Wallthickness Design Report

GAMBA EXPORT LOADING LINE (SHELL GABON)

Wall thickness Report

Issued Date

PROJECT NUMBER: 13027 Sht. No. Rev. No.

17/12/13 DOCUMENT NUMBER : Z.202.1 2 of 25 B

REVISION CONTROL SHEET

REV.NO SECTION NO. SUMMARY OF CHANGES

B Table 4.1 WT changed


B Table 5.2 Design parameters confirmed




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TABLE OF CONTENTS

1.0 INTRODUCTION .............................................................................. 4

General ......................................................................................... 4 Scope of work ............................................................................... 4

2.0 UNITS, ABBREVIATIONS & NOMENCLATURES .......................... 6

System of Units ............................................................................. 6 Abbreviations ................................................................................ 6 Nomenclature ................................................................................ 6

3.0 REFERENCE DOCUMENTS ........................................................... 9

Company Engineering Standards .................................................. 9 International Codes, Standards and Guidelines ............................. 9 Project Reference Documents ....................................................... 9

4.0 SUMMARY, RESULTS, CONCLUSIONS & RECOMMENDATIONS10

Summary & Results ..................................................................... 10 Conclusions & Recommendations ............................................... 10

5.0 DESIGN DATA .............................................................................. 12

Fluid category .............................................................................. 12 Design Pressure & Temperature ................................................. 12 Line Pipe Design Data ................................................................. 13 Corrosion Allowance ................................................................... 13 Design Factors ............................................................................ 13 Dimensional Tolerances .............................................................. 14 Water depth & Ground Elevation along the route ......................... 14 Tidal and Wave data ................................................................... 15

6.0 DESIGN METHODOLOGY ............................................................ 16

General ....................................................................................... 16 Required Wall thickness .............................................................. 16 Pressure Containment ................................................................. 17 Hydrostatic Collapse due to External Pressure ............................ 17 Propagation Buckling................................................................... 18 Design Loads .............................................................................. 18 Results ........................................................................................ 19

APPENDIX A – WALL THICKNESS CALCULATIONS .................................. 20



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1.0 INTRODUCTION

General

Shell Gabon is operating and producing oils from numerous fields located in the

western part of Gabon. Crude is treated and exported from the Gamba Terminal

to tankers through a 30 inch dual offshore export line connected to a SBM via a

PLEM and 2 x 16 inch floating hose strings (risers).

The total length of the existing export line is about 10.7km from the export pump

in Gamba terminal to a PLEM (1.3km located onshore and 9.4km located

offshore).

Figure 1-1: Project Location

Shell Gabon intends to replace the existing export pipeline. Zeetech B.V. has been

awarded by Shell to perform a concept replacement study for dual pipelines and

Front End Engineering Design (FEED) for the selected concept.

Scope of work

The wall thickness of the both offshore and onshore 22 inch Gamba Export dual

pipelines with material grade API 5L X-65 are calculated based on the following

failure modes have been considered in this analysis.

Internal Pressure containment as per ASME B31.8 & ISO 13623

Propagating buckle pressure & Collapse as per API RP 1111



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The required wall thickness has been calculated by taking into account of the

corrosion allowance and fabrication tolerances. The selected wall thicknesses are

determined in accordance to API SPEC 5L standard wall thickness.



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2.0 UNITS, ABBREVIATIONS & NOMENCLATURES

System of Units

In accordance with Shell DEP 00.00.20.10. (Ref. [1]), the International System (SI)

of units is adopted as the main system of units unless noted otherwise.

Abbreviations

API American Petroleum Institute

ASME American Society of Mechanical Engineers

DEP Design Engineering Practice

FEED Front End Engineering Design

HAT Highest Astronomical Tide

ISO International Standard

LAT Lowest Astronomical Tide

MAOP Maximum Allowable operating Pressure

MSL Mean Sea Water Level

OD Outside diameter

PLEM Pipeline End Manifold

RP Recommended practice

SBM Single Buoy Mooring

SI International System of Units

SMYS Specified minimum yield strength

SPEC Specification

TBC To be Confirmed

WD Water Depth

Nomenclature

Ap Area of Pipe

D Outside Diameter

DFoff Design factor offshore pipeline

DFon Design factor onshore pipeline



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dmax Design water depth for collapse & buckling criteria

