welding symbols on drawings pdf
The need to specify welds
The need to specify welds 1
It is sometimes argued that it is unnecessary to specify welds on
drawings and that the welder should be relied upon to deposit a suitable weld.
This practice can be extremely risky because the type and
size of the weld must be appropriate for the parent material and
service conditions of the fabrication, and the necessary information
and data are normally available only in the design office.
the instruction ‘weld here’
three ways to follow this instruction.
The instruction ‘weld here’, illustrated in
on a drawing because it is open to a number of different interpretations
a single fillet weld.
This weld is simple
and therefore cheap to apply but could be seriously deficient in
a double fillet weld, which takes longer to
apply. Unless access is available to both sides of the joint, it will be
impossible to weld it.
illustrates a T-butt/groove weld.
This weld normally
requires edge preparation on a horizontal member, and therefore is
more complex and expensive.
However, it may be essential for
certain service conditions.
It can be seen from the previous examples that major problems
will arise unless welded joints are carefully specified by the design
The situation is particularly critical where, for example, work
is placed with a subcontractor and the instructions need to be especially precise.
When it is required to indicate a weld on a drawing, it may seem
that the weld can simply be drawn as it will appear. In the majority
of cases, symbolic representation can be used to cut down the time
needed to complete the drawing and improve clarity.
To save time in drawing the edge preparation for a butt/groove
weld or the shape and size of a fillet weld, a set of weld symbols
can be used. These symbols are placed on a horizontal reference line.
This line is attached to an arrow line which points to the location
of the weld .
In the ISO system there are two parallel
reference lines, one solid and one dashed.
In the AWS system a solid
reference line is used.
The butt/groove welding symbols
illustrates a single-V butt/groove weld, which is the
commonest form of edge preparation for this type of weld.
This weld will be
limited to a maximum section thickness depending on the welding
If a backing strip is used, the section thickness can be
Guidance on edge preparations is included in BS EN 29692 and
ISO 9692: 1992, in which the range of thickness recommended for
this type of weld is 3–8mm.
Without a backing strip, a maximum section thickness of 4mm is
recommended with a gap equal to the thickness.
With a backing
strip, a gap of 6–8mm is recommended. Dimensions of edge preparations are not included with weld symbols in ISO 2553 but these
can be included with AWS symbols. This can make a drawing
complex and, in some cases, may lead to confusion.
It is preferable
to include details of edge preparations in a Welding Procedure Specification (WPS).
As stated previously, when ISO 2553 is used, the dimensions of
the edge preparations are not included as part of the welding symbol
and should be given as part of the WPS.
With the AWS system, the
depth of the groove can be specified by a number on the left hand
side of the weld symbol.
This dimension, subtracted from the
section thickness, will indicate the size of the root face
Welding symbols 2
Welding symbols 2 9
Fillet and edge welds, backing run or weld,
flare groove and bevel welds, and plug or
The symbols for fillet and edge welds, backing run or weld,
flare groove and bevel, and plug or slot welds are shown in Fig
Welding symbols 3
Spot and seam welds, surfacing, and steep
flanked butt welds
The symbols for resistance and arc spot and seam welds are shown
with reference lines (ISO) to indicate clearly the position of the
symbols in relation to the line.
AWS symbols would be similarly
placed on the reference line for resistance welds and below the line
for arc welds.
These symbols spot welds.
The upper illustration
resistance spot weld or projection weld requiring access from both
The lower illustration an arc spot weld made from one
side of the joint.
The reference line is on one side of the symbol.
illustrates seam welds.
The upper illustration
a resistance seam weld requiring access from both sides of the joint.
The lower illustration shows an arc seam weld made from one side
of the joint.