Tensile Testing Overview
Tensile testing is a destructive test that measures the elastic and plastic deformation of a material when subjected to a tensional applied force. The equipment senses the instantaneous force required to deform the specimen up to its breaking point. Tensile testing is extremely important for multi-metal materials to determine quality and reliability for industrial equipment fabrication.
ASTM E8/E8M and ASME SA370 are two common specifications that describe the methods and test specimen used to determine the tensile properties of a material: yield strength, tensile strength, elongation, and reduction of area. Most material specifications require minimum values which are certified on Material Test Reports (MTR).
There are large differences in how clad suppliers test and validate their products, and the disparity is growing. Testing clad metals, tensile testing being one of those methods, is vital to ensure safety, performance, and operating environment requirements are met before fabrication begins.
Tensile Testing with Multi-Metal Clad
For clad metal alloys used in the construction of process equipment like pressure vessels and heat exchangers, the cladder metal is typically not taken into account in the evaluation of stresses and calculation of minimum required metal thickness. Colloquially speaking it is a “paint” from a mechanical perspective. However, the backer metal mechanical properties must meet required minimum properties even after all explosion cladding, forming and heat treatment operations are performed.
NobelClad requires metal alloys to be supplied with certified MTRs, and the company confirms its properties prior to material release for our proprietary explosion welding production process, DetaClad™.
After cladding, NobelClad routinely performs tensile testing, and certifies results, of the base metal properties in accordance with clad specifications and order requirements. It is very common to perform tensile testing of the clad base metal in multiple heat treatment conditions, for example, with head forming or post weld heat treatments (PWHT).
Most clad specifications do not define a through thickness clad tensile test. In fact, clad Shear Test is the most common bond strength test performed on clad metals. The clad metal is simply too thin to produce a meaningful clad tensile specimen.
In shipbuilding applications, specification Mil-J-24445A for aluminum-to-steel bonded transition joints, defines a “ram” tensile test specimen. NobelClad produces these transition joints under the tradename Detacouple™. If the cladding metal is too thin, the ram will shear through the cladding metal without breaking the bond zone. Nevertheless, the tensile strength of the clad interface can be an important consideration when structural components are to be welded to the clad surface of equipment and for tube sheets in certain shell and tube heat exchanger designs.
To overcome these limitations, NobelClad has conducted extensive testing to establish the relationship between bond shear strength and tensile strength and to characterize our superior proprietary explosion welding process, DetaClad. To learn more about NobelClad’s DMC 100 Specification, which includes a supplemental requirement for clad through thickness tensile testing, contact a NobelClad engineer today.