VAL-065 Cleaning, Derouging and Passivation of the Stainless Steel Parts of the Purified Water System

5.1 Passivation Treatment

Passivation is the process of forming a protective oxide film on stainless steel.  The corrosion resistance of stainless steel is due to a thin chromium oxide layer on the surface of the metal.  The chromium oxide layer renders the metal surface passive or resistant to corrosion.  Failure to develop and maintain the chromium oxide layer results in an increase in the activity of the metal surface and can lead to corrosion in a corrosive environment. Passivation treatment is to be selected by Site Engineering Department.  Nitric acid is more aggressive and is the engineering preference for passivating at ambient temperature. Phosphoric and Citric acids are preferable from a safety viewpoint.

When diluting the acid, ALWAYS ADD ACID TO WATER.  NEVER ADD WATER TO ACID.

Treatment Type 1

Solution shall contain 25-45 (w/v) % Nitric Acid.  Parts shall be exposed to this solution for 20 to 120 minutes at a temperature of 21^oC to 32^oC.  The solution and residual effluent must be monitored closely.  While very effective as a passivator, this solution may have environmental ramifications.

Treatment Type 2

The solution shall consist of 10 (w/v) % citric acid and 2 (w/v) % EDTA (ethylenediaminetetraacetic acid).  Parts shall be exposed to this solution for 1 to 10 hours at a temperature of 65^oC ± 5^oC.  EDTA is a chelating agent that keeps iron in solution over a wide pH range.  Sodium Gluconate is an alterative chelating agent that could be used in place of EDTA.  This solution has high reactivity with free iron, is less sensitive to exposure time, is far less corrosive to other materials, is less costly, and is considered environmentally friendly when used properly.

Treatment Type 3

Solution shall contain 20 (w/v) % Phosphoric acid.  Parts shall be exposed to this solution for a minimum of 4 hours at a temperature of 65^oC ± 5^oC.  Phosphoric acid is a weak oxidizing acid

Treatment Type 4

The solution shall consist of a commercially available pre-formulated passivating chemical such as CITRISURF 3050.  The solution shall consist of 7-14 (w/v) % CITRISURF 3050.  Parts shall be exposed to this solution for 1 to 4 hours at a temperature of 65^oC ± 5^oC.

Derouging Treatment

The phenomenon of rouging has been attributed to the destruction of the chromium oxide layer on the stainless steel surface and the formation of an iron oxide rich corrosion layer.  Rouging is a known problem in pharmaceutical water systems that are generally constructed from austenitic CrNiMo steel grade AISI 316L.  It is known that rouging is promoted by elevated temperatures above 60^oC. Derouging can be performed using a number of different chemical formulations.  Listed herein are the chemicals and derouging procedure for each formulation. Essentially derouging is a passivation treatment, with the dual function of removing the rouge and passivate the stainless steel surface.

Treatment Type 5

Solution shall contain 30-45 (w/v) % CITRISURF 8050.  Parts shall be exposed to this solution for 6 hours at a temperature of 65^oC ± 5^oC.  The exposure time can be changed depending on the level of rouging.  For this treatment type the duration shall start from the time when the solution reaches the operative temperature.

Treatment Type 6

Solution shall contain 5-25 (w/v) % of Phosphoric acid, 0-10 (w/v) % citric acid and up to 5 (w/v) % Sodium Gluconate.  Parts shall be exposed to this solution for a minimum of 4 hours at a temperature of 65^oC ±5^oC.  For this treatment type the duration shall start from the time when the solution reaches the operative temperature.

Cleaning (Alkaline Treatment)

An alkaline treatment is required to remove any organic matter or biological fouling from the system.  Invasive repairs or newly installed systems require an alkaline clean to remove grease, oil, cutting fluids from the surface of the stainless steel before passivation treatment, to allow full access by the treatment.

Treatment Type 7

Solution shall contain 0.3 % sodium hydroxide by volume.  Parts shall be exposed to this solution for a minimum of 1 hour at a temperature of 20^oC ±5^oC.  The concentration and contact time of the sodium hydroxide can be changed depending on the user requirements.

Treatment Type 8              

Commercially available alkaline solution containing surfactants can be used to remove any grease or organic matter.  An example is the use of Alconox soap solution. Approval from Quality Compliance is required for any surfactant based cleaning agent and a proven method for residual removal must be used before release of the equipment for use.

5.2 Treatment Selection

It is generally recommended that the purified water system be cleaned with an alkaline cleaning agent prior to passivation. The alkaline treatment will remove any organic deposits such as dead biofilms from the stainless steel surface to allow full contact of the surface with the acid during passivation. The derouging procedures contained in this SOP are passivation treatments that are effective in removing rouge and simultaneously increase the rate of formation of the chromium oxide layer on the stainless steel surfaces.