dmin Design water depth for Hoop stress criteria

E Young’s modulus

fo Collapse factor

fp Propagating buckling factor

Hmax Wave Height

HWL Highest water level

oC Temperature in degrees Celsius

Pb Specified minimum bursting pressure

Pc Collapse pressure

Pe Elastic collapse pressure

Pe_max External Hydrostatic pressure for Collapse & Buckling

Pe_min External Hydrostatic pressure for hoop stress

PiH Maximum Operating Pressure

Pp Critical buckling pressure

Py Yield pressure at collapse

Ta Axial tension in pipe

tCA Corrosion allowance thickness

Teff Effective tension in pipe

tf Fabrication tolerance thickness( 8% of tprovide)

tmin Minimum pipeline wall thickness

tminI Minimum pipeline wall thickness based on D/t ratio

tminp Minimum thickness including Corrosion allowance

tprovide Final thickness of pipeline

treq Required thickness

Ty Yield tension in pipe

U Minimum ultimate tensile strength

UCcom Combined load check

WDmax Maximum water depth

WDmin Minimum water depth

ϑ Poissons ratio



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ρsea Seawater density

σa Axial stress in pipe wall

σhd Circumferential hoop stress due to Fluid pressure



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3.0 REFERENCE DOCUMENTS

The following company standards, codes and standards have been utilized in the

wall thickness calibration.

Company Engineering Standards

[1] Shell DEP 00.00.20.10, the Use of SI Quantities and Units, 2005.

[2] Shell DEP 31.40.00.10, Pipeline Engineering (amendments/ supplement to

ISO 13623), 2010.

[3] Shell DEP 34.00.01.30, Minimum Requirements for Structural Design and

Engineering, 1998.

[4] Shell DEP 34.28.00.31, Steel Structures, 1996.

International Codes, Standards and Guidelines

[5] ISO 13623, Petroleum and Natural Gas Industries, Pipeline Transportation

Systems, 2009.

[6] DNV OS F101, Submarine Pipeline Systems, 2010.

[7] API RP 1111, Design, Construction, Operation and Maintenance of Offshore

Hydrocarbon Pipelines– Limit state Design, 2009.

[8] ASME B31.8, Gas Transmission and Distribution Piping Systems, 2007.

[9] API Specification 5L, Specification for Line Pipe, 44th Edition, 2007.

Project Reference Documents

The following related project documents are referenced.

[10] Design Basis Doc. No:13027-ER-001

[11] Concept Evaluation - Gamba Export Loading Line, Doc.No: Z.100.1.

[12] Gabon Metocean Geophysical and Environmental data collection, Doc. No:

GSL-08207-GPH-003.



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4.0 SUMMARY, RESULTS, CONCLUSIONS & RECOMMENDATIONS

Summary & Results

This section presents the summary of results in accordance with the calculations

performed in Appendices A of this report.

The analyses have been performed considering the following pipe outer

diameters, material grade and manufacturing process:

22 inch (559 mm) Outer Diameter Pipe, API Spec 5L - X65 Material Grade

(Seamless).

Analyses have been performed to confirm the required wall thicknesses for the

above mentioned pipe parameters for the following assessment criterion:

Pressure Containment(bursting)

Hydrostatic System Collapse

Buckle Propagation

Design methodology of the above-mentioned analyses has been presented in

Section 6.0 of this report. Based on the calculations performed, the results have

been summarized in the following table.

Table 4.1: Summary of wall thickness Results

Pipe OD(mm)

Material Grade

tCA (mm)

Governing Load Case

tf (mm)

Minimum Required WT(mm)

Selected WT(mm)

559 X65 0.0 Hydrotest 8% 5.74 10.0

559 X65 3.0 Internal Pressure 8% 8.74 10.0

Conclusions & Recommendations

The proposed wall thickness for dual pipelines is based on API 5L Specification

Standard wall thickness and meets all requirements of the wall thickness checks.



Issued Date



It is recommended that a single wall thickness fulfilling all wall thickness checks

be proposed for both offshore and onshore sections. The results are tabulated in

the following table.

Table 4.2: Recommended wall thickness from PLEM to landfall

Pipe

OD(mm)

Material

Grade

WT(mm) D/t

558.8 X65 10.0 58.84

Note:

No buckle arrestors are required based on the cases analyzed for buckle propagation in

the calculations.

The Diameter to the wall thickness (D/t) ratio for the recommended wall thickness is in

accordance with reference [2].



