Rouge Classification & Derouging Technical Guide
Comprehensive reference for rouge identification, classification, and remediation in pharmaceutical water systems per ASME BPE-2019 standards. Includes Class I, II, III specifications, analytical methods, removal protocols, and re-passivation requirements per ASTM A967.
What Is Rouge & Why It Matters
Rouge refers to iron oxide deposits on stainless steel surfaces in high-purity water systems, particularly those operating under USP water specifications. These deposits indicate active or historical corrosion processes that can compromise system integrity, product quality, and regulatory compliance per FDA 21 CFR 211.67.
The ASME BPE-2019 standard (Section SD-3.13) defines rouge classification based on physical characteristics, chemical composition, and removal difficulty. Understanding these classifications is critical for selecting appropriate remediation protocols per ASTM A967 and ASTM A380 standards.
Proper rouge remediation requires accurate classification, appropriate chemistry selection, complete removal verification, and mandatory re-passivation per ASTM A967 protocols.
Rouge Classification System (ASME BPE)
Click each classification below for detailed specifications, formation mechanisms, and treatment protocols
Class II Rouge
Moderately Adherent Corrosion Product — Chemical Removal Required
Corrosion product formed at the stainless steel surface under oxidizing conditions, typically in hot water systems above 65°C. Requires chemical removal and mandatory re-passivation per ASTM A967.
• Color: Dark red to purple
• Uniform surface coating
• Chemical removal required
• FeCr₂O₄ (chromite) present
• Cr:Fe ratio 0.1–0.5
• Ni enrichment possible
• High temperature oxidation
• Inadequate passivation
• Thermal cycling stress
• Temperature: 60–70°C
• Contact time: 4–8 hours
• Multiple treatments typical
Class III Rouge
Tightly Adherent Scale with Substrate Damage — Most Severe
Severe corrosion with subsurface metal alteration. Often requires aggressive chemical treatment or electropolishing. May necessitate equipment replacement if substrate integrity is compromised per ASME B31.3 criteria.
• Color: Black to dark gray
• Subsurface penetration
• May require mechanical removal
• Cr content <1%
• Severe Cr depletion
• Carbide precipitation possible
• Pure steam generators
• Crevices and gasket faces
• Never-passivated systems
• Electropolishing required
• 12–24 hour treatments
• Consider component replacement
Rouge Classification Comparison Matrix
Quick reference for identification, chemistry selection, and treatment parameters by rouge class
| Parameter | Class I | Class II | Class III |
|---|---|---|---|
| Visual Appearance | Orange to red-brown, powdery | Dark red to purple, uniform coating | Black to dark gray, scale/pitting |
| Adherence Level | Loosely adherent (wipes off) | Moderately adherent | Tightly adherent, integrated |
| Surface Damage | None — external contamination | Minor — surface-level | Severe — subsurface penetration |
| Primary Chemistry | Citric acid 0.5–2% | Citric 4–6% + EDTA chelant | Phosphoric 10–15% or HNO₃ blend |
| Temperature Range | 50–60°C (122–140°F) | 60–70°C (140–158°F) | 70–80°C (158–176°F) |
| Contact Time | 2–4 hours | 4–8 hours (multiple cycles) | 12–24 hours (multiple cycles) |
| Re-passivation | Recommended | Mandatory — ASTM A967 | Mandatory — Extended protocol |
| Typical Removal Time | 4–8 hours total | 1–2 days | 2–5 days or equipment replacement |
Analytical Methods for Rouge Characterization
Proper classification requires appropriate analytical techniques to determine rouge type and severity
Visual Inspection
Initial assessment per ASME BPE SD-3.13. Color, coverage pattern, and distribution provide first indication of rouge class.
Detection: Qualitative only
Use: Initial classification
Swab Testing
Surface sampling for quantitative metal analysis. Determines Fe, Cr, Ni content per USP methodology.
Detection: 1–10 μg/swab
Use: Surface contamination level
ICP-MS Analysis
Inductively Coupled Plasma Mass Spectrometry for ultra-trace metal quantification in rinse water.
