Using Finite Element Analysis Combined With Strain Gage Testing to Do Proof Test to Establish MAWP

Abstract

An amine reboiler was constructed with very large openings in one semi-elliptical head. The openings extended beyond the “spherical” portion of the head into the knuckle region. The vessel was designed to 1998 ASME Section VIII Division 1 (VIII-1). Initially the manufacturer of the amine reboiler vessel chose the proof test after the calculations submitted to the approval agency were not accepted. Non-destructive strain gage proof testing per VIII-1 UG-101(n) was planned, but the minimum proof test pressure to achieve the desired MAWP exceeded the maximum firetube flange test pressure therefore an alternate method was chosen. Finite element analysis (FEA) was done in addition to the strain gage testing. The strain gage results at the maximum hydrotest pressure were used to verify the FEA calculations. The FEA calculated strains were higher than the measured strains. This indicated that the assumptions made in the computer model were conservative. By combining FEA with strain gauge testing, the design was proven to meet Code requirements.