Corrosion Failure Modes and Materials of Construction in Nitric Acid Plants: 5-Day Specialized Training Course

Course Overview

This intensive 5-day nitric acid plant corrosion training provides specialized knowledge of corrosion mechanisms, failure modes, and materials selection for nitric acid manufacturing facilities. Designed for materials engineers, corrosion specialists, plant engineers, and maintenance professionals.

Target Audience: Materials engineers, corrosion specialists, integrity engineers, plant engineers, maintenance managers, metallurgists, and technical professionals in nitric acid facilities.

Course Objectives:

• Understand corrosion mechanisms in nitric acid environments

• Master materials selection for different plant sections

• Identify common failure modes and root causes

• Implement corrosion prevention strategies

• Apply inspection and integrity management techniques

Day 1: Nitric Acid Process and Corrosion Fundamentals

Morning Session: Process Overview

Understanding the Environment

Foundation of nitric acid manufacturing:

Process Description:

• Ammonia oxidation (Ostwald process)

• Catalytic oxidation: ammonia to NO (850-950°C)

• NO oxidation to NO₂

• Absorption in water: forming dilute and concentrated acid

• Plant capacities: 500-2000 MTPD

• Single, dual, and triple pressure processes

Nitric Acid Concentrations:

• Weak acid: 50-70% HNO₃

• Concentrated acid: 98-99% HNO₃

• Azeotropic concentration: 68.4%

• Concentration methods: extractive distillation

• Temperature effects on corrosivity

Corrosive Species:

• Nitric acid (HNO₃): oxidizing acid

• Nitrogen oxides: NOx, NO, NO₂

• Nitrous acid (HNO₂): highly corrosive

• Dissolved oxygen effects

• Velocity and erosion-corrosion

Afternoon Session: Corrosion Mechanisms

How Corrosion Occurs

Understanding corrosion fundamentals:

General Corrosion:

• Uniform metal dissolution

• Passivity and passive film formation

• Passivity breakdown conditions

• Temperature and concentration effects

Localized Corrosion:

• Pitting corrosion: chloride influence critical

• Crevice corrosion in flanges

• Selective grain boundary attack

• Deposit-induced corrosion

• Under-insulation corrosion (CUI)

Intergranular Corrosion (IGC):

• Sensitization of stainless steels

• Grain boundary chromium depletion

• Weld heat-affected zones (HAZ)

• Carbide precipitation mechanisms

• Prevention through material selection

Stress Corrosion Cracking (SCC):

• Chloride SCC in austenitic stainless steels

• Transgranular crack morphology

• Required conditions: stress, environment, material

• Temperature thresholds (>50°C critical)

• Catastrophic failure potential

Other Mechanisms:

• Erosion-corrosion in high-velocity areas

• Cavitation in pumps and valves

• Corrosion fatigue under cyclic loading

• Galvanic corrosion between dissimilar metals

Day 2: Materials Selection

Morning Session: Weak Acid Section Materials

Materials for Absorption Systems

Mastering material selection:

Stainless Steel Grades:

• AISI 304/304L: limited applications

• AISI 316/316L: improved resistance

• Duplex stainless steels: 2205, 2507

• Super austenitic: 904L, AL-6XN, 254SMO

• Alloy 20: excellent for weak acid

Selection Criteria:

• Acid concentration and temperature

• Chloride content: most critical (<25 ppm)

• Velocity and turbulence

• Equipment criticality

• Cost-effectiveness

Equipment-Specific Materials:

• Absorption towers: 304L or higher grades

• Coolers and condensers: 316L minimum, titanium preferred

• Pumps: 316L, duplex, super austenitic

• Piping: 304L/316L for dilute acid

• Storage tanks: stainless or lined carbon steel

Titanium Applications:

• Unalloyed titanium: Grade 1, Grade 2

• Excellent corrosion resistance

• Primary use: heat exchangers, condensers

• Cost and hydrogen embrittlement considerations

Afternoon Session: Strong Acid and High-Temperature Materials

Advanced Materials

Understanding severe environment materials:

Concentrated Acid Service:

• Aluminum and aluminum alloys: excellent for >82% acid

• 1100, 3003, 5052 aluminum grades

• Passive film formation

• Temperature limitations (<50°C optimal)

• Chloride and heavy metal sensitivity

High-Temperature Section:

• Platinum-rhodium alloys: catalyst

• Stainless steels: 310S, 330 for ductwork

• Inconel alloys: 600, 601, 625

• Heat-resistant cast alloys

• Refractory materials

Nickel-Based Alloys:

• Hastelloy C-276: excellent resistance

• Inconel 625: high temperature performance

• Alloy C-22, C-2000: superior performance

• Applications: valves, critical equipment

• High cost limiting use

Alternative Materials:

• Glass-lined equipment

• Fluoropolymer linings: PTFE, PFA

• Rubber linings: natural and synthetic

• Fiber-reinforced plastics (FRP)

• Graphite and ceramic materials

Day 3: Common Failure Modes and Case Studies

Morning Session: Typical Failures

Understanding Plant Failures

Identifying common failure modes:

Chloride-Induced Failures:

• Chloride SCC: most catastrophic

• Sources: cooling water leaks, contamination

• Pitting precursor to SCC

• Rapid propagation

• Prevention through chloride control

Sensitization Failures:

• Intergranular attack in HAZ

• Knife-line attack adjacent welds

• Carbide precipitation during welding

• 304/304H versus 304L differences

• Stabilized grades (321, 347)

