Page 216 - Trenchless Technology Piping Installation and Inspection

180 Cha pte r F o u r

Joints There are several types of welded joints available for steel
pipe, each suited for a specific application:
1. Bell-and-spigot lap-welded joints
2. Butt-welded joints (single-V butt-welded, and double-V butt-
welded)
3. Butt strap welded joints
4. Mitered lap-welded joints
There are also a number of nonwelded joints:

1. Bell-and-spigot rubber gasket joints
2. Harness joints
3. Carnegie shape rubber gasket joints
4. Mechanical couplings
5. Split-sleeve mechanical coupling

For steel casing pipe used in boring and pipe-jacking applica-
tions, it is important that there are no irregularities in alignment at
the joints. If the casing is not straight, the ability of the contractor
to keep the pipe in-line and on grade is affected. Lap-welded joint
products are not recommended for jacking and boring installa-
tions. Though spiral-welded pipes can be used for casing, it is a
common practice to use a straight seam or seamless pipe. For joint-
ing, both ends of the pipe can be beveled for welding, as in the
single-V butt-welded joint, Fig. 4.33. Another recommendation for
achieving a good circumferential weld at the joint is to bevel one
end of the casing pipe to a standard 37° bevel, and square cutting
the other end.
For casing and pressure pipe trenchless applications, a patented
product line, Permalok, offers two mechanical push-on joints. It is
particularly attractive to the trenchless excavation industry because
the joints are designed to be flush with the interior and exterior sur-
faces of the pipe (see Fig. 4.34). This joint type eliminates the time
required for welding traditional-type steel pipes. Although using the
Permalok pipe is approximately 2.5 times faster than welding, it costs
more. Permalok joints are used for HDD, pipe ramming, and hori-
zontal auger boring. Joint quality is further enhanced because the
Permalok connector is consistently round and perpendicular to the

FIGURE 4.33 Single-V butt-welded joint.