Thermal Imaging vs Ultrasonic Thickness Testing for Corrosion Malaysia

Thermal imaging and ultrasonic thickness testing can both support corrosion inspection, but they do not measure the same thing.

A thermal camera is useful for scanning a large area and locating unusual temperature patterns.

An ultrasonic thickness gauge is used to measure the remaining thickness of a suitable material at a selected point.

For factories, shipyards, storage facilities and maintenance contractors in Malaysia, choosing the correct method depends on whether the objective is rapid screening or quantitative wall-thickness measurement.

Quick Comparison

The two methods are often complementary rather than competing.

What Is Thermal Imaging?

A thermal camera detects infrared radiation from a surface and converts it into a temperature image.

It may help identify:

• Hot spots

• Cold spots

• Uneven heat transfer

• Moisture-related cooling

• Insulation problems

• Process abnormalities

• Electrical heating

• Areas with different thermal response

Thermal imaging is non-contact and can cover a larger area relatively quickly.

However, the camera records surface temperature, not direct corrosion depth or remaining steel thickness.

What Is Ultrasonic Thickness Testing?

An ultrasonic thickness gauge sends an ultrasonic pulse into the material through a probe.

The instrument measures the time required for the sound to travel through the material and return from the opposite surface.

Using the correct sound velocity, it calculates the material thickness.

Ultrasonic thickness testing may be used on suitable components such as:

• Steel plates

• Storage tanks

• Pipelines

• Pressure vessels

• Ship structures

• Machinery parts

• Fabricated components

The method is especially useful when only one side of the material is accessible.

However, successful measurement depends on the material, surface condition, geometry, probe, calibration and access.

What Does Each Method Tell You?

Thermal Imaging Answers:

• Where is the surface hotter or colder?

• Which area behaves differently?

• Is heat transfer uneven?

• Is there a possible insulation, moisture or process problem?

• Which part of a large asset should be inspected more closely?

Ultrasonic Thickness Testing Answers:

• What is the remaining material thickness at this point?

• Is one location thinner than another?

• Has measurable wall loss occurred?

• How does thickness vary across a measurement grid?

• Which area is approaching the engineering minimum?

A thermal anomaly is not automatically corrosion.

A low ultrasonic thickness reading confirms local wall loss but does not automatically identify why the material became thinner.

Can a Thermal Camera Measure Corrosion Thickness?

A standard handheld thermal camera does not directly measure corrosion thickness.

Hidden corrosion may affect heat flow and create a visible thermal difference under suitable conditions.

This may occur during:

• Natural heating

• Natural cooling

• Industrial operation

• Controlled external heating

• Active thermographic inspection

However, the thermal pattern is influenced by many factors, including:

• Steel thickness

• Corrosion size

• Corrosion depth

• Surface coating

• Emissivity

• Environmental temperature

• Wind

• Rain

• Sunlight

• Inspection distance

• Camera performance

Therefore, suspicious thermal areas normally require verification with another suitable inspection method.

What Is Active Thermography?

Active thermography uses a controlled external energy source to heat or stimulate the inspection surface.

The thermal camera records how different areas heat and cool over time.

An area affected by hidden corrosion or another subsurface condition may respond differently from sound material.

Active thermography may involve:

• Flash heating

• Long-pulse heating

• Lamps

• Induction

• Hot air

• Other controlled excitation

This is different from simply pointing a handheld thermal camera at an ambient-temperature steel plate.

Active thermography normally requires:

• Controlled heating

• Suitable thermal camera

• Time-based recording

• Stable inspection conditions

• Technical image processing

• Reference samples or validation

• Trained interpretation

It is a specialised nondestructive testing technique rather than a basic temperature-checking method.

Advantages of Thermal Imaging

Large-Area Screening

A thermal camera can quickly scan tanks, machinery, panels or building components.

Non-Contact Inspection

The operator can inspect from a distance where visibility and safety conditions permit.

Visual Documentation

Thermal images help communicate the location and shape of an abnormal temperature pattern.

