Piping strain is a huge contributor to machinery vibration and damage. High piping flange loads are often caused when the piping system is too rigid. Piping design using common pipe modeling software tools such as Caesar, AutoPipe, or others can easily review the piping stress levels and compare to allowable piping codes. Review of the piping flexibility and limiting nozzle loading as recommended in NEMA SM23 should be done on all rotating machinery.
Flexibility analysis should be done on all equipment that operate with higher temperature piping. Thermal growth is often the primary loading mechanism for high flange loads, but it can also be contributed to by pressure and cold to hot shifts in various nozzle positions on attached equipment.
In addition to general design deficiencies, one of the other significant contributors to excessive nozzle loading is failed, improperly installed, or inadequately maintained supports. When the supports are the effective, the attached equipment nozzle loads can increase tremendously.
Some machinery will demonstrate odd vibration variations from cold to hot conditions. In some cases, vibration on machinery can dramatically change due to weather such as rain or wind. When this occurs, one of the common causes will be lack of adequate flexibility in the piping system.
Correcting the pipe supports or rerouting the pipe to increase the flexibility can greatly reduce nozzle loading and distortion of the connected equipment. This can result in lower vibration at operating conditions or eliminate the sensitivity to ambient or process conditions.
Piping flexibility analysis involves a review of the piping system layout and installation of the piping supports. This normally requires review of the installation in the field. Once the piping system is understood, the flexibility and nozzle loads are analyzed using ANSYS finite element analysis or Bentley Systems AutoPipe software.
In some cases, it will be necessary to instrument the field piping using strain gages or other data recording instruments to verify actual thermal movements and loading on the associated equipment.