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Pipelines and surge direction as the problem vibration, will Neil Parkinson is a analysis. resonate to the same level out-of-phase in chartered engineer

The ? nal order to cancel it out. This is especially with more than 30 stage of any useful if there is no steelwork nearby on years’ experience in pipework which to attach a visco-elastic damper. vibration manage- assess- Although pipework vibration can be ment and structural ment is to dif? cult to visually detect, knowledge of asset integrity. He has recommend EI Guidelines and safe limits as well as held the position of corrective an understanding of the six assessment technical director for AV Technology technical director for AV Technology actions phases and the most effective corrective since 1993. He holds a BSc in engineer-since 1993. He holds a BSc in engineer- to reduce actions can prevent the kind of vibration- ing science from the University of ing science from the University of and cyclic operation as well as the vibration induced pipework fatigue which can Warwick and was elected a fellow of the Warwick and was elected a fellow of the construction quality of infrastructure. levels break a pipeline and hit the headlines. Institute of mechanical engineering in Institute of mechanical engineering in

Visco-elastic damper

This may include assessment of process and the 2011.2011.

* 2nd edition 2008, current edition. ISBN 978 0 85293 453 1.

machinery and types of valves as well likelihood of future vibration-induced as supporting structures. It also assesses fatigue failures. Although one solution to the chance of ? ashing or cavitation, and pipework fatigue is to remove the excita- includes a calculation process for scoring tion mechanism altogether, this may be likely excitation factors – which are com- quite intrusive, requiring modi? cation of bined with conditional and operational the process conditions or the pipework factors to predict the likelihood of failure geometry. As this disrupts production for each pipe branch. and may involve temporary shut-down,

No limits

Visual inspection is a quick and effective generally a non-intrusive retro? t solu- method of identifying potential areas for tion is preferred as a means of providing concern and ? agging up areas for improve- increased resistance to vibration.

ment relating to pipe infrastructure. This

Some corrective actions can be very may include installing more effective pipe straightforward. For example, it is very supports or replacing worn or damaged common for pipelines to rest on supports supports, proper bracing of SBCs, avoiding without any additional protection against fretting and poor geometry, and allowing fretting damage, in which case a second- for thermal expansion of tubing. ary “doubler” plate can be installed for

In the basic piping vibration measure- additional support and strength with- ment phase, specialist engineers will ? rst out modifying any processes. However, use a single axis accelerometer con- unsuccessful or incomplete attempts nected to a portable data collector to take at supporting pipework can result in initial vibration levels, ranging from 1Hz no reduction of vibration or even an up to 300Hz. These measurements are exacerbation of the problem. SBCs are presented as vibration amplitude versus frequently braced to the deck or nearby frequency and enable the vibration to be structures, for example, but to adequately classi? ed as acceptable, concern or prob- counteract vibration they should in lem, based on EI guidelines. fact be braced back to the parent pipe.

If, following the basic measurement Bracing solutions can also be ? tted in phase, vibration is found to be at concern the wrong place, supporting the pipe

Our innovative mindset makes us freerunners in heart and or problem level, or for pipework with a itself rather than the main mass such as soul; when appropriate or higher frequency vibration of more than a valve, while poorly maintained bracing necessary, we push the 300Hz, the next phase is based on spe- can loosen and return the pipework to its envelope of our competencies. cialist measurement techniques. A vari- original level of excitation.

After all, what matters in the ety of more in-depth tests are deployed Another common mistake is to brace end is the result: the perfect depending on circumstances, including: the pipework in only one plane, where deck that meets the highest standards in terms of dynamic strain measurement and fatigue vibration can cause movement in several functionality and durability. analysis; experimental modal analysis; directions. The most effective bracing

Bolidt ship decks are rugged, operating de? ection shape analysis; and system will be able to accommodate any shrink-resistant and able to dynamic pressure (pulsation) measure- geometric alignment of SBC, with a stiff withstand varying loads and ment. Engineers also have a choice of truss design to resist movement on any weather conditions.

Bolidt, no limits.

specialist predictive techniques, apply- plane. Similarly, for mainline pipes, ing sophisticated modeling tools and visco-elastic dampers are effective in www.bolidt.com multi-channel instrumentation systems all degrees of freedom as they provide to assess in more detail the dynamics of dynamic damping movement in all direc- speci? c pipelines throughout their life- tions and over a wide frequency range. cycles. Specialist predictive techniques Another option for mainline pipework include ? nite element analysis, compu- is a dynamic vibration absorber, which tational ? uid dynamics, and pulsation when tuned to the same frequency and oedigital.com September 2014 | OE 89

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