Failure Along Spiral Welds in Gas Pipeline

Abstract

A 16 km. long, 18” Gas pipeline (HP055) was in service to transport High Pressure Gas from an oil gathering center in West Kuwait (WK) area since 2001. The Pipeline carried wet sour gas. It was inspected in 2008 using high resolution MFL-ILI tool. No significant corrosion was found. In late 2012, a leak developed in the pipeline. The leak was due to a crack along a spiral weld on the bottom. Inspection during repairs revealed severe internal pitting on the bottom. The pipeline continued to leak several times in the next year, eventually resulting in decommissioning of the pipeline. Another ILI could not be carried out due to operational constraints and frequent leaks. The Pipeline was critical in the operation of the oil gathering center, and the loss of it severally affected the gas/oil export target and the flaring reduction commitment. An internal failure investigation was inconclusive, though indicating possibility of sulfide stress cracking. The failure investigation work was then entrusted to TWI, UK. A failed section of the pipeline was sent to their facilities and various tests including Chemical analysis, tensile test, residual stress measurement, SSC/HIC test, microstructure analysis, and analysis of corrosion products were carried out. The outcome of the tests and conclusion was very surprising. This paper describes in detail the leaks, inspection of leak locations, and the failure investigation findings and conclusions.

Crosspoint Localization of Spiral and Girth Welds of Spiral Steel Pipelines

“…Spiral steel pipe has lower cost and larger size than that of seamless steel pipe. In 2016 [1], China has upgraded the steel grade of gas transmission pipeline from X52 to X80, increased the pressure of gas transmission pipeline from 6.3MPa to 12MPa, and the transmission capacity of single pipeline has reached 30 billion m 3 /a, and the gas explosion test proved that the strength of spiral welded pipe has higher strength than that of straight welded steel pipe [2][3][4]. Therefore, spiral steel pipe occupies a large share in oil and gas pipeline [5][6].…”

“…One section in a field spiral pipeline has two spiral-girth weld crosspoints, which are the spiral starts at the inlet and the outlet. Strength at the crosspoint is much lower than that at other parts of a spiral pipeline, and cracking here is easier to occur [7][8][9][10][11]. It is required to excavate the soil outside the buried pipeline from a suitable direction, and expose the spiral-girth weld crosspoint for careful inspection.…”