Marking lifting equipment30 June 2010
Derrick Bailes, technical consultant, Lifting Equipment Engineers Association, explains the reasons why we should mark lifting equipment, and how to do it most effectively.
Lifting equipment is marked for a variety of reasons, the most important of which is to give it a unique identity. It will be certified in some way before first use and throughout its life it will be inspected at regular intervals in line with the prevailing local legislation. The ID mark, as it is usually called, is the link between the item and the documents recording its initial certification and in-service inspections. Therein lies the first potential problem for the buyer.
The initial certification will depend upon the legislation and standards worked to. In Europe, the Machinery Directive requires an EC Declaration of conformity and the harmonised European Standards usually require a manufacturer’s certificate. Often these two documents are combined into one.
Some items are manufactured in large batches and every item in the batch bears the same ID. Typically forged items such as shackles and eyebolts are marked by the forging die so it is impractical to provide a unique ID by that method. When sold, the item can legitimately be related to its documentation by the batch ID alone. However once in service, the batch ID alone is not adequate.
Consider the person making a report of an in-service inspection. Knowing that there may be literally thousands of similar items with the same ID, that person would be very foolish to identify the one being inspected by the batch ID alone.
The usual solution is to add a suffix to the batch ID by hard stamping. Although this will be an added cost, it can be done much more efficiently under workshop conditions before being taken into service than later under site conditions.
Therefore either arrange for your supplier to do it or have it done within your own organisation before issue for use. Either way, the original documentation should be annotated with the extra information.
The next question is what the extra marking should be. If left to the supplier they may simply add a number in sequence. So if you buy four shackles of the same size they will be suffix numbered 1-4. However next time you buy four they may well have the same batch ID and also be numbered 1-4.
Even going to a different supplier may not help as there are relatively few manufacturers compared to suppliers and the batches can be huge. The space available for stamping is limited so the extra marking must be kept to a minimum. Therefore users should consider having control of their own sequence and specifying the extra marking to their supplier or internal facility.
Some large user organisations go further and have their own plant number which effectively supersedes the batch ID. For such a system there needs to be a cross reference between the original ID and the plant number to provide traceability.
When designing a plant marking system, the number of characters required must be commensurate with the space available bearing in mind the other information which is already marked on the item by the manufacturer.
The other information marked by the manufacturer on shackles will be the safe working load or working load limit and the grade. Eyebolts will have the same plus the thread size and type.
Hard stamping displaces material and if too large or too deep will be a local stress raiser. A common mistake is to use too large a stamp. A flat stamp on circular section material will have to indent deeper in the centre compared to the top and bottom. Often the result is an incomplete character. The bigger the stamp relative to the material diameter, the worse this gets. Attempts to deepen the marking by repeated strikes only makes a mess and does more damage. A smaller stamp does less damage and is actually easier to do and to read. It also minimises the length of the marking.
Hard stamping should be restricted to low stress areas such as the straight sides of a shackle, and kept away from high stress areas such as the crown. British Standard eyebolts have raised flat areas at the sides of the eye for marking. They are quite small but adequate if the stamp size is kept to the minimum. If more space is required, the outside of the collar can be used but not, as I once saw, the machined face on the underside of the collar.
The visibility of hard stamping can easily be improved by filling it in with a contrasting colour. Inspectors often carry a stick of chalk as a temporary highlighter but there are more durable options.
The plant number concept can also be applied to items which do have an individual manufacturing ID but which, because the items come from a variety of sources, will not have their IDs in a single style or sequence.
Slings are generally supplied with an individual ID. General purpose chain slings are usually manufactured to order from standard components and the complete assembly marked with a robust metal tag attached to the master link. As this is a relatively soft non-load bearing material it can easily be stamped with all the necessary information. However tags can become detached so it is a useful precaution to mark the side of the master link with the ID. In the event of the tag being lost, it will provide traceability back to the documentation from which all other information can be recovered.
Wire rope slings are usually manufactured with ferrule secured eye terminations. Single leg slings are marked by stamping directly into the ferrule. This is a circular section so again, the stamps should not be too large. Aluminium ferrules are quite soft and a large stamp applied with a heavy hand can result in a very deep impression but considerable local damage. Multi-leg wire rope slings are marked by a tag similar to that used for chain slings.
