What Is Hardness Testing?
Hardness Testing is a mechanical property measurement method that determines a material's
resistance to localised plastic deformation — providing a quantitative indicator of material
strength, temper condition, and heat treatment status. In the context of NDT and asset integrity
inspection, hardness testing is deployed primarily to:
- Verify that weld heat-affected zones (HAZ) have not been hardened beyond acceptable
limits — reducing susceptibility to hydrogen-induced cracking (HIC) and stress corrosion
cracking (SCC)
- Confirm that post-weld heat treatment (PWHT) has achieved the intended material
softening in welds and HAZ material
- Detect in-service material degradation — including embrittlement, graphitisation, and
temper embrittlement in high-temperature process plant components
- Verify material condition as part of fitness-for-service (FFS) assessments under API 579 or
equivalent standards
Hardness Scales and Methods:
- Vickers (HV) — precision indentation method; widely specified in welding standards;
applicable across a wide hardness range
- Brinell (HB/HBW) — for castings, forgings, and coarser-grained materials; specified in
many material standards
- Rockwell (HR) — rapid measurement; multiple scales for different material hardness
ranges
- Leeb Rebound (HL) — portable, field-deployed dynamic hardness method; converts to
Vickers, Brinell, or Rockwell equivalents; the primary method for in-situ field hardness
testing of installed components