Method Statement for Cleaning Flushing and Passivation of Chilled Water Piping

This statement outlines a procedure for performing cleaning, flushing, and passivation of an HVAC chilled water system on-site, which will be executed by a third party or an independent entity.

Objective

The primary objective of the cleaning, flushing, and passivation process is to eliminate particulate matter such as sediment, sand, scale, iron oxide deposits, welding residues, and other impurities present in a newly installed pipe network. The passivation phase serves to protect the system from corrosion.

The pre-operational flushing and cleaning process is crucial because the presence of these impurities can significantly impact the efficiency of the cooling system and impede the flow within the network.

Furthermore, these contaminants hinder the formation of uniform protective passivation layers, which can lead to corrosion within the system. As a result, it is imperative to ensure a thorough pre-operational cleaning/flushing regimen is conducted before the system is commissioned for regular operation.

Treatment of Chilled Water System

A chilled water system operates as a closed-loop recirculation system, maintaining temperatures typically ranging from 5.5 to 14 degrees Celsius. In this closed-loop configuration, water circulates within a sealed circuit with minimal evaporation or exposure to external elements that could alter its composition.

Such systems often demand a high level of chemical treatment due to minimal water losses, which proves cost-effective. High-quality makeup water is typically introduced to ensure optimal system performance.

Heat transfer occurs within the closed cooling water loop through standard heat exchange equipment. Heat is then dissipated from this closed loop to a secondary cooling cycle, achieved through either evaporative cooling, once-through water cooling, or air cooling.

Water velocity within the closed system typically falls within the range of 0.9 to 1.5 meters per second.

Temperature differentials usually average between 5.5 and 14 degrees Celsius, although certain systems may surpass these values significantly. Closed-loop systems generally experience minimal makeup water requirements, except for instances such as pump seal leaks, expansion tank overflows, and surface evaporation through system vents.

Regular analysis is essential to monitor and maintain correct treatment chemical residuals during periodic makeup water addition.

Closed systems commonly consist of various metal combinations, leading to a notable susceptibility to galvanic corrosion. In the context of closed chilled water systems, the potential for dissolved oxygen-induced corrosion is substantial due to the presence of dissolved oxygen molecules.

In a theoretical sense, the formation of scale is anticipated to be a minor concern within chilled water systems, given that the water is not concentrated through evaporation. Nonetheless, when there is a high rate of water makeup, additional scale is formed with each fresh infusion of water.

Over time, this cumulative scaling becomes significant. Additionally, there is a possibility for the precipitation of sludge, rust, and suspended solids at low points within the system. These particles can adhere to heat transfer surfaces and solidify, creating tenacious deposits.

Consequently, to address this issue, scale inhibitors and dispersants are typically integrated into closed system treatment protocols, particularly in scenarios with elevated makeup rates.

Due to the enclosed nature of the recirculating water within a closed system, the occurrence of fouling from airborne particulates like silt and sand is relatively restrained.

However, the potential for fouling caused by microbial growth becomes relevant in closed systems where substantial makeup water is introduced or instances of process leaks promote bacterial proliferation. To manage such concerns, biological control measures tailored for closed systems are implemented.

Thus, two primary challenges are commonly encountered in chilled water systems:

1. Corrosion
2. Microbiological fouling

Chilled Water Piping Flushing Process

The primary aim of the flushing procedure is to effectively eliminate a substantial amount of particulates and contaminants from the piping system. This process is crucial for diminishing the likelihood of blockages within the system and establishing optimal conditions for a successful chemical cleaning regimen, followed by subsequent water treatment.

Inevitably, contaminants such as mill scale, jointing compounds, and construction debris are present within newly constructed pipe networks. If these impurities are allowed to persist in substantial quantities, they can lead to potential blockages at strainers, control valves, and smaller bore heat exchangers. Moreover, the presence of microorganisms could trigger additional corrosion and promote microbial growth.

The initial step towards mitigating these issues involves a thorough flushing of the system using clean water. However, it’s important to note that system flushing alone may not effectively eliminate contaminants like adhered metal oxides from the internal surfaces of the pipes.

During system operation, the expansion and contraction of the piping due to thermal variations can cause these deposits to dislodge and re-enter the fluid stream.