Erosion-Corrosion:

• High-velocity acid attack

• Pump impeller failures

• Valve trim erosion

• Piping elbow failures

• Design velocity limitations

Under-Insulation Corrosion:

• External chloride SCC

• Water ingress mechanisms

• Temperature cycling condensation

• Insulation material selection

• Inspection challenges

Afternoon Session: Case Studies

Learning from Failures

Analyzing actual incidents:

Case Study 1: Absorber Tower SCC:

• Catastrophic rupture incident

• Root cause: chloride contamination

• Material: 304L stainless steel

• Contributing factors: stress, temperature

• Corrective actions: upgrade, monitoring

• Lessons learned

Case Study 2: Heat Exchanger Failures:

• Pitting and crevice corrosion

• Material selection inadequacy

• Upgrade to titanium tubes

• Design improvements

• Maintenance changes

Case Study 3: Piping System Failures:

• Erosion-corrosion at flow changes

• Velocity-induced attack

• Design modifications

• Material upgrades to duplex

• Inspection frequency

Root Cause Analysis:

• Investigation procedures

• Sample collection

• Laboratory analysis: metallography, SEM

• Mechanical testing

• Chemical analysis

• Determining root causes

Day 4: Prevention and Monitoring

Morning Session: Prevention Strategies

Proactive Management

Implementing prevention programs:

Material Selection Excellence:

• Proper grade selection

• Chloride limits for materials

• Temperature and concentration mapping

• Safety factors

• Life-cycle cost analysis

Design for Prevention:

• Avoiding crevices and dead-legs

• Proper drainage

• Smooth flow transitions

• Gasket material selection

• Insulation system design

• Accessibility for inspection

Process Control:

• Chloride monitoring (<25 ppm critical)

• Temperature control

• Acid concentration management

• Velocity control

• Contaminant exclusion

• Water quality management

Protection Methods:

• Protective coatings and linings

• Temporary inhibitors during shutdowns

• Nitrogen blanketing

• Cathodic protection considerations

Afternoon Session: Monitoring and Inspection

Detecting Corrosion Early

Implementing monitoring programs:

Corrosion Monitoring:

• Corrosion coupons: weight loss

• Electrical resistance (ER) probes

• Linear polarization resistance (LPR)

• Ultrasonic thickness monitoring

• Online analyzers

• Data trending

Non-Destructive Testing:

• Visual inspection

• Ultrasonic thickness testing (UTT)

• Radiographic testing (RT)

• Magnetic particle testing (MT)

• Liquid penetrant testing (PT)

• Eddy current for tubes

Inspection Planning:

• Risk-based inspection (RBI)

• Critical equipment identification

• Damage mechanism assessment

• Inspection frequency

• Shutdown versus online inspection

Water Chemistry Control:

• Cooling water chloride monitoring

• Conductivity measurement

• pH control

• Dissolved oxygen monitoring

• Microbiological control

Day 5: Advanced Topics and Integrity Management

Morning Session: Welding and Fabrication

Proper Construction Practices

Understanding fabrication requirements:

Welding Procedures:

• Qualified WPS for stainless steels

• Low heat input

• Interpass temperature control

• Filler metal selection (low carbon)

• Shielding gas purity

• Back purging requirements

Heat Treatment:

• Solution annealing: 1040-1120°C

• Rapid cooling

• Preventing sensitization

• Stress relief considerations

• Verification testing

Welding Aluminum:

• Oxide removal

• Inert gas shielding

• AC welding requirements

• HAZ characteristics

• Post-weld inspection

Quality Control:

• Visual inspection criteria

• NDT requirements

• Corrosion testing: ferric sulfate

• Hardness testing

• Surface finish requirements

Afternoon Session: Integrity Management

Comprehensive Asset Management

Developing management systems:

Regulatory Compliance:

• OSHA PSM 1910.119

• EPA RMP compliance

• Mechanical integrity programs

• Process hazard analysis

• Management of change

Industry Standards:

• ASME codes

• API 570: Piping Inspection

• NACE corrosion standards

• ASTM material specifications

Integrity Management Elements:

• Equipment inventory and criticality

• Damage mechanism identification

• Inspection and testing plans

• Fitness-for-service assessments

• Remaining life calculations

• Repair strategies

Performance Metrics:

• Corrosion-related failure rates

• Inspection compliance

• Mean time between failures

• Maintenance costs

• Safety indicators

• Continuous improvement

Future Trends:

• Advanced monitoring technologies

• Digital twins and predictive analytics

• Machine learning

• Nanotechnology coatings

• New corrosion-resistant alloys

Course Deliverables

Participants Receive:

• Comprehensive corrosion manual

• Materials selection charts

• Inspection procedure templates

• Failure analysis case studies

• Regulatory compliance checklists

• Professional certificate

• Online resources access

Interactive Components:

• Metallographic examination

• Failed component analysis

• Material selection exercises

• NDT demonstrations

• Group workshops

Why This Training Is Essential

Key Benefits:

• Prevent catastrophic failures

• Optimize material selection

• Extend equipment life

• Enhance plant safety

• Ensure regulatory compliance

ROI:

• Reduced unplanned shutdowns

• Lower maintenance costs

• Improved plant availability

• Decreased safety incidents

Keywords: nitric acid corrosion, materials of construction, stainless steel selection, chloride stress corrosion cracking, intergranular corrosion, titanium heat exchangers, aluminum nitric acid, corrosion failure analysis, NDT inspection, integrity management