2.7 Verification, Test Machines, Calibration & NDT Methods

Verification, Test Machines, Calibration and NDT

Verification is the evidence-based process used to show that lifting equipment meets specified requirements. It begins with design and manufacture, continues through conformity assessment and installation, and returns after repairs, modifications or safety-significant events. It is broader than proof loading.

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Verification Methods

The applicable product or design standard determines the evidence. It may include material certificates, design calculations, dimensional checks, manufacturing inspection, proof tests, sample break tests, functional tests and non-destructive testing. Not every method suits every product. For example, destructive testing is normally performed on representative samples, not the item entering service, and overload testing can harm equipment when it is not justified.

A proof test demonstrates performance at a specified force without unacceptable permanent change. A breaking test continues to failure on a sample to verify minimum breaking force. A functional test checks controls, brakes, limits or safety devices. None of those automatically replaces a competent person's thorough examination of the actual in-service item.

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Test-machine Control

A displayed number is reliable only inside the machine's calibrated range and uncertainty. The test procedure must establish:

• the required force accuracy and resolution;
• the load cell and machine range;
• traceability to recognised measurement standards;
• calibration or verification interval;
• loading rate, alignment and fixtures;
• environmental conditions; and
• acceptance criteria and record content.

Those values come from the standard being worked to and the laboratory's quality system. Do not apply a remembered ±1%, ±2% or 12-month interval to every test. ISO 7500-1 classifies verification of uniaxial testing machines, but the product procedure still determines which class, range and interval are acceptable. A calibration certificate also identifies the valid range and uncertainty; extra decimal places do not improve accuracy.

Before testing, confirm that fixtures do not introduce bending or side load. The operator should approach the target smoothly, avoid shock, hold for the specified time where required, and inspect or measure the item using the stated post-test criteria.

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Common NDT Methods

Visual Testing

Visual examination is the first method: clean the surface, provide adequate light and access, and look for cracks, corrosion, wear, distortion, heat damage and unauthorised repair. Magnification and dimensional gauges may extend it.

Dye Penetrant Testing

Dye penetrant reveals surface-breaking discontinuities in clean, non-porous materials. Penetrant enters the opening, excess is removed, and developer draws out an indication. It cannot find a fully subsurface defect, and poor cleaning can mask or create indications.

Magnetic Particle Testing

MPI is used on suitable ferromagnetic materials. Magnetisation causes flux leakage at a surface or near-surface discontinuity, attracting the detection particles. Field direction matters, so more than one magnetisation direction may be needed. MPI is not suitable for aluminium or austenitic stainless steel.

Ultrasonic Testing

Ultrasonic testing sends high-frequency sound into the component and interprets reflected signals. It can find internal discontinuities and measure thickness, but geometry, surface condition, calibration blocks and operator skill affect results.

Radiography and Eddy Current

Radiography produces an image from penetrating radiation and requires stringent exposure control. Eddy-current testing detects changes in conductive material near the surface and can be useful for wires, tubes and sorting applications. Method selection follows the material, likely defect orientation, access and acceptance standard.

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Hardness, Impact and Material Tests

Brinell, Rockwell and Vickers tests measure hardness by different indentation methods; the correct method and conversion depend on material and specification. Hardness is not the same as tensile strength or toughness. A Charpy V-notch test measures energy absorbed when a notched specimen fractures at a specified temperature, providing an indication of notch toughness.

NDT indications are not automatically rejectable defects. A qualified procedure states how the indication is evaluated and which acceptance criteria apply. Conversely, “no indication” does not prove unlimited life.

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In-service Boundary

LOLER thorough examination is a systematic assessment by a competent person. Testing or NDT is added where the examination scheme, history, condition, manufacturer or suspected deterioration justifies it. HSE states that most lifting equipment does not require routine testing during every thorough examination.

After an authorised repair or modification, decide what design review, inspection, NDT, functional test or load test is needed before return to service. Record the equipment identity, procedure, instruments, results, acceptance criteria and authorisation. The governing principle is right method, right range, right criterion—not “test everything as hard as possible.”