Piping Vibration Analysis and monitoring is important to the success and efficiency of any piping system. Excessive vibration can lead to some practical problems. Flanges may start leaking. Pipes can be knocked off their supports or result in pipe fatigue failure.

Piping design codes have been created to help engineers design more efficient piping systems. The piping system’s integrity depends on the considerations and principles used in design, construction and maintenance of the system. Some of the most commonly used piping design codes are ASME B 31.3, B31.1, B31.4, B 31.8 etc. However, since design is a vast subject and every process and plant is different, most of the piping codes are somewhat inadequate to deal with vibration analysis. Codes and standards provide a general framework but don’t address vibration and its impact in a detailed manner. Thus, the potential damage and impact of vibration is somewhat ignored during the design phase. Often many designers restrict their analysis to simple static analysis without paying much attention to vibrational and dynamic aspects.

But at the same time, the vibrational forces of piping systems have increased to a very large extent because of increasing flow rates of process industries. The usage of high strength flexible material during design also contributes to the vibration tendency of piping systems.

But first, one must first understand the causes of piping vibration.

Vibration is defined as the continuous to and from motion from an equilibrium point. There are many causes that lead to vibration in a piping system. Here are the most common causes:

3 Most Common Causes of Piping Vibration:

1. Excessive Pulsation
2. Mechanical Resonance
3. Inadequate Supports and/or Support Structure

Factors that contribute towards the above causes are:

• Flow induced: Turbulence of flowing liquid causes Flow-induced vibration.
• Equipment mechanical forces: Rotating and reciprocating equipment like pumps, compressors etc produce excitation forces.
• High frequency acoustic vibrations generated by relief valves, control valves or orifice plates.
• Pressure Pulsations from reciprocating equipment.
• Water Hammer (Surge) or Momentum changes due to sudden valve closure.
• Cavitation/ flashing caused by vapor bubble collapse
• Sudden flashing of fluid.

Since the main factors affecting vibration are the strength of excitation and the flexibility of the piping system, there are two methods to solve piping vibration issues – either by reducing the level of excitation or providing more support to withstand the applied dynamic forces.

Effects Of Piping Vibration And Associated Risks:

Vibration can result in equipment damage, fatigue failure on process piping, and also cause fatigue in small branch connections including relief lines, instrumentation ports, nozzles, drains, and valves. The result of vibration on compressor and pump packages also causes reliability issues.

Identifying Risks:

A high number of pipe failures due to vibration are related to small-bore connections (SBCs). This is because of several reasons:

• Huge unsupported valves
• Concentration of stress concentrations at the main pipe weld or other vessel
• Lack of timely vibration audit and fatigue risk
• Gaps between the SBC design intent and site fabrication especially local support/bracing

In order to create safe and secure piping systems, free from unwarranted vibration, the individual piping components must not be mechanically resonant to the system excitation forces. Also, ensure there are no unnecessary bends as they offer a strong coupling connection between the mechanical system and pulsation excitation forces.

Engineers can identify piping vibration risks at any phase in the asset life cycle, but companies need to take a systematic approach. Taking a preventive approach with piping vibration analysis such that its potential impact can be resolved at the design phase.

Summary

Vibration is an inescapable reality of piping design systems. There are several causes that result in vibration and it can have severe impact on onshore and offshore facilities. Risk-based assessments are one of the most cost-effective and reliable methods to identify, measure, inspect and thwart vibration and fatigue hazards. However, system changes made to ease piping vibration should be carried out to balance the differential thermal expansion of the pipe. Since pipe stress analysis can conflict with vibration audit requirements, maintaining the balance is crucial to avoid stress failures.

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