Guide to Flushing and Pre-Commission Cleaning of Pipework

It’s often easy to take the performance of engineered-water systems for granted. Ensuring that they perform as they should can be helped significantly by following the correct pre-commission cleaning and flushing procedures of the pipework systems at the pre-handover stage. There is a lot to think about when you’re carrying out a pre-commission clean or on-line flush of a water system, and irrespective of whether the responsibility for doing this is with the client, main contractor or engineering sub-contractor, there are a few key steps that you need to follow to ensure success.

Check availability & quality of water for the pre-commission cleaning

The very first thing which has to be checked is that the water supply that will be used for the cleaning and flushing process is adequate. The supply will also need a double-check non-return valve fitted.

As well as making sure that there is enough water for the flush to be completed, water quality should also be checked at this stage. We recommend that you take a sample of the water before starting the flushing process (pre-flush). If there are any concerns about the levels of bacteria or any other forms of contamination in the water then this can be dealt with by pre-treating the water with a suitable biocide as it flows into the system. These actions should make sure that the levels of bacteria are low, and that the water quality is suitable for the flushing process.

Learn more about water testing here

Understand the local drainage system before flushing starts

Remember that before you start you’ll need to organise a licence that will allow you to discharge the waste water from the pre-commission cleaning and flushing process into the local drainage system. This water will be contaminated with water treatment chemicals and this needs be taken in to account.

You should also ensure that the foul drain you’ll be using can cope with the amount of water you will be sending down it?

Additionally, do you know the exact locations of water supply and drains that are on site? Your engineering contractor or water treatment company will need this information before starting the on-line flushing process.

Test the integrity of the water system

It is always good practice to test the integrity of the water system before you start. You can do this by pressure testing and filling the system to expel all air before the flushing process begins. Have bypasses fitted close to the valves where required, and make sure all units are on bypass before you start flushing. This makes sure that no debris which is flushed from the system gets into any units. You should also make sure you leave all main valves in the fully open position.

Follow recognised standards and guidance for the pre-commission clean

You should refer to the British Standard BS 8552:2012 and the accompanying BSRIA BG29/2012 guidance note for a comprehensive guide to system flushing and pre-commission cleaning. These documents set out what a contractor should do both before the flushing starts, and during the process. For example, contractors carrying out flushing should agree what sort of water testing and sampling should be carried out after the flush is completed. These documents offer detailed guidance as to what sort of water samples should be taken, and how many.

Ensure a suitable power supply is available

You’ll need to use pumps to force the water through the system, and this needs to be hooked up to a reliable power supply. Any issues with power supply can delay the flushing process, so look at portable and back-up generators and other solutions in case of power failure.

Do you need additional pumps?

If your water system pumps can cope with the increased velocity of flushing, then you won’t need to consider any additional or temporary pumps, but the only way of working this out is by doing the calculations beforehand.

Remember that if you’re using additional pumps you’ll need to use isolation valves on the system to cut the risk of short circuiting.

Chemical cleaning products & biocides

If you are using chemicals as part of the cleaning process, use the same results and dosage calculations to determine the system volume and optimal rates for the final inhibitor and biocide chemicals that will be added to the system once the cleaning and flushing is complete.

Set & agree a realistic programme of works

Set out and agree a realistic programme of works for the pre-commission cleaning for both the client and the contractor carrying out the work. This schedule should cover things such as drainage, the water supply, required contact times for specific chemicals, and what type of chemical cleaners, inhibitors or biocides will be used.

Most good chemical cleaning and flushing programmes will include several of the following processes:

Flushing – static and dynamic
Clean and degrease the system
Biocide treatments
Removal of any oxides on pipework/system surfaces
Final flush and disposal of effluent to drain
Dose chemical inhibitors

If as part of the flushing and cleaning you are extending or upgrading an existing pipework system, then you should always take water samples from the existing system and these should be tested. This will tell you whether you need to do anything to correct issues with the existing system, before adding anything extra.

Keeping records of the cleaning & flushing works is essential

It’s essential to keep detailed records of what you’re doing as the flushing works progress. The key pieces of information to record are flushing velocity and water sampling results, and this is often where many pre-commissioning companies fall down. Simply sampling the water at a single location, usually the plant room, isn’t sufficient; various samples should be taken from the most distant points of the system on a regular basis to help build a more complete picture of the process and its effectiveness.

Risk assessments, method statements and more

You’ll also need to carry out a risk assessment before starting work, along with a method statement, setting out all of the considerations listed above and how you intend to tackle them. You’ll also need safety data information for all chemicals used in the pre-commission cleaning process. Additionally you should always make sure the people involved in the system flushing are experienced and competent to do their job.

Specialist pre-commission cleaning solutions

Contact Water Treatment Services today to discuss your pre-commission cleaning requirements. We can provide expert advice and support in accordance with the latest BSRIA guidance (BG 29/2012) during the final commissioning stages for all newly installed and refurbished closed circuit heating and chilled water systems.

With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained engineers, in-field water treatment service specialists and technicians we can offer cost effective engineering support services throughout the UK and Ireland.