Corrosion Mon

Module from the Inspection and NDE Curriculum curriculum.

Module 6 - Corrosion Monitoring · Learning Objectives · 1. Compute short-term and long-term corrosion rates · 2. Compute remaining life from current thickness vs retirement · 3. Apply retirement thickness (greater of pressure Tmin or structural T/2) · 4. Use online corrosion monitoring: ER probes, LPR, FSM · 5. Conduct MTI probe station - use inline UT where possible · Corrosion Rate and Remaining Life · Short-term CR = (t_previous - t_actual) / (delta time yr). Long-term CR = (t_initial - t_actual) / (time since installation). Use greater of CR values. Remaining life RL = (t_actual - t_retirement) / CR. Set next inspection at min of (max per Class) or (RL/2). · Online Corrosion Monitoring

Device	Principle	Application	Accuracy	Response Time	Notes
ER (Electrical resistance) probe	R change as element thins	Most fluids	+/-0.1 mil/yr	Days-weeks	Direct CR
LPR (Linear polarization)	Small voltage perturb	Conductive liquids	Varies	Seconds	Snapshot CR
Weight loss coupon	Weigh at removal	Any	Good baseline	Weeks-months	Gold standard
FSM (field signature)	Multi-electrode ERmap	Large areas	Moderate	Minutes	Scanning
Ultrasonic monitor	Permanent UT	External	+/-0.01 in	Minutes	MTI
Hydrogen probe	H2 flux through membrane	Wet H2S	Qualitative	Hours	Permeation monitoring
pH and ORP	Water chemistry	Cooling water	Continuous	Seconds	Crude OH

Source: Inspection_NDE_Curriculum_v1.xlsx · Sheet: Corrosion Mon

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