wire rope breaking strength vs working load quotation

It’s rare for a week to go by here at Industrial Wire Rope without discussions about tensile strength or working load limit. We take it for granted that most people in our industry know there is a difference in the meaning of these terms. Yet, these terms and others are highly interrelated, and we thought an overview of them on one page might be a helpful reference. For those who want to dive deeper into the definitions and how they apply on the job, we’re also providing links to sources with additional information.

Let’s start with Tensile Strength. As we described in a post from 2017, “Tensile strength is a measurement of the force required to pull something such as rope, wire, or a structural beam to the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress that it can take before failure, for example breaking.”

In our immediate world, tensile strength is the force required to break the ropes we offer. Tensile strength is determined by testing. Obviously, it is different for every type of rope, being a function of the material and construction of each type.

Although tensile strength is a definitive quantity measuring the force required to break a rope, working load limit is a measure that takes a wide range of variables into account. And always, the tensile strength of a material is greater than the recommended working load limit.

The working load limit provides consideration for factors such as the abrasion, friction and rubbing the rope is subjected to, the variance in temperature extremes it is exposed to, harmful substances that may come into contact with it, age, and even knots in the rope. Working load limit is defined as “the maximum load which should ever be applied to the product, even when the product is new and when the load is uniformly applied”.

Working load limit is always a fraction of tensile strength, allowing for a generous margin of safety. For wire ropes, it’s common for the working load limit to be set at 20% of tensile strength. However, you generally don’t have to be concerned about doing the math on your own. Rope manufacturers typically mark the working load limit on the products, so the information should be readily available to you.

Rope strength is a misunderstood metric. One boater will talk about tensile strength, while the other will talk about working load. Both of these are important measurements, and it’s worth learning how to measure and understand them. Each of these measurements has different uses, and here we’re going to give a brief overview of what’s what. Here’s all you need to know about rope strength.

Each type of line, natural fiber, synthetic and wire rope, have different breaking strengths and safe working loads. Natural breaking strength of manila line is the standard against which other lines are compared. Synthetic lines have been assigned “comparison factors” against which they are compared to manila line. The basic breaking strength factor for manila line is found by multiplying the square of the circumference of the line by 900 lbs.

As an example, if you had a piece of ½” manila line and wanted to find the breaking strength, you would first calculate the circumference. (.5 X 3.14 = 1.57) Then using the formula above:

To calculate the breaking strength of synthetic lines you need to add one more factor. As mentioned above, a comparison factor has been developed to compare the breaking strength of synthetics over manila. Since synthetics are stronger than manila an additional multiplication step is added to the formula above.

Using the example above, letÂ’s find the breaking strength of a piece of ½” nylon line. First, convert the diameter to the circumference as we did above and then write the formula including the extra comparison factor step.

Knots and splices will reduce the breaking strength of a line by as much as 50 to 60 percent. The weakest point in the line is the knot or slice. However, a splice is stronger than a knot.

Just being able to calculate breaking strength doesn’t give one a safety margin. The breaking strength formula was developed on the average breaking strength of a new line under laboratory conditions. Without straining the line until it parts, you don’t know if that particular piece of line was above average or below average. For more information, we have discussed the safe working load of ropes made of different materials in this article here.

It’s very important to understand the fundamental differences between the tensile strength of a rope, and a rope’s working load. Both terms refer to rope strength but they’re not the same measurement.

A rope’s tensile strength is the measure of a brand-new rope’s breaking point tested under strict laboratory-controlled conditions. These tests are done by incrementally increasing the load that a rope is expected to carry, until the rope breaks. Rather than adding weight to a line, the test is performed by wrapping the rope around two capstans that slowly turn the rope, adding increasing tension until the rope fails. This test will be repeated on numerous ropes, and an average will be taken. Note that all of these tests will use the ASTM test method D-6268.

The average number will be quoted as the rope’s tensile strength. However, a manufacturer may also test a rope’s minimum tensile strength. This number is often used instead. A rope’s minimum tensile strength is calculated in the same way, but it takes the average strength rating and reduces it by 20%.

A rope’s working load is a different measurement altogether. It’s determined by taking the tensile strength rating and dividing it accordingly, making a figure that’s more in-line with an appropriate maximum load, taking factors such as construction, weave, and rope longevity into the mix as well. A large number of variables will determine the maximum working load of a rope, including the age and condition of the rope too. It’s a complicated equation (as demonstrated above) and if math isn’t your strong point, it’s best left to professionals.

