FFS Forum: Piping Analysis Software as a Tool in Fitness-for-Service Assessments

Overview

Piping stress and flexibility analysis are extremely common in a process plant environment. The B31.3 code, Process Piping, directly addresses the design of such piping systems. To simplify this analysis, designers and engineers often use customized piping analysis software.

Generally, piping analysis software is a software package that is highly optimized for piping system input, analysis, and output. These packages include extensive databases of, for example, piping materials (stiffness and allowable strength), pipe sizes and schedules, flange dimensions and weights, elbows, bends, and o-lets. Inputs are optimized for point-to-point input of the nominal pipe run dimensions. Post-processing routines evaluate specific B31.3 code allowable stresses – the so-called “code check.”  

Piping analysis software typically uses finite element analysis (FEA) to solve for deflections and stresses, but it’s a very trimmed-down version of FEA to meet the specific needs of piping work. In this installment of the FFS Forum, I will discuss some key elements of piping analysis software that should be of particular interest to those considering its use in fitness-for-service (FFS) assessments.

Before we proceed, I do have a few caveats:

• Most of my expertise is with B31.3. Many (perhaps most) of my comments would apply to a much broader set of piping codes, but given my limited familiarity with those other codes, I’ll limit my comments to the application of B31.3.
• Also, all my experience is with the Caesar II software. There are other software packages on the market, but Caesar is certainly familiar to anyone doing piping analysis, and it’s the one I’ve used. If you’re using a different software, there may be some differences.

Role in FFS Assessments

Piping software is designed to evaluate piping stresses against code requirements.  Basically, it’s design software. However, the outputs include basic stress, deflection, and load information and can be useful in FFS assessment. But as always, the user must understand both the inputs and outputs.

Much of FFS assessment is discussed in terms of pressure vessels, but there are differences between piping and pressure vessels, such as:

• Different materials
• Allowable stresses
• Treatment of primary and secondary loads
• Cyclic thermal stress is a major consideration in most piping systems
• Elastic follow-up is a more frequent issue for piping systems

All of these are good reasons why specialized piping analysis software can provide valuable assistance in FFS assessments.