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As presented at EPRI
(Electric Power Research Institute) Winter 2018 Copyright Bengal Resources & Assoc., Inc. 2018


POSITIONAL CHANGE MONITORING (i.e. distortion/displacement)

The fact that machinery moves during operation is established and well documented. Many manufacturers of rotating equipment provide expansion data for their products derived from theoretical calculations. It is Bengal Resources’ position that no matter how painstakingly careful one is in approaching these calculations, and no matter how sophisticated the mathematical approach, unavoidable limitations are encountered when applying pure theory to field situations. Further, thermal growth is not the only contributor to positional change of on-line machinery.

Some variables posing problems to theoretical growth calculations for alignment are:

  • Piping size and length
  • Downstream temperature variations ( and their effect on piping)
  • Variations in load
  • Machine frame distortion due to torque
  • Non-homogeneous materials composition
  • Non-uniform machinery cross-sections
  • Uneven heating of material
  • Foundation problems
  • Frequent and significant changes in ambient temperature
  • Process effects (changes in operating pressure, temperature)
  • Mechanical looseness
  • Oil film thickness


A good alignment target takes all significant factors into account. The objective is to deliberately misalign the machine assembly off-line so that it runs into a "straight line" when activated. Occasionally, the solution to thermal growth problems requires expansion joints or additional securing of pipes. Nevertheless, the problem with on-line monitoring is: "How do I get realistic data"?

The approach to positional change measurement employed by Bengal Resources is to apply several methods of measurement (i.e. laser, optical, and theoretical calculations of temperature gradients) at a reasonable cost. Our goal is to learn more about the physical behavior of a machine assembly so that we may intelligently recommend a course of action to eliminate poor machinery performance. Frequently, that course of action is a recommended cold alignment target. Sometimes a change in piping may be required. On occasion, the source of alignment problems is foundation movement. Regardless of the causal nature of a movement problem, Bengal Resources has the necessary equipment and expertise to confirm positional change.


Permalign and Rotalign
Pro M3 system measuring thermal growth;
Agricultural Products Manufacturer in Nebraska.

Optical and Laser Measurement;
Compressor Thermal Growth;
Gas Transition Facility, Minnesota

Optical measurement axial movement of a
crossover pipe, using a jig transit


Laser and Strain gauge measurement of
steam turbine foundation pedestal movement in Ohio.


Casing Distortion Measurement on Steam Turbine

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Phone:  404-312-4642


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107 Walter Payton Drive Ste 102, Columbia MS 39429