AMPP Senior Corrosion Technologist cheat sheet

Carbon equivalent (IIW): CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15; CE above ~0.40 raises weld cracking risk in carbon steels.

Galvanic series ranks alloys by corrosion potential in seawater; the more active (anodic) member of a couple corrodes, and potential separation drives the rate.

Pitting resistance equivalent number: PREN = Cr + 3.3(Mo) + 16(N); values above ~40 indicate high resistance to chloride pitting in stainless steels.

Sensitization of austenitic stainless occurs when chromium carbides precipitate at grain boundaries (roughly 425-815 C), depleting adjacent chromium below ~12 percent.

Anodic polarization curves showing an active-passive transition identify alloys capable of passivation; the passive current density indicates the maintenance current needed.

Austenitic stainlesses are generally not susceptible to hydrogen embrittlement but are prone to chloride stress corrosion cracking above ~60 C.

Carbon steel corrosion rate roughly doubles per 10 C rise in temperature up to ~80 C, after which oxygen solubility decline can reduce rates.

Hardness above ~22 HRC in carbon and low-alloy steels increases sulfide stress cracking susceptibility per NACE MR0175/ISO 15156.

Corrosion inhibitor efficiency: %E = (CR_blank - CR_inhibited)/CR_blank x 100; measured by weight loss, LPR, or RCE.

Film-forming amine inhibitors partition to the metal surface; their performance depends on continuous or intermittent injection to maintain a persistent film.

Oxygen scavengers (sulfite, hydrazine, DEHA) remove dissolved O2; sulfite is unsuitable above ~150 C due to breakdown to sulfide.

pH control targets: cooling water typically 7.5-9.0; boiler water coordinated phosphate programs maintain pH 9.5-10.5 to prevent caustic and acidic attack.

Scale inhibitors (phosphonates, polyacrylates) work by threshold inhibition and crystal distortion; over-dosing can cause precipitation of the inhibitor itself.

Biocide programs alternate oxidizing (hypochlorite, chlorine dioxide) and non-oxidizing (quaternary amines, glutaraldehyde) agents to limit resistance.

Residual monitoring (e.g., 1-5 ppm sulfite, 0.1-0.5 ppm amine) confirms chemical delivery; treat residuals as a leading indicator of treatment efficacy.

Coating resistance: R = rho * t / A, where rho is resistivity, t is dry film thickness, and A is area; thicker films increase resistance.

Surface preparation per SSPC-SP 10 (Near-White) or SP 5 (White Metal) is required for immersion service; residual chloride below ~3-5 ug/cm2 is a common acceptance limit.

Anchor profile typically 1.5-3.5 mils (38-89 um) for high-performance systems; excessive profile can leave peaks uncoated.

Holiday (pinhole) detection uses high-voltage spark testers; voltage is set by dry film thickness per manufacturer (commonly ~100 V per mil).

Cathodic disbondment resistance is critical for coatings on cathodically protected structures; test per ASTM G8 or G95.

Fusion-bonded epoxy (FBE) and three-layer polyolefin are standard for buried pipelines; FBE thickness is typically 350-500 um.

Coating adhesion is measured by pull-off (ASTM D4541) or knife/tape tests; failure mode (adhesive vs cohesive) guides remediation.

CO2 corrosion (sweet) prediction uses models such as NORSOK M-506 or de Waard-Milliams; corrosion rate increases with CO2 partial pressure and temperature.

H2S partial pressure above 0.05 psi (0.0035 bar) triggers sulfide stress cracking considerations for susceptible steels per NACE MR0175.

Flow regime matters: slug and annular flow increase wall shear stress and can strip inhibitor films; stratified flow promotes water wetting.

Water wetting is the prerequisite for internal corrosion; oil-wet surfaces may be protected even without chemical treatment.

Erosion-corrosion threshold often approximated by API RP 14E: V_e = C / sqrt(rho_m), with C = 100 (continuous) or 125-200 (intermittent).

Pigging and batch treatment are used to distribute inhibitors and remove solids; intelligent pigging (ILI) detects metal loss with MFL or UT tools.

Inhibitor residual and coupon/LPR monitoring confirm treatment; corrosion coupons give time-averaged rates, ER probes give real-time trends.

Criterion: -850 mV (Cu/CuSO4) polarized potential or 100 mV polarization shift; native (IR-free) potentials are used to avoid IR drop error.

CP current requirement: I = A * i * (1 - E), where A is coated area, i is bare current density, and E is coating efficiency (fraction).

Anode resistance (vertical rod, Dwight formula): R = (rho / (2piL)) * (ln(4L/d) - 1), where rho is soil resistivity, L length, d diameter.

Sacrificial anodes: magnesium for high-resistivity soils (<~3000 ohm-cm), zinc for low-resistivity/seawater, aluminum for offshore.

ICCP rectifier output is set to maintain protection; current increases as coating degrades, and a rising current trend signals coating failure.

Close-interval surveys (CIS) with a moving reference electrode locate coating defects and confirm protection along a pipeline.

Stray current corrosion occurs where DC current leaves a structure to earth; mitigation uses drainage bonds or sacrificial anodes at the discharge point.

Confined space entry requires atmospheric testing for O2 (19.5-23.5 percent), LEL (<10 percent), and H2S (<10 ppm or site limit) before and during entry.

Hot work near coatings or tanks requires gas testing; LEL readings above 10 percent prohibit hot work, and continuous monitoring is required.

Job Safety Analysis (JSA) identifies hazards, controls, and responsibilities before work; it is reviewed with the crew and updated when conditions change.

Cathodic protection rectifiers are DC hazards; lockout/tagout and voltage verification precede work on rectifier circuits.

Chemical handling requires SDS review, PPE selection, and spill response planning; incompatible chemicals (acids and hypochlorite) must be segregated.

Lifting and rigging plans govern anode and pipe handling; load charts, tag lines, and exclusion zones are documented in the lift plan.

Emergency response includes muster points, communication, and rescue plans for confined space and elevated work; rescue equipment must be staged before entry.