Page 18 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Abbreviations, Terminology and Welding Symbols

of weld will be determined by the joint set-up but the most
commonly used welds are butt or fillet welds.
Full penetration butt welds are normally the strongest type
of weld with the strength contained within the throat of the
weld, as indicated in Fig. 1.2(a). The throat is equal to the
thinnest of the parent materials to be joined.
Fillet welds also contain their strength in the throat and
the design throat size is normally (but not always) based on
the leg size, as shown in Fig. 1.2(b). In visual inspections we
can normally work out the design throat size of a mitre fillet
with equal leg lengths by multiplying the leg length by 0.707.
Conversely, the leg length can be calculated by multiplying
the design throat by 1.414.
Butt weld joint preparation consists of preparing both
edges and then arranging them together to permit the
required depth of weld penetration to be achieved. Full
penetration welds are the most common but many applica-
tions will only require partial penetration if the welded joint
is either lightly loaded or is just a sealing weld.
The main purpose of the joint preparation is to permit the
required level of fusion between the joint faces. The type of
weld preparation applied will therefore be dependent upon
the thickness of the material and the welding process to be
used. Some typical butt weld joint preparations are shown in
Fig. 1.3.
Single-sided preparations allow welding to take place from
one side whereas double-sided preparations require welding
to be done from both sides. A major disadvantage of having
access to only one side is that the other side of the initial root
run cannot be accessed to carry out removal of welding-
induced defects. An example of this would be where a large
gap was required to permit fusion throughout the whole
cross-section of the weld but excessive penetration then
occurred. Good control and formation of the root weld must
therefore be maintained at the time of welding, and this can
be assisted by using the root control measures shown in Fig.
1.4.

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200901QG Welding chap1.3d Page 3 of 16