Test Instruction
A test instruction specifies how a weld is to be tested: test method, equipment settings, test scope, and acceptable limits. Without clear guidelines, every inspector tests differently – leading to inconsistent results and missed flaws. It ensures reproducible test statements and prevents costly rework or component failure.
Physical-Chemical Mechanism of Action
The test instruction specifies the physical method used to inspect the weld: ultrasonic waves are coupled in, X-rays penetrate the part, or dye penetrant seeps into surface cracks. It determines the exact parameters such as frequency, voltage, dwell time, and signal evaluation. Only with consistent test conditions can the readings be reliably correlated with the actual flaw state.
Metallurgical Relevance & Welding Risks
A missing or incorrect test instruction leads to two risks: Critical flaws like cracks, lack of fusion, or porosity go undetected because the wrong method is chosen or the inspection area is not fully covered. Or the method is set too sensitively – then harmless indications show up, leading to unnecessary repair welds. Both cost time, money, and can weaken part strength.
Workshop Practice & Instructions
Before any inspection, the valid test instruction must be available at the work station and understood by the inspector. It contains specific requirements: test method per standard (e.g., visual inspection per ISO 17637, ultrasonic per ISO 17640), calibration status of equipment, inspection extent in percent, acceptance group per ISO 5817, and required surface preparation. If there are deviations – such as incorrect surface roughness or insufficient lighting – the inspection must be stopped and corrected.