Modern non-destructive tests are used by manufacturers for several reasons, ranging from product reliability verification to improved product design or manufacturing process control and cost reduction. In the ever increasing search for lower cost and higher efficiency, products are designed to be lighter, smaller and more fuel efficient than they used to be while still bearing the same load – or more – as before.
This is achieved, for example, through the usage of new materials. And the American Society for Nondestructive Testing cautions “there is a record of an aircraft being built from an alloy whose work hardening, notch resistance and fatigue life were not well known. After relatively short periods of service some of these aircraft suffered disastrous failures. Sufficient and proper non-destructive tests could have saved many lives”.
Aerospace is one of the many areas in which NDT methods are used to detect material defects and is the main focus of this article. For obvious reasons, it is vital for a testing method to be able to detect flaws, in both raw materials and parts being manufactured, without impairing the use of the component. This starts with each individual component, adding up to the final assembly; in this case, the airframe or the aircraft engine.
However, for aerospace, it is not enough to perform non-destructive tests: it is also vital to monitor those involved in the administering of these tests to ensure that this function is being performed, interpreted, the results accurately reported and – where applicable – issues are being resolved appropriately. A major part of the role of supplier surveillance has been allocated by the industry to the Performance Review Institute (PRI), partnering with a number of aerospace primes through the Nadcap Program.
Nadcap is the leading worldwide cooperative program of major companies designed to manage a cost-effective consensus approach to special processes & products and provide continuous improvement within the aerospace & automotive industries. Nadcap is part of PRI’s Customer Solutions & Support, which exists to provide quality customer-driven and cost-effective business solutions to continually improve organizations throughout the world. NDT is one of the special processes included in the scope of the Nadcap accreditation services.
Major aerospace organizations such as Airbus, The Boeing Company, GE Aviation and Rolls-Royce, Honeywell Aerospace and Pratt & Whitney work together with industry suppliers to develop the standards that a supplier must comply with in order to become, and remain, Nadcap accredited. Increasingly, aerospace prime manufacturers have mandated Nadcap accreditation for their suppliers, as this is a globally recognized industry-wide standard of work designed to maximize the probability that a part manufactured in Beijing is of equal quality to a part manufactured in Bangalore.
Nadcap covers the following NDT methods:
- Liquid Penetrant Inspection (LPI)
- Magnetic Particle Inspection (MPI)
- Ultrasonic Testing (UT)
- Radiographic Testing (RT)
While the types of NDT methods have not significantly changed over time, they are certainly more sophisticated than they used to be. This means that industry must continually identify more robust methods for safeguarding the reliability of NDT. Nadcap is the primary system that the aerospace industry has been using since 1990 to achieve this goal. Nadcap conducts over 900 NDT audits around the world each year. Extensive data is collected on nonconformances that are identified during these audits and compiled. This data is then shared with the industry, prime manufacturers and suppliers alike, to attempt to improve the quality of the products and conformance to the standards.
As well as special process work, the special process personnel must also be of the highest quality. To meet customer demand, PRI has developed eQuaLearn, a professional development branch of PRI and which offers courses in topics such as Root Cause Corrective Action, Internal Auditing and Problem Solving Tools, as well as more technical topics such as Pyrometry. These courses were developed with input and validation from industry experts. l
Mark Aubele is Senior NDT Staff Engineer for NDT at PRI