When you are interested in buying fasteners such as Inconel hex head cap screws or Monel 400 hex tap bolts, one of the most important things you would need to account for is the performance of the fasteners. This is important since it determines how long they will last before needing any replacement, and also how long the product you are fastening will last.
It is always a prudent measure to ensure that you understand the different ways in which the fasteners can be damaged, so that you can get ones that will resist this. One of the categories of damage that you definitely need to be familiar with is hydrogen embrittlement.
What is hydrogen embrittlement?
This refers to a chemical process by which various metals become brittle with time, and end up fracturing particularly if they are subjected to very high loads. This is a common method by which the fasteners fail a few months or even years after installation. It is a phenomenon that was first discovered in the late 1800s, and is normally caused by unintentional introduction of hydrogen into the fasteners during finishing or manufacturing. The hydrogen can also be introduced into the fastener during operational use, such as when they are exposed to high concentrations of hydrogen.
Which sorts of fasteners are usually most affected by this?
Different types of metals can be affected by hydrogen embrittlement. However, high strength stainless steel is normally the most affected. In addition to that, this is also a concern for fasteners that will be used in environments where they will be exposed to high levels of hydrogen including:
- In cathodic protection
- In pickling
- During phosphating processes
- During electroplating
- When it’s likely to be exposed to arc welding
This means that if you are going to use the fastener in any of the above settings, you would need to take extra precautions to watch out for embrittlement, or get fasteners that can resist this.
How to deal with the problem
There are a number of ways of dealing with the problem. If the fastener has cracked, the only option would be to replace it. However, if not, the process of hydrogen embrittlement can be reversed by getting rid of the hydrogen source if possible. After this is done, the hydrogen in the metal can diffuse out of it safely. This process can sometimes be accelerated by subjecting the fasteners to higher temperatures.
Preventing hydrogen embrittlement
There are various strategies that can be employed to prevent the process from happening including:
- Heating the fasteners after using them in chemical or electrochemical procedures that are likely to produce a lot of hydrogen.
- Coating the surface of the fastener using ferrosilicate
- Preheating and postheating a fastener that you intend to arc weld so as to remove any hydrogen in it
You might also find it useful to buy high quality fasteners which are carefully manufactured. This way, you will be sure that they will not have any hydrogen in them after a few years of use.
Started my career in the fastener world in 1969 at, Parker Kalon Corp. a NJ based screw manufacturer located in Clifton, NJ working in inventory control, scheduling secondary production and concluding there in purchasing. In 1971 I accepted a sales position at Star Stainless Screw Co., Totowa, NJ working in inside sales and later as an outside salesman, having a successful career at Star I had the desire with a friend to start our own fastener distribution company in 1980 named: Divspec, Kenilworth, NJ. This was a successful adventure but ended in 1985 with me starting Melfast in August 1985 and have stayed competitive and successful to date. Melfast serves the OEM market with approximately 400 accounts nationally.