AMPP Corrosion Technician flashcards

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

CSE reference electrode

Copper/copper-sulfate half-cell used as the reference for structure-to-soil potential measurements; the -850 mV criterion for steel is stated versus this electrode.

Instant-off potential

Structure-to-soil potential measured immediately after interrupting CP current, removing IR drop so the true polarized potential is read against the -850 mV criterion.

100 mV polarization criterion

Alternative CP acceptance criterion in which at least 100 mV of potential shift from native to polarized state demonstrates adequate protection of the structure.

Sacrificial anode

Galvanic anode (magnesium, zinc, or aluminum alloy) that corrodes preferentially to protect the structure, chosen when resistivity is low and current demand is modest.

Impressed current system

CP system using an external DC power source and inert anodes (MMO, high-silicon cast iron) to deliver high current in high-resistivity or high-demand environments.

Stray current corrosion

Corrosion caused by current from an external source discharging from the structure into the electrolyte; identified by potential shifts and mitigated by bonds or drainage.

Anode resistance formula

Dwight equation R = (rho/(2*pi*L))*(ln(4L/d)-1) gives the resistance to earth of a single vertical anode from soil resistivity and anode dimensions.

Surface preparation standard

SSPC-SP 5/NACE 1 (white metal) and SP 10/NACE 2 (near-white) define blast cleanliness levels; preparation is the largest factor in coating life.

Anchor profile

Surface roughness created by abrasive blasting, typically 1.5 to 4 mils for epoxy systems, measured by replica tape or profilometer.

Holiday detection

Testing for pinholes and thin spots using a low-voltage wet sponge on thin films or a high-voltage spark tester on thicker coatings.

Cathodic disbondment

Loss of coating adhesion around a defect caused by alkalinity and hydrogen generated by CP current; tested per ASTM G8 or G95.

Soluble salt contamination

Chlorides and sulfates left on the substrate that cause osmotic blistering and premature failure; removed and verified by conductivity testing before coating.

Coating conductance

Inverse of coating resistance; a well-coated structure shows low conductance and low CP current demand, while a failed coating shows high conductance.

Galvanic series

Ranking of metals by corrosion potential in seawater; coupling metals far apart on the series increases galvanic corrosion risk.

Area ratio effect

Galvanic corrosion of the anode accelerates when the cathode area is large relative to the anode area; design should avoid small-anode-to-large-cathode couples.

PREN formula

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

Sensitization

Chromium carbide precipitation at grain boundaries in austenitic stainless steel during heating (425-815 C), depleting chromium and causing intergranular corrosion.

Hydrogen embrittlement

Loss of ductility in high-strength steels caused by absorbed hydrogen, aggravated by overprotection that produces hydrogen at the cathode.

Oxygen depolarization

Cathodic reaction O2 + 2H2O + 4e- -> 4OH- that dominates carbon steel corrosion in neutral aerated water and is limited by oxygen diffusion.

Anodic inhibitor

Inhibitor that promotes passive film formation (chromate, nitrite, molybdate); underdosing can convert general attack into severe localized pitting.

Cathodic inhibitor

Inhibitor that slows the cathodic reaction, often by precipitating a barrier film (zinc salts, polyphosphates), reducing overall corrosion rate.

Filming amine inhibitor

Adsorption-type inhibitor forming a hydrophobic film on metal, widely used to protect condensate return lines and oil and gas pipelines.

Langelier Saturation Index

Index comparing actual water pH to saturation pH; positive indicates scaling tendency, negative indicates corrosive tendency in cooling water systems.

Oxygen scavenger

Chemical such as sulfite or hydrazine that removes dissolved oxygen in boiler feedwater; sulfite is avoided above about 200 C.

Biocide treatment

Oxidizing (chlorine) or non-oxidizing (glutaraldehyde) chemicals used to control microbiologically influenced corrosion in cooling and process water.

Corrosion cell elements

Anode, cathode, electrolyte, and electrical path; removing any one element stops the corrosion reaction, which is the basis for most mitigation methods.

Faraday's law

Mass loss = (I*t*M)/(n*F), relating corrosion current and time to metal loss using atomic mass, electrons transferred, and Faraday's constant 96,485 C/mol.

Corrosion rate conversion

1 microamp per square centimeter corresponds to about 0.0116 mm/year for iron; mpy = 0.128 * current density * (equivalent weight/density).

Crevice corrosion mechanism

Oxygen depletion and chloride buildup inside a tight gap create an active anode; mitigated by design that avoids tight crevices and by alloy selection.

Erosion-corrosion

Accelerated metal loss from combined flow and corrosion, localized at elbows, tees, and downstream of orifices; mitigated by velocity limits and material selection.

NACE MR0175 / ISO 15156

Standard for materials resistant to sulfide stress cracking in oil and gas; selection depends on H2S partial pressure, pH, and chloride content.

Uniform corrosion

Even metal loss across the surface, measured by weight loss or linear polarization; the least dangerous form because life can be predicted.