A client has a new tank farm, and six (6) storage tanks are in identical service, and three (3) others are in similar service. So the question I get often is…
Since these tanks are identical in their design AND service, can we use inspection data from one (1) tank to assess the conditions of the other tanks of identical design and service?
The short and easy answer is YES, and here’s why…
API 510, Chapter 6: Interval/Frequency and Extent of Inspection
…
6.5.3 Same and Similar Service Equipment
When a vessel has been internally inspected, the results of that inspection can be used to determine whether an on-stream inspection can be substituted for an internal inspection on a similar pressure vessel operating within the same or similar service and conditions. The inspection of one vessel (preferably the worst case) may be taken as representative of the whole train when the following conditions are observed:
a) two or more pressure vessels are installed in series and no potentially corrosive contaminants are introduced at an intermediate point in the train or otherwise become present that could potentially affect the vessel integrity;
b) the operating conditions in any part of the train are the same;
c) sufficient corrosion history has been accumulated.
Risk assessment or RBI analysis may be useful when considering the extent of same service applicability in determining internal and on-stream inspection requirements based on comparing one pressure vessel to other pressure vessels and the number of pressure vessels to be inspected within a grouping.
However, if the vessel is subject to environmental cracking or hydrogen damage, the results of an internal inspection on a similar service pressure vessel cannot be used to substitute an on-stream inspection for an internal inspection.