Chapter 29 Shielded Metal Arc Welding 789
Copyright Goodheart-Willcox Co., Inc.
horizontal pipes fi xed in position end to end, the weld
must be made all around the circumference of the joint.
AWS designates this as a 5G weld. A 5F weld is formed
when a horizontal pipe is connected to a fl at surface or
fl ange in a vertical plane. If the pipe is nearer a
45° angle than horizontal, the AWS designations are
6G and 6F. Skilled pipe welders are some of the highest
paid welders. See Figure 29-17.
Surface Preparation
Surface preparation includes cleaning and fi tting
the pieces to be welded. Under ideal conditions,
surfaces to be welded should be clean from all
contaminants and oxides. Surface contaminants
have an insulating effect that results in the need for
higher amperage. Contaminants on the surface of
welded materials can cause weak points or inclusions.
Inclusions are foreign materials, such as slag, trapped within the fi nished
weld. Some electrodes, such as E6010 and E6011, have better cleaning
properties than others. However, clean and properly fi tted surfaces always
yield better results for the welder.
Cleaning prior to welding may be as simple as brushing with a wire
brush, Figure 29-18. Cleaning reclaimed steel may entail removal of rust, oil,
grease, dirt, and paint residues. New steel may also have oily residues or mill
scale from the manufacturing process. When cleaning with a wire brush is
not enough, edges need to be dressed with a grinder prior to welding.
Welded parts should be closely fi tted with a small but uniform gap
between them. Thin materials can be welded with virtually no gap. Thicker
metals require some type of edge preparation to enable adequate weld
Lisa F. Young/Shutterstock.com
Figure 29-16. Overhead welding refers to the position of the electrode, not the location of
the welder. Both welders shown are welding in the overhead position.
Wes Hancock, Caldwell High School
shinobi/Shutterstock.com
Figure 29-17. Pipeline welders work mostly
outdoors and are well paid.