Supermartensitic stainless steels with improved corrosion properties
The objective of the project was to optimise supermartensitic stainless steels (SMSS) that under specific pipe welding conditions should lead to a superior heat-affected zone (HAZ) stress corrosion cracking (SCC) resistance. Actual welds made in a contemporary SMSS heat showed the favourable effect of using a high heat input for the second pass. Also, a new simplified test method that can be used for screening purposes against SCC of SMSS welds was able to be developed within the project. Unfortunately, similar welds produced in an optimised SMSS heat still revealed some SCC tendency. New experimental heats showed the different effects of carbon and chromium on SCC resistance while it was demonstrated in general that low residual oxygen content during welding were beneficial. Finally, plates from the optimised SMSS heat were actually welded at heat input conditions that should have produced sensitive or non-sensitive joints. Against all expectations 'immune' joints also cracked under severe corrosion conditions. In conclusion, both the material's composition and the welding conditions constitute no tool for improving adequately the SCC resistance at the HAZ of welded joints. Whenever the risk for SCC is realistic, it is strongly advised to shortly heat treat girth welds prior to service, probably because of the healing effect on Cr-depleted areas. Certainly the carbon content of the pipe material should be as low as possible while the chromium and molybdenum content should be maximised. These precautions should prevent time-consuming and costly repair procedures by effectively prolonging the life time of a pipeline.
Bibliographic Reference: EUR 22813 EN (2007), 84 pp. Euro: 15
Availability: Katalogue Number: KI-NA-22813-EN-S The paper version can be ordered online and the PDF version downloaded at: http://bookshop.europa.eu
ISBN: ISBN: 978-92-79-05297-2
Record Number: 200719249 / Last updated on: 2007-07-05
Original language: en
Available languages: en