Consequently, the objectives of chemical cleaning encompass both the loosening of surface deposits for subsequent removal and the establishment of a stable inner surface layer. This stable layer, when maintained through a well-defined water treatment regimen, serves as a defense against further corrosion.

It’s crucial to highlight that an improperly executed chemical cleaning procedure holds the potential to yield unfavorable outcomes. The choice of cleaning agents must align with the materials constituting the system.

Significantly, the effectiveness of the chemical cleaning process hinges upon the execution of comprehensive system flushing before and after the chemical treatment. This dual-flushing approach ensures the elimination of dislodged material and residual chemicals.

The cleaning process must be conducted seamlessly to prevent the development of additional corrosion over time.

Furthermore, it’s important to recognize that solely employing forward flushing, or even a two-stage process involving forward flush and backwash, might not yield the same level of contaminant removal as a two-stage approach.

The process of performing both forward flushing and backward flushing operations is imperative due to the inherent challenges associated with transporting particles through upward-bending sections and preventing their accumulation in unintended traps like valve bodies.

Employing a dual-directional flushing approach ensures that particles which may resist movement in one direction can be propelled in the opposite direction.

For effective system flushing, the water velocity must be adequately high to entrain and transport the majority of dirt and debris within the system. While it’s possible for larger particles to infiltrate the system, the majority of debris tends to have a diameter below 5mm.

Curves transitioning from horizontal to vertically downward, as well as those from downward to horizontal or within the same plane, do not hinder the movement of debris.

The necessity of flushing from horizontal to upward vertical can be initially avoided and subsequently addressed through a reverse flushing process within the system.

Application of Chemicals/Method of Operation

Cleaning/Flushing Start Up Checklist

General:

In preparation for commencing any pre-cleaning endeavor, the following essential considerations must be addressed:

• Verify the consistent availability of a fresh water supply (temporary or permanent, as required).
• Confirm the accessibility to power and electricity resources (temporary or permanent, as needed).
• Ensure the presence of a continuous labor force or manpower on a 24-hour basis.
• Validate the availability of chemicals necessary for the flushing and cleaning operations at the site.
• Verify the completion of installation work.
• Precisely identify both the feed and drain points.
• Establish provisions for drainage from the lowest points within the system.
• Confirm the availability of requisite safety equipment at the site and confirm that workers are adequately trained in safety protocols.
• Verify the operational status of the system pumps or arrange temporary flushing pumps as deemed necessary.
• Identify and locate all air vents situated within the circuit.
• Transform the entirety of the newly established chilled water piping into a singular gradient by establishing necessary bypass connections to the heat exchangers, air handling units (AHUs), and fan coil units (FCUs), where applicable.
• Ensure that the bypass connections are adequately dimensioned.
• Verify and guarantee that all isolating valves facilitating circulation within this circuit are fully operational.
• Implement required bypasses for all precision valves and cooling coils as necessary.
• When applicable to the specific project, adhere to safety precautions during chemical handling. Individuals engaged in chemical mixing are to wear gloves and goggles. Clean water shall be made available at the site by the contractor. Essential handling instructions for chemicals, as outlined in the Material Safety Data Sheets (MSDS), shall be conspicuously displayed at the chemical dosing location.
• Provide samples and employ suitable sample containers: The Mechanical, Electrical, and Plumbing (MEP) Contractor is responsible for presenting samples in transparent bottles, readily procurable locally, during various stages of the treatment (as specified in the checklist). These bottles shall bear labels detailing the time and location of the sample extraction point.

Preparation

To ensure the successful completion of the flushing procedure, it is imperative that all elements outlined in the pre-cleaning/flushing startup checklist, as detailed above, are provided prior to initiating the process.

Methodology for Chemical Cleaning / Flushing

The procedure encompasses the following sequential stages:

• Initial static flush employing plain water
• Dynamic flushing • Chemical cleaning
• Final inhibition and passivation
• Reinstatement of plant components and back flushing.

Initial Static Flush with Plain Water

Introduce plain water into the system using either the mains supply or controlled water source along with temporary pumps.

Upon system filling, perform two consecutive drainage cycles for the entire system.

Re-fill the system.

Activate system circulation using the designated pump for a duration of 8 hours.

During circulation, visually inspect and clean the Y-strainer at the pump suction at least once per hour.

