AMPP Senior Corrosion Technologist flashcards

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

Carbon equivalent threshold

A calculated value combining carbon and alloying elements; values above about 0.40 in carbon steels indicate elevated weld cracking risk and require preheat or controlled procedures.

PREN formula

Pitting resistance equivalent number equals Cr plus 3.3 times Mo plus 16 times N; higher values indicate greater resistance to chloride pitting in stainless steels.

Sensitization of stainless steel

Chromium carbide precipitation at grain boundaries in the 425-815 C range depletes adjacent chromium below about 12 percent, leaving the steel susceptible to intergranular corrosion.

Galvanic corrosion principle

When two dissimilar metals are coupled in an electrolyte, the more active metal becomes anodic and corrodes faster; the potential difference and area ratio drive the rate.

Hydrogen embrittlement susceptibility

High-strength steels (hardness above about 22 HRC) are prone to hydrogen embrittlement and sulfide stress cracking; austenitic stainlesses are generally more resistant.

Inhibitor efficiency formula

Percent efficiency equals the blank corrosion rate minus the inhibited rate, divided by the blank rate, times 100; measured by weight loss, LPR, or resistance methods.

Oxygen scavenger limits

Sulfite removes dissolved oxygen but breaks down to sulfide above about 150 C; hydrazine and DEHA are used at higher boiler temperatures.

Boiler pH control

Coordinated phosphate programs maintain boiler water pH around 9.5 to 10.5 to prevent caustic attack and acidic corrosion of the steel.

Biocide alternation

Alternating oxidizing agents such as hypochlorite with non-oxidizing agents such as glutaraldehyde limits microbial resistance and biofilm regrowth in cooling systems.

Scale inhibitor mechanism

Phosphonates and polyacrylates inhibit scale by threshold effects and crystal distortion; over-dosing can precipitate the inhibitor itself and foul the system.

Coating resistance formula

Resistance equals resistivity times dry film thickness divided by area; thicker, more resistive films provide better barrier protection against electrolyte contact.

Surface preparation standard

SSPC-SP 10 (Near-White) or SP 5 (White Metal) is required for immersion service; residual chloride is commonly limited to about 3-5 micrograms per square centimeter.

Anchor profile range

A typical anchor profile of 1.5 to 3.5 mils (38-89 micrometers) improves adhesion; excessive profile can leave peaks uncoated and cause early failure.

Holiday detection voltage

High-voltage spark testers detect pinholes; voltage is set by dry film thickness, commonly about 100 volts per mil, per manufacturer guidance.

FBE pipeline coating

Fusion-bonded epoxy is a standard buried pipeline coating applied at about 350-500 micrometers thickness; it provides good adhesion and cathodic disbondment resistance.

Coating adhesion testing

Pull-off testing per ASTM D4541 measures adhesion strength; the failure mode (adhesive versus cohesive) indicates whether surface preparation or coating chemistry is at fault.

CO2 corrosion drivers

Sweet corrosion rate increases with CO2 partial pressure and temperature; models such as NORSOK M-506 or de Waard-Milliams estimate rates for carbon steel.

H2S threshold

An H2S partial pressure above 0.05 psi (0.0035 bar) triggers sulfide stress cracking evaluation for susceptible steels under NACE MR0175/ISO 15156.

Water wetting requirement

Internal corrosion requires water contact with the steel; oil-wet surfaces may remain protected even without chemical treatment in multiphase flow.

Erosional velocity limit

API RP 14E approximates erosional velocity as C divided by the square root of mixture density, with C of 100 for continuous and 125-200 for intermittent service.

Pigging and ILI

Pigging distributes inhibitors and removes solids; in-line inspection with magnetic flux leakage or ultrasonic tools detects and sizes metal loss.

Internal monitoring methods

Corrosion coupons give time-averaged rates, electrical resistance probes give real-time trends, and linear polarization resistance gives instantaneous rates for electrolyte systems.

CP protection criterion

A polarized potential of -850 mV versus copper-copper sulfate, or a 100 mV polarization shift, indicates adequate cathodic protection when IR drop is accounted for.

CP current requirement

Current equals coated area times bare current density times one minus coating efficiency; degraded coatings increase current demand and rectifier output.

Anode resistance formula

For a vertical rod, resistance equals soil resistivity divided by twice pi times length, times the natural log of four times length over diameter minus one.

Sacrificial anode selection

Magnesium suits high-resistivity soils, zinc suits low-resistivity soils and seawater, and aluminum alloys are used for offshore structures and pipelines.

Close-interval survey

A moving reference electrode measures potential along a pipeline at short intervals, locating coating defects and confirming protection level distribution.

Stray current corrosion

DC current leaving a structure to earth causes accelerated corrosion at the discharge point; mitigation uses drainage bonds or localized sacrificial anodes.

Confined space atmosphere limits

Entry requires oxygen between 19.5 and 23.5 percent, flammable gas below 10 percent LEL, and H2S below the site limit, typically 10 ppm.

Hot work gas testing

Combustible gas readings above 10 percent LEL prohibit hot work; continuous monitoring is required near coatings, tanks, and confined spaces.

Job Safety Analysis

A JSA documents hazards, controls, and responsibilities for a task; it is reviewed with the crew and updated whenever conditions or scope change.

Chemical segregation rule

Incompatible chemicals such as acids and hypochlorite must be stored separately; SDS review, PPE selection, and spill response planning precede handling.