Why Is Factory Pipe Wall Thickness Decreasing? Corrosion Testing Guide Malaysia

Meta Description: Discover why industrial pipe walls become thinner and how ultrasonic thickness gauges and water-quality instruments support corrosion monitoring in Malaysia.

Industrial pipes can lose wall thickness because of corrosion, erosion, chemical attack and operating conditions.

The exterior may still appear acceptable even when material loss has occurred internally. If thinning is not detected, the pipe may eventually develop leakage, reduced pressure capacity or unexpected failure.

An ultrasonic thickness gauge allows maintenance teams to measure remaining pipe-wall thickness from one accessible side without cutting the pipe.

Common Causes of Pipe Wall-Thinning

The most common causes include:

Internal corrosion
External corrosion
Erosion from high-velocity flow
Corrosion under insulation
Condensation
Unsuitable water chemistry
Chemical attack
Localised pitting
Galvanic corrosion
Microbiologically influenced corrosion

1. Internal Corrosion

Internal corrosion develops when the process fluid reacts with the pipe material.

Possible contributing factors include:

Low or high pH
Dissolved oxygen
Chlorides
Conductivity
Water temperature
Contaminants
Stagnant water
Incorrect chemical treatment

The outside surface may not show the actual internal condition.

2. External Corrosion

External corrosion may result from:

Rain
Washdown water
Chemical splash
High humidity
Damaged paint
Poor drainage
Outdoor exposure
Contact with wet surfaces

Inspect areas near pipe supports, clamps, floors and walls because moisture may remain trapped there.

3. Erosion

Fast-moving liquid, gas or suspended solids can remove material from the pipe wall.

Erosion is often more severe at:

Elbows
Tees
Reducers
Valve outlets
Pump discharge sections
Injection points
Changes in pipe direction
High-turbulence areas

Measurement plans should include these higher-risk locations.

4. Corrosion Under Insulation

Moisture can enter damaged insulation and remain against the pipe surface.

Possible warning signs include:

Wet insulation
Damaged cladding
Rust staining
Water dripping
Bulging insulation
Temperature differences
Corrosion near insulation joints

Thermal imaging may help identify unusual surface-temperature patterns, but it cannot directly confirm corrosion beneath insulation.

5. Condensation

Cold pipes can develop condensation when their surface temperature falls below the surrounding air’s dew point.

Condensation may lead to:

External corrosion
Wet insulation
Water dripping
Damaged coating
Slippery floors
Mould or staining nearby

Use temperature and humidity measurements to evaluate condensation conditions.

6. Unsuitable Water Chemistry

Cooling-water, chilled-water, boiler and process-water systems can corrode because of poor chemistry.

Depending on the system, useful measurements may include:

pH
Conductivity
TDS
Dissolved oxygen
Chloride
Turbidity
Temperature

Water chemistry should follow the approved treatment programme.

7. Chemical Attack

Process pipes may carry acids, alkalis, solvents or other chemicals.

Material loss may increase because of:

Incorrect pipe material
Higher chemical concentration
Higher temperature
Contamination
Process changes
Damaged internal lining

Confirm chemical compatibility before changing materials or operating conditions.

8. Localised Pitting

Pitting corrosion creates small but deep areas of material loss.

A limited number of widely spaced measurements may miss severe localised pitting.

Use:

Closer measurement spacing
A defined grid
Multiple readings around the pipe circumference
Additional inspection methods where required

9. Galvanic Corrosion

Galvanic corrosion can occur when dissimilar metals are electrically connected in the presence of an electrolyte.

Possible locations include:

Mixed-metal pipe joints
Flanges
Supports
Valves
Fittings
Fasteners

Material selection and isolation arrangements should be reviewed by qualified personnel.

10. Microbiologically Influenced Corrosion

Some water systems may experience corrosion associated with biological activity.

Possible environments include:

Cooling-water systems
Fire-water systems
Stagnant pipe sections
Wastewater
Low-flow areas

Specialist water analysis may be required to confirm the cause.

Where Should Pipe Thickness Be Measured?

Higher-priority locations include:

Elbows
Low points
Dead legs
Reducers
Branch connections
Near valves
Injection points
Pump discharge pipes
Condensate lines
Pipe supports
Insulation damage
Areas with coating failure
Previously repaired sections

Measuring Around the Pipe Circumference

Corrosion may not occur evenly.

Take readings at several positions around the pipe, such as:

Top
Bottom
Left side
Right side

The bottom may be important where water, sediment or condensate collects.

The top may be important in systems where vapour-space corrosion occurs.

How to Use an Ultrasonic Thickness Gauge

Step 1: Identify the Pipe Material

Confirm the base material and correct sound velocity.

Step 2: Select the Measurement Point

Use a documented inspection grid.

Step 3: Prepare the Surface

Remove loose rust, scale and dirt sufficiently to obtain stable probe contact.

Step 4: Verify the Instrument

Follow the manufacturer’s procedure using an appropriate reference.

