Synthetic slings have made significant strides in popularity in the US over the past 40 years, to the extent that they have now become ubiquitous, says Mike Gelskey.

George Coull says the situation is similar in the UK: “In recent years, there has been a marked move away from chain and wire rope types towards man-made fibre webbing and round slings,” which tend to be lighter, easier to manoeuvre and not so damaging on the load.

In both nations, maintenance, mechanical, manufacturing and shipping departments have come to realise the strength to weight ratio advantage of synthetic slings over alternative, “heavy metal” sling types. Ease of use, flexibility and storage has made the synthetic sling the sling of choice, assuming that suitability exists for the application.

Synthetic web and round slings are available in a multitude of designs and materials. The material of choice for web slings in the US is nylon, while Gelskey says the rest of the world pefers polyester webbing slings. Actually, webbing slings, until recently, were the sling of choice by US riggers. The change in the US sling market is towards round slings incorporating polyester and high performance fibres.

Gelskey highlights some of the contributing factors:

• ï„·The availability of yarn from a global supply and demand perspective

• ï„·The realisation that certain fibers have comparative advantages when chemical and ultraviolet light factors are taken into consideration

• ï„·The economy of production for certain sling types, whereby multiple slings are produced simultaneously

• ï„·The awareness that certain sling designs provide increased service life by providing multiple hook and load contact points

There has also been change in the UK. The types of slings available and the regulations governing their use have altered dramatically over the past few years says Coull. He agrees that an increasing emphasis on safety and risk assessment within regulations has been a contributory factor in the trend towards man-made fibre webbing and round slings. “Lighter slings make for easier manual handling, which inevitably reduces accidents in the workplace,” says Coull.

There are, however, some applications which favour other types of sling and even fibre rope slings, which though generally on the decline, are still widely used throughout industry.

The supply of domestic nylon fiber in the US was dealt a devastating blow by the recent series of catastrophic weather events. Certain facilities that specifically produced the chemical components for nylon fiber extrusion were literally devastated.

Combine the loss of production, with a heated up world economy starving for other petrochemical products, for example, fertiliser, gasoline, aircraft fuel and the greater margins on the latter when compared to nylon fiber profit margins and a very bleak picture for the US emerges, says Gelskey.

Common ground

But, largely, there’s common ground. For example, every application has parameters that will necessitate an evaluation and selection of materials by the responsible sling user.

Stretch or elongation can be desirable or detrimental. Nylon fibre provides shock absorbency to a greater degree than polyester fibers. Nylon web slings stretch at twice the rate (6-8% at work load limit), when compared with polyester slings. Sling longevity can be increased as stretch is minimised over contact surface areas by selecting lesser stretching materials, like polyester and high performance fibres.

Another factor that enters into the selection of sling type and material are the components that interface with the synthetic sling. The size of the hook, shackle or connector used in the sling system or assembly should be taken into account. Spatial relationships, particularly at the connection point(s) can make the difference between success and failure.

Chemical compatibility is another important factor in any rigging application. For example, the relationship between the sling and chemicals present in the environment. The responsible sling user will evaluate the chemical properties that are inherent in the materials used in the construction of the sling, prior to purchase and use. Variations in exposure time, temperature and concentration factors will turn non-damaging chemicals into severely deleterious ones.

When a nylon sling is wet, the resulting loss of strength is approximately 15%. When the nylon sling returns to a dry state, the strength is normalised to the initial value. Polyester and high performance fiber slings do not lose strength when wet. Independent tests done by Lift-It Mfg. Co. confirm the loss of strength mentioned in the DuPont Technical Information Multifiber Bulletin X272, dated July 1988.

Nylon web slings continuously exposed to sources of UV light can lose 40 to 60% after exposure periods ranging from 12 to 36 months. Polyester web slings lose at a greater rate, initially (30% in the first 12 months), but interestingly, the loss seems to subside and level off after the initial 12 month period.

This summary for the loss of strength for nylon and polyester web slings can be found in the US study conducted by the Web Sling and Tiedown Association (WSTDA) in “Summary Report of the Ultraviolet (UV) Degradation Testing Program for Synthetic Web Slings.” The report number is WSTDA-UV-Sling-2003 and is available at www.wstda.com.

