Phased-array ultrasonic testing (PAUT) in lieu of radiography (RT) on small-bore boiler tubes

Radiography of convection bank tube welds and other pressure part welds has been the industry go-to method for many years. However, production rates are slow and there are many occupational health and safety issues to be managed, often requiring temporary evacuation of the site during radiography events or restricting radiography to out of normal hours. Fabrication codes and standards across the world have recognised other non-destructive testing methods to quantify the integrity and soundness of weldments, especially ultrasonic techniques when looking for internal imperfections or defects in materials and weld configurations. These have proven very reliable within the pressure-equipment industry and will continue to do so. Ultrasonic methods and applications have continued to evolve since their introduction by improvements with advanced technologies and electronic hardware to achieve higher quality results and efficiencies in test-data acquisition. One of the additional benefits of an ultrasonic technique is that it can be carried out with minimal impact on other work in the area, i.e. there are no requirements for other staff to move from the area, as is necessary with conventional radiography. A phased-array ultrasonic technique has, therefore, been developed for use as an alternative to conventional radiography techniques in the testing of small-bore boiler tubes. Given clear and uninterrupted access to the work area, up to 70 butt welds can be tested per shift. Ultrasonic testing may be used in lieu of radiography for testing of welds in material thicknesses of 12.7 mm or less. The PAUT method has been validated for inspection of small-bore pipe butt welds such as convection bank tubes for compliance to codes such as AS4037 (1999) Pressure Equipment – Examination and Testing and ASME B31.3 – Code for Pressure Piping. ALS have developed robust inspection procedures for the application of PAUT in lieu of RT on carbon steel and limited application to austenitic stainless steels. This has been achieved through rigorous validation on a range of representative samples containing real defects and has evolved and improved over many years through application to tens of thousands of welds across dozens of projects. Key words Phased array, ultrasonic, small bore, radiography