Step 5: Apply Couplant

Couplant helps ultrasound enter the material.

Step 6: Position the Probe

Hold the probe steadily against the surface.

Step 7: Repeat the Reading

Confirm that the result is stable and repeatable.

Step 8: Record the Result

Document the point, thickness, date, material and surface condition.

Why Couplant Is Required

Air between the probe and metal prevents effective ultrasound transmission.

Couplant fills small gaps between the probe and surface.

Use a material that is:

Suitable for ultrasonic measurement
Compatible with the pipe surface
Appropriate for the operating environment
Recommended by the instrument manufacturer

Can Thickness Be Measured Through Paint?

Some advanced gauges provide through-coating or multiple-echo functions.

A basic gauge may include the paint thickness in the result or produce an unstable reading.

Before measuring through paint, confirm:

Gauge capability
Probe type
Coating condition
Required accuracy
Manufacturer instructions

Pipe Curvature and Probe Selection

Small-diameter pipes can be difficult to measure because the probe may not sit flat.

Consider:

Pipe diameter
Probe-face size
Probe orientation
Surface roughness
Expected thickness
Temperature

A smaller or suitably designed probe may be required.

High-Temperature Pipe Measurement

A standard probe may be damaged by a hot surface.

High-temperature measurements may require:

High-temperature probe
Suitable couplant
Short contact time
Temperature compensation
Special procedure

Do not place a normal probe on hot pipework without confirming its temperature capability.

Creating a Pipe Thickness Grid

A useful record may include:

Point	Location	Nominal Thickness	Previous Reading	Current Reading	Observation
P1	Straight section	Recorded	Recorded	Recorded	Baseline
P2	Elbow outer radius	Recorded	Recorded	Recorded	Monitor
P3	Pipe low point	Recorded	Recorded	Recorded	Further investigation

Include a diagram or photograph showing every measurement location.

Estimating Thickness-Loss Rate

When comparable readings are available from different dates, technicians can estimate how quickly thickness is changing.

However, corrosion may accelerate, slow down or occur locally.

Remaining-life and fitness-for-service decisions should be made by appropriately qualified personnel using the applicable engineering requirements.

Coating Thickness vs Pipe Wall Thickness

Instrument	Main Measurement
Coating thickness gauge	Paint or protective coating above metal
Ultrasonic thickness gauge	Remaining thickness of the pipe material
Water-quality meter	Conditions that may contribute to corrosion
Thermal imaging camera	Surface-temperature patterns

For coated pipes, several instruments may be required.

Supporting Water-Quality Measurements

Depending on the system, useful instruments include:

Portable pH meter
Conductivity meter
TDS meter
Dissolved-oxygen meter
Turbidity meter
Water thermometer

MTM Precision supplies options including:

AZ Instrument AE8601 pH meter
Benetech GM765 and GM766 pH meters
AZ Instrument AE86065 turbidity meter

Basic Pipe-Thinning Investigation

Step 1: Review the Pipe Service

Identify the fluid, temperature, pressure and operating history.

Step 2: Inspect the Exterior

Check coating, insulation, supports, leakage and corrosion.

Step 3: Create a Measurement Grid

Include high-risk areas and several points around the circumference.

Step 4: Measure Thickness

Use the correct material velocity, probe and couplant.

Step 5: Compare Historical Readings

Look for both general and localised loss.

Step 6: Test Water or Process Conditions

Review relevant chemistry and process changes.

Step 7: Investigate the Cause

Determine whether the pattern suggests corrosion, erosion, condensation or chemical attack.

Common Thickness-Measurement Mistakes

Avoid:

Taking only one reading
Measuring only easy-to-access straight pipe
Ignoring elbows and low points
Using the wrong sound velocity
Measuring through paint without checking gauge capability
Using insufficient couplant
Ignoring pipe curvature
Using a standard probe on a hot surface
Grinding away excessive material during preparation
Comparing different locations
Recording readings without a diagram
Treating one acceptable reading as proof that the whole pipe is sound

Important Safety Reminder

Industrial pipes may contain hot, pressurised, toxic, flammable or corrosive materials.

Thickness measurement does not remove these hazards and does not by itself confirm that a pipe is safe for continued service.

Always follow:

Site permit requirements
Safe-access procedures
Process-hazard controls
Appropriate PPE
Manufacturer instructions
Applicable inspection requirements
Decisions by competent personnel

Ultrasonic Thickness Gauge Supplier in Malaysia

MTM Precision supplies ultrasonic thickness gauges for factory pipework, cooling-water systems, boiler pipes, compressed-air receivers, storage tanks and corrosion-monitoring applications.

We can help customers compare measurement range, pipe diameter, material type, probe selection, surface temperature and through-coating requirements before selecting an instrument.

Contact MTM Precision

MTM Precision Sdn. Bhd.

Showroom & Service Centre

No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia

🌐 Website: www.mtmpre.com.my
📧 Email: mtmpre@yahoo.com
📱 WhatsApp: +6016-660 7346