Oil and gas-Case study: Fitness for service

Fitness for service


Business Need
Our client needed to demonstrate that a corroded header could continue in use to avoid an unplanned shutdown.



The efficient and safe operation of structures and equipment such as pressure vessels, offshore platforms and pipelines is vital for their continued profitable operation. Often there is a requirement for demonstrating that continued operation of critical components will be safe until maintenance can be carried out in the next shutdown.

In this example Frazer-Nash provided a very rapid response to an oil major, providing valuable results when they most needed them. Survey data had shown that there was significant material loss on a header, and they needed to show that it was safe for continued use until it could be replaced.


An API 579 Level 3 assessment is the accepted method for showing that a component is fit for further operation. In order to carry this out a finite element model of the header was created to run in Abaqus.

Initially no detailed survey data was available, so the model was created with a bounding width and depth of material removed. This analysis did not show adequate margins against failure, so when more detailed data became available the model was refined with local regions removed.

The elastic-plastic collapse analyses on this model showed that the remaining capacity was sufficient, allowing the component to remain in service.

An additional assessment for defect tolerance was also carried out since the survey could not show that there were no flaws in the region of the thickness anomaly.


The project duration from initial request to the supply of verified results was less than 5 days. The results allowed the operator to continue to use the component until the next shutdown.

This is one example of numerous similar studies we have carried out for our clients, reducing the down time for their facilities.