Load testing is a process that involves applying load to a structure or lifting equipment. A proof load test is a subset of the load test. It helps determine the load-bearing capacity of a structure or equipment. Testing the efficacy of heavy-lifting equipment is of utmost importance because it helps determine the load-bearing capacity of the lifting equipment.
Technically speaking, load testing involves lifting heavy loads with the help of specially designed proof load test machines. The equipment used most frequently here include cranes and other load-bearing structures.
The ultimate goal of the proof load test is to gain an idea about the tensile strength and the load-bearing capacity of the lifting equipment. The test is based on elongation under force. Hydraulic cylinders having high accuracy displays are used to get a precise idea of the force applied.
Still confused? Well, this post aims to shed more light on proof load testing and its implications in the heavy-lifting industry.
What Is Proof Load Testing?
A proof load test involves applying controlled force for a definite time interval to a load-bearing equipment. Specially designed hydraulic cylinders with independent load cells are used to get a proper insight of the force exerted over the material. The test ensures that the equipment is safe to use within the minimum allowable working load.
A proof test is performed on several lifting and rigging equipment to ensure their efficacy. The tests verify that the machinery or heavy equipment has passed the onsite test. It also verifies that it can lift the designated load without causing any damage to man or machine.
The load test procedure is mostly performed on a static pull test. The test assures the potency of the machine to lift loads as designated without causing any structural damage. In most cases, a load that is 1.1 to 1.5 times the designated load is used.
In North America, proof load testing is compulsory to meet the various standards set by the Occupational Safety and Health Administration (OSHA), the American Society of Mechanical Engineers, and the American National Standard Institute.
A few standards of proof test that determine the ability of the lifting equipment to bear loads include:
- ASME B30.9: on lifting slings
- ASME B30.10-1.7: on hooks
- ASME B30.16: on overhead hoists (underhung)
- ASME B30.17: on overhead and gantry cranes and trolleys
- ASME B30.20: various below-the-hook lifting devices
- ASME B30.20: for manual lever hoists
- ASME B30.26: for various lifting accessories: shackles, eyebolts, turnbuckles, links, rings, swivels and compression hardware
- OSHA Section 1926.251(a)(4) covers special custom lifting accessories that are proof-tested prior to use to 125% of the working load limit
- ANSI N14.6: application-specific for special lifting devices for shipping containers for nuclear materials weighing more than 4500 kgs
What Is Working Load Limit?
Now that you have a fair understanding of what proof test is, let’s find out more about the term ‘working load limit.’ Going by the books, the working load limit is the maximum load that can be applied during a proof test to a piece of equipment.
However, you need to ensure that no damage is being done. This is sometimes also referred to as Maximum Allowable Working Load (MAWL), Safe Working Load (SWL), and Normal Working Load (NWL).
The working load limit is not just the calculation of the minimum breaking strength of any equipment. It also indicates the safety limit of the equipment beyond which it may be unsafe to use. It’s often referred to as the minimum breaking point.
The factor is calculated based on compiled failure testing data and the reliability of a few specific designs. To put it simply, the safety factor narrowed down by the site engineers determines how far beyond the normal usage the lifting equipment can be considered safe for use.
The engineers also perform a controlled test to ensure that the equipment can safely exceed the MAWL. In the process, hydraulic cylinders are used to generate a specific Newton of force over a specific time interval while testing the material. This helps determine the elongation and ability of the material to retain its shape under the given force and time parameters.
A proof load test is done on the following equipment to determine the working load limit:
- Overhead cranes and supporting runways
- Patient hoists
- Motor vehicle lifts
- Building cleaning cradle and suspension equipment
- Goods and passenger lifts
- Telehandlers and forklifts
- Lifting accessories
- Chain blocks
- Web slings
Why Is Proof Load Testing Necessary?
As discussed, a proof load test is performed to meet the safety standards laid down by OSHA. According to the guidelines, a proof load test is mandatory for any equipment that will be used to lift heavy loads. It ensures that the equipment is safe to use and operate.
OSHA guidelines state that it’s the employers’ responsibility to provide a safe workplace to employees. The employer should ensure that all workers work with safe and easy-to-use equipment. Compliance with these guidelines helps minimize injuries and protects people’s lives. Failure to abide by the guidelines, on the other hand, can lead to severe damage to life and property, and even hefty penalties.
Proof load testing has been effective in preventing accidents at the workplace, as it helps ensure that the lifting equipment is working within its maximum potency. So, it’s absolutely essential to have the equipment thoroughly tested by performing the load test procedure as it guarantees a good running condition.
Simply put, a proof load test is mandatory to affirm that any new or even existing equipment is safe to use. It helps ensure that critical equipment is safe to use and operate. The test also instils a sense of confidence among the workers that they are working in a safe and secure environment.
Heavy lifting equipment must be tested every year to ensure that it is safe and working without any issues. The test must be performed by trained experts, and a load test certificate must be issued post the test.
Apart from load test, other vital inspections are also performed. This includes welding inspections, structural checkups, visual inspections, nondestructive tests, magnetic particle inspections, and more.
Proof load testing is mandatory to ensure the efficacy of the lifting equipment and ensure that it’s working properly. There’s no denying that it helps avoid accidents and other unfortunate incidents that can occur otherwise. Periodic proof load testing by trained experts ensures that the device is ready and safe for use at the operational level.