Titanium Flange Grades Compared: Gr2, Gr7, Gr12, Gr5 — Selection Tree for PL, WN, Threaded and Blind

Published by Engineering Team, Shaanxi Qianyi Tuoda Technology Co., Ltd on 2026-10-19

Titanium Flanges are the most specified connection in corrosive process piping, and also the most frequently got wrong. Two flanges described as "DN100 titanium flange" can differ in price by a factor of two or three, and the more expensive one is not always the right answer.

More importantly, about 80% of titanium flange failures are not a titanium material problem. They are a problem with the combination of sealing face, gasket and bolting. That distinction is where the money is.

Market structure: what buyers actually specify

Among Titanium Flanges used in Chinese chemical projects, weld neck (WN) accounts for roughly 65%, plate / slip-on (PL) about 25%, and threaded and blind flanges about 5% each. By grade, Gr2 (TA2) takes around 60% of the market, Gr7 (TA9) and Gr12 (TA10) about 15% each, and Gr5 (TC4) about 8%.

That distribution tells you something useful: selection is driven by service conditions and sealing reliability, not by grade preference. Most applications genuinely are Gr2. The expensive mistakes are the ones where Gr2 was used and Gr7 was needed.

Five questions that decide the selection

1. What is the pressure rating?

Rating	Type	Reason
PN ≤ 6 (≤ 0.6 MPa)	Plate / slip-on (PL)	Lowest cost for low pressure
PN10–16 (1.0–1.6 MPa)	PL or slip-on with hub	General medium-low pressure
PN25–40 (2.5–4.0 MPa)	Weld neck (WN) — required	Hub carries the bending load
PN63–100 (6.3–10 MPa)	WN, forged integral	High pressure
PN ≥ 160 (≥ 16 MPa)	WN with upgraded alloy	Ultra-high pressure
Vacuum service	WN with spiral wound gasket	Vacuum sealing requirement

2. What is the temperature?

Temperature	Grade	Note
≤ 150 °C	Gr2	Fully adequate; the economic general-purpose choice
150–250 °C	Gr2	Still usable; welding procedure needs control
250–350 °C	Gr7 / Gr12	Pd or Mo-Ni alloyed grades are more stable
≥ 350 °C	Gr5 (Ti-6Al-4V)	Higher high-temperature strength
≥ 400 °C continuous	Consider nickel alloy	Titanium is no longer the right answer

3. What is the medium? This is the decisive question

Titanium resists most media extremely well, but its behaviour in reducing acids (dilute hydrochloric, dilute sulphuric) and in strong oxidising acids (concentrated nitric, hot concentrated sulphuric) is completely different. The alloy additions exist precisely for this.

Medium	Grade	Why
Dilute sulphuric acid (≤ 10%)	Gr7 (TA9)	Palladium addition resists reducing acids
Dilute hydrochloric acid (≤ 5%)	Gr12 (TA10)	Molybdenum and nickel resist chlorides
Concentrated nitric acid (≥ 65%)	Gr2	Commercially pure titanium is strongly oxidising-resistant
Wet chlorine	Gr12	Better crevice corrosion resistance
Seawater, brine	Gr2 / Gr12	Titanium is essentially immune to seawater
Acetic acid, organic acids	Gr2	Stable in general organic acids
Wet FGD (Cl⁻ + F⁻)	Gr12	Mo-Ni resists combined attack
Caustic soda (NaOH)	Gr2 with caution — nickel preferred	Titanium is not ideal in concentrated alkali

4. What pipe is it connecting to?

Pipe	Connection	Key point
Titanium pipe	Titanium flange with titanium stub end	Dissimilar metal contact accelerates corrosion
Titanium-clad steel pipe	Titanium / steel composite flange	The transition section must be properly made
Stainless steel pipe	Permitted, with insulating gasket	Prevents galvanic corrosion
Carbon steel pipe	Titanium / steel composite flange — mandatory	Direct connection is not acceptable

5. Is this an export order?

Roughly 90% of export projects draw to ASME B16.5, while domestic projects use HG/T 20592 or GB/T 9112. The two systems differ in dimensions (inch versus millimetre), facing designations (RF / RTJ / LM versus RF / FM / M / T / RJ) and pressure classification (Class versus PN). They will not bolt together. A supplier can make either — but the enquiry has to say which.

