SUMMER 2018

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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.
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