Proofload

Proofload, or proof load, refers to the application of a specified force to a component, assembly, or structure to demonstrate that it can perform its intended function under service conditions. It is a form of proof testing used across engineering disciplines to verify design adequacy, manufacturing quality, or proper installation. The term is sometimes written as proofload or as two words; context usually clarifies its meaning.

The test involves applying a controlled load—typically a multiple of the service or design load but below the material’s expected ultimate strength—using hydraulic, pneumatic, or mechanical actuators. The load is applied gradually, held for a defined period, and then removed. Measurements of displacement, strain, leakage, or other responses are recorded to assess whether the component remains within allowable tolerances. Acceptance criteria usually specify no excessive permanent deformation, no leakage, no cracking, and no unsafe residual conditions after unloading.

Applications include lifting equipment and rigging, fasteners and joints, structural members, pressure vessels, and aerospace or automotive components. It is common in certification, quality assurance, repair validation, and pre-installation testing. In many standards, the proof load is selected to reveal defects or poor workmanship without causing catastrophic damage; it is distinct from destructive testing and from the ultimate or collapse load.

The concept of proof load is complemented by related notions such as proof testing procedures, load-rating, and safety factors, and is guided by national and international standards and manufacturer specifications.