Equipment: Steam Reformer 20Cr-32Ni-Nb, cast, Alloy-800, UNS-N08800, Outlet piping 8in header and 1.25in pigtails system in high temperature service

Problem: Sagging of pig tails tubes and the collection header, misalignment of pulley locations causing the sling wires to clash with the piping insulation and being off-centered between two adjacent pig-tail piping. Similarly, deformation of the outlet piping system was reported along with tilting of sliding supports and movements / resting positions away from their intended design positions and similar such potential issues were reported.

Analysis: A piping stress and flexibility analysis had been completed in accordance with ASME B31.3 requirements, using the beam elements with 6 degrees of freedom with commercially available software, CAESER-II. The advantage of symmetry was considered and appropriate boundary conditions were applied. Static analysis was done to evaluate sustained, operating & expansion stress categories. All displacements of the piping system were verified with field observations and the operating characteristics of Counter-weights & Variable Spring Hanger supports were verified with field measurements and were evaluated for suitability according to the existing design conditions.

Results Conclusion:The results of the analysis established the conclusions that the thermal travel combines with high coefficient of friction at the existing supporting structural members due to lack of anti-friction mechanism causes the trapeze type supports to swing along the axis of the header creating a gap, at the edge, essentially resulting tilting of sliding supports. This also effects the transverse action which caused the wire-ropes to clash with the pigtail piping insulation due to extremely tight design clearances. The results also confirm that sagging of the 8in€� header was not possible and although it may apparently seem so, this field observation could may be a result of improperly installed and / or damaged insulation which is giving this effect. It is also very unlikely that the 8in€� header and  1¼€� pigtails piping have suffered permanent plastic deformation.

Benefits: Overall, the resulting SUS, EXP & OPE stresses of the Hydrogen Reformer Outlet Piping were found to be well within the code allowable values and there is no immediate concern to its mechanical integrity.