Treatment type 7 or 8 is required to remove any organic matter or biological fouling from the system.  It is generally recommended that an alkaline clean be performed prior to passivation treatment.  The use of treatment types 1, 2, 3 and 4 will be used where the system has not developed rouge as with newly installed systems.  Treatment types 3, 5 and 6 will be used on existing systems where rouge has developed.

It is recommended that passivation treatment type 4 be used as part of the plant maintenance strategy for passivating the purified water tank and ringmain. CITRISURF 3050 is a preformulated blend of citric acid and chelating agents and provides a simple and efficient

method of performing the passivation of the purified water system.  It is recommended that a concentration of 10 (w/v) % of CITRISURF 3050 be used for a duration of 1 hour at 65^oC

±5  ^oC.  Since the ringmain holds approximately 500 litres of water in the pipework, the purified water tank  should be filled to 1300L with RO water and then to obtain a working concentration of 10 (w/v) % of CITRISURF 3050, 200kg of concentrated CITRSURF 3050 be charged in the purified water tank .  The above mentioned volume and working concentration of 10 (w/v) % of CITRISURF 3050 will require only one 200kg drum of CITRISURF 3050, minimizing material handling requirements.

The concentration of the passivation and derouging solution can be varied based on the assessment of a chemist / chemical engineer.  High concentrations of strong acids such as nitric acid can etch the stainless steel surface.  A risk assessment needs to be performed for the concentration and contact time of the acid with the stainless steel surface.  An increase in acid concentration will generally lead to a reduced contact time for the treatment method.

The calculation for the amount of chemical required for a given treatment should take into account the dead volume in the ringmain pipe work (approx. 500L) and the minimum working volume in the purified water storage tank is generally considered to be 1500L, or 30 % high tank level.

5.3 Cleaning, Derouging and Passivating the Ringmain

5.3.1 Obtain a Cleaning, Derouging and Passivating Form to complete the cleaning and passivation report.

5.3.2 The chemical staging area should be pre-approved by EHS.  Proper use of signage should be used to identify the danger associated with the chemicals.  A barrier tape has to be used to define the boundary of the chemical staging area and prevent unauthorized entry within the taped area.

5.3.3 Prior to preparation and transferring any passivating / cleaning chemicals ensure that all safety and environmental measures are in place.  Wear the listed protective gear in Section 4.5 of this SOP and ensure spill and first aids kits are available for rapid response to any mishaps.  All bulk chemical drums should be placed on bunded pallets.

5.3.4 Lockout all manual user point valves located on the ringmain within the core area with valve lockout devices and attach a lockout tags on the actuated valves.  Ensure all valves are fully closed and capped prior to attaching the lockout tags and lockout devices.

5.3.5 Initially fill the system with at least 1000L of RO water and circulate for a minimum period of 30 minutes.  Obtain the Piping and Instrumentation Diagram (P&IDs) for the purified water generation system and the ringmain.  With the help of the P&IDs check the integrity of all accessible valves and fittings by conducting a walk through of the entire system.  During the walk through of the RO generation room and all user point valves located in the ringmain check for leaks.

5.3.6 Close valve to prevent the cleaning agent re-circulating into the 0.22 micron filter.

5.3.7 Adjust the volume of purified water in the tank so as to have the right solution concentration with the addition of chemicals and ensure the system is at ambient temperature.

5.3.8 Manually close actuated drain valve by firstly removing the compressed air line to the valve, then attaching a lockout tag on the valve.  It is important to have drain valve in a closed position and locked out to prevent any accidental discharge of hazardous chemicals into the drain system from the HMI interface.

5.3.9 Prepare the cleaning / passivation chemicals as required in a separate vessel constructed of suitable material or use a pre-blended formulation.  If chemicals have to be blended onsite a risk assessment must be performed.

5.3.10 If a transfer pump and hose is to be used for pumping the chemicals then a safety check of the transfer line should be performed both visually and by simulation of the actually pumping operation.  RO water collected in a separate drum should be pumped from the chemical holding area into the purified water storage tank to ensure that there is no leakage prior to pumping any hazardous chemicals.

NOTE: If industrial grade chemicals are used then a strainer should be used on the transfer line to prevent any foreign particulate matter from contaminating the purified water system.

5.3.11 It is recommended a twin set CB radio to be used to monitor the chemical transfer process from the chemical staging area to the purified water tank.  During the chemical transfer a person is to be stationed in the RO room and a person will be stationed at the chemical staging area from where the chemicals will be pumped.  The twin set CB radio will be used for communication between the operators stationed at the chemical staging area and the RO room.  In the event if the hose detaches or sprangs a leak in the RO room, the CB radio allows for rapid communication to stop the pumping operation.

