This article presents current research on the problem of rouge in clean steam generators and their distribution systems, as well as possible deleterious effects on capital equipment and final drug products.
By: Drew C. Coleman and Daryl L. Roll
Pharmaceutical clean (pure) steam systems consist of a generator, distribution tubing or piping, thermodynamic or balanced pressure thermostatic traps, control valves, pressure-reducing regulators, pressure gauges, pressure-relief valves, and volumetric totalizers. Most of these components are made of 316L stainless steel and contain fluoropolymer gaskets (most commonly polytetrafluoroethylene, also known as PTFE or Teflon), as well as semi metallic or other elastomeric materials. These components tend to corrode or degrade in service, potentially compromising the quality of the final clean steam (CS) utility product.
This project investigated stainless steel coupon samples from four CS system case studies, testing condensate for metals and particles, and conducting a risk assessment of potential corrosion effects on process and critical utility systems. Examining the corrosion byproducts involved preparing sample coupons of corroded tubing and components from distribution systems.9
These case studies investigated a variety of surface conditions, and included analysis of typical rouge products and corrosion effects. The referenced sample surfaces were evaluated for rouge deposits by visual inspection, scanning electron microscopy (SEM), auger electron spectroscopy (AES), and electron spectroscopy for chemical analysis (ESCA)/x-ray photoelectron spectroscopy (XPS). These techniques reveal the physical and atomic properties of the corrosion and deposits, and identify potential contributions to the critical utility fluid properties or final product.1
Stainless steel corrosion products are encountered in a variety of forms, such as a ferric oxide rouge layer (red or brown) on the metal surface found under- or overlying the thicker ferrous oxide layer (dark gray or black).2 The rouge layer is crystalline in structure and potentially dynamic, or capable of migrating downstream. The ferrous oxide (black rouge) layer tends to thicken over time as the deposit becomes more pronounced; its migratory presence is evidenced by particles or deposits found on sterilizer chamber surfaces and on equipment or vessels after steam sterilization. Laboratory analyses of condensate samples illustrate the particulate nature of the rouge as well as the level of soluble metals in the CS fluid.4
While there are multiple causes of these phenomena, the CS generator is often a significant contributor. It is not uncommon to notice ferric oxides of rouge (red/brown) on the surface, with ferrous oxides (gray/black) at the steam discharge, with both types slowly migrating throughout the CS distribution system.6
The CS distribution system is a branching configuration that has multiple use points, terminating at distant areas or ends of a main header and various branching subheaders. The system may include a series of regulators to reduce pressure/temperature at certain use points; these may be sites for corrosion. Corrosion can also occur in hygienically designed traps placed at various points within the system to remove condensate and air from the mobile clean steam, in downstream piping/tubing to drains, past the traps, or in condensate collectors. Reverse migration is evident in most cases, with rouge deposits forming above the traps and growing upstream into adjacent use point piping or into subheaders and beyond; the rouge that forms in traps or other components is found upstream from this source and continues to migrate both upstream and downstream.
Rouge in steam systems can be found in all forms including:
At use points, ball valves or valve housings exhibit significant rouge accumulation. Certain stainless steel components also demonstrate moderate to high levels of a disparate metallurgical structure, including delta ferrite. Ferrite crystal structure is suspected of lowering corrosion resistance, even though its content may only be 1%–5%. In addition, ferrite does not possess the corrosion resistance of austenitic crystal structure, therefore, it will corrode preferentially. Ferrite can be detected accurately with a ferrite meter or semi-accurately (and with significant limitations) using a magnet.
From system inception, when a new CS generator and distribution tubing is first commissioned and energized, several potential factors for corrosion are present:
Further, as a function of time, these corrosion factors may produce corrosion products as they meet, combine, and overlap with a blend of ferrous and ferric rouge. Generally, black rouge is first seen in the generator; rouge then emerges at the generator discharge piping and eventually throughout the CS distribution system.
Drew Coleman holds an Unlimited Steam Engineer’s License and is also a Licensed Chief Operating Engineer. He has worked for Genentech, Amgen, ICOS Corporation, and ID Biomedical, where he directed the design of BL-3 facilities and processes to produce novel recombinant vaccines. He founded Biodynamics International in 1991 to consult in the areas of facility and process design, validation, and operations. Coleman completed the Executive Leadership Program at Harvard University, JFK School of Government, and is a graduate of the Kodokan Judo Institute in Tokyo. He is active as a consultant to pharmaceutical and biotechnology companies and evaluates process engineering, utilities, water for injection, and pure steam systems. He has been an ISPE member since 1985, and was named ISPE Committee Person of the Year in 1992.
Daryl Roll, PE, is Astro Pak Corporation’s Technology Officer, leading the development and management of corporate technology objectives and support requirements. Additionally, Daryl serves as the primary senior technical advisor to clients and employees for corrosion, surface chemistry and stainless steel passivation. He is a member of the ASME BPE Subcommittees for surface finish, material joining and metallic materials (member) requirements, and a leading contributor for the passivation, rouge, and surface chemistry task groups. His papers on passivation and rouge control have been published in Pharmaceutical Engineering, IEEE Micro, and Chemical Engineering Journal. Daryl holds a degree in Chemistry and Earth Science from the California State University of Fullerton and a Professional Engineer’s license from the State of California.