Unless piping is designed and installed to accommodate the increase and reduction in length which results from heating and cooling cycles, repetitive movement could concentrate at a point in the line and lead to unpredicted failure of catastrophic consequence.

EXPANSION RATES

The rate of expansion depends on the properties of a specific material. It is worthy of note that plastic pipes expand at rates far greater than copper. Some more than eight times that of copper. Thus, even more care is required with installations where these materials are used.

Longitudinal expansion of copper piping can be calculated by the simple formula:

Expansion = tube length (m) x temperature rise ( °C ) x  0.0177

A useful approximation for standard hot water lines is to allow 1mm expansion for each 1m of straight pipe run.

METHODS FOR ACCOMMODATING PIPING MOVEMENT

Expansion Offsets

In domestic installations and simple layouts, expansion is usually addressed by appropriately placed bends in properly supported pipework. It is important that there is freedom of movement at bends, branches and offsets.

There must be clear space to permit movement and adequate free length of pipe around the bend or along a branch to avoid undesirable stress. The radius of a bend is to be sufficiently large enough to accommodate the expected expansion rate. Bends must have uniform curvature and be free from distortion and damage.

Expansion and Contraction Devices

In commercial and industrial pipework, it may be necessary to install special in-line devices because of the expected cyclic movement. 

Expansion devices:
·Absorb changes in length of pipe that result from temperature and pressure fluctuations caused by the medium flowing inside and the external environment.
·Can avoid problems such as premature fatigue cracking due to thermal expansion or contraction, misalignment and vibration. In addition, they may be retrofitted in piping that has failed because of high imposed stress.

In general, there are 4 types of devices to select from. They consist of bends, loops, expansion joints/bellows and flexible pipe.

Bends and loops require significant space. As they are made for specific conditions, it is unlikely that they will be available as off-the-shelf items. Tube benders, formers and sand bending may be needed to make bends and loops.
Critical aspects are: the minimum radii depend on the length of line and the calculated maximum temperature increase; the formed tube is to be free from distortion, wrinkles, flattening, ovality and damage; and the final minimum thickness at any point, in the bend or loop, must be no less than that of the connecting pipes.   

Expansion joints and flexible pipe devices are connected in direct line with piping and do not need as much space as loops and bends. They eliminate buckling and can be designed to absorb axial, angular and lateral movement. Usually ttthey are eaaasy to disassemble, at a later date, if required. It is important to adhereto the manufacturer’s installation instructions as placement and support of these devices is critical.

Typical applications are found in airconditioning, large commercial runs, industrial processes, petrochemical, power generation piping and many other industries.
These devices are usually available from specialist pipe fitting suppliers such as Adip/Tyco.

NEED TO KNOW MORE?

If additional information is required, it is suggested that the following references may be helpful.
 
(a)Sections 2.8 Thermal Movement & 4.5 Expansion Joints in the technical manual “An Introduction to Technical Plumbing Skills” at the Copper Development Centre Australia web site: www.copper.com.au/cdc/
(b)The Plumbers Handbook at www.kembla.com.au
(c)The Plumbing and Drainage Standard AS/NZS 3500.4 Hot Water
 
Information on Adip/Tyco expansion joints may be obtained direct from the company or at web site www.tycoflowcontrol.com.au/brands3

Special thanks to Pat Salazar of Crane Copper Tubes for his work on this article.