Proof Load Testing

A proof load test applies a specified force — typically 1.25 to 2 times a component's rated working load limit — to verify structural integrity before the component is placed in service. Required by ASME B30 for below-the-hook lifting equipment and by OSHA for certain rigging configurations, the test uses a calibrated dynamometer to apply and verify the test load.

Yes. A proof load test performed with an uncalibrated instrument cannot demonstrate that the correct test force was applied — defeating the purpose of the test and creating legal and compliance liability. The calibration certificate of the instrument is part of the required test documentation. Dynamic Measurement Systems' NIST-traceable certificates are designed to satisfy proof load test audit requirements.

The working load limit (WLL) is the maximum load a device is rated to carry in normal service. The proof load is the test force applied during certification — typically 1.25 to 2 times the WLL. The proof load verifies a safety margin above the rated WLL. It is a one-time verification test load, not the safe working load.