What is Working Load Limit of Chains

Definition of Working Load Limit

The working load limit is the maximum static load that the chain can withstand under normal use conditions. It is what we commonly call “WLL. It can accurately reflect the safe load that the chain can withstand. It is also a key parameter when designing, selecting, and using the chain to ensure safety during use.

Factors Affecting WLL

The working load limit (WLL) of a chain is influenced by many factors. Different materials, usage environments, and manufacturing processes will have different effects on the WLL of the welded chain.

Material

Carbon Steel: Carbon steel chain has a low WLL and is only suitable for light applications.
Alloy Steel: By adding elements like chromium and molybdenum, the strength and toughness of the material are greatly improved. This makes alloy steel chains much stronger and can be used for some heavy machinery.
Stainless Steel: Stainless steel chains are corrosion-resistant, and can be used in marine or chemical environments, but their WLL is about 80% of carbon steel chains.

Manufacturing Process

Heat Treatment: Quenching and tempering can effectively improve the hardness and toughness of welded chains, increasing their WLL.
Welding Process: Automated flash welding or argon arc welding can replace traditional manual welding. Using full weld techniques ensures the weld is full, smooth, and free of bubbles or cracks, improving the hardness of the welded joints.
Surface Treatment: Hot-dip galvanizing or coating can enhance rust resistance and surface hardness, which can also improve the WLL of the chains.

Size and Structure

Wire Diameter: This refers to the diameter of the wire used to produce the welded chain. WLL is proportional to the square of the wire diameter. For example, a 12mm diameter chain has 4 times the WLL of a 6mm chain.
Pitch: The length of the pitch (such as short-link or long-link chains) can affects WLL directly. Short-link chains have a higher WLL than long-link chains of the same wire diameter and material.
Chain Link Shape: Welded chain links are usually oval rather than round because oval links have higher tensile strength.

Load Type

Static Load: A load that increases slowly and the WLL can be used directly according the load.
Impact Load: If a chain is used as a safety chain to stop a falling object suddenly, the pulling force on the chain will be 2-3 times the object’s weight, so it is necessary to choose a chain with a higher WLL.

Environmental Factors

Temperature: Carbon steel chain will be brittle at low temperatures, and the high temperatures will reduce the strength of chains, so the steel chains with higher WLL should be chosen for low or high temperature environments.
Corrosion: When used in seawater, the chain should be used at only 50% or even 30% of its WLL, and the surface corrosion of the chain needs to be checked regularly.

Wear and Tear

The welded chain will wear out after long-term use, and its WLL will gradually decrease. It needs to be checked regularly to prevent safety accidents.

Relationship Between WLL and Related Parameters

Breaking Strength

Breaking strength is obtained through testing, by applying an increasing load to the chain until it breaks. The force that the chain withstands at the moment of breaking is its breaking strength, also known as breaking force. This force has the most direct relationship with WLL.

Safety Factor

The safety factor is an important parameter of steel chains, it can measure the safety margin between the breaking force and the actual working load, ensuring the safety of the chain during use and that it will not be damaged even in an accident.

The working load limit (WLL) can be calculated using the breaking strength and the safety factor:

WLL= Breaking Strength/Safety Factor

For example, if a chain has a tested breaking strength of 10 tons and a safety factor of 5, then its WLL is:

WLL=10÷5=2 tons

Additionally, different applications require different safety factors.

For example:

If the steel chain used in the lifting industry, the generally safety factor is 4 or 5.

But if the chains used in applications that involving human safety, the safety factor may even up to 8, such as stage rigging etc.

WLL-Related Standards

ISO Standards

ISO 1834: This standard specifies the classifications and working load limits (WLL) of welded steel chain, such as grades such as G80 and G100. Its test range includes tension, fatigue, bending, etc.

ANSI Standards

ASME B30.9: This is the American standard for lifting chains, which requires the chain to be sampled for breakage test before shipment.
OSHA Regulations: It is mandatory to use chains with WLL labeling, and overloading is illegal.

DIN Standards

DIN 5685: This German standard for high-strength chains, it defines the chemical composition and hardness range of Grade 80 and Grade 100 chains.

Please note that the WLL has different requirements under different standards.

For example, under the ISO standard, a 10mm G80 welded chain has a WLL of approximately 8 tons,and the safety factor is 4. However, since DIN standard is more strict, a 10mm G80 chain of the same material and manufacturing process has a WLL of about 7 tons under DIN standard.

How to Choose the Right Chain with Suitable WLL

When selecting a chain, in addition to size and material, the working load limit (WLL) is the most important factor. It ensures that the chain will not deform or break during use.

The following example explains how to choose the most suitable chain for WLL in a more intuitive way:

Application: Using lifting equipment to lift a 10-ton object.
Safety Factor: Since this is a high-risk application, a safety factor of 5 is selected.
Load: At the moment of lifting, the impact force can reach 1.5 times the weight, so we need a total load of 10*1.5=15 tons, which is a safe load

According to the safety factor and the required loading, we can calculate the breaking force of the required chain as:

15*5=75 tons

So we can choose the most suitable chain according to the breaking tension of the chain, i.e., 18mm G100 chain, which has a breaking force of 80 tons, and it can meet our needs.

Environmental Considerations

If the chain is used in a marine environment, 316 stainless steel should be selected for corrosion resistance.

However, stainless steel has lower strength than alloy steel, so we need to calculate according to the specific circumstances to appropriately reduce the WLL in order to improve its breaking strength and increase safety.

Summary

WLL, which means working load limit, is the most direct safety data of the welded steel chain. It needs to be selected based on material, usage environment, production process, and actual working conditions. The key points are:

When choosing WLL, the load must be calculated according to the worst-case scenario.
Because different steel chain manufacturers have different production processes, the actual WLL may vary. So, follow the manufacturer’s data and do not estimate without a basis.
After choosing the steel chains with correct WLL, it needs to be checked regularly during use and recorded in detail to avoid wear over time, which may reduce WLL and cause safety accidents.

For product specifications related to this topic, see Your Trusted Stainless Steel Chain Supplier and Tow Chain.