However, if you want to make an educated guess at the recommended working load of a rope, it usually falls between 15% and 25% of the line’s tensile strength rating. It’s a lotlower than you’d think. There are some exceptions, and different construction methods yield different results. For example, a Nylon rope braided with certain fibers may have a stronger working load than a rope twisted out of natural fibers.

For safety purposes, always refer to the information issued by your rope’s manufacturer, and pay close attention to the working load and don’t exceed it. Safety first! Always.

If you’re a regular sailor, climber, or arborist, or just have a keen interest in knot-tying, be warned! Every knot that you tie will reduce your rope’s overall tensile strength. Some knots aren’t particularly damaging, while others can be devastating. A good rule of thumb is to accept the fact that a tied knot will reduce your rope’s tensile strength by around 50%. That’s an extreme figure, sure, but when it comes to hauling critical loads, why take chances?

Knots are unavoidable: they’re useful, practical, and strong. Splices are the same. They both degrade a rope’s strength. They do this because a slight distortion of a rope will cause certain parts of the rope (namely the outer strands) to carry more weight than others (the inner strand). In some cases, the outer strands end up carrying all the weight while the inner strands carry none of it! This isn’t ideal, as you can imagine.

Some knots cause certain fibers to become compressed, and others stretched. When combined together, all of these issues can have a substantial effect on a rope’s ability to carry loads.

Naturally, it’s not always as drastic as strength loss of 50% or more. Some knots aren’t that damaging, some loads aren’t significant enough to cause stress, and some rope materials, such as polypropylene, Dyneema, and other modern fibers, are more resilient than others. Just keep in mind that any knots or splices will reduce your rope’s operations life span. And that’s before we talk about other factors such as the weather or your rope care regime…

Quoted breaking strength of rope is usually the optimum strength achieved under laboratory conditions, in accordance with prescribed test procedures, on new rope, pulling at a slow, steady rate in a straight line. Real life applications normally involve many different types of forces and factors which will cause the rope to fail at much reduced loads. Accordingly, the safe working load of any rope is much lower than its nominal strength.

The following article reprinted with permission from Cordage News, a publication of the Cordage Institute provides a good overview of factors to consider when determining the safe working load of the rope.

TOTAL POTENTIAL LOAD (TPL) is the weight to be lifted, towed, restrained, suspended, or secured, not just in a static condition, but in a dynamic condition. Examples: the jerking of a weight being lifted, the heaving of a vessel, the slalom of a water skier, the falling of a body, the swaying of scaffolding, the tethering of a balloon, the wind pressure on antenna guys, a truck being towed out of the mud, and a boat being towed through waves – these and many other situations like them produce dynamic forces with a total potential load that may well exceed, sometimes substantially, the static weight of the load, and this must be taken into account.

A DESIGN FACTOR (DF) must be selected based on the TPL, the degree of risk to life, limb and property and the conditions of use. This, in turn, is used to establish the WLL using the formula Minimum Breaking Strength divided by the Design Factor (WLL = MBS + DF).

For critical applications a Design Factor greater than 12 may be necessary. Users must determine the DF as they are the only one who can assess service conditions and establish operating procedures. The TPL applied to a cord or rope should never exceed the WLL. If uncertain, a qualified engineer should be consulted.

Understand that most of the people out from the industry always face the problem of having no idea with the terms of wire rope when receiving quotation. In this update, we will explain in the most simple way and hopefully it is applicable to anyone.

6X36 = Construction of wire rope (There are quite a lot different constructions available for different application for example like, 6X25, 6X29, 6X31, 4X39, 19X7, 8X26 etc.)

RHOL = Right hand ordinary lay, it is the wire lay direction and very important to select the right direction of wire when dealing with multi-reeving, crane and hoist application.

EIPS (1960) = Extra improved plow steel and 1960 stands for the tensile strength 1960N/mm2. The figure is telling you the grade of wire rope, lower or higher tensile strength will result in different breaking strength.

UNGALVD = Ungalvanized, the surface finishing of wire rope. Galvanized and Ungalvanized are the basic surface finishing selection with different grade of lubrication.

G411 THIMBLE EYE = Thimble eye model. Soft eye will be stated with the effective working length and the size of soft eye is based on nominal diameter x 15times according to EN131411 standard.