After the circulation period, open drain valves situated at the system’s lowest point.

Direct the flushed water to the stormwater drain or dedicated disposal tanks on-site.

Refill the system and initiate dynamic flushing.

Dynamic Flush

Maintain continuous system circulation, utilizing dedicated flushing pumps.

Initiate the supply of clean water to the system (or temporary supply if applicable).

Gradually open drain valves positioned at the lowest point across the entire system, adjusting the flow rate to achieve suitable makeup and drainage.

Note: The drainage flow should never exceed the clean makeup water flow to prevent system pressure loss and drainage issues.

During dynamic flushing, it is crucial to ensure that the circulating water’s velocity is sufficiently high to dislodge all debris from the system’s pipelines.

Velocity Requirement

The flushing water’s velocity must be adequate to entrain and transport the majority of debris within the system. While larger particles could potentially infiltrate the system, most debris typically has a diameter below 5mm. The system pumps must meet one of the following conditions:

Or

Attain a velocity in the system that is at least 10% higher than the design velocity achievable when all permanent system pumps are in operation. • Maintain a minimum velocity to remove particles up to 5mm in accordance with BSRIA AGI / 2001.

The following outlines the minimum velocities to be sustained within the system for various nominal pipeline sizes.

Please take note that while the system will comprise various pipeline configurations, the specified velocity mentioned earlier must be attained within the larger pipe segment of the system.

It is imperative to conduct flow measurements at each available branch and riser measuring station to verify the attainment of correct fluid velocities.

In the event that the pumps are unable to match or achieve these defined parameters concurrently, it will be necessary to strategically manipulate the system. This manipulation will involve selectively closing specific sections to direct the total pump flow through an open section, thereby achieving the desired flow velocity.

Subsequently, the closed section will be reopened, and the initially open section will be closed. This sequence is crucial to prevent any prolonged adverse effects on the pump due to “Closed Head” conditions.

Perform the processes of filling, draining, and circulating until the water appears visibly clear.

While carrying out dynamic flushing, it is mandatory to periodically inspect and clean all strainers that experience fluid flow until no further deposits are detected.

Temporary filters must undergo regular inspection and cleaning throughout the dynamic flushing procedure. Upon completion of dynamic flushing, all temporary filters must be isolated prior to chemical cleaning.

The third-party water treatment entity will confirm the acceptance of water quality. The confirmed quality should adhere to the specified parameters listed below or match the quality of the water being introduced into the system, whichever exhibits the “highest” quality level.

Prior to initiating the chemical cleaning process, close all drain valves that were opened during the dynamic flushing phase.

Introduce the specified quantities of cleaning agent (as recommended by the chemical supplier) into the system using a temporary tank/pump setup or manual dosing equipment.

The chemical, referred to as B-12, should be dosed at a rate of 1-1.5 kg per cubic meter of system volume. Circulation of the chemical solution should be maintained for a continuous period of 24 to a maximum of 72 hours.

Activate the pumps to initiate circulation, which should persist for a minimum of 24 hours until a consistent level of dissolved iron is observed and recorded.

Sustain the circulation process until two consecutive samples, obtained at a two-hour interval, yield identical dissolved iron values.

Once the dissolved iron concentration stabilizes at a consistent level, clear the system of contaminated water by executing the filling and draining sequence outlined in step B.

This procedure should continue until water samples collected from at least two distinct drain points within the system meet the specified water quality parameters mentioned below.

Alternatively, the water quality should match that of the water being introduced into the system, selecting the “highest” quality criterion.

The discharged flushed water can be directed into the on-site stormwater drain, contingent upon adherence to the water disposal regulations stipulated by the municipality.

Alternatively, the flushed water can be transported by tankers and disposed of at an appropriate location.

Final Inhibition Procedure

Once the desired water condition is attained through system circulation, proceed to close all drain points linked to the Circulation pump.

Introduce passivation and microbiocide chemicals into the system at this stage. Allow the water to circulate for a duration of 4 hours. Apply corrosion inhibitor chemical 2910 at a dosage of 3.4 kg per cubic meter of the system volume. Incorporate microbiocide chemical 651 at a rate of 0.05 kg per cubic meter of system volume.

