The stress of grinding or welding
Ben Dobbs, Head of Global Standards and Legislation at the Lifting Equipment Engineers Association (LEEA), answers a frequently asked question about grinding and welding.
One of the frequently asked questions we receive at LEEA is: ‘can I grind and weld steel components and accessories that are in use?’ The answer is no, not without the permission of the Original Equipment Manufacturer (OEM).
When out in the field it may be tempting to grind or weld components or accessories such as hooks, shackles or chain slings for the purpose of quick repair or even to modify it for a specific task. However, grinding and welding can cause stress raisers. These are areas where stress is significantly higher than the surrounding area, which can lead to failure. OEMs may permit grinding out minor surface defects, such as die casting flash (excess material), but this is usually addressed in the manufacturing processing. If so, they should provide guidelines in their user instructions, but they will not permit welding or any other modification, without their knowledge and written consent.
Additions or changes to a product once placed on the market or in service, will need to be investigated and approved by the OEM and verified by a competent person following the work carried out and before use. Effectively, this is the modification of lifting equipment after manufacture and once placed on the market or in service.
Grinding
Grinding of forged or cast steel accessories and components, such as shackles, is not recommended due to the potential to weaken the material and introduce stress risers. While grinding can remove surface imperfections, excessive grinding can disrupt the grain flow and introduce stress concentrations, which can lead to premature failure.
Any grind marks found should be treated as defects affecting the safety of the equipment and it is the competent person’s decision whether they are severe enough to fail the equipment.
Grinding is sometimes seen in ad hoc sling assemblies of various accessories where numerous Working Load Limits (WLLs) may be present. This is usually carried out to reduce the risk of misidentification of the sling assembly’s WLL, which should be identified by a sling tag. It may also occur on a runway that may have been fitted with a hoist of higher WLL than that marked on the beam itself.
Welding
Welding is also not recommended on components or accessories, as it can significantly alter the material properties of the metal being worked. It can potentially lead to reduced strength and increased risk of failure, especially in critical applications such as lifting operations.
A common example in accessories is seen where a shackle pin is welded to the body to create a permanent fitting. Where this has been carried out, LEEA would assume that a risk assessment identified that there was a risk of the pin unscrewing, hence the weld.
This may not however reduce the risk sufficiently, and the company in question carrying this out would be held accountable for not selecting equipment fit for the application. It is highly likely that the reasoning behind this may breach legislation due to demonstratable incompetence and poor selection of equipment. A nut and cotter type pin or other type of mechanical securing component would be the appropriate choice. Should the weld result in failure and injury, the enforcing authorities may take a very dim view of this although it is a common practice.
If components or accessories are welded after leaving the OEM, then the owner of the equipment will need to accept full responsibility and will also need to hold comprehensive documented evidence – including (but not limited to) OEM’s permission in writing, risk assessment, welder qualifications, welding specifications and procedures, test records and full traceability. Manufacturers doing this will need to meet the supply legislation requirement for new products and be able to provide the evidence that the complete product is safe to use.
Grinding or welding carried out after initial manufacture is not recommended for the above reasons. Competent persons would normally quarantine or condemn components that have been modified due to their training. They would need to see evidence in writing to pass them.
Find the answers to more frequently asked technical questions at LEEA’s FAQ page at leeaint.com/faqs. For further lifting equipment guidance, consult the LEEA Code of Practice for the Safe Use of Lifting Equipment (COPSULE).
