Anomaly Description:
Operations reported a leak of flexsorb on line 051-CDM31-10-150K01 of column D-503 between nozzles N5 and N10. External inspection found there was a leak through a hole with a diameter less than 1mm on the piping straight section and 40mm wide within HAZ of the flange connection attachment weld. The leak was repaired temporarily for a short-term period. An ultrasonic thickness test was performed within the leaking area as well as on the adjacent sections of the piping. The thickness of the damaged straight section is T = 3.6 ÷ 4.6mm, the thickness of the adjacent sections is T = 8.9 ÷ 9.6mm.

Root causes:
At current, the damage mechanism is not identified.

Integrity concerns:
The original thickness of the damaged pipe section does not meet the requirements of class 150K01 (T = 7.92mm). It is not possible to calculate the corrosion rate because the thickness initial value is uncertain. Due to this piping being below specification further deterioration of piping could cause worsening leaks and ultimately failure. Operations of the piping with these non-conformities are not allowed.

Clamp Design:
By using a patch and strap, the leak through the hole could temporarily be stopped and enable Beruseal to do a carbon fibre composite repair to rebuild wall thickness and stop the leak (Diamond wrap cannot be applied to leaking components unless leaks can be stopped).

Due to the wall loss being concentrated next to the welding, Beruseal designed and manufactured a strongback restraint system that would be able to withstand the total circumferential failure of the welding. The strongback was a multi part system that would restrain the elbow together with the complete assembled flange.
An FEA analysis was performed to calculate stresses in the strongback components in the event of failure of the design pressure.

Seal:
A successful seal of the leak was achieved by the application of the patch to do a diamond wrap composite wrap and with the addition of the restraint system a permanent repair was implemented (20-year life expectancy).