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Distributor's Link Magazine Summer 2018 / Vol 41 No3


30 THE DISTRIBUTOR’S LINK Carmen Vertullo Lead Trainer, Fastener Training Institute® FASTENER TRAINING INSTITUTE ® 5318 East 2nd Street #325, Long Beach, CA 90803 TEL 562-473-5373 FAX 661-449-3232 EMAIL WEB HYDROGEN EMBRITTLEMENT IN FASTENERS CASE STUDIES - PART 3 This is the third in our series of articles on case studies of hydrogen embrittlement in fasteners. If you are not familiar with hydrogen embrittlement I recommend that you read the previous issue’s case studies and three other articles I have written on the subject for the Distributor’s Link Magazine. This case is about a fastener failure that occurred long ago, when I first came into the industry. It was my first, and one of the easiest and most straight forward hydrogen embrittlement failure investigations I have conducted. It involves one of the simplest and least expensive fasteners we know of, a roll pin – also formally known as a spring pin. Before we get to the case, let’s lay some groundwork on some of the other non-threaded fasteners that are susceptible to internal hydrogen embrittlement (IHE). One of the keys to knowing which non-threaded fasteners are of concern comes from the product description of the case at hand. The product is a “spring pin”. When we think of steel and add the word “spring” invariably we are introducing high hardness into the equation. A fastener that has any kind of spring in its function will most likely be of a hardness well above that where hydrogen embrittlement can come into play. The most common IHE susceptible non-threaded fasteners are lock washers, conical washers, spring pins, U-Nuts, retaining rings and spring clips. Before I came into the fastener industry I worked in an aerospace job shop where one of our products was coil springs, which were often electroplated. I knew about IHE susceptibility in these springs and we were required to bake and TECHNICAL ARTICLE test them. We had occasional failures, as coil springs are very hard and hardness is the primary factor in IHE susceptibility. Fast forward a few years and I am now working for a fastener supplier where we regularly provided plating services to our customers. The practice at that time was to bake anything grade 8 or PC 10.9 and above, case hardened screws and lock washers. We plated. We baked. We tested. We did not run into any IHE issues. Until one day. One of our customers was a manufacturer of large security safes. These were about the size of a refrigerator and we provided all of the fasteners needed for the safes. These included socket screws, machine screws, washers, shims, spring pins and dowel pins. Most of them were used in the safe locking mechanism. None of them were plated. They were a pretty good customer and we were an excellent vendor. One day we got an angry call from the customer demanding a visit and complaining that our poor quality fasteners required them to cut the doors off of several safes when they could not get the lock mechanism to open the door. A few bad jokes about forgetting the safe combination did not help matters. Upon entering the customer’s shop floor I was shown the torched-off safe doors and a disassembled lock mechanism. On the table next to the lock mechanism was a broken zinc plated spring pin. I don’t recall the exact size, but it was around ¼” x 1”. My first reaction was “that’s not our pin”, because I knew we did not provide them any plated product. CONTINUED ON PAGE 108


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