Effective pre-commission cleaning of new systems is absolutely critical.
Unfortunately, the important nature of this operation is often overlooked or
undervalued. The objective of a pre-commission clean of a closed system is to
remove all grease, oil, biofilm, corrosion deposits, flux and jointing compounds
and general debris from the system. This will then present a clean metal
surface on which the corrosion inhibitor can act to prevent corrosion of the
system over its lifetime - if a corrosion inhibitor is not direct
contact with the metal surfaces, it cannot inhibit corrosion!
If suspended solids, biofilm, grease and oil remain in the system these
will produce a layer on the pipework which will mean that the inhibitor cannot
reach the metal surface and thus cannot prevent corrosion. A raw water flush does not remove these layers of contaminants from the pipework
surface, a chemical cleaner is required.
It is often the case that
unrealistically short time periods are given for pre-commission cleaning as the
critical nature of this operation may not be fully understood. Different chemical products have varying
minimum contact times. For example,
BSRIA BG50 states contact time should be anything from ‘12 hours to 3
weeks’, so if the available contact time for the cleaner is short, LCS can
advise on the appropriate product and contact time to work effectively within
the time available, but please be aware that pre-commission
cleaning may not be fully effective, or even possible at all, in a very short window!
If particles of installation debris remain in the system, erosion corrosion may
result under the velocities of normal operation. Some jointing compounds
contain chloride which in itself may accelerate corrosion of certain metals.
For these reasons the significance of a thorough pre-commission clean carried
out over a ‘realistic time window’ cannot be over-emphasised.
The pre-commission cleaning of hot water heating and chilled systems has also
become more critical over recent years. This is mainly due to the equipment
used being more susceptible to blockages at strainers, control valves and small
bore heat exchangers. System contaminants such as mill-scale, jointing
compounds and fabricating debris need to be removed by chemical cleaning and
high velocity flushing. This will then allow the on-going water treatment
regime to work effectively in preventing corrosion and microbiological fouling.
Older systems that have accumulated deposits due to a lack of correct water
treatment can also be cleaned using a similar method.
