Eight Revised ASTM International Steel Standards Help Address “Creep” Issue in Boilers
Eight ASTM International steel standards were recently revised to help address the issue of creep (time-dependent deformation at elevated temperature and constant stress that can lead to failure) for certain steels (9% chromium-1% molybdenum).
According to ASTM International member Kenneth Orie, a new “Type 2” designation introduced for Grade 91 steels in these standards culminates research efforts in recent years showing that chemical composition can play a vital role in the performance of these enhanced steels used at higher temperatures in what is known as the creep-regime.
Orie says that a key focus of research from the Electric Power Research Institute (EPRI) relates to these specialized alloy steels used at elevated temperatures in boilers. Industry stakeholders had expressed concerns that compositional control and especially the presence of unspecified elements could potentially lead to failure,and, more importantly, brittle failure, which tests have shown to have occurred without warning and without any ductility.
Orie chairs subcommittee on steel plates for boilers and pressure vessels (A01.11), and also serves as liaison to the American Society of Mechanical Engineers working group on creep-strength enhanced-ferritic (CSEF) steels. He says ASME supported the concept of establishing maximum permissible limits for unspecified elements as well as a new set of allowable stresses for Grade 91 steel used in the creep-regime.
He introduced the requirements that would conform to the more restrictive chemistry dictated by EPRI recommendations as a supplemental requirement in an ASTM International specification for plate products (A387). This was eventually incorporated directly into a 2017 revision of the standard (A387-17a) as Type 2 while the existing Grade 91 was designated as Type 1.
Orie says that EPRI recognized the need to quickly replicate that across all applicable product forms – including forgings, pipe, and tube – due to related ASME actions. Several subcommittee chairs under ASTM International’s A01 Committee on Steel, Stainless Steel, and Related Alloys (A01.06, A01.09, A01.10, and A01.22) launched revisions in October 2017 to revise seven additional standards (A182, A213, A234, A335, A336, A369, and A691). These were approved less than five months later, on March 1.
Orie credits exceptional cooperation among the chairs in achieving this quick progress, which, in turn, allowed these specifications to recently be approved for adoption into a key publication (Section IIA) in time for the 2019 ASTM Boiler and Pressure Vessel Code Edition.
“The efficiency of the ASTM International process and the fast actions of subcommittee chairs in responding to this critical safety situation shows how A01 supports not just the power industry but also the needs of all steel-consuming industries,” he says.