Rouging generation and effect
The rouge in the systems is the phenomena of CORROSION, which is the result of air, water or a chemical agent that comes in contact with metal. This contact causes oxides (corrosion) on the metal, and this is commonly called “rouge”.
Considering that the most used material for piping/vessels in the pharma industry is stainless steel (AISI 316L), the most common constituent of rouge is ferrous (ferric oxide). The rouge in the system depends on the operational characteristics of the system itself:
- Water flow;
- Water temperature;
- Water time of "residence";
- Methodology of procedure at the point of use
- Higher water temperature, raising the rouge rates.
Destruction of the passive layer is accelerated by:
- Highly corrosive environments (steam - chlorides, corrosive products; high temperature – stress, erosion);
- Improper surface conditions (improper welding, surface defects, inadequate cleaning, and inadequate passivation).
The effects of the rouge are the following:
- Increasing surface roughness, consequently reduction of cleanability and sanitization;
- Increasing microbial excursions, consequently high possibility to incur product contamination;
- Equipment life reduction;
- Type of corrosion (localized corrosion - small pits and hole, stress cracking, crevice corrosion, galvanic corrosion, uniform corrosion).
Kind of rouge
The rouge is commonly defined by the classification of “Tyrberg and Ledden”:
Corrosion deposit originated at some point of the system and deposited downstream. Usually, the finishing surface of the steel remains good and at this stage the rouge can be easily removed).
Adherent corrosion originated by a not passivated/wrong passivated steel surface (e.g., on the welding). The normally protective film due to passivation is altered and could cause underlying damage on the surfaces.
A corrosion that presents black or blue color, commonly called magnetite, which forms on high temperature steam systems surfaces. The top layer can be wiped off and is non-reactive; it behaves like a passive layer.
Frequency of intervention and rouge limits
In the pharma field the rouge on the water systems has been an issue for many years; some analytic/scientific methodologies have been developed to recognize the need of derouging and passivation, such as periodic intervention or visual inspection and looking for the rouging phenomena on the systems.
In any case, periodic intervention is not convenient for many reasons:
- Derouging and passivation in the event the rouge inside the system is not present;
- Cost for the intervention;
- Shut down of the systems;
- Product quality issues.
In a pharmaceutical environment, ensuring product quality is paramount. Precisely documenting that all constituent components do not have an adverse influence on the product is imperative, so ensuring the constituents and their delivery systems do not adversely affect the product must be proven continually with data and documentation.
500 nm can be a good gauge to determine the rouge limit value to initiate derouging and passivation. The 500 nm level is 0.5 micron, which is a very small level.
To monitor the systems, the best solution is to install an on-line rouge monitor to measure metal loss.
Derouge the system
To derouge the system, usually it is possible to use:
- A robust alkaline cleaning to remove organic residues;
- An acid treatment to remove iron oxides:
- nitric and citric acid ASTM referenced (able to regenerate the passive layer), also a sulfuric / phosphoric solution can be used;
- Process monitoring sampling to assess the effectiveness of the treatment.
Common procedures to derouge
Following are common procedures to treat the rouge:
- Isolate the system to be treated.
- Use existing validated procedures to clean and rinse the system to remove organic/product residues’.
- All non-stainless steel materials should be disconnected.
- Check the system for eventual leakage.
- Consider the acid solution product to use for the derouging, paying close attention to the HSE procedure.
- Introduce de-ionized water or WFI to the system and introduce the acid solution at a percentage of 10%. The solution should be adequately agitated.
- Heat the solution to 60°C (140°F) to 80 °C (176°F) with recirculation.
- Monitor the process with a colorimeter to check the iron content.
- Recirculate the system for three to four hours.
- Increase the acid solution by about 5%.
- Continue the process for at least another half hour.
- Monitor the system by a colorimeter before stopping the process.
- If the monitoring of the iron content is the same as on step 8, the derouging process is finished. Vice versa, the process should continue at least until the iron content changes.
- At the end of the process, drain the solution according to proper regulatory procedures; this could include neutralization before disposal.
- Rinse the system with hot de-ionized water or WFI, maintaining each cycle for at least 15 minutes. The number of rinses depends on the system.
- Monitor the rinse by conductivity, TOC and final sampling.