Debasis tm (t + C.A ) as per ASA B 31.3 piping code and td (tmin+ C.A) as per API 650 are essentially the same. Each code calls by different terminology to name as tm (ASA B 31.3) and td (API 650). As per ASA B 31.3 you have to apply pressure-temperature correction factor if the temperature exceeds > 200 F, the minimum allowable stress for design temperature. In API 650, since it is generally constructed for atmospheric storage tanks, mostly allowable stresses come within the range at < 200 F . Trust this clarifies your question C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India June 22 E-mail: nishi@vsnl.com >As per ASME B 31.3/ para 304.1.1(a)(Process piping- Presure >Design) Minimum Required Thickness (tm) is INCLUSIVE of >corrosion allowance with formula >(tm = t + c ), where t= pressure design thk. and c = sum of >total allowances whereas as per API 650 ( Welded oil storage >steel tanks) Minimum Required Thickness (tm) is EXCLUSIVE of >corrosion allowance with formula (td = tmin + c.a.), where >td= design thk., c.a. = corrosion allowance. > >A disscussion will be helpful with your valued inputs.