TA2 Titanium Coil: Material Basis and Supply Forms
TA2 is the Chinese designation for industrial pure titanium under GB/T 3620.1 and corresponds closely to ASTM Grade 2, UNS R50400, with a titanium content of 99.2% minimum. It is the workhorse grade of the petrochemical industry because its passive titanium dioxide film tolerates the chloride, bromide and organic acid environments that destroy austenitic stainless steels, and because it remains readily formable and weldable in the shop.
In petrochemical purchasing, the word coil covers two distinct products. The first is cold-rolled strip wound into coils and supplied to ASTM B265 or GB/T 3621, typically 0.3 mm to 3.0 mm thick and up to 1250 mm wide, used for vessel and column linings, cladding, internals, gaskets and fabricated sheet components. The second is coiled tube made to ASTM B338 or GB/T 3625, wound into coils, U-bends or helical bundles for coil-type heat exchangers, reboilers, immersion coils and condensers. Specifying the correct one matters: strip is ordered by thickness, width and temper, while coil tube is ordered by outside diameter, wall thickness and bend radius.
Why Petrochemical Duty Pushes Stainless Steel Out
Organic acids, halide ions and elevated temperature act together. In the oxidation section of a purified terephthalic acid plant, acetic acid and bromide promoters create a medium that corrodes 316L by pitting within tens of hours once temperatures exceed about 135 °C. Design specifications for that service therefore call for titanium above 135 °C, and titanium coils, linings and exchanger bundles replace stainless steel throughout the hot circuit. The same logic repeats wherever a chloride-bearing or strongly acidic stream meets a hot metal surface, which is why titanium coil has become a standard construction material rather than an exotic option.
Documented Applications in Chemical Plants
Terephthalic acid and polyester feedstock. A complete titanium equipment train for an oxidation unit typically includes around 16 oxidation reactors together with solvent dehydration towers, heaters, condensers and reboilers. A 450,000 t/a terephthalic acid line in eastern China was built with 56 titanium equipment items plus a large inventory of titanium piping and valves. One oxidation reactor on a similar line stands 32 m tall, 4 m in diameter at the top and 5.3 m at the bottom, encloses a volume of about 505 m³ and weighs as much as 175 t, all in titanium construction.
Acetic acid and acetaldehyde. In acetaldehyde oxidation, propylene oxidation to acetone and related routes, the corrosive burden comes largely from the catalyst system, and stainless steel corrodes noticeably faster than titanium. Titanium was first applied commercially to ethylene oxidation to acetaldehyde in 1963, and Chinese plants have run titanium equipment in that duty since 1976. Abroad, titanium-lined reactors up to 9.6 m high and 3 m in diameter operate alongside heat exchangers, catalyst regeneration towers and acetaldehyde solution coolers, an equipment set of around eleven titanium items. A 30,000 t/a acetone unit of this type carries about twelve titanium equipment items containing some 40 t of titanium.
Urea synthesis. Titanium-lined urea synthesis towers have been in service worldwide since 1963, with close to 10,000 units operating today and no significant corrosion reported on the lining. The comparison is stark: in the same service, 316L stainless steel corrodes at roughly 4.1 to 4.5 mm per year. Titanium has also been used since the 1970s for carbon dioxide vapour towers, heat exchangers, mixers, pumps and valves.
Crude oil refining. For high-sulfur, high-salt crudes, titanium equipment is the preferred solution in atmospheric distillation service, wastewater treatment, desulfurization separation tower condensers and steam extraction tower radiators. Cast titanium seawater pumps, titanium condensers in catalytic cracking fractionation, deep-cooling condensers and porous titanium distributor plates have all logged more than ten years of normal operation.
Chlorinated hydrocarbons. Chlorination reactions are difficult for stainless steel. Titanium has been used for dichloromethane distillation towers, trichloroethane heat exchangers, condensation and fractionation towers, trichloroethylene condensation towers, perchloroethylene heat exchangers and chlorinated coil heaters. In vinyl chloride production, cooling towers, wastewater vaporisation towers and wastewater storage tanks lined with Ti-0.2Pd have run for nearly a decade without corrosion, and titanium piping, joints and gas distributors have served for many years.