Grade cross-reference: Chinese, US and UNS designations

Chinese	ASTM	UNS	Nominal composition	Flange usage
TA1	Grade 1	R50250	Commercially pure titanium	Occasional (high ductility)
TA2	Grade 2	R50400	Commercially pure titanium	Mainstream, ~60%
TA3	Grade 3	R50550	Commercially pure titanium	Minor (slightly higher strength)
TA9	Grade 7	R52400	Ti-0.2Pd	Reducing acids
TA10	Grade 12	R53400	Ti-0.3Mo-0.8Ni	Wet chlorine, FGD
TC4	Grade 5	R56400	Ti-6Al-4V	High pressure, high temperature

If you are replacing a Gr2 flange that failed in dilute sulphuric acid after a few years of service, note that the replacement cost — material, labour and downtime combined — typically runs several times the price difference between Gr2 and Gr7. That is the cheapest insurance in the plant.

The four flange types and where each one stops being appropriate

Type	Pressure	Temperature	Max size	Limitation
Plate / slip-on (PL)	PN ≤ 16	≤ 200 °C	DN600	Fillet weld fatigues; not for cyclic or high pressure
Weld neck (WN)	PN16 – PN160	≤ 600 °C (grade dependent)	No practical limit	Higher cost — 1.4 to 1.8 times PL
Threaded (Th)	PN ≤ 16	≤ 200 °C	DN150	Difficult to machine in titanium; sealing less reliable than welded
Blind (BL)	Matches mating flange	Depends on grade	DN2000+	Requires a gasket — never bolt a blind dry

Two practical notes on the less common types. Threading titanium is harder than threading steel — the material is gummy and wears tooling — which is why threaded Titanium Flanges are rarely specified. Where "removable plus high pressure" is the requirement, a weld neck flange with a mating blind is usually the better solution. And blind flanges perform very well in low temperature, high pressure and corrosive service: a Gr2 blind on a DN600 PN40 spare line at LNG temperature has run for eight years without leakage.

Standards across regions

Application	China	US	Europe	Japan
General pipe flanges	GB/T 9112-2010	ASME B16.5	EN 1092-1	JIS B2220
Chemical service	HG/T 20592-2009	ASME B16.5 Class	EN 1092-1 PN	JIS B2220
Pressure vessel flanges	JB/T 4702-2007	ASME B16.5	—	—
Large diameter	GB/T 13402-2010	ASME B16.47	EN 1092-1	JIS B2220
Pressure class basis	PN (MPa)	Class (lb)	PN (bar)	PN (kgf/cm²)

Class to PN conversion worth memorising: Class 150 ≈ PN20, Class 300 ≈ PN50, Class 600 ≈ PN100. ASME B16.5 is what almost every European and North American customer inspects against, so confirm the basis before quoting — this is the single most common cause of a flange that arrives correct and does not fit.

Facings and gaskets — where leaks actually start

Facing	Code	Pressure	Service	Gasket
Raised face	RF	PN ≤ 40	General	Non-asbestos / flexible graphite
Male-female	M/F	PN16 – PN63	Flammable, explosive	Spiral wound with inner and outer ring
Tongue-groove	T/G	PN16 – PN63	Highly corrosive	Spiral wound or PTFE
Ring joint	RJ	PN ≥ 63	High pressure, high temperature	Metal ring joint gasket
Flat face	FF	PN ≤ 10	Low pressure	Non-asbestos / rubber

RF is used on more than 80% of Titanium Flanges. RF with a flexible graphite gasket and inner/outer steel rings covers PN16 to PN40 and most media. Two exceptions worth remembering: for strongly oxidising acids such as concentrated nitric, use PTFE; for high temperature high pressure (≥ 400 °C with ≥ 4 MPa), use a spiral wound gasket with inner and outer rings.

Five causes of sealing failure — and how to prevent each

1. Wrong gasket. Non-asbestos rubber sheet specified on a steam line above 200 °C will age and leak within months. Above 150 °C, specify flexible graphite or spiral wound. Asbestos gaskets have been phased out and should not appear on a new specification at all.

