The design of process piping is often directly related to the design of pressurised equipment in order to limit loadings on equipment connections due to the restraint of thermal growth. The flexibility analysis of piping systems is therefore a logical extension of the range of design services offered by FCL. FCL engineers have accumulated considerable experience in the mechanical design of piping systems for both the petro-chemical and nuclear industries.

Case Study: Process plant operators have occasion to modify the operation of the process plant in their care. This can result in a requirement to re-rate items of process equipment in order to reduce emissions or increase plant capacity. The same applies to process piping. FCL engineers have recently completed the analysis of a system of large diameter refractory lined pipe to establish the acceptability of a proposed increase in design temperature.

The system was complex and involved modelling of equipment items and their supporting structures in order to correctly represent the boundary conditions restraining thermal growth of the piping. Sensitivity studies were carried out to establish the influence of the refractory lining on the flexibility of the piping system. Piping flexibility analysis was undertaken using CAESAR II software.

The sustained stress and expansion stress range were assessed against limits in ASME B31.3 and the magnitude of reaction forces at equipment connections assessed in accordance ASME Section VIII Division 2 Appendix 4. Limiting values of pipe expansion stresses were established to ensure a margin against rupture of the refractory material at the hot face. The analysis demonstrated that the piping design was suitable for the proposed increase in design temperature.

FCL's involvement in this project enabled the plant operator to complete the work in advance of a major turnaround.