📋 Case Study

Stainless Steel in Food Processing

Chloride-induced pitting in weld heat-affected zones (HAZ) of 316L vessels leading to product contamination

🏗️ Project Overview

High-pressure CIP (Clean-in-Place) system for dairy processing plant (85°C, 2% NaOH, 1% HNO₃, 500 ppm chlorine residual)

🎯 Challenge

Chloride-induced pitting in weld heat-affected zones (HAZ) of 316L vessels leading to product contamination

🔧 Design Approach

Upgraded to 2205 duplex stainless steel with automated orbital GTAW welding, post-weld pickling + electrochemical passivation per ASTM A967, and real-time chloride monitoring

📐 Design Diagram

AI-generated project design illustration

📐 Key Calculations

Critical Chloride Limit

f(CPT, pH, temp)

Result: ≤120 ppm at 85°C

Derived from ISO 15156-3 Annex D for duplex grades

Passivation Quality Index

ASTM A967 Copper Sulfate Test time-to-red-color

Result: ≥60 sec

Validates Cr-rich passive layer continuity

📊 Results

Zero product recalls linked to metal leaching; 40% reduction in unscheduled vessel replacements

💡 Lessons Learned

• •CIP chemical concentration drift >±5% invalidates corrosion models
• •Weld root oxidation increases pitting susceptibility 7× vs. cap side

✅ Key Takeaways

• 1CIP chemical concentration drift >±5% invalidates corrosion models
• 2Weld root oxidation increases pitting susceptibility 7× vs. cap side