Case study

Sector: Oil and Gas

Objective: Inspect, assess, repair and monitor chloride stress corrosion cracking (SCC) in a timely and cost effective manner.

Client benefits: Severely cracked equipment was safely returned back to service with minimal business interruption and cost. New equipment has since been procured and a risk based inspection (RBI) plan put into place to monitor SCC throughout the plant.

Project background: When severe, unexpected, external Chlorine SCC was detected by a small leak in a business critical item of equipment in a high volume gas processing plant, a rapid and effective plan had to be established in order to put the equipment back in to service with minimal impact on the business. TWI immediately deployed two engineers to site, one integrity engineer and one inspection engineer, to oversee and react to the inspection findings. Initial advice was to replace the vessel, but given the lead time for replacement equipment of 10 months and production losses of $5M per day, safe temporary measures had to be put in place.

Solution: Cracking was detected throughout the vessel at almost every weld. Inspection findings were fed back to the UK office where finite element (FEA) models of the equipment were constructed. The FEA was used to extract stresses at key locations allowing fitness for service (FFS) fracture mechanics to be used to develop limiting flaw size curves. The curves were used by the on-site inspectors to screen cracks and make rapid run/repair decisions. TWI welding engineers were then pulled into the project to provide weld repair procedure advice. Specimens were couriered back to the UK for rapid analysis by the materials department to confirm the morphology of the cracking and the mechanism.

For more information please contact: aim@twi.co.uk