What’s the difference between API and ASME standard ?

A lot of people in oil industry ofen think about this question: “What is the difference between an ASME and API code? In fact, ASME is actually a construction codes that cover design, fabrication and new construction issues but after they are put in service API codes governs the continued operation, inspection and repairs. For example, ASME Section VIII covers fabrication of pressure vessels but once the pressure vessel are put in service, API 510 takes place. Process piping in refineries, terminals or petrochemical plants are designed and built per ASME B 31.3. After they are placed in service, API 570 governs inspection and repairs.

ASME VIII, V and IX is actually a construction codes that cover new construction issues, rather than the ultimate in fitness for service (FFS) criteria or technical perfection. They are written entirely from a new construction viewpoint up to the hand over or putting the equipment into used. These codes are strictly not written with the activity of in-service inspection, repair or alteration in mind. They are definitive about the technical requirements or acceptance criteria that they set.

Meanwhile the API inspection codes such as 510, 570 & 653 and their supporting recommended practice documents are totally different. They are not construction codes and less definitive. They are based around accumulated expertise from a wide variety of equipment applications and situations. The content is more about in-service inspection, repair, alteration and rerating of equipment that are already in place or in used. That’s why they also contain technical opinion as well as fact and the technical areas that they address can be diverse and uncertain. You can see in API codes when it involves decision with design issues, the inspector is directed to consult or get approval with design engineer.

Originally, in 1934, a code for safe practices in the design, construction, inspection, and repair of pressure vessels to be used in the petroleum industry were published by joint committee of API and ASME entitled “API/ASME Code for Unfired Pressure Vessels”. The code was discontinued in 1956, leaving the ASME Code to cover only for new construction issues and later in 1958, API 510 were first published, intended to assure the industry to preserved the uniform maintenance and inspection practices.