SEM/EDX Analysis
Scanning Electron Microscopy with Energy Dispersive X-ray for morphology and elemental mapping.
XRD Analysis
X-Ray Diffraction for crystalline phase identification. Determines specific iron oxide compounds present.
Electrochemical Testing
Cyclic polarization and potentiodynamic scans to evaluate pitting potential and corrosion rate.
CXP Derouging & Re-Passivation Process
Our systematic approach ensures complete rouge removal with mandatory re-passivation per ASTM A967
Rouge Assessment & Classification
Comprehensive visual inspection with documentation. Swab testing at critical locations. Classification determines chemistry selection and treatment duration.
Pre-Operational Cleaning
Alkaline degreasing at 140–160°F removes organic contamination that interferes with derouging chemistry. Flow velocity verification ensures complete system coverage.
Chemical Derouging Cycle
Class-specific chemistry circulated at controlled temperature. EDTA-enhanced formulations for Class II/III. Multiple cycles for heavily contaminated systems. Real-time concentration monitoring.
Neutralization & Rinse
Complete acid neutralization followed by multiple WFI/DI rinse cycles. pH and conductivity monitoring to source water baseline. System drain and dry air/N₂ purge.
Re-Passivation (Mandatory)
Citric acid passivation per ASTM A967 Practice 3. 4–10% concentration at 60–71°C for controlled contact time. Restores protective chromium oxide layer.
Verification & Documentation
Copper sulfate test, ferroxyl test, water break test per ASTM A967. Complete documentation package including all test results, chemical certificates, and before/after photography.
Rouge Prevention & Control Strategies
Prevention is more cost-effective than remediation. Implementation of these strategies can reduce rouge formation by >90%
🏗️ Design Considerations
- Eliminate dead legs (L/D <6 per ASME BPE)
- Maintain velocity >3 ft/s — use flow calculator
- Specify 316L or AL-6XN stainless steel
- Electropolish critical surfaces (Ra <0.5 μm)
- Orbital welding with proper purge
- Calculate system volume for proper treatment
⚙️ Operating Parameters
- Temperature <65°C when possible
- Conductivity <1.3 μS/cm
- TOC monitoring <500 ppb
- Chloride <50 ppb
- Dissolved O₂ <20 ppb for hot systems
- Proper water treatment per technical water guide
🔧 Maintenance Program
- Annual passivation schedule
- Quarterly borescope inspections
- Monthly water quality testing
- Preventive derouging before Class II develops
- Trend analysis and documentation
- Coupon analysis program
📋 Monitoring Protocols
- Visual inspection schedule at defined locations
- Borescope surveys annually
- Iron testing <10 ppb acceptance
- Swab testing at problem areas
- Predictive maintenance metrics
- GMP documentation per 21 CFR 211.67
Related Technical Resources
Additional guides, calculators, and technical references for high-purity system maintenance
Derouging Services
Professional rouge removal and re-passivation for pharmaceutical water systems.
View Services →Pharmaceutical Passivation
GMP-compliant passivation for bioreactors, tanks, WFI systems, and process piping.
Learn More →ASTM A967 Guide
Complete technical guide to chemical passivation standards and methods.
Read Guide →Citric vs Nitric Passivation
Detailed comparison of passivation chemistries for different applications.
Compare Methods →Chemical Dilution Calculator
Calculate precise concentrations for citric acid, nitric acid, and cleaning solutions.
Use Calculator →Flow Rate Calculator
Determine required velocities and GPM for effective system flushing.
Calculate Flow →Piping Volume Calculator
Calculate system volumes for accurate chemical dosing requirements.
Calculate Volume →Industry Glossary
50+ essential terms for industrial cleaning and passivation professionals.
View Glossary →Rouge Contamination Requires Expert Remediation
Don't risk FDA observations or product contamination. CXP Solutions specializes in rouge classification, derouging, and re-passivation per ASME BPE and ASTM standards. Zero accidents in 10+ years. Owner involvement on every project.