we are fabricating vessel of thickness 38mm, service tempreture is -29degree celcius, as per ucs-66 impact test is required but if we dont want to do impact test on this what basis i can do it

Assume your material i SA-516 normalized (If not normalized I presume you will have no chance to skip impact testing), you may see if you have 4% plus thk than that required by calculation and using Fig. 66.1M you may skip impact testing for shell plate but you have to verify forging and piping as well (which usually they are thinner). And bolting (see Fig.UCS-66 (second page)).

Assume carbon steel, provide all WPS with pre-heat 95 °C you are not requested to perform PWHT. Then applying UCS-68(c) you may reduce the temperature calculated of exemption, of 17 °C.

Without design an accurate assessment cannot be made. Mauro

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I israrahmed got 14 yeras of work experience in QA/QC of welding and fabrication, Including WPS and welder's qualification as per ASME-IX,AWS and api-1104.

israr,

Since you specified as per UCS-66.
I assumed that MDMT reduction factor using S-ratio is already considered.
If PWHT is not required by Code (most likely you need PWHT for 38mm), you can do it to further lower down the material MDMT. Impact testing is mandatory if material MDMT is warmer than -29 degree C.

In any case, i could not see any reason why you refused to do impact testing as it is not very costly.

Regards,
Noel Tan

Please do not forget to test the weld material, the PQR coupon and consider the required production test plates.

Considering that impact tests will document verification of safety against brittle failure, it is a good idea to test. Consider that -29C is colder than ice cream!

DK

I doubt 38mm and with MDMT -29 does required impact test ?
What is material specification ?
You might very wel not required Impact test...

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Niraj