For more than 20 years, bolted steel structures have been more costly to maintain and more likely to fail than they should. This is due to a loophole in the European safety standards.
Frank Götz, senior sales engineer at Nord-Lock Group points to insufficient clarity in the EN 1090-2 standard. He meets a lot of design engineers in his daily work who are using double nuts, check-lock nuts or tab washers to secure their steel structures, all fully convinced that they are following the standard and are using a secure locking device. However, the safety standard is difficult to interpret and often leads to misunderstandings - lack of a better solution, or the belief that they are following the standard, means many design engineers carry on specifying these old-fashioned locking systems. The general perception is that costly re-tightening is something you just have to accept and pay the price for.
There are however solutions that are safer, more cost efficient, and that are following the EN 1090-2 standard. “Many actors are not aware of the better solutions on the market and what money they potentially can save by using them,” says Götz.
According to Nord-Lock, the most viable solution meeting the EU standard is its wedge-locking washer. Nord-Lock washers use tension instead of friction to prevent bolted joints from loosening. The initial cost for bolts secured with Nord-Lock washers is often higher than common alternatives, yet Götz would argue the extra cost is normally already consumed by the time taken to finish the first assembly. Taking into consideration the added costs for maintenance that non-wedge-locking methods can necessitate, the Nord-Lock washers give contractors an advantage in a life cycle cost perspective.
When using double-nuts or check lock nuts as locking elements, it is common to check for loosened bolts and re-tighten them after a few days. which may double the cost for man-hours. Tab washers are often considered as safer but their performance can vary significantly depending on the operator and installation is also time-consuming, with an added risk of injury.
The annual maintenance routines also imply checking a percentage of the bolts before possibly having to then re-tighten every single one.
Nord-Lock states its washers are fast to assemble and the wedge-effect that is created between the cams ensures that the joint preserves its initial pre-load. The bolt stays tight for its entire lifetime despite vibrations, dynamic loads and environmental fluctuations.
“Nord-Lock washers are allowed according to EN1090-2 Standard. They can easily decrease the overall life cycle cost for many construction types,” says Götz, adding: “the standard needs to be clearer to facilitate design engineers”.
Recently Nord-Lock Group also launched Steel Construction (SC) washers, designed for use with HV/HR bolts. These bolts use the same wedge-locking principle as the original washers and are commonly used in steel structures which are often heavily exposed to vibration.
Having spent a decade in the fastener industry experiencing every facet – from steel mills, fastener manufacturers, wholesalers, distributors, as well as machinery builders and plating + coating companies, Claire has developed an in-depth knowledge of all things fasteners.
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