MECH SPLICED = Mechanical splicing is the process of using hydraulic pressure to press the aluminum sleeve or metal sleeve and a loop is formed. This phrase is always telling you the terminal of both end wire rope. It can be plain, socketed, fuse tapered or eye formed.

Wire rope could have a lot of variation upon the application which I will cover in the next update. The essay above is good enough to tell the basic and hope it helps for procurement department while dealing with steel wire rope. Last but not least, selecting the right wire rope is crucial to your company"s long term expenditure and safety purposes. Do not take the risk because of cheap.

Working load limit is also known as safety working load, abbreviated as W.L.L, it is the maximum safe working load that a piece of lifting equipment, without fear of breaking. It usually varies based on what type of rigging or safety equipment and are identified by manufacturers.

The minimum break strength aka Minimum Breaking Load (MBL) refers to the required force at which your load equipment will fail. It is expressed in pounds, and/or tonnes, and will actually fail if you go over the guaranteed strength.

The Working Load Limit is the maximum load which should ever be applied to the product, even when the product is new and when the load is uniformly applied – straight line pull only. Avoid side loading. All catalog ratings are based upon usual environmental conditions and consideration must be given to unusual conditions such as extreme high or low temperatures, chemical solutions or vapors, prolonged immersion in salt water, etc. Never exceed the Working Load Limit.

The term “Proof Test” designates a quality control test applied to the product for the sole purpose of detecting defects in material or manufacture. The Proof Test Load (usually twice the Working Load Limit) is the load which the product withstood without deformation when new and under laboratory test conditions. A constantly increasing force is applied in direct line to the product at a uniform rate of speed on a standard pull testing machine. The Proof Test Load does not mean the Working Load Limit should ever be exceeded.

Do not use breaking strength as a criterion for service or design purposes. Refer to the Working Load Limit instead. Breaking Strength is the average force at which the product, in the condition it would leave the factory, has been found by representative testing to break, when a constantly increasing force is applied in direct line to the product at a uniform rate of speed on a standard pull testing machine. Proof testing to twice the Working Load Limit does not apply to hand-spliced slings. Remember: Breaking Strengths, when published, were obtained under controlled laboratory conditions. Listing of the Breaking Strength does not mean the Working Load Limit should ever be exceeded.

An industry term usually computed by dividing the catalog Breaking Strength by the catalog Working Load Limit and generally expressed as a ratio. For example: 5 to 1.

A load resulting from rapid change of movement, such as impacting, jerking or swinging of a static load. Sudden release of tension is another form of shock loading. Shock loads are generally significantly greater than static loads. Any shock loading must be considered when selecting the item for use in a system.

Working Load Limit is an important term often used on job sites and when discussing slings and other rigging equipment. It is important to have a comprehensive understanding of Working Load Limits, as well as understand how it’s different from other ratings. This will help you to safely use all of your rigging products.

Working Load Limit is defined as the maximum load to be applied to a product when the load is uniformly applied in a straight line pull only. Avoid side loading or angular loading unless otherwise noted by the manufacturer. According to OSHA, “Employers must ensure that rigging equipment not be loaded in excess of its recommended safe working load as prescribed on the identification markings by the manufacturer.” (OHSA 1926.251(a)(2)(ii)). For that reason, all rigging equipment must have identification that clearly states the working load limit. Qualified Riggers should then always be sure to check the working load before using their rigging products. This will help ensure their safety and the safety of others around them.

There are several other ratings that differ from Working Load Limit, such as Breaking Strength. Breaking Strength refers to the point at which the rigging will fail. Always use Working Load Limit when choosing rigging, not breaking strength. Breaking strength is helpful, however, when looking at a piece of rigging’s design factor. Design Factor is simply the ratio between Working Load Limit and Breaking Strength. For example, the Eye Grab Hooks – OG have a Design, or Safety, Factor of 4:1 which means the Working Load Limit is ¼ of the Breaking Strength.

When using your rigging, you need to know the weight of the load in addition to the Working Load Limits of the equipment used for the lifting. There are a lot of items to consider for safe rigging, and they can all be covered in one of our training courses. Additionally, our article “How to Recognize When A Sling Should Be Removed from Service” is a great outline on inspecting your slings.

In the shipping industry, items like winch straps and ratchet straps use two common measuring metrics. One of them is the working load limit, while the other is the strap’s break strength. At first glance, it’s understandable why some people might mix the two up. They kind of mean the same thing, don’t they? In this article, we’ll look at break strength vs. working load limit, explaining the differences and why those differences are so important.

