AMPP Corrosion Technologist flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

IR-free potential

A structure-to-electrolyte potential measured with the CP current momentarily interrupted, removing resistive voltage drop so the reading reflects true polarization at the pipe surface.

100 mV polarization criterion

A CP criterion where the structure is polarized at least 100 mV negative from its native (unprotected) potential, measured as the difference between instant-off and native readings.

Sacrificial anode system

A CP method using a metal more active than the structure (magnesium, zinc, aluminum) that corrodes preferentially and discharges protective current to the structure.

Impressed current system

A CP method using an external DC power source and inert anodes to drive protective current to a structure, suited to high-current-demand or large buried structures.

Copper-copper sulfate electrode

A reference electrode used in soil CP measurements; potentials are reported versus Cu/CuSO4, and the -850 mV criterion is referenced to it.

Stray current corrosion

Corrosion caused by direct current from external sources (transit, welding, other CP systems) discharging from a structure into electrolyte at a focused location.

Anode resistance formula

For a vertical anode, R = (rho/(2*pi*L))*(ln(4L/d)-1); it estimates anode-to-earth resistance from soil resistivity and anode dimensions to size anode output.

Overprotection

A condition where CP potential is more negative than needed, causing hydrogen evolution, coating disbondment, and possible embrittlement of high-strength steels.

Anchor profile

The microscopic surface roughness created by abrasive blast cleaning; adequate profile (typically 1.5-4 mils) improves mechanical adhesion of the coating.

SSPC-SP-10

A surface preparation standard for near-white blast cleaning, removing nearly all visible contaminants and leaving only faint shadows, suitable for demanding coating service.

Dew point rule

A coating application rule requiring surface temperature to be at least 3 C (5 F) above the dew point and rising to prevent condensation under the film.

Wet-to-dry film thickness

DFT = WFT x volume solids fraction; used to set the wet film gauge reading that will yield the specified dry film thickness after solvent evaporation.

Holiday detection

Testing a coating for discontinuities using a high-voltage spark tester (thick films) or low-voltage wet sponge (thin films) to find pinholes and thin spots.

Cathodic disbondment

Loss of coating adhesion around a defect caused by alkali generated at the cathode when CP current flows to the exposed steel at the holiday.

Zinc-rich primer

A primer with high metallic zinc content that protects steel galvanically, sacrificing zinc to protect exposed steel at scratches and defects.

Galvanic series

A ranking of metals and alloys by corrosion potential in a given electrolyte (e.g., seawater), used to predict which metal will be anodic in a couple.

PREN formula

Pitting resistance equivalent number = %Cr + 3.3*%Mo + 16*%N; higher values indicate greater resistance to chloride pitting in stainless steels.

Passive film

A thin, self-repairing oxide layer (e.g., chromium oxide on stainless steel) that slows corrosion; breakdown by chlorides leads to pitting.

Sulfide stress cracking

Brittle cracking of high-strength steels in wet H2S service, controlled by hardness limits and material selection per NACE MR0175/ISO 15156.

Crevice corrosion

Localized attack in oxygen-depleted gaps (gaskets, lap joints) where differential aeration creates an anodic site; avoided by design or higher-alloy material.

Duplex stainless steel

A stainless steel with roughly equal austenite and ferrite, giving higher strength and better chloride stress-corrosion resistance than 300-series austenitics.

Erosion-corrosion

Accelerated metal loss where flowing fluid removes protective scale or films; risk rises above a critical velocity and at fittings like elbows and tees.

Sweet corrosion

CO2 corrosion of carbon steel in the absence of H2S; rate depends on CO2 partial pressure, temperature, pH, and flow, and protective iron carbonate scale can reduce it.

Sour corrosion

Corrosion in the presence of H2S, forming iron sulfide films; associated with pitting and with cracking risks in susceptible high-strength steels.

MIC

Microbially influenced corrosion, often from sulfate-reducing bacteria that generate H2S under biofilms; sessile surface populations are more relevant than planktonic counts.

Water wetting

The condition where an aqueous phase contacts the pipe wall; without water wetting, internal aqueous corrosion cannot proceed, so it is a key control target.

Corrosion coupon

A weighed metal specimen exposed in a line to measure corrosion rate by mass loss; placement must match the flow regime of concern.

Anodic inhibitor

A chemical that slows the anodic reaction by promoting passivation; underdosing can concentrate attack at breaks in the film as localized pitting.

Filming amine inhibitor

A corrosion inhibitor whose polar head adsorbs on steel and whose hydrocarbon tail forms a hydrophobic barrier; continuous injection maintains the protective film.

Threshold scale inhibition

A mechanism where sub-stoichiometric doses of phosphonates or polymers prevent crystal growth and adhesion rather than chelating all scale-forming ions.

Oxygen scavenger

A chemical (sodium sulfite, hydrazine, carbohydrazide) that removes dissolved oxygen in boiler and closed systems to prevent oxygen pitting.

Biocide treatment

Chemical dosing (oxidizing like chlorine or non-oxidizing like glutaraldehyde) to control biofilms and MIC; dosing must account for demand and contact time.