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5.0 DESIGN DATA

Unless otherwise stated, all design data considered in the wall thickness

calculations for the proposed offshore pipeline, presented in the following

subsections, have been obtained from the Specification –Design Basis (Ref. [10]).

Fluid category

Fluids transported by the pipeline system are to be categorized according to their

hazard potential with respect to public safety (Reference.2, Table 1).

Table 5.1: Categorization of Fluids

Fluid Category

Description

A Typical non-flammable water-based fluids.

B Flammable and/or toxic fluids that are liquids at ambient temperature and at atmospheric pressure conditions. Typical examples are oil and petroleum products. Methanol is an example of a flammable and toxic fluid.

C Non-flammable fluids that are non-toxic gases at ambient temperature and atmospheric pressure conditions. Typical examples are nitrogen, carbon dioxide, argon and air.

D Non-toxic, single-phase natural gas.

E Flammable and/or toxic fluids that are gases at ambient temperature and atmospheric pressure conditions and are conveyed as gases and/or liquids. Typical examples are hydrogen, natural gas (not otherwise covered in category D), ethane, ethylene, liquefied petroleum gas (such as propane and butane), natural gas liquids, ammonia and chlorine.

As the product to be transported through the pipelines oil, the product belongs to

Category B.

Design Pressure & Temperature

The operating/ design pressure and temperatures have been extracted from

design basis (Ref. [10]) and presented in the following table.

Table 5.2: Design Pressure & Temperature

Parameter Unit Value

Design Pressure barg 60

Design Temperature oC 60



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Line Pipe Design Data

The line Pipe material properties extracted from the Design Basis (Ref. [10]).and

are tabulated in the following table.

Table 5.3: Line Pipe material Properties

Parameter Unit Value

Dual pipelines OD mm 559(22”)

Material Grade - API 5L X65

Specified Minimum Yield Stress Psi/MPa 65000/448

Young’s Modulus MPa 207 x 103

Density kg/m3 7850

Poisson’s ratio ϑ 0.3

Corrosion Allowance

The corrosion allowance 3.0mm shall be considered as specified by Company.

Design Factors

Design factors considered for the wall thickness analysis as tabulated below table.

Table 5.4: Design Factors

Description Value

offshore onshore

Hoop stress

design factor

General 0.77 -

Landfall 0.67 -

General route - 0.77

Crossings - 0.67

Temperature derating factor 1.0

Collapse design factor, fo 0.70

Propagating buckling design factor, fp 0.8



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Dimensional Tolerances

Dimensional tolerances for the dual pipelines are as follows, in accordance API

Spec 5L for Line Pipe (Ref. [9]):

- Wall thickness: -8%, +19.5%

- Out of roundness: no greater than 0.75

Water depth & Ground Elevation along the route

The maximum water depth along the offshore pipeline are taken from the Design

basis (Ref. [10]).

Figure.5-1: Seabed profile along the Existing Pipeline route.

Figure.5-2: Ground Elevation along the Existing Pipeline route



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Table 5.5: Water Depth

Description KP (from – To) Min.Water Depth (m) Max.Water Depth (m)

Offshore dual Pipelines 0.000-10.700 0.0 24.0

Tidal and Wave data

Tidal and wave data considered in the design are taken from the Gabon LNG

Metocean Geophysical and Environmental data (Ref. [12]) and those values are

tabulated as below:

Table 5.6: Tidal & Wave data

Description Unit Height

Highest Astronomical Tide(HAT) m 1.99

Mean Sea Level ( MSL) m 1.01

Max.Wave Height, Hmax (Assumed) m 7.0



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6.0 DESIGN METHODOLOGY

General

This section presents the design methodology for the wall thickness checks for the

proposed dual pipelines. Pipeline wall thickness shall be calculated in accordance

with API RP 1111, ISO 13623 & ASME B31.8 (Ref. [7], Ref. [5] & Ref. [8]) to ensure

that the pipelines are strong enough to withstand both the Operating and Hydrotest

conditions.

Wall thickness design shall also consider collapse and buckle propagation due to

external Hydrostatic pressure.

Figure.6-1: Dual Pipelines concept layout.

Required Wall thickness

The required wall thickness shall considerer corrosion allowance and fabrication

tolerance as follow:

𝑡𝑟𝑒𝑞 = 𝑡𝑚𝑖𝑛 + 𝑡𝐶𝐴 + 𝑡𝑓 (Eq.6.2.1)

The final selected wall thickness refers to API Spec. 5L and shall be not less than

𝑡𝑟𝑒𝑞.



