We have an existing vessel originally designed in 1967 for a design temp of 150^F. There now exists the possibility of auto-refrigeration, so the vessel MAT needs to be determined per API-579 section 3.
After performing a Level 2 , Method A for all of the components over the pressure range of 0 to the MAWP and plotting the governing component's MAT vs the auto-refrigeration curve for the depressurized liquid (attached) the MAT exceeds (is warmer) than the auto-refrigeration curve.
If I read section 3.4.3.2 correctly, a field hydro test can be performed to lower the MAT per figure 3.8 if no impact tests are performed.
My question is: "If a field hydro test is performed is the minimum metal temperature during the hydro test 30^F above the maximum MAT?".
After performing a Level 2 , Method A for all of the components over the pressure range of 0 to the MAWP and plotting the governing component's MAT vs the auto-refrigeration curve for the depressurized liquid (attached) the MAT exceeds (is warmer) than the auto-refrigeration curve.
If I read section 3.4.3.2 correctly, a field hydro test can be performed to lower the MAT per figure 3.8 if no impact tests are performed.
My question is: "If a field hydro test is performed is the minimum metal temperature during the hydro test 30^F above the maximum MAT?".