Quality assurance destructive testing

The second approach - creation of systems for non-destructive testing quality assurance in compliance with ISO standards 9000 series - considers the quality system as an assembly of organisational strueture, procedures, processes and resources necessary for overall quality management at the laboratory. This approach requires methodieal development. 

The trainee will visit other departments in the head office to learn about the supporting facilities which are available such as non-destructive testing, metallurgical and failure analysis, hazard analysis and quality assurance. Emphasis is laid on safety, i.e. the integrity and safety of the plant in operation and on the surveyor s own personal safety. It is important that the trainee understands the techniques involved, particularly the limitations of their application. 

Any good quality-assurance system should also assess the quality of performance in practice as well as in theory. With no currently available, effective, non-destructive test, critical areas or components may only be assessed for voids (acoustic methods are useful here) and, where possible, proof loaded. Other than this, test coupons or parts need to accompany the components themselves through the assembly process so that appropriate, systematic destructive tests may be carried out. A check-list for safety critical items is given in Table 6.1. 

Ceramographic methods have proven indispensable in the characterization of thermally sprayed coatings, in which non-destructive testing methods for purposes of quality assurance have only limited applicability. Characteristic properties of a coating, such as its thickness, structure, porosity, and adhesion to the base material, as well as the hardness of individual phases or the overall composite, can be accurately evaluated by applying these ceramographic methods to the polished section. 

Particular attention needs to be paid to establishing an effective system of quality assurance for adhesive connections. Non-destructive test methods based on ultrasound, X-rays or the measurement of electrical or thermal conductivity are available but only of limited value in practice. Specific data on adhesion cannot always be obtained by these methods. This section examines the issue of quality assurance from a practical point of view. Many years of experience have shown that only a quality assurance system that takes into account the specific features of adhesive bonding technology can produce consistently satisfactory results over an extended production period. The information outlined here should be viewed as a general checklist to be adapted to the specific requirements of each manufacturing environment. 

An effective quality assurance system for elastic adhesives depends on continuous monitoring and checking of all quality-related parameters. If these are maintained within the prescribed limits, then the quality of the adhesive connection is guaranteed with little or no need to supplement these control measures with time-consuming and costly destructive testing. The overall cost of quality assurance can therefore be kept down to a commercially acceptable level. 

Contrary to the belief that 100 percent inspection means 100 percent quality, 100 percent inspection is not only impractical but also unreliable, ineffective, and impossible in the case of destructive testing. Acceptance sampling drastically reduces the cost of inspection and in most cases provides better quality assurance than 100 percent inspection due to lower inspector fatigue and boredom. At this point, it is important to understand that the acceptance sampling technique does not control quality but it helps in determining the course of action. Based on the acceptance sampling plan, one may decide to accept or reject a particular lot. 

---