Pressure vessel inspection and testing is an extremely detailed process. It comprises a comprehensive list of activities and tests. It also includes the standards that have to be adhered to during the pressure vessel design and construction process. These include:
- ASME Boiler and Pressure Vessel Code (BPVC)
- Choice of pressure vessel construction materials
- Pressure vessel heads
- Impact tests
- Dimension inspection
- Radiographic testing
Essential Points for Pressure Vessel Inspection and Testing
An understanding of the aforementioned points will give you a better idea of the intricate process of pressure vessel inspection and testing. These are discussed in detail below.
ASME Boiler and Pressure Vessel Code: Section VIII of the ASME BPVC elaborates on the construction code for pressure vessels, which also includes pressure vessel inspection and testing. Section VIII is divided into three basic groups â€“ construction codes, reference codes, and in-service codes. The reference codes group refers to guidelines provided in BPVC Sections V and IX for non destructive testing. The in-service codes group deals with inspection of the pressure vessel once it has been placed into service.
Pressure Vessel Construction Materials: This aspect discusses the specific materials that can be used to create the plates for pressure vessel construction. The materials are chosen by referring to the list of ASME and non ASME plate materials provided in the BPVC. The plate material is also inspected for chemical composition, weight, thickness, width, length, and mechanical properties.
Pressure Vessel Heads: There are 3 basic types of pressure vessel heads â€“ Ellipsoidal, Hemispherical, and Torispherical Heads. Design elements such as materials, pressure, and temperatures are examined to finalize the overall thickness of the head in respect to the thickness of the shell.
Impact Tests: These are conducted when the design process of the pressure vessel has been completed and the construction process is yet to begin. Steels and alloys that are used to construct the pressure vessel display severe changes in terms of toughness and fracturing when they are placed in sub-zero temperatures. Impact tests are designed to ensure that the chosen material will be able to maintain its strength at varied temperatures.
Dimension Inspection: This is done to test all the fabrication tolerance requirements that may not be mentioned in Section VIII of the BPVC. Pressure vessel dimension inspections consist of the following:
- Plates and pipes mill under tolerance
- Formed heads tolerances
- Out-of-roundness of shell
- Nozzles and attachments orientation
- Nozzles and attachments projection
- Nozzles and attachments elevation
- Nozzles and attachments levelness
- Weld mismatch
- Weld reinforcement
Radiographic Testing: Radiography tests are conducted on pressure vessels when any of the following incidents take place.
- The pressure vesselâ€™s butt welds can be used to contain dangerous substances
- The vesselâ€™s butt welds exceeds specified thickness values
- The butt welds in unfired steam boilers are higher than 50 psi in terms of design pressure
All of these tests and processes ensure that the pressure vessel is built to meet global application standards.