Frequency of Pressure Vessel Inspections According to API 510
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Equipment inspections in an industrial plant are essential to ensure the safety and operability of the plant. Inspection plans should detail both the inspections to be carried out, mentioned in the previous blog article, and the frequency with which they should be carried out.
Firstly, it is essential to carry out pressure vessel (PV) inspections during installation to ensure that the equipment is safe for operation and has not suffered significant damage during transport to the installation site.
Following this, the scheduled inspection intervals in an inspection plan are defined through careful planning and accumulated experience, considering several key factors such as:
In the event of changes to the vessel’s conditions, such as significant changes in the process fluid, or in the pressure and/or temperature conditions, new inspection intervals must be established based on the updated service conditions.
Another recognized methodology for inspection planning is Risk Based Inspection (RBI). This methodology, accepted in API 510, enhances traditional planning by prioritizing inspections based on the risk associated with possible failures, where risk is a function of both the likelihood of failure and its potential consequences. RBI, described in API RP 580, allows for inspection intervals to be established that may exceed predefined limits in justified cases.
External Inspection:
Unless justified by RBI, the interval between external visual inspections for above-ground pressure vessels shall not exceed 5 years or the interval required for internal/in-service inspections.
External inspection intervals for vessels in discontinuous service shall not differ from those for vessels in continuous service because the external environment remains unchanged during periods of discontinuous service.
Internal, In-Service Inspection, and Thickness Gage:
Unless justified by RBI, the interval between internal, in-service, or thickness gage inspections shall not exceed the lesser of one-half of the remaining useful life of the equipment or 10 years.
Similar/Same Service:
When a vessel has been internally inspected, the results of that inspection may be used to determine whether an internal inspection may be substituted for an in-service inspection on a similar pressure vessel operating in the same or similar service and conditions.
Pressure Relief Devices:
Pressure relief devices shall be inspected, tested, and maintained in accordance with API RP 576 and API 510. Unless documented experience and/or an RBI evaluation indicates that a longer interval is acceptable, inspection and test intervals shall not exceed:
Deferral of Repair Recommendation Dates:
Repair recommendations that cannot be completed by the scheduled due date may be deferred for a specified period, by a documented change in the required completion date. This deferral must be recorded and approved by appropriate inspection personnel, including the inspector and supervisor.
Notwithstanding inspection intervals and recommendations, a substantial portion of section 6 of this code is devoted to providing technical justifications for deviating from such intervals. This section effectively promotes a risk-based inspection (RBI) approach to the evaluation of Pressure Vessels (PVs), by establishing certain “limits” that must not be exceeded. By interpreting the section from this perspective, its content becomes more coherent and less confusing.
For more information: API 510 | Pressure Vessels Inspection and Repair
Written by: Javier Tirenti