AME has inspected a pressure vessel that has failed, luckily not in a catastrophic way, and not where it could have had detrimental effects on passer-by’s. The first photo below was taken towards the end of 2014 when it was inspected. Ultrasonic Thickness Testing was taken on the bottom and shell of the vessel with no signs of any issues. Due to the surrounding pipework etc, the top of the vessel was not accessible. The second photo, taken this week, two years on, shows the location of the failure on the top of the vessel, while the third photo shows a close up of the failure.
Some points to note:
- The vessel is now 16 years old with a probable design life of 25 years,
- The vessel failed during normal operating pressure – not over pressure,
- The staining running away from the failure zone would suggest corrosion has been occurring for some time,
- The tell-tale staining would not have been obvious from ground level,
- The vessels’ location was out in the open, it was relatively clean of debris build up on the top of the vessel, and
- The rest of the vessel appears in good condition.
- A defect in the metal below the protective coating on top of the vessel has allowed corrosion to occur from the outside,
- Excess moisture internally has been evaporating, then condensing on the top of the vessel corroding a week spot until the shell thickness was too weak to retain the internal pressure, or
- Being a gold mine, a corrosive substance may have been dripping onto the outer shell from above.
Outcomes from this failure:
- Access to the entire vessel must be readily available,
- All vessels need to be thoroughly examined, not just sections or accessible parts,
- Consideration needs to be given to the age of the vessels,
- Ensure the internal inspection regime as in accordance with Table 4.1 of AS3788:2006.
- An internal inspection may or may not have picked up this problem prior to failure.
Have you got any Pressure Vessels that require inspection? Get in touch with our Asset Management specialists and highly trained plant inspectors to discuss your requirements. Call us on Perth (08) 9466 7444 | Kalgoorlie (08) 9091 3553
DISCLAIMER: The statements, views and opinions presented in this article are those of the author. Asset Management Engineers Pty Ltd does not warrant the correctness of the information provided or its fitness for any purpose.