DETRIMENTAL CONDITION

POSSIBLE MODE OF CORROSION

EFFECTIVE
COUNTER MEASURES

Hot, uninhibited reducing acids (HCl, Br, H₂SO₄, H₃PO₄)

General corrosion

Observe temp/conc. Limits

Add oxidizing species as inhibitors

Select a more resistant Ti alloy(Gr. 7, 11, 16, 17, 18, 19, 20, 26, 27, 28, 29)

Metal-metal, gasket-metal, and deposit-metal crevices in hot (³ 75° C) chlorides or other halide salts

Crevice corrosion

Observe pH/temp limits

Select a more resistant Ti alloy (Gr. 7, 11, 12, 16, 17, 18, 19, 20, 26, 27, 28, 29)

Ennoble crevices with localized surface treatments

Hot, acidic, hydrolyzable salt solns (MgCl₂, CaCl₂, ZnCl₂, FeCl₃)

Pitting, crevice corrosion

Select a more resistant Ti alloy
(Gr. 7, 11, 16, 17, 18, 26, 27, 28, 29)

Smeared-in surface iron in hot brines (>75° C)

Pitting

HNO₃/HF pickle to remove embedded iron

Hot, strongly alkaline media

Excessive hydrogen absorption and eventual embrittlement

Observe pH/temp limits

Thermal oxidation

Add oxidizing species

High temp oxidizing bromide media

Pitting

Select low-Fe, unalloyed Ti

HNO₃/HF pickle

Thermal oxidation

Totally anhydrous organic streams

Pitting (stress cracking in dry methanol)

Add traces of water (add >2 wt.% water for methanol)

Excessive impressed cathodic potentials

Hydrogen absorption/ embrittlement

Observe potential limits, use potentiostatic control and stay noble to -0.85V in seawater or near-neutral brines

Electrically isolate Ti component

Protect Ti surface with polymeric coating or lining/sheathing

Thermal oxidation

Galvanic couples with active metals in hot electrolytes

Hydrogen absorption/embrittlement

Use electrically-isolating joints/connections

Coat the Ti (cathode) surface with a polymer

Use compatible resistant alloys

All Ti alloy design

Stray AC/DC currents

Anodic pitting

Ground or insulate equipment properly

Dry Cl₂/enriched O₂ gas

Ignition/burning

Add moisture to chlorine (moist, wet gas)

Observe oxygen pressure/vol.% limits

Avoid surface damage