To correct the problem, the original snubber was replaced with one that had an overall available stroke of 12 inches, allowing the initial set point to be increased to a cylinder position of 3 inches of extension. But, because the original set point of the snubber allowed a maximum of only 1 inch of contraction, the continued pipe movement stressed the snubber beyond its capabilites once it reached its fully contracted position (zero extension), thus damaging the support assembly.
However, a more thorough review of the pipe system revealed that, prior to reaching full operating conditions, the movement of the pipe created a condition in which the overall length of the snubber should have been reduced (retracted) by 1.5 inches. Review of the pipe’s position indicated that it was correct according to the original design specifications. An overall analysis indicated that the final operating (hot) position of the pipe would require that the snubber extend 4.5 inches (which could be accommodated by the remaining stroke of the hydraulic snubber cylinder).Īfter being put into service, the seals of the snubber were damaged, indicating that the cylinder, at some point, had been completely retracted or extended. In the initial (cold) position, a hydraulic snubber, attached both to stationary structural steel via an end bracket and to a pipe element via a three-bolt clamp, was installed at a cylinder position of 1 inch extension, with a total stroke available of 6 inches. The following is an example illustrating the necessity of thoroughly reviewing all movements associated with pipe deflection during a given thermal cycle. In real life: the consequences of not accounting for all movement in a process cycle When active and passive support assemblies, comprised of standard components, cannot meet specific system requirements, designers can add auxiliary components, which are designed to extend the range of motion that these supports can accommodate during normal operation. This means that designers may be able to accommodate greater pipe movement by incorporating longer support assemblies into the design, rather than introducing additional support components. For example, hanger assemblies can accommodate translational motion producing swing angles of +/- 4 degrees maximum. The amount of stroke provided as part of the snubber design determines how much pipe movement is allowed under normal conditions.ĭesigners must consider that the above support configurations all allow some movement depending upon the overall size, orientation, and configuration of the assembly. Under normal operating conditions, snubbers simply “follow” the movement of the pipe, but when subjected to shock loading, the snubber, which can be mechanical or hydraulic, is activated and thereafter acts as a rigid restraint.
Snubbers: Used to restrain piping undergoing unwanted abrupt movement in one axis. An anchor will completely restrict pipe movement in all three dimensions while bearing the weight, side, and thrust loads. A guide will uphold the weight of the pipe while restricting movement in up to two dimensions. A load bearing support will uphold the weight of the pipe while allowing possible movement in all three dimensions. Pipe support functions include load bearing, guiding, or anchoring.
However, disturbances such as severe weather, impact, abnormal vibration or seismic events, will activate these otherwise passive supports, which then function as active anchoring devices. We designate support configurations whose primary capabilities are always engaged as active, whereas passive support configurations simply follow the movement of the pipe during normal operation. Pipe support assemblies can be classified according to both their level of engagement (active or passive) and function (load-bearing, guiding, or anchoring). Using pipe supports to accommodate movement
Case Study: Engineered Support for Vibration problem.1400 Pipe Shoe Solution for Vibration in Piping
Emergency Custom Steel Structure and Support Design and Fabrication.Spring Support and Expansion Joint Audits.Pipe Stress Analysis for Plant Personnel.Pipe Stress Analysis Case Study – Pump Discharge.High Temperature Pipe Supports (Hot Shoes).Pipe Shields Insulated Pipe Supports (Cold & Hot Shoes).Insulated Pipe Supports (Figures 4500-4800).