Sour Environmentally Assisted Fatigue of Welded SCR Materials: Post-Weld Finishing Treatment Evaluation

Abstract

The current work aims to point out the influence of sour brine environment on the fatigue resistance of welded SMLS (seamless) steel pipe used for design and fabrication of risers for oil and gas development. A C-Mn steel X65 pipe 10.75″ (273.1 mm) outside diameter (OD) and 25.4 mm wall thickness (WT) was chosen for this program. The Welding Procedure designed for girth welds manufacturing involved the use of Lincoln STT-GMAW™ process for the root pass and SAW process with twin wire configuration for the fill and cap passes. This welding procedure presents a special post-weld finishing treatment, which consist in flapping the inner and outer weld overfills to produce a flush profile between weld metal and outer/inner pipe surfaces. The experimental approach focused on quantifying the effect of H2S using a sour brine environment. For this purpose, intermediate-scale fatigue data in the sour brine environment, using full thickness’ strip specimens extracted from the welded SMLS (seamless) pipe, have been generated. Intermediate-scale fatigue tests in air have also been obtained to provide a baseline for comparison with the sour brine data. Those results have been compared with full-scale fatigue tests in air environment. Finally, results were statistically analyzed to determine which standard fatigue design curves best represent the measured S-N fatigue endurance in air and sour brine environments. Results were also compared with available literature and results on other seamless’ welded pipe of the same API 5L, Grade X65 steel in comparable environments.