Hardness testing can be undertaken on the surface of components, leaving only a small indentation behind. Therefore, it is still classified as a non-destructive test, and can provide additional information about a metals condition.
There are a variety of hardness test standards, such as Brinell, Vickers and Rockwell, but all rely upon the metal surface being pressed by a shaped indenter. Either the size of the indentation or force required give an indication of the metal’s hardness i.e. its resistance to localised plastic deformation.
Whilst hardness itself is a useful indication of the metals mechanical properties, it is also referenced in a variety of industry standards including NACE MR1075 / ISO 15156. This standard focuses on metals for use in H2S-containing environments in oil and gas production, where sulphide stress cracking is a potential concern in such ‘sour’ conditions. Metals with a high hardness are more susceptible to the propagation of cracks, therefore hardness is used as a control for material selection. The maximum hardness for Alloy 718 and Alloy 925 is 35HRC, whilst it is 36HRC for duplex and super duplex stainless steels if to be used as downhole tubular components and as packers and other sub-surface equipment.
Langley Alloys has the in-house capability to undertake hardness testing of bars to the Brinell standard, usually at the request of customers who require additional product information.