Page 216 - Welding of Aluminium and its Alloys

11

Weld defects and quality control

11.1 Introduction

Previous chapters have covered those defects and losses in strength that
may be described as arising from metallurgical effects. This chapter covers
those defects that may be described as defects of geometry, their causes and
the non-destructive testing techniques that may be used to detect them.
Many of these defects are caused by the welder, because of either a lack
of care or a lack of skill, and emphasise the need for adequate training.
Similarly, if non-destructive testing is to be correctly performed and
defects accurately identified and sized, well-trained and experienced non-
destructive evaluation (NDE) operatives are needed. A simple and
inexpensive non-destructive examination technique that is sometimes
overlooked is that of a thorough visual examination by a suitably trained
and experienced welding inspector. Such an examination will identify many
defects, particularly those of shape as listed in Section 11.2 below.

11.2 Defects in arc welding
A list of weld defects and their causes is given in Table 11.1. Other defects
not listed are mainly those of geometry and include misshapen and incor-
rectly sized welds,variable cap width and height,weld face roughness,incom-
plete weld fill and asymmetry of fillet welds. These are all welder-induced
problems,requiring improved shop-floor discipline and/or welder retraining.
If the required acceptance level for the defects listed above is not con-
tained within a relevant application standard then it is the responsibility of
the designer to select the appropriate quality level. A readily available
specification to which the designer may refer for guidance is BS EN 30042
‘Arc Welded Joints in Weldable Alloys, Guidance on Quality Levels for
Imperfections’. This document contains three quality levels, B stringent, C
intermediate and D moderate, the choice of which depends upon design
considerations, subsequent fabrication activities such as rolling or pressing,

199