Operating Equipment Inspection

Some problems become visible only while equipment is operating or transferring heat.

Inspection Prioritisation

Thermal screening can help identify areas that deserve ultrasonic or other detailed testing.

Limitations of Thermal Imaging

Thermal imaging may be affected by:

• Surface emissivity

• Reflections from shiny metal

• Changing sunlight

• Wind

• Rain

• Wet surfaces

• Inspection angle

• Distance-to-target ratio

• Camera resolution

• Small temperature differences

• Uneven external heating

A clear image does not necessarily mean that hidden corrosion is absent.

Similarly, a hot or cold area does not automatically prove that corrosion exists.

Advantages of Ultrasonic Thickness Testing

Quantitative Thickness Measurement

The instrument provides a thickness value at the test point.

Single-Side Access

Many components can be measured without reaching the opposite surface.

Corrosion Mapping

Multiple readings can be organised into a grid to show wall-thickness variation.

Trend Comparison

Marked points can be measured during future inspections to evaluate changes over time.

Local Verification

Ultrasonic testing can confirm whether a thermally suspicious area has measurable wall loss.

Limitations of Ultrasonic Thickness Testing

Ultrasonic measurement may be affected by:

• Heavy rust

• Rough surfaces

• Thick or loose scale

• Coating condition

• Poor probe contact

• Curved components

• Very thin materials

• Laminated structure

• Incorrect sound velocity

• High material temperature

• Complex geometry

A suitable couplant is normally required to transmit sound between the probe and the test surface.

Surface preparation may also be necessary.

The operator must calibrate the instrument correctly and understand whether the displayed echo represents the true back wall.

What Is Couplant and Why Is It Needed?

Air between the ultrasonic probe and the material can prevent effective sound transmission.

Couplant fills the small air gap and helps transfer the ultrasonic pulse into the component.

Common couplants may include gels or other suitable liquids selected according to the material, surface and temperature.

The couplant must not:

• Damage the coating

• Contaminate the product

• React with the material

• Create a safety problem

• Become unsuitable at the test temperature

For hot surfaces or special applications, a suitable probe and couplant must be selected.

Can Ultrasonic Testing Measure Through Paint?

Some ultrasonic thickness gauges and measurement modes may be able to reduce or compensate for coating influence under suitable conditions.

However, capability depends on:

• Instrument design

• Probe type

• Measurement mode

• Coating thickness

• Coating condition

• Material

• Surface roughness

A general-purpose gauge should not automatically be assumed to measure metal thickness accurately through every coating.

If the instrument cannot separate the coating response, the displayed result may include the coating or become unstable.

Confirm the application before purchasing the gauge.

Thermal Imaging vs Coating Thickness Meter

A coating thickness meter serves another purpose.

It measures a suitable coating over a metal substrate.

For example:

• Paint over steel

• Protective coating over iron

• Powder coating over metal

• Non-conductive coating over aluminium

It does not normally measure the remaining thickness of the steel underneath.

The correct distinction is:

• Thermal camera: surface-temperature pattern

• Coating thickness meter: coating over the metal

• Ultrasonic thickness gauge: remaining material thickness

A corrosion inspection may require all three, depending on the maintenance question.

Example 1 – Storage Tank Inspection

A maintenance team observes staining and coating deterioration on a storage tank.

A practical workflow may be:

1. Conduct a visual inspection.

2. Review drawings and previous thickness records.

3. Use thermal imaging during suitable operating conditions to locate abnormal heat-transfer areas.

4. Mark suspicious positions.

5. Perform ultrasonic thickness measurements at those positions.

6. Expand the measurement grid if low readings are found.

7. Compare results with nominal thickness and engineering limits.

8. Document the location, readings and surface condition.

Thermal imaging helps prioritise the inspection area.

Ultrasonic testing provides the local wall-thickness values.

Example 2 – Insulated Pipe

A thermal camera may show an unusual hot or cold pattern along an insulated pipe.

