Rethinking pre-commission cleaning
Thoroughly cleaning a pipework system before it is commissioned and ensuring it remains clean is vital to the success of commissioning and the subsequent life of the pipework — so much so that it requires proper management. Reginald Brown of BSRIA explains the latest guidance.
If you have experienced a serious pipework failure in a new building there is a good chance that somebody involved in the project will contact BSRIA for advice. Rarely will it be something we have not encountered before, and a brief discussion of the background will usually highlight several deficiencies in the way the project has been implemented. In the case of early corrosion failures in heating and chilled water systems (within three years of construction) there are several recurring themes.
• Delays between first fill and pre-commission cleaning, resulting in prolonged stagnation.
• Inadequate maintenance of water treatment between pre-commission cleaning and practical completion.
• Persistently high dissolved oxygen.
• Lack of circulation in use.
If the pipework system survives the first three years following construction without any major problems then the chances are that, subject to normal levels of maintenance, it will achieve a life of 25 years or more.
So, if the risk factors are rather obvious, why are they not being managed?
The underlying problem identified by BSRIA and the working group for revision of the pre-commission cleaning guide was the lack of explicit guidance for the management of the system before and after pre-commission cleaning. The revised guide (BG29/2011 Pre-commission cleaning of pipework systems) therefore extends the recommendations for managing water quality from first fill through to practical completion, after which the client’s water-treatment contractor takes over responsibility for on-going maintenance and health of the system.
BG29 includes guidelines for the following.
• Quality of fill water.
• System monitoring between first fill and pre-commission cleaning.
• Water quality seven days after completion of pre-commission cleaning.
• System monitoring between pre-commission cleaning and practical completion.
• Water quality at practical completion.
The earlier BSRIA pre-commission cleaning guide (AG1/2001) only considered the system water quality immediately after pre-commission cleaning. The timeline of activities is illustrated in the diagram (below).
For most projects it is sensible for the additional monitoring and any remedial water treatment prior to practical completion to be carried out by the pre-commission cleaning specialist, though a water-treatment specialist can potentially provide the same service.
However, while pre-commission cleaning is a well-defined activity with a clear scope and achievement guidelines, the subsequent monitoring and water-treatment activity must be responsive to developing system conditions which in turn are influenced by commissioning activities, engineering changes and remedial works prior to practical completion.
For these reasons the cleaning or water-treatment specialist should not accept prior responsibility for achieving the practical-completion guidelines but operate in a support role, providing the necessary monitoring and water treatment as a service to the main contractor under a separate contract. That will, for example, include checking and re-dosing the system with inhibitor immediately after engineering works requiring temporary drain down. Note the trends in the results of regular monitoring during this period and ensure they are taken into account for the practical completion assessment.
The sampling and monitoring regime in BG29/2012 (slightly updated from BG29/2011) is consistent with the new standard BS 8552:2012 Sampling and monitoring of water from building services closed systems — Code of practice. BS 8552 explains when, where and how to sample for water quality throughout the life of the building and what to analyse for — but does not set guidelines. The guidelines for water quality from first fill to practical completion are set in BG29. Guidelines for water quality after practical completion should be set in consultation with a water treatment specialist with due regard to the type and materials of construction of the system and the water treatment regime being applied.
Adherence to BG29 cannot prevent corrosion of heating and chilled water pipework, but applying the recommended sampling and monitoring regime should provide early warning of developing problems and enable remedial action to be taken before there is irrevocable damage. This is particularly important for thin-wall steel piping systems that are intolerant of corrosion, but the guidance will benefit all closed pipework systems and associated plant.
Reginald Brown is head of energy and environment at BSRIA.