Passivation and Derouging Services: ASTM A967 / ASME BPE for 316L Stainless Steel
Industrial passivation, rouge removal and surface optimization solutions for 316L stainless steel surfaces in conformity with ASTM A967/A380 and ASME BPE.
What Is Passivation?
Passivation is the process of chemically removing free iron particles from the stainless steel surface and forming a corrosion-resistant chromium oxide (Cr2O3) layer on it. The process increases the chromium/iron (Cr/Fe) ratio at the surface, which preserves the service life and hygienic character of the stainless steel. ASME BPE sets minimum surface requirements for process qualification samples: a Cr/Fe ratio of at least 1.3 when measured by XPS/ESCA (X-Ray Photoelectron Spectroscopy), at least 1.0 when measured by AES or GD-OES, and an oxide depth of at least 15 Å.
Passivation Steps and Chemical Methods
Before passivation, the surface must be fully cleaned to obtain a successful result. Pre-cleaning (alkaline cleaning and acid cleaning/pickling) is an integral part of this process.
Chemical Methods
- Citric acid passivation: Generally used in a concentration range of 4-10%. Because it is environmentally friendly, easy to use and chelates iron, it is the main method preferred in ASME BPE and modern pharmaceutical systems.
- Nitric acid passivation: A traditional method applied at 20-30% concentrations. Nitric acid, a strong oxidizer, allows the passivation layer to form quickly, but it must be applied with care because of its environmental effects and safety risks.
Rouge Removal (Derouging)
Especially in WFI and purified water (PW) lines, iron oxide deposits called rouge (Class I, II, III) form over time under the effect of high temperature.
- Class I rouge: Predominantly particulate deposit that migrates with the flow and can be wiped off with a cloth; the surface beneath is unchanged.
- Class II rouge: A localized, active form of corrosion that can be associated with attack by chlorides or other halogens.
- Class III rouge: A very stable, magnetite-type surface oxidation formed at high temperature, as in pure steam systems; it turns gold, blue and black as the layer thickens.
Standards and Verification Tests
The passivation processes we apply are tested and reported to show conformity with international standards (ASTM and ASME BPE).
Standards
- ASTM A967: Standard specification for chemical passivation treatments for stainless steel parts.
- ASTM A380: Standard practice for cleaning, descaling and passivation of stainless steel parts, equipment and systems.
- ASME BPE (Bioprocessing Equipment): The standard that sets design, material, fabrication and passivation/cleaning requirements for equipment used in the bioprocessing industry.
Verification Tests
Ferroxyl Test (ASTM A380)
A highly sensitive test used to detect free iron particles remaining on the surface. In the presence of free iron the solution turns blue.
Water Break Test
Detects whether there is organic contamination (oil, grease and the like) on the surface. If water flows over the surface in a continuous sheet the surface is clean; if droplets form, contamination is present.
Industry Applications and Frequency
Passivation should be repeated not only at first installation but at regular intervals over the life of the system (generally annually), or after mechanical interventions on the system (welding, repair).
Pharmaceutical Systems
ASME BPE-compliant passivation for PW (purified water) and WFI (Water for Injection) distribution loops, clean steam generators and production tanks.
Biotechnology Equipment
Treatments applied to maximize the surface corrosion resistance of fermenters, bioreactors and ultrafiltration systems.
Food & Beverage Production
Periodic passivation and scale/rust cleaning of 316L stainless steel lines in dairy, soft drink and specialty food production plants, to maintain hygiene standards.
Planning a project? Send us your flow rate, feed water source and target water quality to [email protected] — our engineers will reply with a technical proposal.