UT Corrosion Thickness Gauges
PosiTector UTG CPosiTector UTG CAPosiTest UTG CX
Thru-Paint Thickness Gauge
PosiTector UTG M
Cast Iron Thickness Gauge
PosiTector UTG CLF
Precision UT Thickness Gauge
PosiTector UTG PPrinciples of OperationUltrasonic Material VelocityTheory of Operation

Ultrasonic Wall Thickness Gauges

Ultrasonic Wall Thickness Gauges (ultrasonic thickness gauges, UT gauges, etc.) measure the wall thickness of materials such as steel, plastic, and more using ultrasonic technology. Ideal for measuring the effects of corrosion or erosion on tanks, pipes, or any structure where access is limited to one side. Multiple echo (UTG M) Thru-Paint models measure the metal thickness of a painted structure without having to remove the coating.

What is Ultrasonic Thickness Measurement?

Ultrasonic thickness measurement techniques are used to measure a wide range of substrates and applications for loss of thickness due to corrosion or erosion. Gauges are designed for measuring the thickness of metallic (cast iron, steel and aluminum) and non-metallic (ceramics, plastics and glass) substrates and any other ultrasonic wave-conductor provided it has relatively parallel top and bottom surfaces.

An ultrasonic thickness gauge facilitates rapid inspection of the thickness of large metallic structures at small measurement intervals, providing a high-detail thickness map of a scanned surface. When access is only available from one side of the substrate, ultrasonic wall thickness measurement is the most efficient way to monitor the effects of erosion or corrosion and is instrumental to both quality assurance and quality control.

Product photo of a PosiTector UTG Corrosion probe measuring on a rusty pipe

UT Corrosion Thickness Gauges

PosiTector UTG C Series

Corrosion probes measure the wall thickness of materials such as steel, plastic, and more. Ideal for measuring the effects of corrosion or erosion on tanks, pipes, or any structure where access is limited to one side.

  • 5 MHz dual element transducer
  • Our most popular probes for measuring the effects of corrosion on steel substrates
  • Select from cabled, integral, and Xtreme probes
Image of PosiTector UTG C

PosiTector UTG C

Corrosion with Cabled Probe

Image of PosiTector UTG CA

PosiTector UTG CA

Corrosion with Integral Probe

Image of PosiTector UTG CX

PosiTector UTG CX

Corrosion with Xtreme Probe

Product photo of the PosiTector 6000, coating thickness gauge for all metal substrates with cabled probe

Thru-Paint Thickness Gauge

PosiTector UTG M

Features Thru-Paint capability to quickly and accurately measure the metal thickness of a painted structure without having to remove the coating. Also ideal for measuring blasted materials and other applications requiring a more durable wear face.

  • 5 MHz contact probe with wear resistant alumina probe tip and cabled probe
  • Multiple-Echo technique averages 3 or more echoes for accurate and reliable readings
  • Toggle between Single and Multiple-Echo modes
  • Multiple Echo mode eliminates coating thickness
  • Single Echo mode detects pits/flaws and increases measurement range
Image of PosiTector UTG M measuring the thickness of a yellow pipe; stats mode is on the screen
Product photo of the PosiTector 6000, coating thickness gauge for all metal substrates with cabled probe

Cast Iron Thickness Gauge

PosiTector UTG CLF

Low frequency probe measures the wall thickness of attenuative materials such as cast/ductile iron, cast aluminum, and cast zinc.

  • Low frequency 2.25 MHz dual element transducer with cabled probe
  • Proprietary algorithm distinguishes back wall reflections from grain noise (reflections) found in cast materials
  • Ideal for measuring attenuative materials such as cast iron
An image of the PosiTector UTG CLF probe measuring the thickness of concrete
Product photo of the PosiTector 6000, coating thickness gauge for all metal substrates with cabled probe

Precision UT Thickness Gauge

PosiTector UTG P

Designed for high resolution measurements and thin materials including metals and plastics. Automatic Multi-Echo mode ensures the best accuracy on thin metals.

  • 15 MHz Single element delay line with cabled probe
  • Automatic single-echo or multiple-echo mode depending on material thickness
  • Automatic probe tip temperature compensation
  • Ideal for thru-paint applications to quickly and accurately measure the metal thickness of a painted structure without having to remove the coating
  • Precision probe ideal for thin materials
  • Minimum steel measuring range: 0.008" (0.2 mm)
  • Minimum plastic measuring range: 0.005" (0.125 mm)
An image of the PosiTector UTG P precision probe measuring PET (polyethylene terephthalate) bottle wall thickness

Principles of Operation of Ultrasonic Wall Thickness Gauges

Why Measure Wall Thickness with Ultrasonic Thickness Gauges?

Erosion

Erosion is the process by which a protective coating or substrate is worn away by friction resulting from repetitive mechanical interaction. Typical causes of erosion include cavitation, impingement by liquid or solid particles, and relative motion against contacting solid surfaces or fluids.

Corrosion

Corrosion is the process by which a substrate and its properties are damaged or worn away by a chemical action or change. In metals, deterioration attributed to corrosion is most often caused by an oxidation process.

Erosion and Corrosion Testing

Using non-destructive inspection methods minimize safety concerns, ensure code compliance, and reduce the frequency of major repairs (and subsequently costs). As an example, marine applications have a significant risk of catastrophic substrate failure due to undetected substrate corrosion or erosion. However, costs associated with corrosion or erosion damage can be more subtle. Consider the case of a propeller blade that has experienced wear or damage. A likely impact is a decrease in the efficiency of the propeller, translating directly to a decrease in horsepower and an increase in turbulence (vibration). This results in a decrease in maximum speed and an increase in fuel consumption. Furthermore, cavitation caused by the damaged propeller creates a surrounding environment that is even more damaging to the propeller itself.