Possible causes include:

• Wet insulation

• Missing insulation

• Internal process change

• Air leakage

• Surface damage

• Possible corrosion under insulation

The thermal image does not confirm corrosion under insulation.

Further inspection may require:

• Insulation assessment

• Moisture inspection

• Removal of a selected insulation section

• Ultrasonic thickness testing

• Other suitable NDT methods

Do not report corrosion solely from the thermal pattern.

Example 3 – Ship or Coastal Steel Structure

Salt, humidity and water exposure can accelerate deterioration of coastal and marine steel.

Thermal screening may help compare accessible sections when there is a suitable temperature difference.

Ultrasonic measurements can then be taken on:

• Plates

• Structural members

• Tanks

• Pipes

• Selected corrosion areas

Surface preparation and measurement-grid planning are important for meaningful thickness results.

When Should You Choose Thermal Imaging?

Consider thermal imaging when the objective is to:

• Scan a large area

• Locate thermal anomalies

• Inspect operating equipment

• Check insulation performance

• Identify moisture-related patterns

• Prioritise detailed inspection

• Document temperature distribution

• Perform non-contact preliminary screening

Models such as the UNI-T UTi260A, UTi260B and UTi320E, as well as other suitable industrial thermal cameras, may support general inspection applications depending on the required image detail, target size, distance and temperature condition.

Confirm the actual application before choosing a model.

When Should You Choose an Ultrasonic Thickness Gauge?

Consider ultrasonic thickness testing when the objective is to:

• Measure remaining wall thickness

• Create a corrosion map

• Compare thickness over time

• Check pipes, tanks or plates

• Quantify suspected metal loss

• Inspect when only one surface is accessible

• Support an engineering assessment

Before selection, confirm:

• Material

• Expected thickness

• Surface condition

• Coating condition

• Component curvature

• Operating temperature

• Required accuracy

• Data-storage requirement

• Reporting requirement

When Should You Use Both?

Use both methods when:

• A large area must be screened efficiently

• Thermal anomalies need thickness verification

• Only selected locations can be prepared for contact testing

• The asset is operating and produces useful heat patterns

• Corrosion location is uncertain

• The inspection team wants both visual screening and quantitative measurements

A combined workflow can reduce unnecessary point measurements while ensuring that suspicious areas are checked properly.

However, the final inspection plan should follow the asset risk, applicable procedure and engineering requirements.

Common Selection Mistakes

Buying a Thermal Camera to Measure Wall Thickness

The camera cannot directly replace an ultrasonic thickness gauge.

Assuming Every Thermal Anomaly Is Corrosion

Temperature differences may have many causes.

Using an Ultrasonic Gauge Without Surface Preparation

Rust, scale and poor contact can create unreliable readings.

Selecting a Gauge Without Confirming the Material

The correct ultrasonic velocity and calibration depend on the material.

Ignoring Curvature

Small pipes may require a suitable probe and orientation.

Confusing Coating Thickness with Metal Thickness

These are different inspection requirements.

Using Only One Thickness Reading

Corrosion may be localised. A planned measurement grid provides better information.

Need Help Selecting Corrosion Inspection Equipment in Malaysia?

Send MTM Precision:

• Asset type

• Material

• Nominal thickness

• Surface and coating condition

• Suspected corrosion location

• Operating temperature

• Inspection distance

• Whether only one side is accessible

• Whether the objective is screening or thickness measurement

• Photographs and available drawings

This information helps determine whether the application requires a thermal camera, ultrasonic thickness gauge, coating thickness meter or a combination of instruments.

MTM Precision supplies industrial testing equipment for factories, shipyards, contractors and maintenance teams in Selangor, Kuala Lumpur, Johor, Penang and throughout Malaysia.

MTM Precision Sdn Bhd
Showroom & Service Centre: No. 29-1 & 29-2, Jalan Bandar 18, Pusat Bandar Puchong, 47160 Puchong, Selangor, Malaysia
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my