There is an obligation on owners of a pressure vessel to ensure it is used in a safe manner and this requires an effective inspection and maintenance program. The owner is responsible for developing, documenting, implementing, executing, and assessing pressure vessel inspection systems and inspection procedures that will meet the relevant requirements. These systems and procedures typically include the following:
- Organization and reports of structure for inspection personnel.
- Documentation and maintenance of inspection and quality assurance procedures.
- Documentation and reports of inspection and test results.
- Corrective action for inspection and test results.
- Internal audits for compliance with the quality assurance inspection manual.
- Review and approval of drawings, design calculations, and specifications for repairs, alterations.
Types of Inspection
Careful visual examination is the most important and the most universally accepted method of inspection. However, this does require entry to the vessel, which itself presents risks to inspection personnel, and also requires a period out-of-service which impacts productivity. By using advanced NDT methods the requirement for internal visual examination can be reduced, or potentially removed. These NDT methods include:
- Corrosion Mapping
- Ultrasonic thickness measurement and flaw detection
- MFL Screening
- Magnetic-particle examination for cracks and other elongated discontinuities
The advances in corrosion mapping by automated systems that can be used on site and in harsh conditions has opened new possibilities for effective management of vessels
Corrosion Rate Determination
Corrosion rate determination is key to calculating working life between inspections and repairs. By using corrosion mapping tools changes in wall thickness over time can be used as a basis for this calculation, and so accurate measurement is a necessity. For a new vessel or for a vessel for which service conditions are being changed, an estimation based on the following can be made.
- A corrosion rate may be calculated from data collected by the owner on vessels providing the same or similar service.
- If data on vessels providing the same or similar service are not available, a corrosion rate may be estimated from the owner’s experience or from published data on vessels providing comparable service.
- If the probable corrosion rate cannot be determined in service determinations shall be made after approximately 1000 hours of service by using suitable corrosion monitoring devices or non-destructive thickness measurements of the vessel. Subsequent determinations shall be made after appropriate intervals until the corrosion rate is established.
For all of these scenarios, good quality inspection data is required, which can be provided from effective NDT inspection tools.
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