected against corrosion by means of hard chrome plating.
Before starting a welding process, the required heating temperature of the heatingelement should be checked and compared with the required temperature, indicated in thewelding procedure.
A welding process can only be started if the heating element has maintained the requiredheating temperature for at least 10 minutes.
The heating plate/element should be cleaned before starting a welding action. This shouldbe done with appropriate cleaning products, specified by the welding equipment supplier.In any circumstance, the coating of the heating element must be free of any damage or dirt within the applicable working (heating) radius sector.
To avoid possible damaging of the heating plate, it is recommended to put the heatingplate, after cooling down, immediately into the protecting holder.
7.5 Solvent Cement WeldingSolvent cement primers and cleaner contain volatile solvents, with fumes heavier than air.Good ventilation of the work areas is essential to prevent the build up of fumes inenclosed spaces.
In case fume extraction is used, the extraction inlet should be positioned at the floor level,or immediately below the working area.
Protective eyewear and solvent resistant gloves shall be used in all circumstances.
Solvent cements are highly flammable. Therefore open fire, sparks, heater equipment or smoking shall not be permitted in the working area.
For environmental reasons, discarded solvent containers should be foreseen. Brushes,paper or clothes containing traces of solvent cement cleaner or primer should collectedseparately and stored in sealed containers.
Under no conditions solvents shall not be poured into the drainage system.
Accidental spillage should be cleaned immediately in order to prevent contamination of piping and fittings or any risk to the environment may occur.
In case solvents are stored in cold conditions, a gradual conditioning of the solvents to theworkplace temperature level shall be taken into account.
