Chapter 11: Inspection & Discontinuities
Inventing is a combination of brains and materials. The more brains you use, the less materials you need.
Charles F. Kettering
Whenever the failure of a weld could lead to financial loss, property damage, personal injury, or death, it is important to know that it will meet its design requirements. These may be set by the designer, fabricator, customer, or law depending on the application. In order to assure compliance with these requirements, a quality control program is needed. A quality control program includes weldor training and qualification, incoming materials testing, record keeping, and weld inspection. This chapter focuses on how welds are inspected and what discontinuities and defects are common in fusion welding processes.
Discontinuities and Defects
What is the difference between a weld discontinuity and a weld defect?
A discontinuity is some interruption of the weld's typical structure, a location in the weld that is not like the usual parts of the weld. It can be a change in mechanical, metallurgical, or physical characteristics of the weld and its immediately surrounding base metal. A discontinuity only becomes a defect when the size of one discontinuity or the number of separate discontinuities (because of their cumulative effect) prevents the weld from meeting the applicable acceptance standard. A defect makes a weld rejectable. A weld with discontinuities may be acceptable under one code and be rejectable under another more strict code, since each code sets its own levels of acceptable discontinuities.
Why are we concerned with discontinuities?