Inspection method · FTR
Thickness, ferrite and surface roughness measurement
Three routine measurements that frequently decide acceptance: remaining wall thickness, ferrite content in stainless welds and surface texture.
01How it works
Ultrasonic thickness gauging measures material thickness from one side using the time of flight of an ultrasonic pulse; it is used on plates, pipes and vessels, including through coatings with suitable gauges.
Ferrite measurement determines delta ferrite content in austenitic and duplex stainless steel welds using magnetic induction instruments calibrated to standards, reported as ferrite number (FN) or percentage.
Surface roughness measurement uses a stylus profilometer to measure parameters such as Ra and Rz over a defined evaluation length, compared with drawing requirements.
02Typical industrial applications
- Pipe and plate wall thickness
- Corrosion allowance verification
- Duplex and austenitic stainless welds
- Machined and ground surfaces
- Sealing faces
- Hygienic surfaces
03Benefits and what it detects
- Quick and portable
- Quantitative results
- Detects common specification deviations
- Non-destructive
04Limitations
- Thickness gauging needs suitable surface and couplant
- Ferrite instruments require calibration and correct interpretation
- Roughness depends on filter and evaluation length settings
- Local measurements only
05Specifying and reviewing the method
Specify locations and number of readings, acceptance ranges and reporting. For ferrite, state the range in FN and the measurement standard; for roughness, the parameter, value and direction.
Other references: ISO 17655 (ferrite in duplex welds), ISO 8249, ISO 21920