Impact Test

MDMT is the Minimum Design Metal Temperature which represents the lowest temperature for a system may be operated. It will be calculated and compared with the min. design temp. of the system.

We used to specify the impact test for all materials working at lower temp. If the used material work at low temp., the MDMT (as determined from ASME code, Section VIII, Division 1, Para. UCS-66) depends on type of material and its thickness, and that MDMT shall be lower than or at least equal to the specified min. design temp. of the system. Otherwise, you have to proceed an impact test for that material at the specified min. design temp. or lower.

And in this case, the material requisition must include a condition states that the supplier have to carry out the impact test (at mill or at lap) where the values of impact V-notch must be fulfill the code requirements, to be cleared through a certificates to be submitted to the owner. Also, for that material and if impact test is required for the system, the WPS's & PQR's must include a statement to proceed an impact test (at the specified min. temp.) for the welded samples of test coupon(s) as per code requirements.

Notes.

1. For material ASME SA-517 Grade 70 (not normalized), belong to Curve B where for thickness 57.2 mm, its MDMT is 19 ^oC (66 ^oF). This means that if your min. design temp. of the system equal to or higher than 19 ^oC, no impact test is required, otherwise you have to proceed impact test for both the raw material (plates) and for the welded test samples.

2. For material ASME SA-517 Grade 70 (normalized), belong to Curve D where for thickness 57.2 mm, its MDMT is -18 ^oC (0 ^oF). This means that if your min. design temp. of the system equal to or higher than -18 ^oC , no impact test is required, otherwise you have to proceed impact test for both the raw material (plates) and for the welded test samples.

3. The results obtained at notes 1 & 2 are based on tr = 57.2 mm, if tr is located less than 57.2 mm, you can use the reduction in MDMT without impact test as located in Fig. UCS-66.1 of ASME code, Section VIII-D1.

4. The attached file demonstrates how to calculate the MDMT for a pressure vessel: MDMT_Calculations_for_a_Pressure_Vessel

5. See the following related topics by CR4 Threads : SA 516 Grade 70 Steels & Minimum Design Metal Temperature (MDMT)