Page 217 - Trenchless Technology Piping Installation and Inspection

Pipe and Pipe Installation Considerations 181

T5 female

T5 male
T7 female

T7 male
O rings
FIGURE 4.34 Interlocking jointing system. (Source: Permalok.)

pipe axis. Its unique machined groove makes stabbing and aligning
easy and quick. Also, the Permalok design, combined with the use of
a sealant such as RTV silicone, prevents leakage under considerable
pressure. Standard specifications, listed in Table 4.19, ensure that all
pipe manufactured by Permalok meet guidelines. The T5 profile was
patented for steel pipe casing applications in 1993 and has been used
in numerous trenchless excavation projects nationwide. The T7 pro-
file is capable of withstanding pressures of up to 300 psi, and is used
in trenchless pressure pipe applications. Figure 4.34 illustrates the
Permalok interlocking jointing system.

Advantages and Limitations Table 4.20 lists some of the advantages
and limitations of steel pipe. With its high tensile strength, steel
pipes are capable of handling high pressures in water transmission
applications. The high compressive strength of steel pipe makes it a
good material for jacking and boring. Assembly of nonweld joints is
relatively easy owing to push-on bell-and-spigot gasket joints. Steel
pipe has been known to adapt well in locations where ground move-
ments occur. Good hydraulic properties of internally lined steel
pipe make it ideal for use in municipal water systems. The avail-
ability of various methods and standards for both internal and
external corrosion significantly prolongs the useful design life of
the pipe.
Though various corrosion protection mechanisms are available,
the pipe is highly prone to corrosion attacks unless the protections are
used. This can be costly. In large diameters, the pipe’s ability to han-
dle external pressure is low. Air vacuum valves must be used in large-
diameter lines to eliminate the possibility of pipe collapse, but this is
an added cost to the system. Welding of pipe joints requires skilled
labor and is time consuming.