Pipe stress simulation and failure analysis of carbon steel flange spool in CO₂gas flow condition

Every year the repair costs for pipe replacement are lost due to corrosion in gas and oil pipelines increasing this can also affect the LPO (Loss Production Opportunity) due to production stoppages, due to the replacement and repair process. Currently investigating the cause of the damage is an alternative prevention to take preventive measures for the occurrence of the same condition, in addition to reducing costs and reducing consumption of new pipes for replacement. This paper examines the metallurgical and stress aspects of the material failure on the Flange Spool T Arm in the SBG-17 well head (upstream) and the Flange Spool Header Manifold (downstream), where the Spool Header Manifold was a combined flow of the SBG-17 and SBG-16 well heads. In the same condition, there was no material failure on the Flange Spool T Arm in the SBG-16 well head. The simulation results show the maximum calculated pipe stress, less than the allowable stress, the lines conform to ASME B32.3 code for the operating temperature of 60oC and 570 Psig respectively. Suspected of corrosion products at the damaged area of sample were iron oxides (FeOOH and/or Fe2O3), iron carbonates (siderite-FeCO3) and iron sulfides (FeS). The form of damage on the weldment flange spool well head only occur on the weld area, due to turbulence the layer of siderite is swiped away leaving local breakdown of corrosion products that exposed the metal to environment then it acts as anodic site where dissolution reaction occurs. The form of damage on the weldment flange spool header not only occur on the weld area, but also occurs at the base metal area. SEM observation on sample revealed the cubic shapes of corrosion products, which were typical for siderite (FeCO3) as the product of CO2 corrosion. This kind of corrosion commonly occur in mature oil wells, combination of high water cut and partial pressure of CO2.