# Ultrasonic thickness gauging

> Ultrasonic thickness gauging measures the remaining wall of a pipe, vessel, tank or structure with a compression-wave probe, typically at fixed condition monitoring locations, to calculate corrosion rates and remaining life.

- Source: https://amps.global/glossary/ultrasonic-thickness-gauging/
- Type: Glossary
- Published: 2026-09-05
- Tags: NDT, ultrasonic testing, corrosion

## Key facts

- Dual-element probes and through-coating (echo-to-echo) modes handle corroded or painted surfaces
- Readings are taken at condition monitoring locations (CMLs, also TMLs) defined by API 510, API 570 and API 653
- Corrosion rate = thickness loss / time; remaining life = (current - minimum required) / corrosion rate
- Gauge and step-wedge calibration is recorded before and after each survey

Also known as: UTG, UTM, wall thickness measurement, thickness testing.

## How it works

The gauge times the echo from the back wall and converts it to thickness using the calibrated sound velocity. Surveys repeat at the same CMLs over years, so the value of the data lies in consistency: the same location, the same method, comparable readings.

## Where it is used

In-service inspection of piping circuits, pressure vessels and storage tanks under API 510, 570 and 653, and for fitness-for-service assessments.

## Thickness gauging in AMPS

Because thickness data belongs to the asset, not just the job, in AMPS every asset and job carries a QR code. Scanning it opens the asset page and the history of jobs performed on it, assets can hold sub-assets, and jobs can be grouped, for example per shutdown. Previous survey reports are one scan away, and the flag system reminds the team when the next inspection is due.

## Related pages

- [Corrosion mapping](https://amps.global/glossary/corrosion-mapping/)
- [API 570](https://amps.global/glossary/api-570/)
- [Inspection interval](https://amps.global/glossary/inspection-interval/)

## Sources

- [Ultrasonic thickness gauge on Wikipedia](https://en.wikipedia.org/wiki/Ultrasonic_thickness_gauge)
- [API - American Petroleum Institute standards](https://www.api.org/products-and-services/standards)