aiwa,
It is really simple. Your Client requested you to provide welded lifting lugs of material compatible with the equipment material, impact tested at -45C (does not seem they asked your opinion on what the MDMT should be). Regardless of your opinion over the sanity of this request, they are paying you to give them what they ask for. Also, the welding of the attachment has to comply with the code and Client specification, ie qualified for -45C if the Client wants that. Tha ASME VIII code allows in some cases a reduction in the testing temperature, you have to read the code to see if you qualify for that reduction. Alternatively, give us details of the design conditions and the forum will advise you the appropriate MDMT.
Cheers,
gr2vessels