Regulatory Intelligence
When checking an existing casing string for injection or disposal conversion, which value belongs in the Directive 051 burst equation?
Category:
Well Integrity
Research Basis
Archive Period
1994-2019
Records Reviewed
6
Primary Topics
casing inspection logs; minimum yield strength; wall loss; conversion wells; MWHIP
Current Reference
AER Directive 051; AER Directive 065; AER Directive 010
Common Question
When checking an existing casing string for injection or disposal conversion, which value belongs in the Directive 051 burst equation?
Archive Findings
The 2019 application correspondence shows a practical error that engineers can easily make: using a published internal yield pressure value as if it were the specified minimum yield strength in the casing equation. The discussion corrected the approach by using the casing's minimum yield strength and then applying wall-loss reduction to calculate internal yield pressure. The same folder also contains the 1994 D051 workshop/guide language that anchors the issue: casing inspection logs must assess casing integrity on a joint-by-joint basis, and maximum burst resistance is based on least wall thickness and minimum yield strength. The archive consistently treats the check as a casing-integrity demonstration, not a simple table lookup.
Engineering Insight
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For conversions, verify the casing grade, outside diameter, nominal wall thickness, and maximum measured metal loss before calculating burst resistance. Do not mix three different concepts: specified minimum yield strength, calculated minimum internal yield pressure, and the proposed MWHIP. When wall loss is present, use the least remaining wall thickness or the maximum metal-loss penetration from the casing inspection log. Keep the calculation trail in the application file so the reviewer can see where every number came from. A strong submission should also explain whether the damaged joint is within the pressure-exposed interval, above the packer, or otherwise isolated from injection service.
Current Guidance
Current Directive 051 section 5.3.1 requires a full-length casing inspection log for any existing well proposed for conversion and requires maximum burst resistance, based on least wall thickness and minimum yield strength, to exceed 1.3 times the maximum allowable wellhead injection pressure. Current Directive 065 now carries the MWHIP framework for disposal applications, so the casing check and the MWHIP justification need to be internally consistent.