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Pressure Containment

The hoop stress formula in API RP 1111 is used to determine minimum required

wall thickness for the dual pipelines. The analyses are performed for the Hydrotest

and Operating conditions.

In this analysis, the minimum required wall thickness is calculated based on the

net internal design pressure, design factor, fabrication tolerance, corrosion

allowance, pipe outside diameter and the SMYS of the line pipe.

The minimum required wall thickness for a given net internal design pressure is

determined using the following formula:

𝜎ℎ𝑑 =(𝑃𝑖𝐻−𝑃𝑒_𝑚𝑖𝑛)(𝐷−𝑡𝑚𝑖𝑛)

2𝑡𝑚𝑖𝑛𝐷𝐹𝑜𝑓𝑓 (Eq.6.3.1)

Hydrostatic Collapse due to External Pressure

The pipeline shall be designed to resist collapse due to external pressure in

accordance with API RP 1111(Ref. [7]).

Hydrostatic Collapse shall be checked for operation condition considering a

corroded, non-pressurized pipe for a depressurization case.

According to section 4.3.2.1 of API RP 1111, the collapse pressure of the pipe

must exceed the net external pressure everywhere along the pipeline as follows:

Collapse Pressure,

𝑃𝑐 =𝑃𝑦𝑃𝑒

√(𝑃𝑦2+𝑃𝑒

2 (Eq.6.4.1)

Yield Pressure at Collapse,

𝑃𝑦 = 2 𝑆𝑀𝑌𝑆 (𝑡𝑚𝑖𝑛

𝐷) (Eq.6.4.2)



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Elastic Collapse Pressure,

𝑃𝑒 =2 𝐸 (

𝑡𝑚𝑖𝑛𝐷

)

(1−𝜗2) (Eq.6.4.3)

Permissible Criteria Check,

𝑃𝑒_𝑚𝑎𝑥 − 𝑃𝑖𝐻 ≤ 𝑓𝑜𝑃𝑐 (Eq.6.4.4)

Propagation Buckling

The propagation buckling pressure shall be determined in accordance with API

RP 1111 (Ref. [7]). Any requirements such as increased line pipe wall thickness

or using buckle arrestors shall be assessed in this section.

The use of buckle arrestors regularly spaced along the pipeline length potentially

subject to propagation buckling will be preferred to an increase of the pipeline wall

thickness.

The propagation buckling assessment has been performed for the pipeline lying

on the seabed after installation, empty and without any internal pressure.

Critical Propagation Buckling Pressure,

𝑃𝑝 = 24 𝑆𝑀𝑌𝑆 (𝑡𝑚𝑖𝑛

𝐷)

2.4 (Eq.6.5.1)

Permissible Criteria Check,

𝑃𝑒_𝑚𝑎𝑥 − 𝑃𝑖𝐻 ≤ 𝑓𝑝𝑃𝑝 (Eq.6.5.2)

Design Loads

The load combinations to be considered in the wall thickness analysis for the

operating & Hydrotest conditions are summarized below:



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Table 6.1: Design loads for Wall thickness analysis

Design Load Design Condition

Pressure Containment Collapse Buckling Propagation Buckling

Operating Hydrotest Operating Operating

Internal

Pressure

design

pressure

hydrotest

pressure

de-pressurized de-pressurized

Corrosion

allowance

100% tCA

removed

un-corroded 100% tCA removed un-corroded

Fabrication

tolerance

tf removed tf removed tf removed tf removed

Water Depth min.WD min.WD max.WD max.WD

Note:

1. Water depths are in accordance with Section 5.7

Results

Based on Mathcad sheets are attached in Appendix A, results of wall thickness

calculation for the 22 inch dual pipelines is presented in the following Tables.

The wall thickness has been selected in accordance with the wall thickness

presented in API 5L specification. No buckle arrestors are required.

The analyses performed herein satisfy the requirements for wall thickness checks

for the pre-project engineering stage.

Table 6.2: Wall thickness Results

Pipe

OD(mm)

Material

Grade

tCA

(mm)

Governing

Load Case

tf

(mm)

Minimum

Required

WT(mm)

Selected

WT(mm)

559 X65 0.0 hydrotest 8% 5.74 10.0

559 X65 3.0 Internal pressure 8% 8.74 10.0



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APPENDIX A – Wall Thickness Calculations



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