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Case Study

Sour service assessment on non-compatible equipment to avoid downtime


Upstream oil & gas client


Fixed equipment/pressure vessels



Client challenge

Our client had fixed equipment in sour service for 5-10 years and it was unknown to the client if that equipment was fit for sour service or not. The client wanted us to perform an assessment on the same and give a recommendation.

How we helped

Due to lack of design data availability with the client for this equipment in question, we ordered the equipment design document (U1As) that the fabricator files with National Board to understand the necessary design details. The vessels that showed lack of helpful heat treatment during fabrication were chosen for detailed inspection.

Detailed inspections consisting of thickness assessment using UT, external and internal visual inspections to see any noticeable damages or the features of internal corrosion and its extent and Phased Array UT (PAUT) were performed at the susceptible locations, like welds and heat affected zones and into the base metal on either sides of each weldment by few inches to review any through thickness cracking due to service over the years.

Powerful results

Results of the detailed inspections showed no visible internal surface damage or blistering that can be caused by sour service. PAUT did not reveal any extent of cracking in the most susceptible areas even after 5-10 years in service for many cases. Thickness readings showed near nominal thickness indicating less corrosion activity in general.

The client was recommended to replace these vessels nonetheless after replacement vessels were received. Shutting down of the service in these vessels to halt production was not deemed necessary as the vessels considered susceptible showed no inherent damage from service even after prolonged use. Re-purpose of these vessels was possible for non-sour service similar rating wells so equipment got scrapped and savings were enhanced for the client.

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