Page 119 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 2 Common processes and techniques

4 Take the pipe from the machine and place a straight edge against the
back of the pipe. Mark the measurement of the second bend at point B
(Figure 2.28). INDUSTRY TIP
5 Put the pipe back into the machine and line the mark up with the centre of With the off-set bend, you
the former. may find it easier to make a
6 Bend the second bend and check with the template. welding rod template bent to

the required angle (say 45°).
Jointing low carbon steel pipe This can be used for both
There are three ways to joint low carbon steel pipe. These are: the first and second bends.
Remember to over-bend
1 threaded joints both bends by 5° to allow for
2 compression joints spring back.
3 welded joints.

We will look at the first two only, as welded joints are generally used only on
larger pipes in industrial applications and installations.

Threaded joints

Low carbon steel pipes can be jointed using threads to BS 21, which are
cut into the end of the pipes using either manual stocks and dies or electric
threading machines (see page 88 of this chapter). There are two kinds of
thread, as follows.

1 Tapered threads: a standard thread cut onto the ends of pipes and KEY POINT
blackheart malleable, male fittings to ensure a watertight, gas-tight or
steam-tight joint. The tube tightens the further it is screwed into the fitting. Male threads are external
2 Parallel threads: a screw thread of uniform diameter used on fittings such as threads; female threads
are internal threads.
sockets.

Threads taper towards the end of the tube Threads remain parallel throughout the length of the tube
p Figure 2.29 Tapered thread (left) and parallel thread (right)

There are two types of fittings that use threads. Fittings for low carbon steel
pipe are made from steel and malleable iron to BS EN 10242 (formerly BS 143) INDUSTRY TIP
and BS 1256. Steel fittings, although stronger than malleable iron, tend to be
more expensive. Malleable iron fittings fall into two groups: All threads are BSPT, which
stands for British Standard
1 Blackheart fittings with tapered female threads are identified by a square- Pipe Threads.
edged bead around the mouth of the fitting. These fittings are quite brittle
and susceptible to splitting if over-tightened.

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