Visual ODS of Piping and Structural Support

A leading chemical manufacturer was experiencing a failure of piping supports on a high-pressure compressor application where pressures exceed 10,000 psi. Several engineering studies had been performed, all indicating that the vibration levels were satisfactory. However, the failures continued to persist. The customer requested a Field Engineering site visit to investigate the issue and identify the root cause.

Structural supports are fabricated from I-beam steel members as vertical supports, with angle steel as horizontal lateral supports for the piping. The supports are subjected to pipe forces in a loading direction that the I-beam webbing and flanges are not designed to withstand. This creates high-cycle fatigue in thinner areas of the I-beam.

A four-stage, high pressure reciprocating compressor, operating at > 20,000 psi utilizes small bore piping and an expansion loop for intercooling between stages of compression. The operating pressures to too high for conventional intercoolers, so the piping is routed to an open area for cooling and returns to the compressor. The off-skid piping near the compressor is supported by structural I-beam elements that are mounted vertically and in sets of two, with smaller angle bracing to provide horizontal support for the piping. Piping passes between the vertical supports and rests on the horizontal angle steel.

Structural vibration data and Visual Operating Deflection Shapes (ODS) were collected and compared to verify the calculated resonant frequencies from Finite Element Analysis (FEA) of the high-pressure piping supports. The Visual ODS provided detailed visual confirmation of the piping deflections, while triaxial accelerometers were used to provide precise displacement, velocity, and acceleration data of the supports at selected locations vertically, horizontally, and axially. This information was used to add stiffening supports and gussets to the structural beams. Additional plating was added to the I-beam web areas and flanges to increase the stiffness of the piping supports, as well as adding mass.