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MDMT

MDMT

(OP)
My employer sent me a few WPS and PQR's and wants me to determine rather they good for -40F MDMT or -20F MDMT. My question is Where do I have to look to determine one from the other and what is all involved with it?

RE: MDMT

You have to start understanding of the MDMT, then impact testing requirements in the code, then understand the WPS and PQR, then you'll be able to undesratnd the difference between MDMT of -40F and -20F. It's not something your employer should have asked you, if he would have had himself understanding of all the above.

RE: MDMT

I would make a few simple checks:
1) Are the parent materials stated in the WPS/PQR suitable for -40F or -20F MDMT (in the code you're using)?
2) Does PQR contain CVN test results? If CVN results are available, do they indicate adequate toughness at -40F or -20F MDMT?
3) Find and check datasheet for welding consumables to see if consumable manufacturer indicates suitability for low temp.

RE: MDMT

Above are first steps only. They will quickly tell you whether the WPS/PQRs are close (or not) to what you require.

RE: MDMT

(OP)
I'm reading up MDMT and Impact testing to better understand them. Just not sure where wouold be the best place to look. Where could I find out if the parent materials stated in the PQR and WPS are sutible for -20F or -20F? I looked at the PQR's and some of them do have CVN test results while others dont. Correct me if I'm wrong, I am looking at the material spec and grade table that refers me to the correct CURVE to use, then with the thickness of the test coupon i could locate the MDMT on that curve? Ex: On one PQR,I have SA-516 grade 70 T= 0.75 which is CURVE B MDMT 15F, and the PQR has CVN test results of -50F on wm, so would it be safe to say that -20F or -40F doesn't apply? Aslo another PQR I have SA-516 grade 70 T= 0.875 with no CVN test results. What would that fall under? Is there other variables I should be looking at and where could i refrence them?

RE: MDMT

You do need to be conversant with the ins and outs of UCS-66 and UG-84 in ASME Section VIII Division 1, as well as the parallels in ASME B31.3 323.2.2~. However, you also need to review ASME Section IX to confirm the thickness ranges qualified, among other things.

There are Code rules that specify the minimum required actual CVN test temperature for sub-size Charpys (in your case, 3/4 size), or conversely, the MDMT qualified for sub-size specimens at a given test temperature. It's a bit convoluted.

Review of WPSs / PQRs is something that I think is handled more intelligently by welders and NDE technologists / technicians than by engineers, unless one happens to be a metallurgist or welding engineer by training.

RE: MDMT

Beyond the scope of the question, but API 650 publishes a chart that shows the one day mean temperature which might provide some insight as to where that temoerature is derived. Of course using more severe conditions are often applied as well.

RE: MDMT

JJ,
Sadly it is very clear that you do not have the skills/knowledge to perform the task that you boss has given to you. This type of work is quite specialised, and can be dangerous if not performed correctly. The skills/knowledge required is usually gained over a lengthy time period, and thus it is not appropriate to expect full training in this forum.
As a first step, I do encourage you to read the design & fabrication codes that are relevant to you.

RE: MDMT

(OP)
I appreciate everyone for their responses and help. Thank you

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