In the UK, the definition of lifting equipment and accessories used in the Lifting Operations and Lifting Equipment Regulations (1998) LOLER make it clear that chain slings and webbing round slings fall under the heading of lifting accessories. As such, they must be thoroughly examined by a competent person at intervals not exceeding six months. They must also be visually inspected by a responsible person prior to use or on a regular basis, taking account of the conditions of service.

This has inevitably led to the need for more specialist operators and consequently there has been a greater emphasis on training and a number of tailor-made courses are available within the industry. It is no longer necessary just to be able to operate machinery, staff now need to be adequately trained and competent in how to fit slings, use them and maintain them.

Employers, says Coull, “should also make sure that they hold the sling certificate of conformity and where produced a test certificate,” not only because the law so demands, he continues, but also because it may be vital evidence in the event of a failure of equipment while in service. The certificate is also documentary evidence of the legal SWL of the sling.

Here, Coull and Gelskey compare notes on two types of slings.

Webbing slings

Webbing slings (commonly known as belt slings in the UK) are used for a variety of lifting purposes. Essentially, they are a textile sling (usually made of polyamide, polyester or polypropylene) which makes them soft and easy to handle, yet they also offer rigidity across their width. These qualities make them ideal for handling those loads which require some support when being lifted as the load is spread across the full width of the webbing, thus avoiding point contact, as is the case with chains or ropes. However, they are less robust and more easily damaged than equivalent capacity wire rope and chain slings.

In the States, the maximum vertical work load realised with webbing slings is 50 US tons. The web sling in this example would be 12 inches wide, four ply thick and endless in configuration. In terms of handling, the sling is 6lbs per foot of sling length.

BS EN 1492-1 is the European regulation governing this type of sling and replaced the British Standard 3481: Part 2. Traditionally in the UK, textile slings were rated on the basis of a minimum factor of safety of 6:1, however, this was amended to 7:1 in 1997 to reflect European legislation. At the same time, a colour code system to signify the WLL of the sewn webbing component was introduced. This is the maximum load that may be sustained when the sling is in a straight pull.

Round slings

Round slings featuring polyester fiber can easily be made on much less labour intensive machinery and in terms of weight comparison would be 4lbs per foot of sling length.

Another big advantage in the production of round slings, says Gelskey, is that smaller capacity slings (1-4 US ton vertical WLL) can be made simultaneously. As good as any web sling fabricator is, that person can only produce one sling at a time.

Nylon webbing and polyester round sling weight comparisons are based upon a 5/1 design factor. Keeping the same design factor in mind, high performance fiber slings (50 US ton vertical) weigh in at 2lbs per foot of sling length.

Round slings are manufactured in the UK in single endless form in a standard range of WLL up to 12t, although the WLL is theoretically not restricted. Although common in Europe, multi-leg roundsling assemblies are rare in the UK and users prefer to obtain single endless slings. This enables a varied range of uses, including the assembly of more than one sling in any particular slinging arrangement.

In 2000, BS EN 1492-2 replaced British Standard 6668: Part 2 and the minimum factor of safety became 7:1. A new colour code system was also introduced to signify the WLL.

In all instances the endless or grommet configuration allows the sling user to constantly rotate the connection and load contact points, enhancing the life cycle of the sling. Eye and eye configuration slings do not afford the sling user the same luxury of rotation and extended service life..


There has been a marked move away from chain and wire rope slings slings 1 Every application has parameters that will necessitate an evaluation and selection of materials by the responsible sling user slings 2 Synthetic slings have made significant strides in popularity in the US over the past 40 years, to the extent that they have now become ubiquitous, says Mike Gelskey slings 3 Chemical compatibility is another important factor in any rigging application. For example, the relationship between the sling and chemicals present in the environment slings 4 The types of slings available in the UK and the regulations governing their use have altered dramatically over the past few years says George Coull slings 5 Employers, says George Coull, ‘should make sure that they hold the sling certificate of conformity and where produced a test certificate’ slings 6 In the UK, the definition of lifting equipment and accessories used in the Lifting Operations and Lifting Equipment Regulations (1998) LOLER make it clear that chain slings and webbing round slings fall under the heading of lifting accessories slings 7