At the conclusion of this phase, retrieve a water sample for analysis. If the dissolved iron level in the sample exceeds the preceding value, a thorough flushing operation must be conducted to restore water cleanliness. Analysis should be performed by an approved water treatment specialist.

Maintain continuous system circulation, including all equipment, for a minimum of 24 hours.

Designated sampling areas must yield water samples for analysis, which will be utilized by the Water Treatment Third Party to verify the corrosion inhibitor level (Nitrite – minimum 700 ppm).

A comprehensive final water analysis, encompassing all requisite parameters, shall be furnished by the Water Treatment Third Party.

Note: Following the addition of the final treatment chemical, it is imperative to maintain the system in a full and continuous circulation state, preventing any stagnant conditions.

Biological Control

Chilled water systems offer a conducive environment for bacterial and microorganism growth. Effective management of biological proliferation within the system is essential. The supplier’s recommendation involves performing a shock dosing of biocide chemical 651 at a rate of 0.05 kilograms per cubic meter.

This biocide is introduced into the system using a manual dosing pot and is administered every three months to curb microorganism growth. Consistent monitoring and maintenance of residual levels are of utmost importance.

Reinstatement of Plant Components and Back Flushing

• Upon achieving the desired water conditions with inhibition, the reinstatement and back flushing of all plant components (such as Coils, Heat exchangers, etc.) can commence.
• Ensure a continuous supply of makeup water.
• Close the bypass route.
• Open the flow isolation valve while ensuring that the return DRV (Differential Return Valve) remains fully closed.
• Gradually open the drain cock, allowing water to discharge into a drain or container until clarity is observed.
• Close the drain cock.
• Shut the flow isolation valve.
• Open the return DRV.
• Gradually open the drain cock, allowing water to discharge into a drain or container until clarity is observed.
• Close the drain cock.
• Close all valves serving the plant components, and if applicable, clean and reinstall the strainer.
• Open both flow and return valves while ensuring the flushing bypass is fully closed.
• Repeat these steps for each previously isolated plant component within the system.

Note: Following the reinstatement of all plant components, the levels of inhibitors must be reassessed and appropriately dosed if needed.

Concise Flushing Procedure Overview

Water Filling

Potable water will be introduced from an elevated point within the chilled water line, preferably located in the AHU (Air Handling Unit) room or downstream of the drain point.

The positioning of the filling point is critical to avoid immediate drainage of fresh makeup water after filling.

Water Sourcing

The existing potable water supply within the facility will serve as the primary source. Alternatively, if necessary, water can be procured from tankers, and this supply will be accurately adjusted to account for the entire system volume.

Circulation of Water

Water circulation will be facilitated by the system pumps. During this circulation process, vigilant attention must be paid to prevent the water temperature from escalating to a level that might jeopardize the pump’s safety.

In cases where such an unsafe temperature is approached, the circulation can be temporarily halted, or a controlled discharge and replenishment of freshwater can be conducted.

Water Drainage

Water evacuation will occur from the system’s lowest point. The drained water can be directed to the floor drain line, or it can be accumulated within a small reservoir and subsequently pumped for dispersion into the external ground soak-away area adjacent to the building.

Guidance from a third-party water treatment specialist will ascertain whether the drained water meets the requisites for disposal into the sewer system, stormwater system, or land pump system.

If none of these options are feasible, the discharged water will be collected within a dedicated tank and subsequently transported off-site by tankers to comply with local drainage regulations.

Introduction of Chemicals

Chemical agents will be introduced into the system using the manual dosing pot situated within the Heat Exchanger room or temporary tank.

Bypass of Critical Equipment

A dedicated bypass line is incorporated for each Air Handling Unit (AHU) and Fan Coil Unit (FCU). The main inlet and outlet valves of the cooling coil will be shut, while the bypass valve will be opened.

In scenarios where a bypass line is not present, the supply and return water pipelines will be uncoupled from the unit and connected to each other using a temporary hose or pipe.

Air Venting

Strategically placed air vents, located at elevated points, will serve as ingress and egress points for air during drainage and filling procedures.

Cooling Coil and Plate Heat Exchanger Treatment

Water circulation through the cooling coil and plate heat exchangers will be withheld until the pipeline cleanliness is ensured and the water quality is deemed satisfactory.

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