Phenol and acetone. The newer cumene route extracts phenol and acetone from isopropyl benzene and its hydroperoxide, and titanium equipment has been applied to it overseas for well over a decade. In the older benzene sulfonation route, titanium reactors, coil coolers and stirrer sleeves are already standard.
Alloy Selection Map for Petrochemical Media
| Service condition | Recommended grade | Reason |
|---|---|---|
| PTA oxidation, acetic acid with bromide above 135 °C | TA2 / Grade 2 coil, lining or tube | 316L pits within tens of hours; titanium stays passive |
| Non-oxidising media, tight crevices, hot seawater above 70 °C | Grade 7 (Ti-0.2Pd) or Grade 12 (Ti-0.3Mo-0.8Ni) | Palladium or molybdenum additions stabilise the passive film in crevices |
| Strength-critical structural parts | Grade 5 (Ti-6Al-4V) | Higher strength where formability demands are lower |
| Risk of hydrogen absorption, especially at welds | Low-iron Grade 2 | Reduced tendency to form brittle hydrides |
| Dry chlorine gas, hydrofluoric acid, hot concentrated hydrochloric acid, hot anhydrous methanol | Titanium not suitable | The passive film breaks down or the metal is chemically attacked |
Fabrication, Lining and Inspection Practice
Coil strip is normally deployed as a loose lining, an explosively bonded clad layer or a weld-overlay on a carbon steel shell. Whichever route is used, the titanium surface must be protected from iron contamination during cutting, rolling and welding, because embedded iron causes rust staining and localised corrosion in service. Welding is by gas tungsten arc with a high-purity argon shield and a purge on the reverse side; a sound weld is bright silver or light straw, and any blue or white oxide is removed and re-welded. Pickling after welding restores the oxide film, and bend radii for coil tube should respect the wall factor limits of the applicable tube specification.
Documentation for petrochemical buyers usually includes EN 10204 3.1 certification with chemical analysis, tensile results and hardness, positive material identification of finished components, eddy current or ultrasonic testing of coil tube, and helium leak testing of liners and clad plates. Because titanium is non-magnetic, material verification relies on chemical or X-ray methods rather than magnetic sorting, so test records are the practical traceability tool on site.
Frequently Asked Questions
Q: What does TA2 correspond to in ASTM terms?
TA2 is the Chinese industrial pure titanium designation of GB/T 3620.1 and matches ASTM Grade 2 closely in titanium content and impurity limits. A purchase order should still state the chemical analysis and mechanical properties required, because batch-to-batch oxygen and iron levels affect strength and ductility.
Q: Is titanium coil suitable for chloride-bearing streams?
Yes, and that is its main advantage. Titanium resists chloride pitting and stress corrosion cracking in brine, seawater, chlorite, hypochlorite and wet chlorine, so it is chosen over 316L wherever chlorides are present with heat. The exceptions to watch are dry chlorine gas, hydrofluoric acid and hot concentrated reducing acids.
Q: Why use Grade 7 or Grade 12 instead of Grade 2?
Grade 2 can suffer crevice corrosion in hot seawater or in non-oxidising media, particularly at tube-to-tubesheet joints and under gaskets. Small additions of palladium in Grade 7 or molybdenum and nickel in Grade 12 widen the passive range so those joints survive. The cost premium is justified whenever a crevice cannot be eliminated by design.
Q: How long does titanium equipment last in urea or PTA service?
Field experience with titanium-lined urea synthesis towers has shown no significant corrosion over decades, against a 316L wastage rate of roughly 4.1 to 4.5 mm per year in the same medium. Titanium condenser and pump installations in refining service have operated normally for more than ten years, so design life is usually set by mechanical wear and maintenance practice rather than corrosion.
Q: What is the risk of hydrogen embrittlement?
Titanium can absorb hydrogen and form brittle hydrides where it is cathodically protected, galvanically coupled to steel, or exposed to hydrogen-rich or strongly reducing conditions, with welds being the most sensitive area. Selecting low-iron Grade 2 stock, avoiding steel contacts and controlling welding cleanliness greatly reduce that risk.
Q: Which documents should accompany a titanium coil shipment?
Expect a certificate of conformity to ASTM B265, ASTM B338 or the equivalent GB/T standard, EN 10204 3.1 inspection documents with heat number, chemical and mechanical results, and the test records agreed at order such as eddy current, ultrasonic or leak testing. Positive material identification results are normally supplied for fabricated items.