Textile slings such as webbing slings and roundslings are marked with a label stitched into the seam of the sling. The back of the label is usually blank and can therefore be used for a plant number written on with a magic marker pen. This is not always durable but can easily be refreshed from time to time. Metal tags should not be used on textile slings. If trapped when under load they can cut the sling.
Some users write directly onto the webbing or the cover of the roundsling. We have recently been asked about the safety of this practice and whether the solvent in the marker pen will cause damage. The short answer is that we don’t know for sure. Examination of sample slings marked in this way has not revealed any signs of damage but that is no guarantee that it will not occur with every possible combination of pen and material types. We therefore discourage the practice unless tests have been made to check for damage. Certainly paint should never be used as, in addition to the possible chemical reaction, it will glue the fibres of the material together and prevent them from flexing.
A modern method of providing a unique identification is the radio frequency identifier. This is a miniature circuit embedded into or attached to the item. Each RF identifier has a unique ID which can be read by a hand held scanner and related to the item within a software database. They are not practical for every item and current costs limit their economic viability to higher value items. Nevertheless they have several advantages. The ID cannot be misread and the direct link to the database eliminates the time and potential errors associated with searching for records in paper lists or keying in the ID.
As well as adding a unique ID or plant number, the user may want a visual indication of whether the item is within a current inspection period. One method I have seen which should never be used is that of hard stamping a date directly into the item. Repeatedly hammering over previous markings is inviting trouble even in low stress areas. Most systems are based on colour codes or tags and each have their advantages and disadvantages.
With regard to colour codes, remember that many people have some degree of colour blindness, particularly males. Therefore consider testing for this condition and if necessary, provide an alternative method of checking the inspection status. A colour system needs sufficient colours to provide a long enough time cycle. Slings and other lifting accessories are usually thoroughly examined or inspected every six months or less. However some items may not be found when due for inspection. A good control and issue system will minimise this but the possibility should be accommodated. Therefore the time cycle should avoid repeating a colour before there is a reasonable chance of all items being accounted for. A minimum time cycle of two years is recommended. Readily visible signs at strategic positions around the site should show the current colour code.
If the site has a lot of equipment then a situation is likely to occur when it is all due for inspection at the same time. This may be inconvenient and require a transition period during which either of two colours is valid.
Consider also whether contractors working on the same site may also be using colour coded lifting equipment. It may be necessary to identify ownership of the item in some way as well as the inspection status.
There are various methods of applying the colour code. On forged items such as shackles and eyebolts, a spot of paint is often used. However over time layers of colour build up and, as the paint wears during use it can become difficult to decide which is the latest. Coloured cable ties are quick and easy to apply and are usually durable enough. Also on the market are a purpose designed variation of the cable tie with space for information to be added such as a date.
Chain and wire rope slings can be colour coded in the same way. Care is needed with roundslings. The hank of fibres inside the protective sheath should be free to bunch together or spread out to match the load. A cable tie pulled tight will prevent the fibres from spreading out and may cause a local overload.
Another product on the market is a soft plastic label in the shape of a small spade. Originally intended for tagging the ears of cattle, they can be used with advantage on items such as roundslings. The flat part has space to mark information such as a date.
Various designs of tags are available as an alternative to or for use in combination with colour codes. Usually there is space for a valid until date and that is the primary indicator of inspection status. However tags on some items can get in the way in use and quickly get removed, accidentally or otherwise. In some applications they may even be a hazard. It is therefore a matter of choosing the most appropriate method for the item and the environment in which it is being used. In all probability a combination of methods will be required.
Finally, whatever method is chosen to identify the item and its inspection status, it should be applied with discipline. Any old markings and tags should be removed to avoid possible confusion. Just like wrong information, confusing information is worse than no information.
About the author
Derrick Bailes is technical consultant (formerly chief executive) for the Lifting Equipment Engineers Association, 3 Osprey Court, Kingfisher Way, Hinchingbrooke Business Park, Huntingdon, PE29 6FN, tel: +44 (0)1480 432 801, fax: +44 (0)1480 436 314, email: email@example.com