AMPP O-CAT flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Four corrosion cell elements
- An anode, a cathode, an electrolyte path, and a metallic return path. Removing any one element interrupts the corrosion cell and stops the reaction.
- Anodic reaction for iron
- Fe -> Fe2+ + 2e-. Iron dissolves and releases electrons that travel through the metal to the cathode, where they are consumed by a reduction reaction.
- Oxygen reduction in seawater
- O2 + 2H2O + 4e- -> 4OH-. This cathodic reaction dominates in neutral, aerated seawater and raises local pH at the cathode surface.
- Galvanic series meaning
- A ranking of alloys by practical corrosion potential in seawater. Widely separated materials form a stronger galvanic couple and the more active metal corrodes faster.
- Faraday's law of corrosion
- Mass loss equals (I x t x M)/(n x F), with F equal to 96,485 coulombs per mole. It converts measured current into a predicted metal loss.
- mm/y to mpy conversion
- One millimeter per year equals 39.37 mils per year. Multiply mm/y by 39.37 to obtain mpy, or divide mpy by 39.37 to obtain mm/y.
- PREN formula
- PREN = %Cr + 3.3 x %Mo + 16 x %N. Higher values indicate greater resistance to chloride pitting in stainless and duplex alloys.
- Carbon equivalent formula
- CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Values above roughly 0.40-0.43 raise hydrogen-assisted cold cracking risk in field welds.
- Splash zone severity
- The region of continuous wetting and drying with full oxygen access and tidal impact. It is the most aggressive external zone and needs coating or sheathing protection.
- Duplex stainless yield strength
- Duplex grades with about 22% or 25% chromium reach yield strengths near 450-550 MPa and resist chloride stress corrosion better than 300-series austenitics.
- HISC risk driver
- Hydrogen-induced stress cracking rises with steel strength and cathodic overprotection. High-strength chain and bolts need potential limits, often not below about -0.95 V.
- Fatigue at tubular joints
- Fatigue life depends on hot-spot stress range and the applicable S-N curve. Weld toe grinding and post-weld heat treatment improve the classified fatigue category.
- API jacket steel grades
- Fixed jackets commonly use normalized or TMCP steels such as API 2H, 2Y, and 2W. Higher-strength grades carry reduced carbon equivalent to preserve weldability.
- ISO 12944 corrosivity categories
- Categories run from C1 for heated interiors to C5 and CX for very high marine and offshore exposure. Offshore topsides typically specify C5 or CX systems.
- NORSOK M-501 purpose
- It defines offshore coating systems by system number, such as atmospheric epoxy systems and thermally sprayed aluminum on carbon steel for splash zones.
- Sa 2 1/2 surface preparation
- A near-white abrasive blast cleaning grade per ISO 8501-1. It is the usual requirement for immersion and high-durability offshore coating systems.
- Blast profile for epoxy
- High-build epoxy systems typically require a 50-85 micrometer angular profile. Profile is measured and recorded because adhesion depends on it.
- Thermally sprayed aluminum
- A splash-zone coating that acts as a barrier and as a sacrificial anode, continuing to protect exposed steel when the coating is damaged.
- Coating holidays and CP demand
- Holidays and damage expose bare steel, raising the cathodic protection current required. Excess bare area can overload anodes and cause underprotection.
- 80-20 coating thickness rule
- No individual thickness reading falls below 80% of the specified nominal, and the average of all readings meets or exceeds the nominal.
- Seawater CP protection criterion
- Carbon steel in seawater is protected at about -0.80 V vs Ag/AgCl/seawater. Stressed or high-strength members often require -0.90 V.
- Overprotection potential limit
- About -1.05 V vs Ag/AgCl/seawater on high-strength steel. More negative potentials increase hydrogen evolution and cracking risk.
- Sacrificial anode mass formula
- Mass = (mean current x design life in hours)/(anode capacity x utilization factor). Mean current comes from surface area times current density.
- Aluminum anode capacity
- Aluminum-zinc-indium anodes in seawater deliver about 2,000 A-h/kg with a closed-circuit potential near -1.05 V vs Ag/AgCl/seawater.
- Zinc anode capacity
- Zinc anodes in seawater deliver about 780 A-h/kg with a closed-circuit potential near -1.03 V vs Ag/AgCl/seawater. Capacity falls at elevated temperature.
- Anode current by Ohm's law
- I = (Eanode - Eprotected)/(Ranode + Relectrolyte). Anode geometry and seawater resistivity set the resistance and therefore the current output.
- Impressed current system use
- Inert anodes driven by a transformer-rectifier supply high current for large structures. They need reliable power and careful potential control to avoid overprotection.
- Risk-based inspection principle
- Inspection effort is ranked by likelihood and consequence of failure, directing resources to the highest-risk equipment and reducing inspection of low-risk items.
- Remaining life calculation
- Remaining life = (current thickness - minimum required thickness)/corrosion rate. Use the highest credible rate from recent inspection intervals.
- Fitness-for-service standard
- API 579-1/ASME FFS-1 assesses corroded or damaged components using remaining wall thickness and remaining strength factor to judge continued serviceability.
- NDT method selection
- Ultrasonic gauging measures wall loss; magnetic particle and dye penetrant find surface defects; radiography and phased-array UT inspect weld volume.
- CP potential survey meaning
- Structure-to-electrolyte potentials more positive than the protection criterion indicate inadequate cathodic protection and require anode or system adjustment.