Therefore, pipes may have the same nominal diameters (outside diameters) but with different
inside diameters because of the different schedule numbers.
The usual schedule numbers are 10, 20, 30, 40, 60, 80, 100, 120, 140 and 160 with the thickness
increasing with the numbers.
These numbers are further classified as Standard (ST), Extra Strong (XS) and Double Extra
Strong (XXS) whereby applications requiring higher pressures will need pipes with thicker walls.
However, in the HVAC industry and for our mini chiller installation, a standard schedule 40 pipe
will suffice.
The steel pipes may be joined by several methods:
1. Arc welding
2. Thread (usually up to 50mm) with PTFE Teflon white tape
3. Flange with gaskets
2. Copper Pipes
Copper pipes are chosen for water piping because of their resistance to corrosion and ease of
installation. The pipes are light and ductile.
However, the cost of these pipes are higher compared with steel pipes (generally by 3 -
5 times).
The sizes of these copper pipes are defined by the ASTM (American Society for Testing and
Materials) standard B88 for water and drain services. See Appendix 2.
There is also another ASTM standard B280 which specifies the sizes of pipes used for
refrigeration services with different wall thickness. This standard uses the outside diameter as
the nominal size.
These pipes are also generally sold in lengths of 6 meters.
Generally, the B88 standard defines 4 types of copper tubes: Type K, L, M and DMV with
descending wall thickness. The most commonly used types are type L and M which have higher
internal working pressures. These may be of hard drawn or soft annealed temper.
The copper pipes may be joined by:
1. Brazing
2. Soldering
3. Flare joint / compression joint fittings
Section: 3 Page 29
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