Can a Thermal Camera Detect Hidden Corrosion on Steel Malaysia

A thermal camera can help locate unusual temperature patterns on steel, but a normal handheld thermal imager does not directly measure corrosion depth or remaining wall thickness.

This distinction is important for factories, shipyards, storage facilities, maintenance contractors and inspection teams in Malaysia.

Thermal imaging may be useful for identifying a suspicious area. However, additional inspection—such as ultrasonic thickness testing—may still be required to confirm actual metal loss.

What Does a Thermal Camera Detect?

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

It may reveal:

• Hot areas

• Cold areas

• Uneven heat flow

• Moisture-related cooling

• Insulation problems

• Abnormal electrical heating

• Process-temperature differences

• Areas that respond differently during heating or cooling

A thermal camera does not see directly through steel.

If hidden corrosion affects how heat moves through the material, it may create a detectable thermal pattern under suitable conditions. The camera records the surface-temperature response—not the corrosion itself.

Can Corrosion Create a Thermal Anomaly?

Corrosion may change:

• Material thickness

• Thermal conductivity

• Heat capacity

• Surface condition

• Bonding between layers

• Heat-transfer behaviour

When the steel is heated or cooled, a corroded section may respond differently from a sound section.

However, whether the difference is visible depends on:

• Corrosion size

• Corrosion depth

• Steel thickness

• Surface coating

• Heating method

• Camera sensitivity

• Inspection distance

• Viewing angle

• Environmental conditions

• Data-processing method

A normal thermal image without controlled heating may not show hidden corrosion clearly.

Passive Thermal Imaging

Passive thermal imaging observes naturally occurring temperature differences.

No external heat source is deliberately applied.

Possible heat sources include:

• Operating machinery

• Hot liquid inside a pipe

• Sunlight

• Process heat

• Electrical loading

• Cooling systems

• Environmental heating and cooling

Passive thermal imaging may help identify suspicious patterns on operating assets.

However, the result can be affected by:

• Changing sunlight

• Reflections

• Wind

• Rain

• Uneven surface emissivity

• Different coating colours

• Internal process conditions

Passive inspection is generally more suitable for locating thermal anomalies than for estimating corrosion depth.

Active Thermal Imaging

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

The thermal camera records how the surface responds over time.

Possible excitation methods include:

• Flash heating

• Lamps

• Long-pulse heating

• Induction

• Hot air

• Other controlled thermal sources

The inspection team then analyses:

• Heating rate

• Cooling rate

• Temperature contrast

• Time response

• Thermal pattern

• Processed image sequence

An area with hidden corrosion or another subsurface defect may heat or cool differently from sound material.

Active thermography is more specialised than using a standard handheld thermal camera for routine temperature inspection.

It requires a suitable heat source, controlled procedure, appropriate camera, stable recording and technical interpretation.

What Recent Research Shows

Recent research has investigated front-side detection of non-visible corrosion using active infrared thermography.

This is relevant because many industrial structures can only be inspected from the accessible surface. The back of the steel plate may be hidden by insulation, construction or operating equipment.

Under the specific laboratory conditions studied, long-pulse heating combined with long-wave infrared imaging produced useful results for detecting and characterising hidden corrosion.

However, the study’s heating power, distance, exposure time and test-piece geometry should not be treated as universal field settings.

Every structure may respond differently.

The research supports the technical potential of active thermography, but it does not mean that every ordinary thermal camera can automatically calculate corrosion depth.

Thermal Camera vs Ultrasonic Thickness Gauge

These instruments answer different questions.

Thermal Camera

A thermal camera can help answer:

• Where is the abnormal temperature pattern?

• Which area should be inspected more closely?

• Is heat flow different across the surface?

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

• Which large area should be prioritised?

Ultrasonic Thickness Gauge

An ultrasonic thickness gauge can help answer:

• What is the remaining material thickness at this point?

• Is the wall thinner than the expected nominal value?

• How does thickness vary across a measurement grid?

• Is there measurable metal loss?

Thermal imaging is useful for rapid visual screening.

Ultrasonic testing is generally more appropriate when the requirement is to quantify remaining wall thickness at selected points.

For many corrosion investigations, the two methods can be complementary.

Thermal Camera vs Coating Thickness Meter

A coating thickness meter is also different from an ultrasonic thickness gauge.

A coating thickness meter may be used to measure suitable coatings over a metal substrate, such as:

• Paint over steel

• Protective coating over iron

• Non-conductive coating over aluminium

• Powder coating over suitable metal

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

For example:

• Thermal camera: identifies an unusual heat pattern.

• Coating thickness meter: measures the coating over the metal.

• Ultrasonic thickness gauge: measures the remaining metal thickness where technically suitable.

Selecting the wrong instrument can produce data that does not answer the inspection question.

Suitable Applications for Thermal Screening

Thermal imaging may support preliminary inspection of:

• Storage tanks

• Process vessels

• Pipelines

• Ship structures

• Coastal steelwork

• Machinery enclosures

• Roof and wall panels

• Industrial facilities

• Insulated equipment

• Painted steel structures

Potential applications include:

• Locating suspicious thermal patterns

• Identifying areas for closer inspection

• Comparing similar sections

• Screening a large surface

• Supporting maintenance planning

• Documenting abnormal temperature behaviour

The camera result should be interpreted together with the asset design, operating condition and inspection history.

