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Technical answers: Pipework defects, ventilation and airflow ratesApril 2016


Jayne Sunley, Information Manager
Information Manager, Jayne Sunley, report on some of the technical questions posed by BSRIA Members.

Q1: Could foam insulation be the reason we are experiencing problems with pitting on copper pipework leading to actual leaks? The copper pipework in question is a chilled water service covered in phenolic foam which is only 4-5 years old. Could the vapour seal on the insulation be damaged leading to condensation forming on the pipe causing pitting and pin-holes?

In order to prove that insulation is the problem you need to establish with all certainty that the perforations are from outside to inside and could not have been influenced by other sources of leakage such as weeping joints of previous pinholes. It would also be worth looking at the insulation manufacturer’s installation guidance to see whether it is the correct grade and has been applied properly. Sometimes there is a protective paper on the inside of the insulation that should not be removed, other manufacturers use an invisible coating or may recommend for steel pipes that a protective coating be applied to the pipe itself prior to installation.

Insulation on copper pipework is not a new issue but the European Phenolic Foam Manufacturers Association issued a statement in 2000 after an initial rash of problems.

Q2: Can stress fractures be the cause of failure with ABS and PVC pressure pipes?

Stress fractures are the most common defect that we see and are caused by excessive application of adhesive and/or the application of mechanical stress to the joint prior to the adhesive being fully cured. Often this happens because the pipes and fittings to be connected are slightly misaligned but can be pushed together. The typical stress fracture is longitudinal crack in the pipe, starting from inside the fitting, or at least near to the fitting. Longitudinal cracks in the middle of a length of pipe are more likely to be a consequence of impact damage or the pipe being dropped prior to installation.

Cracks may be not readily visible until water starts to appear. Once a crack is suspected then the methods applied by ANS using crack detection fluid can be useful to observe the extent of the crack. More detailed investigation requires the affected section to be cut out from the system and sectioned for microscopic examination of both inside and outside surfaces. Further sections can then be cut to separate the material either side of the crack and examine the fracture surfaces.

Q3: I need to be able to access withdrawn or superseded BSRIA guidance, is this still available?

All BSRIA guidance, current and withdrawn, is freely available to BSRIA members on our website. Where a copy is not available it will still be accessible if you contact a member of our Information Centre team. Members using these documents should be aware that they have been superseded or withdrawn for a reason and therefore the content may no longer be correct or current to use in modern projects. Members use these documents at their own risk. For non-members we also sell withdrawn or superseded publications in pdf format.

Q4: Are there any recommendations or regulations in the UK about the ventilation air speed in ducting?

There are no regulations in the UK about air velocities in ductwork, however there are recommendations. Our publication Rules of Thumb gives various recommendations for different applications, for example in offices, 6.0 m/s in main ducts, and 5.5 m/s in branch ducts.

Q5: Clients are increasingly asking about the airflow rate of LED downlights but after doing some research as far as I can see, the airflow rating seems to be of a room/dwelling rather than the particular light fitting in the room. Is this correct?

While airtightness is certainly a requirement of a dwelling or room, to the best of our knowledge there are no specific requirements or limits on individual light fittings. However, each penetration in the ceiling will provide a potential air leakage path and will add to the total leakage. As such, contractors may wish to be sure that if they install a significant number of light fittings they will not exceed the total permitted for the space. Also, the better the light fitting the more leeway there may be for other items to leak while remaining within the overall total allowance. In practice, leakage through fittings will be very dependent on the ceiling material as well as the care of the fitter but leakage rates do give at least an initial baseline.

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