Managing sour service in oil export and onshore pipelines: A case study

Abstract

Thirteen extended H2S excursions (19.64 mg/l maximum) above the Standard Operating Limit (SOL, 6.7 mg/l), recorded for the export and onshore pipeline systems in January 2010, contravened the Pipelines Safety Regulations (PSR) 1996 and triggered an assessment to determine the safety of continued operation in a sour service condition. Sampling and monitoring results were assessed and the pH and H2S partial pressures were found not to align with any of the ISO 15156 SCC regions of environmental severity (0, 1, 2 and 3). Both pipelines were, therefore, considered safe for continued operation as long as pH remained near-neutral above 6.5. Since pH was found to be the main driver for SSCC risk, pH analysis has been recommended for every pig receipt with H2S and CO2 excursions being the main triggers. Also the high risk of HIC should be mitigated by maintaining pH at near-neutral levels. Very low H2S levels have been achieved by pigging, biociding and scavenging and low corrosivities by adequate corrosion inhibition. Weld root hardness of the export pipeline (295 HV10) is out of compliance with ISO 15156 hardness requirements for operating in the SCC region 0 (275 HV 10). Risk-based inspection (RBI) reviews are recommended to determine inspection techniques and frequencies appropriate for all susceptible weldments. © 2013 The Author(s).