Why Hidden Corrosion May Be Missed

A thermal camera may fail to reveal hidden corrosion when:

• The defect is too small

• Metal loss is too shallow

• Temperature contrast is insufficient

• Surface heating is uneven

• The surface is highly reflective

• Wind cools the surface

• Rain or moisture changes the pattern

• The coating has different emissivity

• The camera is too far away

• The inspection angle is poor

• The thermal resolution is insufficient

• Data is captured at the wrong time

A clear thermal image does not guarantee that the steel is free from corrosion.

Thermal imaging should not be used as the only inspection method where safety or remaining wall thickness is critical.

Surface Emissivity and Reflections

Bare or shiny metal can be difficult to inspect using infrared imaging.

Low-emissivity surfaces may reflect:

• The sky

• Sunlight

• Nearby hot machinery

• The operator

• Building structures

• Other environmental sources

A reflected hot or cold object may appear as a false thermal anomaly.

Painted or oxidised surfaces may behave differently from polished metal.

Before interpreting the image, check:

• Surface finish

• Coating condition

• Viewing angle

• Reflected temperature

• Nearby heat sources

• Camera emissivity settings

Do not assume that every visible hot or cold patch represents corrosion.

Malaysian Weather Considerations

Outdoor thermal inspection in Malaysia may be affected by:

• Strong sunlight

• High humidity

• Sudden rain

• Wet surfaces

• Wind

• Cloud movement

• High ambient temperature

• Rapid heating of dark coatings

Inspection timing is important.

Direct afternoon sunlight may create strong temperature differences unrelated to internal corrosion.

After rainfall, evaporative cooling and trapped moisture may also change the thermal image.

Where possible, record:

• Time of inspection

• Ambient temperature

• Weather condition

• Surface condition

• Recent rainfall

• Sun exposure

• Wind condition

• Asset operating state

These details help explain why readings may differ between inspections.

A Practical Corrosion Inspection Workflow

Step 1 – Define the Inspection Objective

Clarify whether the goal is to:

• Locate possible corrosion

• Measure remaining wall thickness

• Check coating condition

• Investigate moisture

• Find insulation problems

• Monitor an operating-temperature anomaly

Step 2 – Review the Asset

Collect:

• Material type

• Nominal thickness

• Coating system

• Operating temperature

• Maintenance history

• Previous corrosion locations

• Drawings or photographs

Step 3 – Conduct Visual Inspection

Look for:

• Rust staining

• Blistering

• Cracking

• Coating separation

• Water paths

• Surface deformation

• Previous repair areas

Step 4 – Perform Thermal Screening

Scan the surface systematically and save both thermal and visible images.

Record operating and environmental conditions.

Step 5 – Mark Suspicious Areas

Identify repeatable thermal anomalies instead of relying on one image.

Compare them with nearby sound-looking areas.

Step 6 – Verify with Another Method

Depending on the requirement, verification may include:

• Ultrasonic thickness measurement

• Coating thickness measurement

• Visual inspection after coating removal

• Other appropriate nondestructive testing

• Engineering assessment

Step 7 – Document the Findings

Record the thermal image, location, environmental conditions and verification results.

Do not report the thermal pattern as confirmed metal loss unless it has been properly validated.

Common Thermal Corrosion Inspection Mistakes

Claiming the Camera Measures Corrosion Thickness

A standard handheld thermal camera displays surface-temperature patterns, not direct metal-loss depth.

Inspecting Shiny Steel Without Considering Reflection

The apparent anomaly may be reflected infrared radiation.

Ignoring Sunlight and Rain

Outdoor conditions may dominate the thermal pattern.

Using Only One Thermal Image

A single image may not show whether the anomaly is repeatable.

Skipping Verification

Suspicious areas should be confirmed using an appropriate inspection method.

Confusing Coating Thickness with Steel Thickness

These are separate measurements requiring different instruments.

Choosing Thermal Inspection Equipment

Before selecting a thermal camera, consider:

• Target size

• Inspection distance

• Required image detail

• Expected temperature difference

• Indoor or outdoor use

• Need for video or time-sequence recording

• Reporting software

• Temperature range

• Focus requirement

• Environmental conditions

• Whether active thermography is planned

Handheld thermal cameras such as the UNI-T UTi260A, UTi260B and UTi320E, together with other suitable industrial thermal imaging instruments, may support general thermal inspection applications depending on the required performance.

The correct model should be selected according to the inspection distance, target size and temperature contrast—not only the maximum temperature range.

Need Help Selecting Thermal and Thickness Inspection Equipment?

Send MTM Precision:

• Asset type

• Material

• Suspected problem

• Inspection distance

• Surface photographs

• Operating temperature

• Whether the objective is screening or thickness measurement

• Indoor or outdoor conditions

• Reporting requirement

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

MTM Precision supplies industrial testing instruments for factories, 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