Published: 20/05/2024

In industries where cranes and other heavy lifting equipment are required for everyday operations, safety and reliability are crucial.

From construction sites to offshore platforms, the strength and robustness of lifting equipment must be regularly assessed to ensure they can withstand the demands of heavy loads and rigorous use.

This is where proof test bags come into play, serving as essential tools for load testing, certification and calibration.

As one of the world’s leading manufacturers of proof test bags, we’ll explore how these bags contribute to the safety of lifting operations across various industries…


What are proof test bags?

Proof test bags – also known as load test bags or crane test bags – are water-filled containers that are used as a very heavy weight to demonstrate the fitness of a load-bearing structure.

Proof test bags are regularly used to assess the maximum weight capacity of cranes and other lifting machinery, which allows for compliance with safety standards, certifications and inspections.

Additionally, proof test bags can stimulate real-world scenarios for training procedures in a controlled environment – or for research and development projects to evaluate the performance of new cranes, lifting attachments or other structural components.

Not only are our proof test bags used in construction, defence and engineering industries, but they are also common in offshore and marine environments – such as oil rigs, ships and offshore platforms – to ensure the safe operation of cranes in challenging conditions.

For example, we designed and manufactured a bespoke 48-tonne capacity bag to be used in a ‘moon pool’ on board a vessel in Asia. We adopted a non-standard cylindrical design, including several circumferential strengthening bands, to achieve the desired load within the available space.


The benefits of proof test bags

Proof test bags offer a range of advantages that contribute to safe lifting operations.

From their ability to provide non-destructive testing, to their versatile load capacities, these bags play a crucial role in ensuring that lifting equipment can safely withstand its intended loads.


Safe load testing

Unlike traditional methods of crane testing, such as the use of concrete or steel weights, water-filled proof test bags are a more versatile and convenient alternative that minimises the risk of damage to the crane or lifting equipment being tested and are far easier to transport than their counterparts.

Our crane test bags are designed with a trunk and pulley assembly system for safe and controlled water drainage after testing. This feature allows for easy and efficient removal of water from the bags, minimising the risk of spills or accidents during the testing process.

Here at Structure-flex, our crane test bags up to 35T are manufactured with a minimum proven safety factor of 6:1, meaning they can withstand forces of at least six times their rated safe working load. Larger bags are tested at 4:1 or via finite element analysis modelling when larger capacities do not fit in any dynamic test rig.

This ensures your testing operations are handled with the upmost strength and reliability.


Versatile and bespoke

Water-filled proof test bags are used for a range of testing operations, including load testing cranes, winches and davits, as well as platforms, structures and lifeboat testing.

Ranging from 1 to 100 tonnes, these bags can accommodate a wide range of testing operations from small-scale tests to heavy-duty evaluations. This versatility ensures that you can select the appropriate bag size for your specific lifting equipment and testing needs.

Here at Structure-flex, we offer bespoke capacity options to accommodate unique requirements or project-specific demands.

We also provide low head options (shorter bags) with capacities from 1 to 15 tonnes to suit testing in limited height environments.

Our custom solutions ensure that you have the right equipment for the job, tailored to your exact specifications.


Robust and durable

Constructed from high-strength PVC-coated polyester textile, crane test bags are designed to withstand the demands of rigorous testing environments, making them not only robust but incredibly flexible.

The PVC coating enhances the bag's resistance to abrasion, tearing and punctures, ensuring durability even under challenging conditions.

Here at Structure-flex, we use radio/high frequency welding on all seams to provide a high-strength join, making them exceptionally water-tight and minimising the risk of seam failure even if dropped during testing.

This thorough construction process results in proof test bags that offer unmatched reliability and performance, making them essential equipment for your load testing operations.


Efficient and portable

Proof test bags are simple to operate, with a single point attachment system allowing for efficient setup and usage during testing procedures.

When not in use, these bags can be easily folded for compact storage, saving valuable space in storage areas or vehicles. This makes them perfect for transporting to testing sites.

Whether you’re load testing cranes on construction sites or assessing lifting equipment in industrial facilities, proof test bags offer convenience and practicality for any testing operation.


How can Structure-flex help you?

At Structure-flex, we have over 30 years’ experience designing and manufacturing for a comprehensive range of testing equipment.

We specialise in the supply of proof load testing bags for a wide range of industries, including marine construction, oil and gas, and crane, winch and davit manufacturers.

With our first-class range of proof test bags and moon pool test bags, we've established an unrivalled reputation for quality and reliability in the industry.

Contact us today to discuss your load testing requirements and discover how Structure-flex can help you: