40 HPM 0416

HPM-04-APR-2016

Got a story? Ring us on 01732 748041 or e-mail twood@unity-media.com TRAINING/TECHNICAL May the force be controlled HPM’s technical expert, John Love, continues his series on dealing with expansion problems... In my last article, I highlighted the problem of dealing with pipe expansion and the possible repercussions of ignoring it, such as the extreme case of an expanding steam pipe pushing down the end wall of a building I outlined the use of using expansion bellows in a straight pipe run with connections to radiators and pointed out that a problem with using bellows is that they may ultimately fail, although this could be after many years. An option could be to use flexible connections onto the radiator valve tails, but this would look unsightly and it is likely that their life expectancy would be worse than the expansion bellows. In case you do not have a copy that article, can I remind you of the basic theory relating to expansion. The coefficient of linear expansion of steel is 0.0113mm/m/°C so with an ambient temperature of around 15°C when pipework is installed and an operating temperature of approximately 80°C flow, there is a 65°C rise in temperature and so each metre run of pipe will expand by 0.73mm. For copper, the coefficient of linear expansion is 0.0169mm/m/°C – approximately 50% greater than for the steel and giving an expansion of 1.10mm/m. NATURAL PIPING FLEXIBILITY There is an alternative way of dealing with expansion of long pipe runs which do not have radiator connections from them and that is to make use of natural piping flexibility at changes in direction. My diagram illustrates a steel pipe run of 12m length between external and internal corners – a not unusual situation in a church. The total expansion will be around 9mm (13mm for copper) and so if the pipe is free to move then one could expect it to move 4.5mm at each end. This is not a great amount and should not be a problem, provided it is not constrained by a pipe brackets close to the corners at 'A' and 'B'. If it is, then the bracket at 'A' will effectively anchor the pipe, preventing any linear expansion movement and, as a result, all the expansion (9mm) will occur in the opposite direction towards the corner at 'B'. If the bracket at 'B' is close to the corner then the expansion force may be quite enough to pull the bracket out of the wall. It is, therefore, essential to position the pipe brackets sufficiently clear of the corners so as to allow pipe movement. The required distance will depend on the piping material and diameter, which will determine the flexibility of the pipe and thus the extent of bending that it can accommodate. With larger size pipes one has to refer to Tables to determine the required distances, but with steel pipes up to 25mm, WWW.HPMMAG.COM Bracketclose to corneranchoring pipe 750mm clearance should be quite sufficient to cope with 4.5mm of movement. I have illustrated a situation where the major expansion occurs along one wall. If there are long pipe runs around the corners then the required clearance will apply to both wall faces. Copper pipe expansion is 50% greater, but the pipe is more flexible and I have never had a problem using the same clearance. The only problem is that since copper is not so rigid there may be a tendency to sag at the corner and it will be more vulnerable to mechanical damage which could bend it. The answer could be to support it from the floor beneath with a munzen clip and backplate, so that the studding allows a degree of lateral movement. A number of years ago, I had a situation where the contractor had correctly identified a potential problem and had put a small 'L' shaped bracket on the wall with the pipe resting on top of it, so that it was free to move in a horizontal plane. Great, but the bracket was steel - much harder than copper, and it gradually wore away the copper at the point of contact and it eventually leaked. A plastic sleeve around the pipe would have done the trick. It is not just the pipe brackets which could cause a problem. If a radiator is positioned so that one of its connections connects to the pipe very close to the corner, then exactly the same problem can occur. I have seen a situation where a radiator was positioned so that one of the pipe connections was very close to an external corner ('B' in the diagram) and the expansion force pulled the radiator bracket at one end out of the wall. If the pipe had been copper the expansion would have been 50% greater and the pipe would most probably have fractured or pulled out of the radiator valve tail. Of course, dealing with expansion in long pipe runs is not just limited to pipes running around walls. You have the same problems with long runs of pipes, at high level below ceilings, in floor ducts and vertical pipes in risers. If you do not have sufficient knowledge of dealing with expansion then it is important to seek professional guidance from a company who specialises in the supply of expansion fittings. 40 APRIL 2016 HEATING & PLUMBING MONTHLY There is a long established firm in Middlesex who have been around for over 60 years and who give excellent advice, even to the extent of telling you how you can avoid having to use their fittings by making use of natural flexibility. Of course, you cannot rely on natural flexibility with large size pipes, but even then you can limit the use of expansion fittings by designing in expansion loops. This is a little beyond the scope of this article, and, I imagine, the type of work most of you are involved with, but type 'articulated expansion joint' into your search browser and click on 'images' and you may be surprised at what you see. Some types of 'tied' expansion fittings allow movement in two planes. Now do the same thing for 'pipe anchors and guides' and you will see the type of anchors and guides that need to be used – the sort of fittings that I used to use with large steam and medium and high pressure hot water systems. So far I have just mentioned metallic pipes – steel and copper – but you may be wondering about the situation with plastic piping which has an even higher coefficient of expansion – polybutylene, polyethylene and polypropylene expansion is in excess of 0.13mm/m/°C. Well, the natural flexibility of the pipe means, within limits, that it will simply distort and flex to absorb the expansion, which is why we never use it in exposed locations because it looks awful. However, you may be using MLC piping which comprises two layers of polyethylene with an aluminium layer between them, and this has a much lower coefficient of expansion than the above 'plastic' pipes – 0.025mm/m/°C which is about 50% greater than copper. In this case you would design to allow for the natural flexibility of the pipe, as with metallic pipes. It is not good practice to use it in a long run in an exposed situation with connections to radiators, as you would with steel or copper, as it will have a tendency to distort and the expansion force will not be great enough to move radiators on their brackets. Always take into account the manufacturers recommendations and the major suppliers of MLC piping produce very detailed technical information which can be downloaded from their websites. John K Love CEng, FCIBSE., FIPHE., FIDHE., MInstR., FConsE A B B racket Bracket Bracket B racket 4.50m m . 4.50m m . 750 750


HPM-04-APR-2016
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