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 Method for Identifying Applicable Pipe End Machining Design for High Fatigue Performance GirthWelds
Hu Yang
Offshore Oil Engineering Co., Ltd.
Tianjin, P.R. China

Ning He
Offshore Oil Engineering Co., Ltd.
Tianjin, P.R. China

Fanli Xu
Offshore Oil Engineering Co., Ltd.
Tianjin, P.R. China

Jiankang Yuan
Offshore Oil Engineering Co., Ltd.
Tianjin, P.R. China

ABSTRACTINTRODUCTION

Pipe ends machining (counter-bore) is one of the practical approaches
for improving the fatigue performance of a welding pipe. This approachmakes the pipe end dimension within the range of the target internal
diameter (ID) and wall thickness (WT), in order to reduce the ID stressconcentration factor (SCF) caused by misalignment due to the pipe
manufacture tolerances.

Due to the presence of a higher stress level and potential defects in theweld toe, stress concentration mitigation is always considered in riser
fatigue design and construction, especially for the high fatigue
performance girth welds. Considering manufacturing tolerances, pipeend misalignment will aggravate the effect of stress concentration. Theground flush of the weld cap is beneficial to eliminate the stressconcentration on the outer diameter (OD), but it cannot apply on the ID.
Generally, the methods used for eliminating the stress level on the riser
ID can be mainly classified into 3 types (Mansour, 2021) as follows:

The counter-bore approach is very efficient for improving the fatigue
life on the girth welds. But it may introduce a more critical position on
the counter-bore area other than on the girth welds if the counter-bore
profile is not well designed, especially for the high performance girthwelds.
This paper investigates all the possible factors which may cause thehigher stress to appear in the base metal of the counter-bore area, andgives the key parameters which impact on it. Based on the fatigue test
methodology and S-N curve based fatigue design procedure, authors
propose a practical method/procedure to design a suitable counter-bore
profile to ensure that this profile does not fail earlier than the girth weld.
The implications of this paper should have significant relevance to thehigh fatigue performance welds design.

KEY WORDS: Counter-bore; Hi-Lo; SCF; Fatigue Test, TWC

1). Pick and rotate pipe on the firing line of the installation vessel forbest fit two welding pipes,2). Survey and sort all riser pipes by certain joints in sequence. Markingand tracking pipes during transportation. Carefully pick up pair of pipeson the firing line of the installation vessel3). Counter-bore the pipe end on the ID.
The counter-bore approach has better fatigue performance and more
efficient line up on the firing line of the installation vessel comparedwith other end-match methods. For the higher fatigue performancewelds, the counter-bore approach may be the only choice to meet thefatigue design criteria.
There are several ways to perform the fatigue analysis and design. In
the offshore oil and gas industry, the most common fatigue analysis

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