Standard Practice for Determining Cracking Susceptibility of Metals Exposed Under Stress to a Hot Salt Environment

Abstract

5.1 The hot salt test as applied to metals is utilized as a secondary design consideration indicator, as cracking has been shown to occur in laboratory tests simulating possible service conditions. Although limited evidence exists linking this phenomenon to actual service failures, cracking under stress in a hot salt environment should be recognized as a potential design controlling factor. 5.2 The hot salt test is not to be misconstrued as being related to the stress corrosion cracking of materials in other environments. It is considered solely as a test in an environment that might be encountered in service. 5.3 Because hot salt cracking under stress is considered a secondary design consideration and service failures have not been attributed solely to this phenomenon, manufacturing processes will be optimized or alloying changes will be made only after consideration is given to primary design factors such as creep resistance of a given high temperature alloy. The usefulness of the test lies rather in limiting maximum operating temperatures and stress levels or categorizing different alloys as to susceptibility, or both, if it is found that hot salt damage may accelerate failure by creep, fatigue, or rupture. 5.4 Finally, the test does not lend itself to the utilization of pre-cracked specimens because cracking reinitiates at any salt-metal-air interface, resulting generally in many small cracks which extend independently. For this reason, specimens that are recommended for utilization in routine testing are of the smooth specimen category.