We’ll start with break strength since this term is more self-explanatory than the other. Put simply, the break strength of a piece of rigging is the amount of weight that would cause the weakest part of the rigging to fail. Ideally, you’ll never actually test a rigging’s break strength, as the weight of the loads they’ll carry will usually be much lower than this limit.

If a cargo strapping system consists of fittings, webbing, and a tensioning device that all have a break strength of 12,000 pounds, that strapping system’s break strength would be 12,000. However, if one of those components (the fittings, webbing, or tensioning device) has a lower break strength of 9,000 pounds, then the entire strapping system has a break strength of 9,000 instead.

The difference in break strength vs. working load limit comes into play when you understand the concept of the working load limit means. A rigging’s working load limit is the amount of weight that it can handle under normal conditions. This number will always be smaller than the break strength, and that piece of rigging should never hold more than its working load limit.

The working load limit of a rigging system is equal to 1/3 the amount of the break strength. As such, a strapping system with a working load limit of 5,000 pounds has a break strength of 15,000 pounds. Remember, the working load limit will determine how much you should allow the system to hold, not the break strength.

Logistick makes our products able to stand the test of time. Our cargo strapping systems have all undergone extensive testing for both working load limit and break strength, so you can rest easy and trust the numbers you see. If you have any questions about our products or how they work, please give us a call. We’ll be happy to help you out.

- Recovery Ropes, Tow Lines, Tow Bridles, Tow Ropes, Winch Ropes, & Winch Lines- - Recovery Ropes, Tow Lines, Tow Bridles, Tow Ropes, Winch Ropes, & Winch Lines – Main Page

Working Load Limit (WLL) is the maximum working load designed by the manufacturer. This load represents a force that is much less than that required to make the lifting equipment fail or yield. The WLL is calculated by dividing the breaking load limit (BLL) by a safety factor (SF). An example of this would be a chain that has a BL of 2,000 lb. WLL of 400 lb. if a safety factor of 5 (5:1, 5 to 1, or 1/5) is used.

When you are looking for internet info. on a subject, you should at least look for material which is not written in pigeon-English. And, the link you have provided leaves a lot to be desired, in my mind. While I don’t think your link is out-n-out wrong, it might be misleading or misunderstood, so you really have to read btwn. the lines. Again, ask your supplier, have him put it in writing in his quote to you, or in a letter. Breaking strength should be pretty clear to all of us; either for the particular wire rope or for the full sling assembly. While rated strength, rated cap’y., and assembly cap’y. could have a hundred meanings. Rated cap’y. to me means some engineering judgement has been applied to the cap’y., not just its physical min. breaking strength. There will be a FoS, and some fittings or rope bending reductions applied. Then your original OP attachment would show these further cap’y. reductions due to hardware, fittings, attachment means and wire rope bending, etc., as well as geometrical variations such as wire rope angle from vert.

Equipment used in lifting or supporting materials, including cranes and load-bearing structures, uses rigging made of chains, synthetic or wire ropes. A proof load test is a process that requires the lift of a specific type of material (the rope or chain) using specially designed proof load test machines.

With the lift, the system is able to measure the tensile strength and load capacity of the material based on elongation under force. Hydraulic cylinders with high accuracy displays are used to provide a reliable measurement of the force applied.

A proof load test is a controlled, measured application of force over a specified time period to a given piece of rigging equipment. A mechanism using specially designed hydraulic cylinders with independent load cells provides an accurate reading of the force exerted on the material (rigging, wire or synthetic rope, chain, etc.). The test will ensure the material exceeds the maximum allowable working load (MAWL) on the material rating.

A working load limit is the maximum load that can be applied to a piece of lifting equipment without fear of the equipment failing. This is referred to in many different ways like maximum allowable working load (MAWL), safe working load (SWL), normal working load (NWL) and, of course, working load limit (WLL).

A working load limit is not simply calculated by finding the minimum breaking strength (MBS) of a piece of equipment. The WLL is a factor of the division of minimum breaking strength and the product’s safety factor (SF). A safety factor is decided on by engineers through compiled failure testing data and reliability of certain designs. The safety factor is meant to be a rating of how far beyond normal use conditions a piece of equipment can still safely perform.

To ensure any type of material (wire rope, synthetic rope, chain or rigging), is able to not only meet but exceed the MAWL (maximum allowable working load), a controlled test is performed.