Cargo Truck Tank Wall Inspection: Thickness Measurement

Referenced products:

DeFelsko’s PosiTector UTG Ultrasonic Thickness Gage non-destructively measures the thickness of cargo truck tank shells and heads.


Cargo tank trucks transporting hazardous materials or waste require routine inspection in accordance with Pipeline and Hazardous Materials Safety Admin., DOT Specification 49 CFR §180.407. This inspection is performed by qualified inspectors in order to ensure safe operation and maintenance of cargo tanks, including those that are used to transport hazardous materials, by identifying any indications of wear, malfunction, or corrosion.

A cargo tank truck on the highway transporting flammable material

The Department of Transportation (DOT) specification outlines six tests that must be performed at regular intervals:

  1. External visual inspection
  2. Internal visual inspection
  3. Lining inspection
  4. Leakage test
  5. Pressure test
  6. Thickness test

If a cargo tank fails any of the above tests or inspections, it will require repair and reinspection prior to returning to service.

This article will discuss the thickness test requirements and our measurement solutions.

Thickness Inspection

Thickness testing must be performed every two years for unlined tanks transporting corrosive materials, when a tank has not been in hazardous materials transportation service for a period of one year or greater, or whenever there are visual signs of damage.

Additionally, the integrity of linings for all lined cargo tanks must be verified at least once a year using a high-voltage holiday detector such as the PosiTest HHD. Any degraded or defective areas of the lining must be removed, and the cargo tank wall below inspected. If corrosion is present, thickness testing must be performed on the area.

Photo—A registered inspector records his findings from the cargo tank he is inspecting

The thickness test must include the following areas of the cargo tank wall, as a minimum:

  • areas of the tank shell and heads and shell and head area around any piping that retains lading
  • areas of high shell stress such as the bottom center of the tank
  • areas near openings
  • areas around weld joints
  • areas around shell reinforcements
  • areas around appurtenance attachments
  • areas near upper coupler (fifth wheel) assembly attachments
  • areas near suspension system attachments and connecting structures
  • known thin areas in the tank shell and nominal liquid level lines
  • connecting structures joining multiple cargo tanks of carbon steel in a self-supporting cargo tank motor vehicle

This inspection requires the use of a wall thickness gage used in accordance with the manufacturer’s instruction. The thickness gauge used for the test must be capable of accurately measuring steel, steel alloy, and aluminum wall thickness to within ±0.002” (±0.06 mm).

Wall thickness measurements must meet the “In-Service Minimum Thickness” requirements as specified in 49 CFR §180.407 to remain in active service. Inspectors must record the minimum thickness measurements as specified in §180.417(b).

DeFelsko’s Measurement Solution

DeFelsko PosiTector UTG Ultrasonic Thickness Gage exceeds the device requirements for measuring the thickness of steel, steel alloy, and aluminum cargo tank walls. They are designed for simple operation and require no formal training to use.

The PosiTector UTG C is available in two configurations, a cabled probe (PosiTector UTG C) and an integral probe version (PosiTector UTG CA) for one-handed operation. A precision model (PosiTector UTG P) is available for measuring tank wall thickness below 0.040” (1 mm).

Chart comparing the UTG C, UTG CA, and UTG P PosiTector wall thickness probes

Generating professional cargo tank inspection reports from the PosiTector UTG is quick and easy. Simply connect the gage to a computer using the supplied USB cable. View reports directly from the PosiTector using a standard web browser or download measurements to the powerful PosiSoft Desktop software. Easily add images, notes and other relevant inspection information to reports. See the PosiSoft Solutions page to learn more.

PosiSoft screen capture for cargo tank job


Cargo truck tank inspection in accordance with DOT Specification 49 CFR §180.407 is essential to ensuring both operator and public safety when transporting hazardous materials. Wear and corrosion may be present anywhere on a tank and its components, so periodic inspection must be done by qualified inspectors in order to identify and repair these potential hazards. The PosiTector UTG is an ideal choice for measuring the thickness of cargo truck tank shells, heads and upper coupler assemblies.

More information regarding the PosiTector UTG Ultrasonic Thickness Gage is available on our PosiTector UTG page.

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