For more information read our article, “Measurement of Effects of Erosion and Corrosion” here.

Closeup image of a PosiTector UTG probe measuring on metal

What are some UT Measurement Applications?

With ultrasonic thickness gauges, an accurate measurement of the remaining wall thickness of a substrate can be taken on pipes, pressure vessels, storage tanks, boilers, or other equipment prone to erosion or corrosion.

Though many industries are affected by erosion and corrosion, the marine atmosphere is one of the most aggressive corrosion environments. Corrosion rates are affected by several elements including sea water, humidity, wind, temperature, airborne contaminants, and biological organisms. Erosion is also common in marine applications due to abrasion from the impact of water and contaminate particles, impingement due to turbulence in high speed liquids, and cavitation due to pressure waves produced by air bubbles. Erosion not only affects the substrate itself but may also damage protective coatings, increasing the likelihood of substrate corrosion. Ships, marinas, pipelines, offshore structures, and desalination plants are all systems that are subject to varying levels of marine erosion and corrosion.

What is the difference between the PosiTector UTG C, PosiTector UTG M, and PosiTector UTG P probes?

The PosiTector UTG C (Corrosion) single echo probe uses a dual-element transducer, a focused “V-path”, and V-path compensation to accurately measure the thickness of metals with heavy corrosion or pitting. The UTG C single echo probe will not ignore the thickness of the exterior coating: for best measurement accuracy, it may be necessary to remove any coating present at the point of measurement.

Closeup of the Posite

The PosiTector UTG M (Multi-echo) probe uses a single element transducer to accurately measure the metal thickness of a new or lightly corroded structure while ignoring the thickness of protective coatings. The ultrasonic beam travels in a straight path to the material’s back wall at 90° relative to the surface. When three consecutive back wall echoes are detected, the probe makes a time-based calculation to eliminate the coating thickness from the gauge reading.

Closeup of the PosiTector UTG M probe

The PosiTector UTG P (Precision) probe uses a single element delay line transducer to accurately measure the thickness of thin materials including plastics and metals. It automatically switches between single-echo or multiple-echo modes depending on material and thickness.

Closeup of the PosiTector UTG P probe

Ultrasonic Material Velocity

What are some common material velocities?

The table below lists the longitudinal wave ultrasonic velocities of some common materials typically measured by ultrasonic thickness gauges. Specific material velocities may vary due to temperature, composition, grain, and other factors. For best accuracy, check the velocity on a sample of known thickness.

Pre-programmed Velocities

Select from a list of common pre-programmed material velocities or enter your own with ease.

Material (Menu Option)
in/μs
Velocity
Min Range*
m/s
Max Range*
in
mm
in
mm
Iron (Iron)
0.179
4547
0.040
1.02
3.800
96.52
SS 303 (SS303)
0.223
5664
0.040
1.02
5.000
127.00
STEEL 1018 (Steel)
0.233
5918
0.040
1.02
5.000
127.00
Al 2024 (Alum)
0.251
6375
0.050
1.27
5.000
127.00
PLEXIGLAS (Plexi)
0.106
2692
0.040
1.02
2.000
50.80
PVC (PVC)
0.094
2388
0.035
0.89
2.000
50.80
POLYSTYRENE (Poly)
0.081
2057
0.035
0.89
2.000
50.80
* Range may change depending on surface roughness, temperature, or material properties

Theory of Operation of Ultrasonic Wall Thickness Gauges

PosiTector UTG probes transmit an ultrasonic pulse into the material to be measured. This pulse travels through the material towards the other side. When it encounters an interface such as air (back wall) or another material, the pulse is reflected back to the probe. The time required for the pulse to propogate through the material is measured by the gauge, represented as t1 and t2 below.

Single Echo

Single-echo PosiTector UTG C (and PosiTector UTG M and UTG P probes in single-echo mode) probes feature a dual element transducer with automatic V-Path compensation. Thickness is determined by measuring t1 (uncoated) or t2 (coated), dividing it by two and then multiplying by the velocity of sound for that material (steel). See Figure 1.

Illustration of the theory of Single-echo probes like the PosiTector UTG C, UTG M, and UTG P

Figure 1

For uncoated materials, t1 related directly to material thickness. When a material is coated, the propagation time is increased and is shown above as t2.

Coatings such as paint have a slower velocity of sound than that of metal. Thus the single echo technique will produce a thickness result greater than the actual combined coating and metal thickness. The result will include a significantly higher, unknown value of paint thickness. Therefore, it is not a simple matter of measuring the thickness of the paint and subtracting it from the single echo measurement result.

Multiple Echo

The PosiTector UTG M and UTG P probes in multiple-echo mode probe determine thickness by measuring the time between at least three consecutive back wall echoes.

Illustration showing PosiTector UTG Theory of Operation, specifically the workings of a Multiple Echo probe when measuring coatings on steel

Figure 2

In Figure 2 above, multiple echo mode measures only the time between echoes. Regardless of whether the steel is coated or not, all times between echoes are the same. In multiple-echo mode the gauge determines thickness by measuring t1 + t2 + t3, dividing it by six and then multiplying by the velocity of sound for that material. The resultant thickness calculation made by the instrument is therefore an accurate measurement of the steel thickness only, disregarding the coating thickness.

The velocity of sound is expressed in inches per microsecond or meters per second. It is different for all materials. For example, sound travels through steel faster (~0.233 in/µs) than it travels through plastic (~0.086 in/µs).

F.A.Q.

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