WINTER 2022

8 THE DISTRIBUTOR’S

8 THE DISTRIBUTOR’S LINK Rob LaPointe AIM TESTING LABORATORY Rob LaPointe is a noted authority in materials and fastener technology. With extensive experience in the management and science of materials testing laboratories combined with master’s degrees in physics and education, he excels at bringing solutions to the client. Working specifically in the fastener testing industry, he has developed expertise in mechanical, nondestructive, metallurgical and chemical testing. With a background of 20 years in physics education, Rob is effective at communicating complex ideas in a simple and understandable manner, communicating well with clients enabling them to make informed decisions about their products and business. AIM is located at 1920 Cordell Court #101, El Cajon, CA, 92020. Tel: 909-254-1278, email: sales@aimtestlab.com or online at www.aimtestlab.com HYDROGEN EMBRITTLEMENT TESTING ON INTERNALLY THREADED PRODUCTS - ARE YOU NUTS? Internal Hydrogen Embrittlement (IHE) in fastener products can be a serious concern for the safety of structures and people in or around them. Many documented cases of unexpected and catastrophic failure have been linked to hydrogen’s embrittling effect in high-strength steel fasteners such as A574 and Class 12.9 plated cap screws. Product standards, including ASTM A574 and plating standards including ASTM F1941 and B633 provide hydrogen embrittlement mitigation and testing requirements for plated high-strength products. In nearly all specifications that mention hydrogen embrittlement as either a warning, mitigation procedure or testing methodology, the reference to IHE implicitly or explicitly is referring to externally threaded fasteners such as bolts and screws. So why don’t we see more IHE mitigation and FIGURE 1 - A PLATED HEAVY HEX NUT COULD BE HARBORING ENOUGH HYDROGEN TO EMBRITTLE THE STEEL. TECHNICAL ARTICLE testing mentioned in specifications relating to nuts? Are nuts capable of failure due to the presence of hydrogen? To answer these questions, let’s first go over some of the basics, including what hydrogen embrittlement FIGURE 2 - INTERNAL HYDROGEN EMBRITTLEMENT FAILURE OCCURRING AT THE FILLET RADIUS OF THE CAP SCREW. is, its effects on high-strength steel when under a load, and the application of force when loading internally and externally threaded fasteners. Hydrogen embrittlement is a permanent loss of ductility in a metal or alloy caused by hydrogen in combination with stress, either externally applied or internal residual stress [1]. In more basic terms – when a high-strength steel fastener is under a tensile (pulling) load and there is sufficient hydrogen in the metal, it can suddenly fracture even if the load on it is less than the rated breaking strength of the fastener. A fastener failure due to IHE is sudden and unexpected. The fracture occurs where stress in concentrated. For externally threaded fasteners, the stress is usually concentrated at the head-body junction, known as the fillet radius, or at the first exposed thread between the engaged threads and the head. Figure 2 shows an IHE failure of a fully threaded cap screw where the fracture occurred at the fillet radius, which is the location of greatest stress concentration when tightened. CONTINUED ON PAGE 92