Impact Test Exemption for Pressure Vessel as per ASME UCS 66

[Mech2325]

Hi all,

As per UCS 66 (b)(3) "When the minimum design metal temperature is colder than −55°F (−48°C) and no colder than −155(−105°C), and the coincident ratio defined in Figure UCS-66.1 is less than or equal to 0.35, impact testing is
not required".

My question in this matter is that, if for example, you want to go below -48°C and the ratio is below 0.35, then what will be the rated MDMT of your vessel in this case. For example the required MDMT is -60°C and the MDMT you are getting is -48°C. Now, if the ratio comes out to be 0.3, for example, what will be the MDMT now. Will it be -105°C??

 

[SnTMan]

Mech2325, first understand that typically the MDMT of a vessel is not generally determined in reference to a single component, all components must be considered.

But, for your example, yes the vessel MDMT may be set as low as -105 C, but it need not be set below the specified MDMT, -60 C in your example.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Mech2325]

Sntman

Thank you for your valuable feedback. Yes, i know, the vessel MDMT comes by taking the warmer of all the components' individual MDMT's. But, in case of carbon steel, the least you can get is -48oC. Now, if the design MDMT is -60o and the ratio from UCS 66 comes out to be 0.34. What will be your final adjusted MDMT??

 

[SnTMan]

I would set it no lower than the required MDMT, -60 C.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Mech2325]

sntMan

Thanks again for your valuable feedback

 

[Chumpes]

hi

even if impact testing may be not required for base metal before assembly as per UCS-66, impact testing may be required for the welding procedure as per UCS-67

regards