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It is normal practice to test 10% of welds by NDT (Non-Destructive Testing). This could be either by Magnet Particle Testing (MT) or Ultrasonic Testing (UT). MT is good for structural steel as the steel has magnetic properties to allow this. All welds for structural elements should to be undertaken by trained and competent welder. These welders are trained and tested (certainly in Europe & US, not so in South Asia i find), and their work is checked regularly by Non-Destructive Testing (NDT) - i.e. visual inspection by someone who understands all aspects of welding, and is probably an experienced Welder who has re-trained to become a Weld Inspector., and is familiar with possible weld defects. Destructive Testing (DT) which is undertaken on samples, and inspected microscopically, is done on sample pieces only, and verifies the welders compentencies etc. In most building projects non-destructive testing (NDT) is undertaken: 1. The welder cleans and visually inspect his own welding; 2. Welding Inspector (QA) inspects all critical welds by visual inspection - 10% of critical members - say connections with high moments and tensile forces. 3. Standards: British (BS), European (EN), International (ISO) Standards: a. BS EN ISO 17640:2017 - NDT testing of Welds: This is the international standard for manual ultrasonic testing of fusion-welded joints in metallic materials thicker than or equal to 8mm which exhibit low ultrasonic attenuation. The standard’s guidelines detail specific testing techniques for metals that show weakened ultrasonic levels at temperatures of up to 60⁰C. It’s primarily designed for full penetration weld joints where both the welded and parent material are ferritic. b. BS EN ISO 5817 Welding: BS EN ISO 5817 is an international welding standard that provides guidelines on quality levels of imperfections in fusion-welded joints (except for beam welding) in all types of steel, nickel, titanium and their alloys. The purpose of this standard is to define dimensions of typical imperfections which might be expected in normal fabrication of fusion welded joints. It provides three sets of dimensional values to apply to a wide range of welded fabrication. They are designated by symbols B, C and D. Quality level B corresponds to the highest requirement on the finished weld. Several types of loads are considered, e.g. static load, thermal load, corrosion load, pressure load. The quality levels refer to production and good workmanship. BS EN ISO 5817 applies to joints with a material thickness ≥ 0,5 mm. It covers fully penetrated butt welds and all fillet welds. Its principles can also be applied to partial-penetration butt welds.