DHT and ISR

If it's obvious, why are you asking? Is this a quizz? A trick question, perhaps?

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thank you

sorry, ISR(Intermediate Heat Treatment) is incorrect, ISR(Intermediate Stress Relief) is correct

The obvious differences between dehydrogenation heat treatment (DHT) and intermediate stress relief (ISR) are temperature and governing documents.

Most ISRs are controlled subcritical heat treatments performed at temperatures within 100 ^oF to 200 ^oF below the metal's lower critical temperature, in accordance with Code requirements (e. g. ASME BPVC) at temperatures between 1100 ^oF to 1350 ^oF, depending on the metal's ASME P-No. classification (carbon and alloy content).

DHT's, on the other hand, are performed for the sole purpose of hydrogen removal, generally at temperatures between 600 ^oF to 800 ^oF for times recommended by such technical guidelines as "Welding Steels Without Hydrogen Cracking" by N. Bailey, et. al. depending on metal thickness.