Page 81 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

PIPING

PIPING 2.31

FIGURE 2.6 Tapered thread screwed joint.

Screwed
A screwed joint can be used for any plain end pipe that has the necessary wall strength to
have threads cut into it. A screwed joint requires that threads be cut on the outside of a pipe
(male threads) and the inside of a fitting (female threads). The threads used for pipes are
known as American Tapered Pipe Threads (APT), and may be referred to as internal (APTI)
or external (APTE). The joint is assembled by placing the male thread inside the female
thread and turning the fitting or pipe until the joint is tight. The male thread is sealed prior
to assembly by pipe joint compound or Teflon tape in order to prevent water from seeping
past the threads. It is important to clear the pipe of any burrs or chips resulting from the
cutting process.
The standard governing the fabrication of this joint for service and utility systems is
ANSI B 2.1: American Standard Tapered Pipe Threads.
This type of joint is inexpensive and easy to fabricate. It is generally restricted to piping
3 in or smaller, because of the great effort required to turn larger sized pipe when making
up the joint.
Refer to Fig. 2.6 for an illustration of a tapered thread screwed joint.

Soldered
Also known as a “sweat joint,” soldering is a process used to join metallic pipe below its
melting point using an alloy that produces a metal solvent action between pipe and solder
at a relatively low temperature.
Solder is an alloy that melts at a temperature of less than 1000°F. Nonpotable water lines
can use a solder of 50-50 tin-lead. The Safe Drinking Water Act banned the use of lead in
solder and flux, requiring the use of lead-free solder. A commonly used lead-free filler alloy
is tin and antimony (95% tin, 5% antimony) and other filler metals, often with proprietary
alloys. Solder comes in the form of a flexible roll approximately 1/8 in in diameter. The
joint is fabricated by placing flux on the clean male pipe and inserting it fully into a clean
socket end on a fitting. The assembly is heated enough to melt the solder. The solder is
then applied completely around the perimeter. Capillary action draws the solder throughout
the entire joint. When the solder cools, it adheres to the walls of both the pipe and fitting
creating a leakproof joint.
Flux is a material with a consistency of paste, spread over the entire pipe end and used
to remove an oxide film and eliminate oxidation during the heat generated by the jointing
process. It also aids in the drawing of solder into the joint by producing a “wetting” action.
The use of a water soluble flux is now a code requirement.

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