API 510, Pressure Vessel Inspection Code
API’s “Pressure Vessel Inspection Code (API 510)” and its “Guide for Inspection of Refinery Equipment, Chapter VI, Pressure Vessels,” give useful guidance to owner/operators for meeting their obligation to maintain safe and reliable equipment. Both documents are included in this manual. Note that Chapter VI is out of print and due to be replaced by API RP 572 in 1990. However, a copy of Chapter VI is included for your reference.
API 510 is more specific about in-service inspection of a pressure vessel for internal corrosion than for any other form of deterioration that may occur. The maximum interval between internal inspections of pressure vessels recommended in API 510 is one-half of the remaining life related to corrosion, with a maximum of 10 years (API 510, Paragraph 4.3).
API 510 contains separate guidelines for pressure vessels used in oil and gas producing operations.
The corrosion allowance specified as a design condition for new vessels is usually determined to give an expected life of 20 or 30 years, based on corrosion-rate data obtained from laboratory tests or based on operating experience with vessels in similar service. It is permissible to adjust the corrosion rate based on the maximum corrosion rate actually exhibited by the vessel, to establish subsequent internal inservice inspection intervals. Actual corrosion rate is the rate established at the first in-service inspection. Large vessels with two or more zones exhibiting different corrosion rates can have different inspection intervals established for each individual zone. It is permissible to determine the depth of corrosion to satisfy these requirements while the vessel is in operation, providing the nondestructive examination (NDE) procedure used can give sufficiently accurate data (API 510, Paragraph 4.1). Vessels that are known to have a corrosion rate of less 0.001 inch/year need not be inspected internally.
The other forms of deterioration that can occur during the operation of a pressure vessel are mentioned in API 510 (API 510, Paragraph 3.5), but it is not specific about the in-service inspections that should be performed nor the intervals between inspections. The experience of the owner/operator inspectors is the primary source for information about potential forms of deterioration that can occur in a vessel under its operating conditions. Visual examination (VT) is the primary inspection procedure. Depending on the form of deterioration, visual examination should be supplemented by other types of nondestructive examinations.
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