Steel Material Selection for Applications In Low Temperature Operating Environment

Abstract For turbine ancillary exhaust system design there is an occasional requirement for structural steel shapes and plates to exhibit impact resistance at −40°F (−40°C) and lower ambient temperatures. For economical purposes the use of 300 series stainless steel in exhaust systems is not always desirable. The simultaneous requirement of a low environmental temperature along with high exhaust temperature of up to 1112°F (600°C) creates a challenge for alloy steel material selection. Standard literature provides extensive background for Charpy V-notch impact testing (referred to as Charpy impact test throughout the paper) and acceptance of materials at low temperatures, but a correlation with heat resistant steels is limited. A case study reviewing carbon alloy steels that meet both low and high temperature limits is explored. The application of ASME BPVC Section VIII Division I guidelines for determining the lowest minimum design metal temperature (MDMT) for impact testing will be summarized. The understanding of Charpy impact test exemption curves along with weld testing requirements, temperature differential allowance and MDMT reduction per ASME BPVC Section VIII Division 1 is reviewed to achieve impact test requirements. Charpy impact test data will be shared for base metal, weld metal and heat affected zone (HAZ) metal of various materials. The resulting test data will be used to determine the appropriate application of different carbon alloy steels. This paper provides a design approach drawing on accepted theory that can be utilized in high temperature applications requiring low temperature impact resistance.