Hardness Testing

Hardness testing measures the resistance of a material to localised plastic deformation caused by an indenter under a specified load. It is one of the most widely performed mechanical tests in the metals industry, providing rapid and reliable data for material identification, weld qualification, quality control and in-service integrity assessment.

QMS Asset Integrity provides hardness testing using Vickers, Brinell and Rockwell methods at our laboratory, as well as portable hardness testing on-site for in-service equipment. Hardness surveys across weld metal, heat-affected zone (HAZ) and parent material are routinely performed to verify compliance with maximum hardness limits specified in welding procedures, fabrication codes and client specifications.

Hardness data is critical for assessing susceptibility to hydrogen-induced cold cracking (HICC), stress corrosion cracking (SCC) and sulphide stress cracking (SSC) in sour service environments.

Vickers Hardness (HV): A diamond pyramid indenter is pressed into the surface under loads from 1 kgf to 120 kgf. The diagonal lengths of the resulting impression are measured under magnification to calculate the hardness number. Vickers is preferred for weld and HAZ hardness surveys due to its small impression size, allowing precise measurement across narrow zones.

Brinell Hardness (HB): A hardened steel or tungsten carbide ball (typically 10 mm diameter) is pressed into the surface under a specified load (typically 3000 kgf for steel). The diameter of the resulting impression is measured to calculate the hardness. Brinell is suited to testing larger, less localised areas and coarser-grained materials.

Rockwell Hardness (HR): An indenter (diamond cone for HRC, steel ball for HRB) is applied under a preliminary load followed by a major load. The depth of penetration under the major load, referenced from the preliminary load position, directly gives the hardness reading on the instrument dial. Rockwell provides rapid results and is widely used for production quality control.