The Rationale for Update of S-N Curves for Single Sided Girth Welds for Risers and Pipelines in DNV GL RP C-203 Based on Fatigue Performance of More Than 1700 Full Scale Fatigue Test Results

Abstract

Deep-water tendon and riser systems are often subjected to severe fatigue loading from waves, currents and vessel movements. The girth welds between successive lengths of pipe or at pipe terminations represent fatigue-critical features where failure would be catastrophic. Hence, validation fatigue testing by full scale pipes of the most critical welds are often performed to ensure adequate quality and/or to document a better S-N curves than those available in standards today like DNVGL-RP-C203 [1] and BS7608 [2]. To better understand the fatigue performance with respect to identify trends, dependencies and critical features that influence the fatigue performance, a JIP on Fatigue of Girth Welds were initiated in 2011. Two phases have been conducted and a total of 1700 full scale one sided girth welds, mostly run by Stress Engineering, have been statistically analyzed. The test data has been interrogated to investigate the effect of as-welded condition, OD ground, OD/ID ground, un-reeled pipe, reeled pipe, thickness and effect of misalignment. Based on these analyses, new S-N curves for risers and pipelines have been included in DNVGL-RP-C203 for non-reeled girth welds. This paper presents the findings and trends from the JIP work which has been the rationale for the updates of girth welds in section 2.10 in DNVGL-RP-C203 2016 edition.

Fatigue performance of riser quality girth welds: Analysis of TWI and DNV's databases

“…The DNV database was established as part of the Girth Weld JIP. 13 It comprises a total of 1780 full-scale data where 410 are inner diameter (ID) cracks and 79 are OD cracks and the remainder were reported as runouts. Most of the tested pipes were in the range of X60 up to X80, where the majority were X65 pipes.…”

“…The DNV Class D and E mean and design SN curves are included. 13 [Colour figure can be viewed at wileyonlinelibrary.com] produce fatigue cracking from a postulated flaw was performed.…”

On Welded and Grouted Connections IN Offshore Tubular Steel Structures

“…The test specimens varied widely in terms of diameter (i.e. from 6 inch to 24 inch) and wall thickness, reeled, cladded, as welded and ground, Horn et al (2018). This new information formed basis for use of higher S-N curves for girth welds in risers and pipelines in the 2016 version of DNVGL-RP-C203.…”

Review on Fixed and Floating Offshore Structures. Part II: Sustainable Design Approaches and Project Management

“…As a result, the designs are carried out using peak loads generated by hurricane wind and waves during the platform design life [129][130][131][132][133][134][135]. In addition, fatigue loads induced by waves over the platform's lifetime, as well as platform motion, are all essential design challenges addressed by standards [136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152]. Strong currents can occasionally impact the platforms, putting the integrity of the entire system at a threat, hence the need for designing offshore structures against harsh weather conditions [153][154][155][156][157].…”