GUIDE: This is how you avoid the bolts becoming the weakest link!

Bolts and other fasteners are critical in a multitude of constructions - from machines that include smaller bolts and nuts, to sheet pile walls, bridges, wind turbines and other large constructions.

There is a risk that the bolt will become the weakest link in a structure and hence the first component for replacement. It may pose a risk to the safety of the construction, just as it may entail large costs in relation to downtime and repairs.

This guide provides you with an overview of factors related to bolts that you should be aware of to ensure the quality of your construction - both before installation, if you need to assess the remaining service life, and if failure occurs.

Bolt fracture surface – a typical bolt fracture occurs just beneath the head or in the first load-carrying threads.

Fracture surface on bolt — Corrosion and other conditions can affect the life of a bolt.

Before installation

To avoid costly damage and replacements, you should examine or test the following issues/topics before installing bolts in your construction.

You probably know what it takes to avoid overloading of a bolt. But what if you need to install it in a position at risk of rust or exposed to hydrogen from corrosion or cathodic protection? We can help you ensure that your specifications meet the demands of the right standards and the right strength class.
Read more about how to identify your material related challenges.
Quality assurance of the bolt before installation can save you significant costs for replacements or, at worst, damage and failure. A test prior to installation can ensure that the bolt has the right chemical composition, hardness, microstructure and other relevant properties.
Read more about test of bolts.
Many machine parts are affected by fatigue loads. We can test whether your bolt can withstand what is required - both in terms of fatigue and tensile strength. It gives you documentation of the material's strength and toughness as well as knowledge of a potential tendency to fatigue fractures.
Read more about mechanical testing of materials.
Bolt fractures are often initiated by corrosion, which can be attributed to the surrounding environment. For example, aggressive and harsh environments can consist of chemical impact, pressure, temperature, etc. You can ensure that your bolt has the right quality and can resist rust and cracking by having it tested in a realistic simulated environment.
Read more about testing of bolts in almost every conceivable environment.

Continuous maintenance and assessment of remaining service life

Once mounted, the bolt is a critical factor as regards the safety and service life of the overall construction. Therefore, it is important to ensure ongoing maintenance and assessment of the remaining service life to avoid for example failure and downtime.

On-site inspection of pre-tensioning and damage

We specialise in various non-destructive (NDT) methods for condition assessment. With NDT it is possible to examine a bolt for cracks, or to examine whether the tightening of a bolt is correct, or whether the integrity of a construction is intact if, for example, a bolt has failed. Read more about inspection with non-destructive testing.

We stay constantly updated and are at the forefront of what is trending, i.e. through participation in development projects. Currently we are part of an EUDP project, which focuses on how to measure the pre-tensioning of bolts without time-consuming calibration and disassembly. Read more about the project here.

When the damage is done

Even if you have taken your precautions, the risk of failures is still present. In that case, the failures should be investigated in order to avoid them in the future.

Typical bolt failures range widely – why did it break?

Damage and breakdowns can be fatal to a construction and to the safety of a plant, a platform or the like. Therefore, it is crucial to do everything to avoid them. Basically, one or more of the following faults are the cause of damage and breakdowns:

Design fault
Manufacture fault
Operational fault.

This applies regardless of whether there is fracture, corrosion, wear, etc. It is important that you find the underlying cause so that you can correct it. In this process, it is important to find out if the damage has occurred as a result of operation or manufacture, just as it is important to ensure that bolts to be installed comply with applicable requirements and standards.

Read more about failure and damage investigation.

Hydrogen embrittlement in bolts – what is it?

We are experiencing an increasing number of failures due to hydrogen embrittlement - typically rapid failures without warning. The hydrogen can either come from manufacturing or operation, e.g. corrosion. Hydrogen embrittlement is often seen in high-strength steels and therefore in bolts, which are essential for the quality and the safety of constructions. There are several factors that you should be aware of to avoid hydrogen embrittlement.

Read more about how we work with hydrogen and materials.