thePetroStreet

How the impact test temperature can be determined using ASME Sec VIII, Div. 1?

1) is it same with design MDMT or dictated by Client specs
2) Any Impact Test Temperature required by Code for certain material

Thanks

Requirement of Impact test is evaluated from UCS 66 of ASME Sec VIII div 1.

1. MDMT is usually defined by the client. In some cases it is not required if you evaluate the impact test requirement temperatures yourself and there is no need for impact test. Otherwise if you are not clear about the impact test requirement temperature, its better to define the MDMT so that vendor evalutes the same.

2. If MDMT is below the impact test exemption temperature evaluated by UCS 66, impact test become mandatory (sometimes materials are exempted as per UCS 20).

3. Please note that impact test exemption temperature depends on the treatment on material after production. If material is normalized the impact test exemption temperature is lower. So if you are purchasing normalized material you have better chance to skip impact testing.

Sadia,
If you conclude from UCS-66 that Impact test is required then code does not defines that at which temperature the material shall be impact tested.

1. Use impact test temperature that can sustain the minimum operating temperature defined by client.
Taking an example, assume MDMT given by client is -70 deg F and when you design the vessel it comes out to be 30 deg F and stress ratio of 0.4 which allows a temperature reduction of 100 deg which means operation at -70 deg F is feasible. So if you get the impact test of material done at 30 deg F even that can allow the minimum operating temperature of -70 deg F.
2. No, as per my information.

Hope that would help.

I agree with Ashfaq, code does not specify the impact test temperature.

1-For MDMT determination, please refer UG-20. (This is “Design MDMT”).Actually Blow down calculations, Steam out conditions, operational upsets define the “Design MDMT”.

2-Conculde”Rated MDMT”, as per UCS-66 curves A, B, C & D.Compre the “Rated MDMT” with “Design MDMT”, if rated MDMT is warmer than Design MDMT than impact test is required. Take advantage of “normalization” and “fine grain practice” if these can be possible as per material properties per ASME Section II-A.

Sometimes we have to change the material grade because for specific materials, impact test by material metallurgy not possible. (Refer ASME Section II-A supplementary material requirements).

3-Use code exemptions to colder the rated MDMT further i.e by using code exemptions UG-20(f), UCS-66 b(1) and (3), UCS-68(C), UG-84(b)(2) and by reference table UG84.4.
Sometimes international clients like Aramco and Sabic do not permit code exemptions.

4-When impact test required, it should always perform at “Design MDMT”, and impact energy values should always provide to material suppliers. Which should be in line with project specifications/relevant code. (Some materials are by default impact tested at certain temperature with specific impact energy values-Refer Asme Section II-A against different material grades).Refer ASME Section VIII, DIv.2 Ed2007 fig 3.3 for clarity regarding impact energy values.

Rana Ghulam Rasool
KSA

Rana,
A very comprehensive reply.
Regarding point 4 of your post, is this mentioned any where in ASME Sec. VIII Div. 1, that the impact test shall always be performed at "Design MDMT"?

Ya, please refer UCS-66(a) where it is described "when fig. UCS-66 is used, impact testing is required for a combination of minimum design metal temperature(see UG-20) and thickness as defined below.....".

Now, It is already described UG-20 refer the "Design MDMT"

The statement you mentioned in the light of UCS-66(a) tells about the requirement of impact testing and it does not specifically mentions that at which temperature impact test (if required) shall be carried out.
UG-20 also does not specify explicitly about performing of impact test at Design MDMT.
But the way forward is to carry out the impact test (if required) at Design MDMT which should be mentioned by the client end.

Combination of MDMT and thickness tell us about impact test requirement as stated by UCS-66.In first para of UCS-66 (a) refer impact testing is required when " MDMT (UG-20 i.e Design MDMT)" and thickness combination is below the curve, " the curve" which is assigned to subject material.When this combination is on or above the curve, impact testing is not required.You can say "Design MDMT" and "Impact test" are interlinked with each other via specified thickness.

The above statement actually clarified that if impact test is required and we are below the assigned material curve, we should perform impact test at "Design MDMT" since for ASME code stamped equipments's MAWP should be code complied . (You know MAWP is at Design MDMT and Design Temp).

RGR