TWI Frequently asked questions
by Alan Smith
Guidance on the assessment of corrosion damage in line pipe from the viewpoint of plastic collapse of the corroded ligament is given in Annex G of BS7910
[1] . Alternative rules for the assessment of corrosion damage in line pipe and more complex geometries are given in API RP 579
[2] though it is not known how thoroughly the assessment procedures for complex geometries have been validated. Simple assessment procedures are given in the ASME B31G procedure
[3] . Using the assessment procedure recommended in BS7910, the yield and tensile strength of the pipe, the length and depth of corrosion, the pipe diameter and operating pressure are required as input information.
More complex corroded regions in line pipe can be assessed using procedures such as the RSTRENG [4] algorithm (available as a computer program). This requires more detailed knowledge of the corroded profile. Alternatively, corrosion can be assessed using finite element analysis [1] (FEA). However, FEA is normally recommended for high value components in situations where it is inappropriate to use simpler assessment procedures.
Particular care must be taken to avoid the risk of brittle fracture. Further guidance is given in ref [5] , together with a comparison of the different methods. The methods described here refer to generally smooth corroded regions or locally thinned regions and the topography of the corroded region should be considered in applying the assessment technique.
TWI has world renowned experience in the structural assessment of corrosion damage, probabilistic assessment of corrosion damage, non destructive inspection and finite element analysis. TWI can also advise on the selection of materials and appropriate joining technologies, for metallic and non metallic systems, plus mitigation measures through surfacing and coating technologies.
References
- 'A critical review and comparison of various methods to evaluate the static strength of corroded pressurised components', TWI Members Report 707/2000, May 2000. Only available to industrial Members of TWI.
Further information
FAQ:
How can I assess corrosion damage at nozzles in steel pressure vessels? FAQ: How do I assess the structural integrity of corroded regions at welds?
