phase II+ UTG-2800 - Appendix B Applications Notes

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Appendix B Applications Notes

Measuring pipe and tubing.

When measuring a piece of pipe to determine the thickness of the pipe wall, orientation of the transducers is

important. If the diameter of the pipe is larger than approximately 4 inches, measurements should be made with

the transducer oriented so that the gap in the wearface is perpendicular (at right angle) to the long axis of the

pipe. For smaller pipe diameters, two measurements should be performed, one with the wearface gap

perpendicular, another with the gap parallel to the long axis of the pipe. The smaller of the two displayed values

should then be taken as the thickness at that point.

Measuring hot surfaces

The velocity of sound through a substance is dependant upon its temperature. As materials heat up, the

velocity of sound through them decreases. In most applications with surface temperatures less than about 100℃,

no special procedures must be observed. At temperatures above this point, the change in sound velocity of the

material being measured starts to have a noticeable effect upon ultrasonic measurement. At such elevated

temperatures, it is recommended that the user perform a calibration procedure on a sample piece of known

thickness, which is at or near the temperature of the material to be measured. This will allow the gauge to

correctly calculate the velocity of sound through the hot material.

When performing measurements on hot surfaces, it may also be necessary to use a specially constructed

high-temperature transducer. These transducers are built using materials which can withstand high temperatures.

Even so, it is recommended that the probe be left in contact with the surface for as short a time as needed to

acquire a stable measurement. While the transducer is in contact with a hot surface, it will begin to heat up, and

through thermal expansion and other effects, may begin to adversely affect the accuracy of measurements.

Measuring laminated materials.

Laminated materials are unique in that their density (and therefore sound-velocity) may vary considerably

from one piece to another. Some laminated materials may even exhibit noticeable changes in sound-velocity

across a single surface. The only way to reliably measure such materials is by performing a calibration procedure

on a sample piece of known thickness. Ideally, this sample material should be a part of the same piece being

measured, or at least from the same lamination batch. By calibrating to each test piece individually, the effects of

variation of sound-velocity will be minimized.

An additional important consideration when measuring laminates, is that any included air gaps or pockets

will cause an early reflection of the ultrasound beam. This effect will be noticed as a sudden decrease in

thickness in an otherwise regular surface. While this may impede accurate measurement of total material

thickness, it does provide the user with positive indication of air gaps in the laminate.

Suitability of materials

Ultrasonic thickness measurements rely on passing a sound wave through the material being measured. Not all

materials are good at transmitting sound. Ultrasonic thickness measurement is practical in a wide variety of

materials including metals, plastics, and glass. Materials that are difficult include some cast materials, concrete,

wood, fiberglass, and some rubber.