Abstract
Hydrostatic pressure testing, or hydrotesting, of oilfield production and storage equipment requires that the damage done to equipment during testing is minimal. In this case study, the storage tanks at a large liquefied natural gas (LNG) terminal were to be hydrotested using the natural brackish water found near the site. Due to environmental regulations and schedule/cost implications, chemical treatment of the hydrotest water was not possible. Concerns over both microbiologically influenced corrosion and preferential corrosion in the heat affected zone of the tank plate welds were the major technical issues.
The hydrotests were conducted successfully using brackish water without chemical treatment. Post-test visual inspection verified that some flash rusting was evident near the heat affected zones but no significant damage was registered. The primary mitigation step taken was temporary cathodic protection of the stainless steel internal piping, ladders, and other fixtures using sacrificial anodes and protective coatings. Additionally, the duration of test was minimized through efficient execution as well as potable water rinsing post-test and de-watering and drying steps immediately after draining. Microbiological testing of the brackish water was conducted prior to and at intervals throughout the test duration to determine if risk of microbiological activity was present.
