A seam weld is a continuous weld made on or between overlapping members of a joint. It is a continuous weld that may consist of a single weld or a series of overlapping spot welds. The seam-weld symbol, =©= may have an arrow side or other side significance, Figure 20.1(a) and (b). Because of the nature of the weld, the symbol is not used with a both sides significance. When an arrow side or other side significance is not intended, the seam-weld symbol is located astride the reference line, Figure 20.1(c). When the symbol is so shown, it indicates the weld is located between the members. A tail must be used with this symbol to indicate the process reference.

Dimensions that can be applied to the seam-weld symbol include:

Size of the weld expressed in fractions or decimals of an inch (with or without inch marks) or in millime­ters when the drawing is metric.

Strength of the weld in terms of the shear strength of the weld in pounds per linear inch or in Newtons per millimeter. When expressed in Newtons, the letter “N” is added to the value.

Extent of the weld.

Center-to-center spacing (pitch) of the weld.

Dimensions are applied on the same side of the reference line as the weld symbol. When the symbol is located astride the reference line, the dimensions can be placed on either side of the reference line.

The size of a seam weld is placed to the left of the symbol and indicates the width of the weld, Figure 20.2.

The value for the strength of a seam weld is placed to the left of the symbol, and is used in place of the size dimension when the strength of the weld is a required specification, Figure 20.3 and Figure 20.4.

The dimension for the length or extent of a seam weld is placed to the right of the symbol, Figure 20.5. However, when the weld extends the full length of the joint, or when it extends the full distance between abrupt changes in the direction of welding, the length dimension is not necessary.

When the seam weld extends less than the full length of the joint, or less than the dis­tance between abrupt changes in the direction of welding, the extent of the weld is shown,

Figure 20.6 and Figure 20.7.

When the center-to-center spacing (pitch) dimension for intermittent seam welds is to be shown, it is placed to the right of the length dimension, Figure 20.8 and Figure 20.9.

A welding symbol specifying the length and pitch of a seam weld without reference to a detail drawing signifies the length and pitch are measured parallel to the axis of the joint to be welded.

When an intermittent seam weld is not made parallel to the joint or axis of the weld, a detailed drawing must be used and reference made to it in the tail of the arrow. For example, the weld shown in Figure 20.10 is to be made at right angles to the joint.

FLUSH-CONTOUR SYMBOL

The flush-contour symbol may be applied to the seam-weld symbol to indicate the member to be made flush. When a flat finish is required, a note is placed in the tail to indicate this. The method for a postweld finish may also be indicated, Figure 20.11. These are not applied to the seam-weld symbol when it is centered astride the reference line as a weld between members is indicated.