MORE PRE-COMMISSION CLEANING INFORMATION
Typical contaminants found in water systems:
Water systems can pick up many unwanted materiel which finds its way into system components during manufacture, storage and installation of the components. These include scale, welding slag and metal swarf which can usually be removed by thorough clean-water flushing. Some deposits are more difficult to remove include lubricants from extrusion of pipework, cutting oil, flux from soldering, and excess jointing compounds.
Scale is a build-up of solid Calcium, Magnesium and Iron compounds which often occurs on the heat-exchanger surfaces inside boilers and condensers, reducing efficiency, increasing operational costs and may lead to equipment breakdown and disrupted production.
Scale forms when even moderately hard water is heated or when the pH or alkalinity of the water changes. The risk of scale forming is proportional to the hardness of the feed water and the age of the system.
Engineered water systems are often contaminated with Corrosion products, and typically the 2 most likely causes of corrosion are electrolylic reaction and corrosion induced by bacteria.
An electrolytic reaction occurs when metal surfaces are connected through in presence of an electrolyte (water). In a system of pipework for example, the metal surfaces are electrically connected by the water. A reaction occurs in the iron in the pipework combining with oxygen and hydrogen from the water, then the dissolved oxygen causes iron oxides to form.
Bacteria-induced corrosion, as may be caused by sulphate or nitrate-reducing bacteria, is capable of creating corrosion issues under water conditions which are otherwise quite stable.
The rate of corrosion is affected by temperature, the nature and amount of contaminants in the water, and also the rate at which the water flows. The chief chemical variables affecting how corrosive the water becomes are the concentration of dissolved oxygen, the quantity of carbon dioxide present, the acidity/alkalinity and the amount of solid material already dissolved in the water.
Biological fouling is also a result of the nature of the feed water and any contaminants which were introduced during manufacture orinstallation.Where temperatures and conditions are appropriate for bacterial growth, an invisible slimy layer (biofilm) can develop inside pipework. The bacteria can then multiply and contribute to the formation of sludge deposits.
Corrosion produced in this manner is unpredictable and typically very localised. Sulphate-reducing bacteria are particularly aggressive causal agents of pitting corrosion. While the majority of pipework appears unaffected, pin-holing will occur in affected areas far more quickly than would be expected.
One way to monitor the condition of a system is by sampling for Pseudomonas, which LCS can do for you. While not thought to be directly responsible for corrosion, Pseudomonas are used as an indicator to determine potential corrosive conditions. We can also carry out more specific test for Sulphate or Nitrate reducing bacteria.
Where systems are dosed with antifreeze and/or corrosion inhibitors, unless systems are also dosed with a suitable biocide and carefully monitored, these additives can act as nutrients for bacteria and the effective level of antifreeze and/or inhibitor are reduced as the bacteria multiply.
There are a myriad of different formulations on the market and selection of the
correct product for a system may be confusing.
The following guidance helps in selecting the correct product for your system:-
1. Neutral pH: given the complexity of newer systems it is generally advisable to select a neutral formulation for pre-commission cleaning. The neutral pH will not attack any of the metals found in closed circuit systems.
2. Removal of biofilm and suspended solids: a product with a high level of polymer is required to ensure good removal of biofilm and also to mobilise suspended solids and keep them moving in the water so that they can be removed from the system during the normal flushing operation.
3. Removal of oil and grease: the presence of an effective surfactant in the cleaner is needed in order to make sure that any oil and grease in the system are solubilised and removed from the metal surfaces.
4. Removal of corrosion deposits: it is often the case that after pressure testing of the system raw water remains within the circuit, sometimes for prolonged periods. This can lead to corrosion on the metal surfaces. The presence of substance which can remove this, i.e. a chelant, is required in order for any corrosion deposits to be effectively loosened, mobilised and dissolved.
5. Passivation of metal surfaces after cleaning: all well
formulated pre-commission cleaners and system flush chemicals will contain
components which passivate the bare metal surfaces after cleaning to prevent /
minimise the occurrence of flash corrosion.
6. Ease of testing: it is important to be able to easily and accurately measure the levels of a pre-commission cleaner within a system. Like any other chemical formulation these will only work optimally if they are present within the system at or above the minimum dose rate.
7. Disposal considerations: Typically Consent to Discharge Trade Effluent would be required. Please be aware that this is a process that can take the utilities company several weeks to complete. LCS would apply for this consent on your behalf, ensuring environmental requirements are met. In some areas it can be very difficult to obtain a permit for the discharge of the effluent after pre-commission cleaning, and we would recommend a pre-commission cleaner with minimal environmental impact, although this may increase contact time.
8. Scale: Just 1mm of limescale in a hot water system can increase energy use by 7%. For older LPHW systems the build-up of scale may be a problem within the system, particularly on the hotter surfaces such as on the heat exchanger itself. This may lead to blockages or failure of the heat exchanger. Although acid cleaning of some system may be an option, a gentler clean with a specialised formulation which re-dissolves the scale is a much safer option in most systems. For information regarding on-line scale removal, click here (softener page) or please contact us.
9. Compatibility of the cleaning chemical with biocides: if a biocidal flush is being carried out in conjunction with the actual cleaning operation then a compatible biocide must be chosen. The biocide chosen must have optimal effectiveness during the contact time available, in other words do not select a biocide which has a 12 hour contact time for use during an 8 hour chemical flush! It is also essential to ensure that the chosen biocide is present at the recommended concentration. This can only really be achieved if the system volume is known very accurately or a biocide is used for which a test kit is available.
Legionella Control Solutions Ltd,
Fusion Business Centre,
Telephone 01709 717100