2. Insufficient or uneven bolt load. Hand tightening distributes load unevenly and the joint leaks at the weakest point. Use a hydraulic torque wrench and tighten in a cross pattern in three to four passes to the specified torque. Critically: Titanium Flanges need 30–40% less bolt load than steel flanges because of the lower elastic modulus. Applying steel-flange torque to a titanium flange crushes the gasket and can deform the facing.

3. Surface roughness out of specification. A Ra of 6.3 μm leaves micro-grooves for the medium to travel along. The requirement is Ra ≤ 3.2 μm for RF and ≤ 1.6 μm for male-female or tongue-groove. Machined flanges should arrive at Ra 1.6 μm by default.

4. Eccentric alignment between flange and pipe. A 5 mm offset when welding leaves the facing unevenly loaded and the weld fatigue-cracked in service. Coaxiality should be within 1 mm for a weld neck, 2 mm for a slip-on, with a jig holding the parts during welding.

5. Galvanic corrosion from mixed metals. A titanium flange with carbon steel bolts and washers in a chloride-bearing medium will corrode the bolts quickly, and a failed bolt is a failed joint. Use titanium bolts and washers, or isolate with insulating sleeves and washers. Where Titanium Fasteners are unavailable, Monel 400 is an acceptable transition.

Five selection misconceptions

"Thicker is safer." Flange thickness is set by the standard. A DN100 PN16 flange is 18 mm because that dimension has been calculated and verified. Machining it to 25 mm adds cost and weight and no reliability.

"Gr2 works everywhere." Gr2 is corroded in wet chlorine, dilute hydrochloric acid and wet FGD service. Its cost advantage exists only in mild service; in aggressive service it is the most expensive choice you can make.

"Any weld will do." A weld neck flange requires full penetration and full-coverage RT or UT, weld quality not below grade B of GB/T 12469-2018, plus post-weld PT and visual inspection.

"A blind flange does not need a gasket." It does. Without one, bolt load acts directly on the facing and damages it.

"Go one pressure class higher to be safe." Stepping up a class increases thickness, bolt size and facing dimensions, and adds 50–100% to cost. Design pressure plus safety factor determines the class — 2.5 MPa means PN25, not PN40.

Questions buyers ask most

Slip-on or weld neck? PN ≤ 16 favours slip-on on cost; PN ≥ 25 requires weld neck. Where the service involves cyclic loading, temperature swings above 100 °C, or a corrosive medium, weld neck is usually cheaper over five years even at low pressure.

Gr7 or Gr12? Gr7 contains 0.2% palladium and is for reducing acids — dilute sulphuric and hydrochloric. Gr12 contains 0.3% molybdenum and 0.8% nickel and is for chloride-fluoride combined attack — wet chlorine and wet FGD. Both cost 30–50% more than Gr2.

Can a titanium flange bolt directly to a stainless flange? Yes, but only with an insulating gasket and insulating sleeves on the bolts. Direct contact accelerates corrosion of the less noble material — usually the stainless — and can cut its service life by half or more.

What goes wrong most often in titanium flange welding? Three things: wrong filler (match ERTi-2 to Gr2, ERTi-7 to Gr7, ERTi-12 to Gr12, ERTi-5 to Gr5); insufficient argon shielding — the face, back and root all need shielding because titanium is highly oxygen-sensitive; and no post-weld stress relief, which is advisable for weld neck flanges of 10 mm and above, at 550–650 °C.

Ordering

We hold 1,500 titanium flanges in stock in Baoji, China's Titanium Valley, and machine to drawing for non-standard sizes. Gr2, Gr7, Gr12 and Gr5; PL, WN, Th and BL; DN15 to DN800; to GB/T 9112, HG/T 20592, ASME B16.5, EN 1092-1 or JIS B2220 as you specify.

Mill test certificates with every shipment, PT and RT reports on request, third-party inspection available, and small batch orders accepted. Send the medium, pressure, temperature, size and standard — we confirm selection, price and shipping date within 4 hours.

Email sales@sxqytd.com · WhatsApp +86 188 2967 9311

This article is technical reference material. Final selection must be confirmed against the project's actual service conditions, drawings and governing standards.