Beneficial Effects of Chemical Treatment and Maintenance Pigging Programs in Returning an Offshore Pipeline to Pre-Hurricane Ike Conditions Following a Breach and the Ingress of Seawater and Sand, and the Effects of Bacteria Generated H_2S

摘要

When Hurricane Ike crossed the Gulf of Mexico in September 2008, one of the major laterals in an offshore gas gathering system was ripped from the trunkline. As a consequence of that breach, approximately 75,000 BBL (11.9 MM liters) of seawater entered the trunkline, and approximately 40,000 BBL (6.4 MM liters) of seawater entered the lateral. A previous paper (NACE #10064) described the repairs, the high levels of hydrogen sulfide (H_2S) that were generated by microbiological activity, the monitoring program, and the chemical treatment and maintenance pigging programs, which were implemented to re-establish control over the SRBs and the H_2S they generated. This paper is a follow up to that report. Although inhibitor residuals have been very high, sand production appears to have temporarily increased as the sand from within the lateral and trunkline is slowly transported uphill to the onshore gas processing facility, "one girth weld at a time." Of interest, the iron counts have become elevated. This may be attributed to the maintenance (cleaning) pigs, which are slowly pushing the sand that entered the pipelines when the pipeline was breached. The pigs, coupled with the transportation of the sand, are apparently scraping and "sand blasting" the walls of the trunkline, thus removing the oxides and corrosion products from the pipeline. This paper also presents results from destructive metallurgical examination of a hot tap coupon or "cut-out" obtained from the trunkline when a new 6" (15.2 cm) OD subsea tie-in (SSTI) was made at the 3:00 o'clock orientation in 2010.