Grade 3 vs Grade 4 nuts
Grade 3 vs Grade 4 nuts
(OP)
Are there any metallurgical reasons why I shouldn't use ASTM A194 Grade 3 nuts (what we bought) instead of Grade 4 (what is currently in place) on some external bolts for heat exchangers in diesel hydrotreater service provided they meet the code requirements for the service?





RE: Grade 3 vs Grade 4 nuts
There must have been some difference to warrant the grade 4, so what's changed now, that you can specify grade 3?
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RE: Grade 3 vs Grade 4 nuts
Grade 3 - 5% Cr- 0.5% Mo, more for higher temperature applications
Grade 4 - is a carbon-molybdenum (0.25%) steel.
The major difference will be increased corrosion performance by the higher chromium steel.