This paper describes how an engineering critical assessment (ECA) was applied in order to decide on and execute repair of heavy size 22 Cr duplex pressure vessels. The aim is to explain how material test data and applicable non destructive examination (NDE) techniques serve as basis for ECA.

Lamellar defects were found in cold formed dished ends due to centreline segregation of inclusions as well as pipe during ingot casting of the material. Inclusions and pipe were enlarged during rolling of plates, and large defects were luckily discovered during the spinning operation of one dished end. This product was rejected immediately by the manufacturer.

First, an ECA was performed in order to evaluate the criticality of such defects in a dished end. This resulted in preparations for repair of three out of six manufactured products. Repair welding of poor material quality in areas with a very complex stress picture is not straightforward. Based on suppliers available CTOD data, an ECA of repair welds was performed in accordance with BSI PD6493: 'Guidelines on the methods for assessing the acceptability of flaws in fusion welded structures'. Adequate Charpy impact values taken from actual products were not judged to be reliable for this purpose.

A second dished end was rejected due to problems in locating the repair weld outside defected areas. Two new dished ends were supplied accordingly, with extensive ultrasonic testing of plates prior to the cold spinning operation which is causing a deformation rate of approximately 20%.