Introduction

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 training and qualification of welders, 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

How is a discontinuity defined?

In welding a discontinuity is any interruption in the uniform nature of a weld:

• Seams and laps

• Laminations

• Weld undercut

• Cracks (usually considered defects)

• Weld porosity

• Non-metallic inclusions

• Hydrogen inclusions

• Many others

How is a defect defined?

A defect is a non-conforming discontinuity, meaning all discontinuities are not defects but all defects are discontinuities.

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...