Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

A Comparison Of Finite Element Based ECA Approaches For Pipeline Girth Weld During Reeling-Lay
Daowu Zhou, Xiaowei Wang, T. Sriskandarajah
Subsea 7Sutton, UK2c∆af∆at∆atot
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ABSTRACT
Three dimensional finite element based ECA is needed for non overmatching welds during reel-lay. Two procedures are presented. One
procedure is based on a tearing-low cycle fatigue concept which isincluded in BS7910. The other procedure disregards low cycle fatigue
but treats the blunting as part of tearing. This procedure is described in
DNV-RP- F108. This paper compares reeling crack growth between thetwo approaches using an 18” diameter alloy overlay pipe. The
comparison reveals that both methods give comparable crack growth.
Detailed comparisons on safety margin are discussed. This work helps
industry to appreciate the confidence level in reeling FE based ECA.

J0.2BLνINTRODUCTION
Offshore pipeline typically requires an over-matching girth weld.
However, the increasing selection of high strength steel and corrosion
resistant alloy (CRA) clad/ lined pipes has created the need to address
the issue of partially over-matching or fully under-matching girth welds.
During reel-lay, strain concentration occurs in the weld region with theweld partial over-matching or full under-matching. The fracture integrityof the weld cannot be addressed through the typical failure-based
diagram (FAD) based engineering critical assessment (ECA). 3D finiteelement (FE) analyses are required in this scenario.

KEY WORDS: reeling ECA; girth weld; clad pipe; Finite elementanalysis; tearing; low cycle fatigue.

NOMENCLATURE
3DCDF
CRACSCTOD
EECA
FAD
FCGR
FE (A)HL
JKODpSENT
WTYs
aflaw length
crack growth due to fatigue
crack growth due to tearing
total crack growth due to fatigue and tearing
blunting limit taken at 0.2mm extension vertical crossing in aJ-R curve
blunting limit taken at 0.2mm extension offset crossing in a JR curve
Poisson ratio

three dimensional
crack driving force
corrosion resistant alloy
carbon steel
crack tip opening displacement
Young’s modulus
engineering critical assessment
failure assessment diagram
fatigue crack growth rate
finite element (analysis)
flaw heightflaw length
toughness or crack driving force
stress intensity or crack driving force
outer diameter
ligament or remaining ligament
Single edge notched tension
wall thickness
yield strength
flaw height

Two distinct ECA procedures based on 3D FE analyses for reel-lay arepresented in the public literature. One procedure is based on a tearinglow cycle fatigue concept in BS7910 (BSI, 2019). Tearing is calculated
when the crack driving force exceeds the blunting limit (crack initiation)and the low cycle fatigue mechanism is used to account for the crack
growth between multiple reeling cycles. The total crack growth is thesummation of the tearing and low cycle fatigue. In contrast, the otherprocedure disregards the low cycle fatigue due to multiple reeling cycle
but treats the blunting as part of tearing. This procedure is followed inDNV-RP-F108 (DNV, 2021). Both methods have been widely used in
the industry.
The purpose of this paper is to present the FE based ECA procedure in
the reeling installation phase. A CRA pipe of 18” diameter subjected toreel-lay from a recent project is used in this study. The FE study includes
all the essential parameters (such as geometry mismatch, material1694