The mantra for reducing the risk of failure in pipework systems should be “keep the fluid moving, but not too fast”, says Reginald Brown
The primary function of a pipe is to transport fluid between two points, without losing any on the way or fostering contamination – if that fluid is water at modest temperature and pressure, then there are numerous possible pipework materials and jointing systems.
In principle, some of these can function reliably for hundreds of years, but none is without risk of developing problems if the design, installation and operational constraints are not properly considered.
In the worst cases, the problems can become painfully apparent even before the installer has left site.
CIBSE guides suggest that pipework installations for heating and cooling in buildings should have an economic life of 25 to 30 years.
However, that may be more to do with the anticipated refurbishment cycles of commercial buildings than the material characteristics of pipework and fittings.
Built to last
Many of us live in mid-20th century housing, with the original heating and hot water pipework showing no sign of imminent failure. If it was possible to construct reliable plumbing in the 1950s, why can’t we do that now?
The answer is that we can and do produce reliable plumbing for most buildings, most of the time.
In fact, modern methods of working mean the hydraulic integrity of the as-installed systems prior to pressure testing is probably far better than it was in 1950.
The issue of concern is the number of high-profile buildings that suffer early corrosion problems or other material defects leading to failures within three years of installation.
Common causes of early failure based on samples submitted to BSRIA are listed above, although no system is immune to failure in a poorly installed or badly maintained system.
If we discount the avoidable design, specification, installation, commissioning and maintenance issues, the residual problems are often associated with stagnation, ie the absence of flow.
This applies to domestic water services and closed heating and cooling systems, although the issues are different.
For domestic water services installed in copper tube, if the building can be put into use within a few days after the pipework systems are first filled, then any remaining construction or disinfection residues will be rapidly flushed away before they can do any damage and a protective patina of copper carbonate will naturally form on the inner surface of the pipe.
This patina reduces the risk of sporadic biofilm development, leading to microbially influenced corrosion (MIC) of bare copper tube. Private houses have short construction programmes and tend to be occupied as soon as complete.
Unfortunately, this is not the case for public and commercial buildings with much longer construction programmes and progressive occupancy after handover. The best corrosion protection for a domestic water system is to use it.
Plastic pipework does not suffer from metallic corrosion but stagnation will encourage the development of biofilms that may adversely affect water quality and increase the risk of colonisation of the system by legionella and other bacteria.
Note that chlorination will kill surface bacteria, but may not completely penetrate and remove established biofilm, so it is preferable to avoid it forming in the first place.
For closed heating and cooling systems, there is usually a period of stagnation between filling and commissioning.
This allows the development of biofilm that will influence subsequent corrosion, particularly of steel pipework and steel components, even after the system is cleaned.
Application of a suitable biocide and monitoring programme between filling and pre-commission cleaning, as described in BSRIA’s Guide to Pre-commission Cleaning of Pipework Systems (BG 29/2012), should reduce that risk, but minimising the stagnation period is better.
Once the systems are cleaned and commissioned, then careful attention should be given to maintaining an effective water treatment regime, reduction of dissolved oxygen supported by periodic circulation and cycling of control valves to ensure that all parts of the system are continually exposed to corrosion inhibitors irrespective of heating or cooling demand.
The mantra for reducing the risk of failure in pipework systems should be “keep the fluid moving, but not too fast”.
If your domestic water, heating or chilled water pipework system has already survived its first three years without problems then, subject to a reasonable standard of maintenance, it probably is good for the next 25.
Reginald Brown is senior consultant, BSRIA Sustainable Construction Group
Air quality – a time for action
With an estimated 29,000 deaths a year from air pollution, The Environmental Audit committee has issued its third report in five years calling for action to be taken. The report is calling for new schools, care homes and hospitals to be built far away from major roads, writes Ian Orme.
With over a thousand schools already near major roads, it is suggested that it would make good economic sense to filter the air coming into the buildings.
Experts believe that the figure of 29,000 is a robust figure – this is unacceptable. Those of us working in the built environment must play our part in addressing this.
As we have got better at making buildings airtight, it is BSRIA’s experience that there are often significant failures in the performance of ventilation systems leading to an unhealthy environment.
In BSRIA’s experience there are five main reasons for poor indoor air quality:
n Design Impractical designs and/or designers “gaming” with calculations so as to demonstrate the standards are met.
n Construction/installation Ductwork can be prone to damage and the practical installation of ductwork, fans, and terminal units does not always equate to what was designed. BSRIA has come across instances of mechanical ventilation systems simply not being connected up to the power supply.
n Commissioning Poor commissioning, such as ventilation dampers, sensors and controls can significantly affect performance. The current approved method of measuring airflow from low pressure ventilation systems is fundamentally flawed, so in practice it
is difficult to identify the true situation
in many buildings, even where a ventilation system has been properly commissioned.
n Maintenance Poor maintenance of filters and sensors can have a significant impact on flow rates and the effectiveness of filtration. Design issues sometimes make cleaning of filters or their replacement or the cleaning of ductwork, somewhat problematic.
n Operation Occupant effects such as not using the ventilation system as per the design intent, manual tampering of controls, sensors and dampers. Where mechanical ventilation works with trickle ventilators, they may be taped shut.
Ian Orme is head of BSRIA’s Sustainable Construction Group