Don't have the API with me, but the chemistry and mechanicals are listed in the API standard. Yield has to be 55,000 psi, but I don't recall the tensile.

Not sure there really is an ASTM equivelent - API tubulars are meant for specific purpose, but K55 is on the 'plain vanilla' side of things, so there may be something out there.

Typically, API tubulars are not the type of material that is easily welded - the CE can reach into the 0.8 range. K55 at least puts some limits on chemistry compared to J55.

If this truly requires welding, it may be worth considering a mock-up. If the service is 'sour', then there will be al kinds of hardness limitations in the weld and HAZ. My limited experience suggests 500+ preheat, and possibly PWHT 1200F minimum. 1150 may not soften this material.