5.3.12 Add the quantity of chemicals into the tank as per the selected treatment method.  The addition of chemicals can be via a transfer pump or manual addition depending on the quantity.  During the transfer of chemicals into the tank ensure that all safety and environmental measures are in place.  Minimum PPE should include goggles / face shield, gloves and Tyvek overall.

When diluting the acid, ALWAYS ADD ACID TO WATER.  NEVER ADD WATER TO ACID.

5.3.13 Change the temperature setting of the ringmain as required by the treatment method and set the required duration in the HMI interface for the distribution loop. The pump speed should be set to the maximum setting of 50Hz for all cleaning and passivation treatments.  Ensure that for treatment types that require an operational temperature

above 60^oC that the duration starts from the time when the solution reaches the operative temperature. The minimum high level in the tank should be 30 % (approx. 1500L) for any chemical treatment.

CAUTION: Water at or above 60^oC can cause 3^rd degree burns in only a few seconds.  Avoid all skin contract.

5.3.14 After transferring the chemicals into the purified water storage tank, the pump and hose assembly shall be rinsed with RO water to remove any residual chemicals.  This step has to be performed in between the transfer of different classes of chemicals.  Example, if an alkaline was pumped first for cleaning and then an acid is required to be pump afterwards, then it is important that the pump and hose be rinsed by pumping RO water before the acid.

5.3.15 If passivation or derouging is to performed after cleaning with an alkaline treatment then the purified water system has to be rinsed after the alkaline treatment.  Residual alkaline solution in the tank and pipework will reduce the working concentration of the derouging and passivation chemicals significantly due to neutralization reaction.

5.3.16 The hose should be dried with compressed air prior to storage, to prevent microbial / fungal growth.

5.4.  Removal and Disposal of Cleaning Chemical

The alkaline or acid cleaning solution can be either collected in waste tote containers or neutralized and disposed into the trade waste stream.  If nitric acid is used as the passivating agent then the acid must be collected in tote containers for disposal.  Citric acid and phosphoric acid based chemicals can be neutralized to a pH of 7 to 10 and discharged to trade waste.  Sodium Hydroxide solutions used for cleaning can be either diluted or neutralized to a pH of 7 to 10 and discharged to trade waste. Cleaning agents with high concentrations of surfactants require environmental impact assessment to determine the disposal method.

Neutralization reactions are exothermic and the exact amount of neutralizing agent can be determined through acid-base titration. If pre-formulated chemicals are used it is recommend that acid-base titration be used to determined the required amount of neutralizing solution. It is important to verify the concentration and volume of the pH Neutralizer required to neutralize the process solution, as to prevent overflow from the tank.

Option 1 Disposal of used chemical solution by an approved contractor.

The process solution can be pumped into waste totes for disposal by an approved contractor.  The first rinse should also be collected in waste tote bins for disposal.

Option 2 Neutralize chemical solution in the storage tank and dump to trade waste.

Ensure all environmental regulations are adhered too and approval of EHS has been obtained prior to discharge of neutralized salt solution into to the trade waste system. The water has to have a pH of 7 to 10 prior to discharge into the trade waste system.

Option 3 Transfer chemical solution into secondary vessel for neutralization 

The process solution can be neutralized in tote containers and then dumped to trade waste system.

NOTE: After neutralization the discharge from the purified water storage tank  can be piped to the Site Site cooling tower system.  Prior to discharging any used cleaning chemicals or neutralized salt solution ensure that the drainage line is diverted to the trade waste stream.

ENSURE THE DRAIN PIPE FROM THE PURIFIED WATER SYSTEM IS DIVERTED TO TRADE WASTE AND NOT TO THE COOLING TOWERS

5.5 Rinsing

5.5.1 Rinse the system until the pH is between 5 and 7 and the conductivity of the final rinse is £ 4.3 mS/cm.  Dump the water to trade waste if the conductivity is greater then 4.3 mS/cm.  Continue rinsing until the conductivity and pH of water is within specification.  Once the conductivity and pH are within specification, conduct a final rinse by dumping all water from storage tank .

5.5.2 Open Valve, remove lockout devices from the ringmain.

5.5.3 Flush a minimum of 10L through all user points and drain valves.

5.5.4 Document temperature, pH and conductivity readings in the cleaning / passivation report should be contained in a controlled Form.

5.6 Return System to Production Use

5.6.1 Change all PLC control setting for tank level, pump speed, temperature and heat sanitize cycle to validated production setting.  Detach all non-system hose and pump from the system.

5.6.2 Sanitize the distribution loop after the completion of chemical treatment and prior to release of the purified water system for production.

5.6.3 Complete the Cleaning, Derouging and Passivating Form and obtain the required approval for the completion of the cleaning / passivation treatment.