The reference line is one of the most important elements on the welding symbol. All the other elements that describe the weld are on or located around this line. The reference line has a leader and arrow that points to where the information applies. It may also have a tail that has information about the process, specification, or other notes that do not normally have an element that describes them. If the elements on the reference line describe the necessary details (as it does in most cases) the tail is not used.
See the examples below:
In the above examples one of the reference lines has multiple arrows that are used to show the same weld in three locations that are relatively close to each other. There is also a reference line that has an arrow break. The break in the arrow is used to indicate the joint member that is to receive the edge preparation.
KEY POINT: the arrow points to the bevel where the bevel needs to be prepared.
One of the most important things about the reference line and the welding symbol is the top and bottom of the horizontal line. The actual symbol that shows the type of weld and the elements surrounding it that detail the weld can be placed on the top of the line or on the bottom of the line.
KEY POINTS: symbols on the bottom of the reference line mean weld the side of the joint the arrow is touching or pointing to. Symbols on the top of the reference line mean apply the weld to the other side of the joint, or the side opposite to where the arrow is pointing.
This method is used because sometimes the welding symbol must be drawn on the blueprint on the other side of the joint. When symbols appear on both sides of the reference line it means weld both sides of the joint.
If the reference line has a weld symbol on both sides of the reference line they may, or may not be the same weld on both sides of the joint. Remember the rule to apply the right weld to the right side.