Wastewater Conveyance - Wastewater Operators - page 180

4.10.2 advantages of Tubing
To this point, with regard to the design requirements, reliability,
and maintenance activities related to using tubing vs. piping, we have
pointed out several advantages of tubing. These advantages can be clas-
sified as mechanical or chemical advantages.
4.10.2.1 Mechanical Advantages of Tubing
Probably the major mechanical advantage of using tubing is its rel-
atively small diameter and its flexibility, which makes it user friendly
in tight spaces where piping would be difficult to install and to main-
tain (e.g., for the tightening, repair, or replacement of fittings). Another
mechanical advantage of tubing important to wastewater maintenance
operators is the ability of tubing to absorb shock from water hammer .
Water hammer can occur whenever fluid flow is started or stopped. In
wastewater operations, certain fluid flow lines have a frequent on/off
cycle. In a conventional piping system, this may produce vibration,
which is transmitted along the rigid conduit, shaking joints, valves, and
other fittings. The resulting damage usually results in leaks, which,
of course, must be repaired. In addition, the piping supports can also
be damaged. When tubing, with its built-in flexibility, is used in place
of conventional iron piping, however, the conduit absorbs most of the
vibration and shock. The result is far less wear and tear on the fittings
and other appurtenances.
As mentioned, sections of tubing are typically connected by means
of soldering, brazing, or welding rather than by threaded joints, although
steel tubing is sometimes joined by threading. In addition to the advan-
tages in cost and time savings, not using threaded joints precludes other
problems. For example, any time piping is threaded it is weakened. At
the same time, threading is commonly used for most piping systems and
usually presents no problem.
Another advantage of tubing over iron piping is the difference in
inner-wall surfaces between the two. Specifically, tubing generally has a
smoother inner-wall surface than does iron piping. This smoother inner-
wall characteristic aids in reducing turbulent flow (and the resulting
wasted energy and decreased pressure) in tubing. Flow in the smoother
walled tubing is more laminar; that is, it has less turbulence. Laminar
flow is characterized as flow in layers—very thin layers. (Somewhat
structurally analogous to this liquid laminar flow phenomenon is wood-
type products such as kitchen cabinets, many of which are constructed
of laminated materials.)
This might be a good time to address laminar flow inside a sec-
tion of tubing. First, we need to discuss both laminar and turbulent
flow to point out the distinct difference between them. Simply, in lam-
inar flow, streamlines remain parallel to one another and no mixing
occurs between adjacent layers. In turbulent flow, mixing occurs across
the pipe. The distinction between the two regimes lies in the fact that
the shear stress in laminar flow results from viscosity, while that in