Plumbing Tubes: Thermal Contraction & Expansion SABS 460 Tubing

Thermal Contraction and Expansion

Thermal Contraction and expansion in pipelines should be allowed for by expansion loops or bends, the dimensions and spacing of which should preferably be such that combined stresses are kept below the fatigue limit.

Table 3:

Radius of Coiled Expansion Loops (For configuration shown in Figures 1A & 1B)

Table 4:

Developed Length of Expansion Offsets (For configuration shown in Figure 1C.



The co-efficient of linear expansion of copper tubing is 0.0166 mm/metre °C between O°C and 100°C. Example: For a 60°C rise in temperature between these limits, the linear expansion would be 1mm per metre and between 20°C and 60°C the linear expansion would be 0.67mm per metre.

Holderbats - Tube Supports and Fixings

The correct selection and installation of tube supports is an important factor in the design of any system. Incorrect use or selection can lead to serious problems in relatively short periods of time. A number of factors should be taken into consideration before selection:

Dissimilar Metals

The use of steel or galvanised materials should be avoided in humid atmospheres or in situations where condensation is likely. In these conditions corrosion of the pipe support could take place. If the use of these materials can not be avoided, they should be totally insulated from the copper pipe. This can be effected by the use of wood, plastic or rubber. Ideally the use of brass or copper supports would be recommended.

Allowance for Expansion

All support brackets or holderbats should be fixed so as to allow free movement of the pipe within the fixture. This is to allow for the expansion and contraction of the pipes during operation of the system and is especially important on hot water lines.

Positioning

Attention should be paid to the positioning of the supports. As a general rule, a holderbat or support should be placed at least 500mm away from a change of direction fitting i.e. tee or elbow.

Don’ts

The use of nails, wire etc as an alternative to the correct fixing should be avoided at all times. This can lead to premature failures due to several factors.

Golden Rule

Do not over tighten, allow the tube to expand without restriction and beware of dissimilar materials.

Pressure Ratings

Working Pressures (Temp. not exceeding 65°C) Working Pressures are based on a working stress in the copper tube wall of 55.55 MPa which provides for a factor of safety on the ultimate strength of between 5.24 & 7.1. Working Pressures (Temp. exceeding 65°C) For working temperatures exceeding 65°C the safe working stress can be determined from the chart.