National inquiry on ISO-standard on test methods for quality control of microstructure of ferritic/austenitic (duplex) stainless steels

ISO/DIS 17781.2 Petroleum, petrochemical and natural gas industries - Test methods for quality control of microstructure of ferritic/austenitic (duplex) stainless steels, is now available for national inquiry. The deadline for comments 29 June 2016.

The draft standard is under the work programme of ISO TC 67/WG 8. The aim of this International Standard is to establish common test methods for quality control of microstructure of ferritic/austenitic (duplex) stainless steels for the oil and gas industry, enabling the manufacturers to apply the same test procedures for their clients.

Duplex stainless steels have a dual phase microstructure consisting of ferrite and austenite. Ideally, these phases are present in equal proportions although in commercial alloys the ferrite phase volume fraction may vary between 35 % and 65 % for products in the solution annealed condition. They are characterized by high chromium (19 % to 33 %) and low nickel contents compared with austenitic stainless steels.

Some duplex stainless steels are prone to precipitation of intermetallic phases and nitrides possibly causing embrittlement and reduced corrosion resistance. The formation of intermetallic phases such as Sigma and Chi occurs depending on exposure time in the approximate temperature range 590 °C to 1000 °C (1 094 °F to 1 832 °F) and decomposition of ferrite to Alpha Prime occurs in the range 300 °C to  540 °C (572 °F to 1 004 °F).

The microstructure of components or fabrication welds is affected by amongst others the thermal-mechanical history associated with hot working, solution annealing and with subsequent forming and welding. The destructive test methods with acceptance criteria specified herein are considered relevant to verify that exposure time at above stated temperature ranges have been within acceptable limits and to ensure that desired corrosion resistance and mechanical properties are obtained in final products.

This standard specifies quality control testing methods and test conditions for the characterization of microstructure in relation to relevant properties in ferritic/austenitic (duplex) stainless steel components supplied in the solution annealed condition and fabrication welds in the as welded condition. The standard supplements the relevant product and fabrication standards with respect to destructive testing methods including sampling of test specimens, test conditions and test acceptance criteria to show freedom from deleterious intermetallic phases and precipitates in duplex stainless steels. In addition, this International Standard specifies how testing and test results shall be documented by the testing laboratory.

To get access to the draft standard, please visit our service “Standards for enquiry”. This service is free of charge, but in Norwegian only.

Sist oppdatert: 2016-06-17