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02038 COMMON PITFALLS DURING SSC AND PITTING TESTING OF SUPERMARTENSITIC STAINLESS STEELS FOR USE IN PIPELINES

The hardness values of weldments of supermartensitic stainless steels exceed limits for “sour service” and testing has to be done.  Most testing has been done by procedure defined in EFC Publication No 172. Some observations during testing have led to a discussion on the relevance of the test methods and procedures.

Product Number: 51300-02038-SG
ISBN: 02038 2002 CP
Author: Stein Olsen and Jakob Enerhaug
Publication Date: 2002
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The hardness values of weldments of supermartensitic stainless steels will exceed generally acceptable limits for “sour service” and qualification testing with simulation of the actual conditions has to be done. Use of international guidelines, e.g. the EFC-17 document, has shown that there is a need to specify more details for the testing. The high temperature oxidation during welding will weaken the pitting resistance for SMSS exposed to slightly sour environment. This will influence the initiation of pitting corrosion and thus the resistance to SSC. The buffer strength in a simulated environment may influence the results and should thus be selected to avoid artificial effects only seen in the laboratory. pH adjustment of a simulated buffer must be done with the test gas in the system. It is important to check that there has not been any significant change in the pH during testing. In high pressure testing, the pH should be checked prior to testing and after the testing with 1 bar CO2. When stressing 4PB specimens with the root intact, the global deflection to be used must be checked and calibrated against strain gauge measurements in the HAZ prior to the corrosion testing. In case of significant low temperature creep, a 4PB specimen will experience stress relaxation. If testing of an intact root surface is required, no standard test methodology is available if this relaxation should be avoided. Keywords: Supermartensitic stainless steels, SSC, testing.

Most testing has been done according to the procedure defined in EFC Publication No 172. It has been reported some special effects observed during corrosion testing3,4 , which has led to a discussion on the relevance of the actual test methods and test procedures. The intension of this paper is to discuss some of these aspects.

Keywords: Supermartensitic stainless steels, SSC, testing

The hardness values of weldments of supermartensitic stainless steels will exceed generally acceptable limits for “sour service” and qualification testing with simulation of the actual conditions has to be done. Use of international guidelines, e.g. the EFC-17 document, has shown that there is a need to specify more details for the testing. The high temperature oxidation during welding will weaken the pitting resistance for SMSS exposed to slightly sour environment. This will influence the initiation of pitting corrosion and thus the resistance to SSC. The buffer strength in a simulated environment may influence the results and should thus be selected to avoid artificial effects only seen in the laboratory. pH adjustment of a simulated buffer must be done with the test gas in the system. It is important to check that there has not been any significant change in the pH during testing. In high pressure testing, the pH should be checked prior to testing and after the testing with 1 bar CO2. When stressing 4PB specimens with the root intact, the global deflection to be used must be checked and calibrated against strain gauge measurements in the HAZ prior to the corrosion testing. In case of significant low temperature creep, a 4PB specimen will experience stress relaxation. If testing of an intact root surface is required, no standard test methodology is available if this relaxation should be avoided. Keywords: Supermartensitic stainless steels, SSC, testing.

Most testing has been done according to the procedure defined in EFC Publication No 172. It has been reported some special effects observed during corrosion testing3,4 , which has led to a discussion on the relevance of the actual test methods and test procedures. The intension of this paper is to discuss some of these aspects.

Keywords: Supermartensitic stainless steels, SSC, testing

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