Alloy Steel Threaded Flanges | A182 F11, F22, F91, NPT

Alloy steel threaded flanges, also known as screwed flanges, are flanges that are formed with an internal tapered thread that can screw into a corresponding pipe end, thus eliminating the requirement for welding to connect the pipe ends. They are used on small bore lines where welding is not permitted or difficult due to the use of ASTM A182 grades F5, F9, F11, F12, F22 and F91. Dimensions follow ASME B16.5 with NPT or BSPT threads. Solitaire Overseas provides these flanges with the required EN 10204 3.1 material certificates and tested material traceability for domestic and export orders.

Technical Data

Specifications Chemical Composition Mechanical Properties Alloy Grades Dimensions Chart Pressure Rating

Specifications of Alloy Steel Threaded Flanges

Specification Parameter	Technical Details & Standard Options
Product Name	Alloy Steel Threaded / Screwed Flanges (NPT / BSPT)
Flange Dimensions	ASME B16.5
Thread Specifications	NPT to ASME B1.20.1 with a 60 degree taper thread; BSPT to ISO 7 and EN 10226 with a 55 degree taper thread
Size Range	NPS 1/2 up to the ASME B16.5 limit for each pressure class (larger sizes supplied as custom engineered items)
Pressure Class / Ratings	ASME B16.5: Class 150, Class 300, Class 600, Class 900, Class 1500 (Class 2500 supplied as non-standard / custom item)
Material Grades (Forged)	ASTM A182 / ASME SA182: Grade F5, F9, F11 (Class 2 and 3), F12 (Class 2), F22 (Class 3), F91 (ASTM A182 F1 available on request)
Flange Face Type	Raised Face (RF) as standard; Ring-Type Joint (RTJ) available on request
Surface Finish & Protection	Light oil coating or black anti-corrosion coating for transit protection
Testing & Inspection	100% Thread Gauging, PMI Testing, Ultrasonic Testing (UT), Magnetic Particle Inspection (MPI)
Certification	EN 10204 3.1 Material Test Certificate (MTC), Third-Party Inspection (TPI) available on request
Value-Added Services	Precision CNC threading with 100 percent thread gauging; custom machining to client drawings

Chemical Compositions of Alloy Steel Threaded Flanges

Element	A182 F1 (%)	A182 F5 (%)	A182 F9 (%)	A182 F11 Cl. 2 (%)	A182 F12 Cl. 2 (%)	A182 F22 Cl. 3 (%)	A182 F91 (%)
Carbon (C)	0.28 max	0.15 max	0.15 max	0.10 to 0.20	0.10 to 0.20	0.05 to 0.15	0.08 to 0.12
Manganese (Mn)	0.60 to 0.90	0.30 to 0.60	0.30 to 0.60	0.30 to 0.80	0.30 to 0.80	0.30 to 0.60	0.30 to 0.60
Phosphorus (P)	0.045 max	0.030 max	0.030 max	0.040 max	0.040 max	0.040 max	0.020 max
Sulfur (S)	0.045 max	0.030 max	0.030 max	0.040 max	0.040 max	0.040 max	0.010 max
Silicon (Si)	0.15 to 0.35	0.50 max	0.50 to 1.00	0.50 to 1.00	0.10 to 0.60	0.50 max	0.20 to 0.50
Chromium (Cr)	Not specified	4.00 to 6.00	8.00 to 10.00	1.00 to 1.50	0.80 to 1.25	2.00 to 2.50	8.00 to 9.50
Molybdenum (Mo)	0.44 to 0.65	0.44 to 0.65	0.90 to 1.10	0.44 to 0.65	0.44 to 0.65	0.87 to 1.13	0.85 to 1.05
Nickel (Ni)	Not specified	0.50 max	0.50 max	Not specified	Not specified	Not specified	0.40 max
Vanadium (V)	Not specified	Not specified	Not specified	Not specified	Not specified	Not specified	0.18 to 0.25
Niobium (Nb)	Not specified	Not specified	Not specified	Not specified	Not specified	Not specified	0.06 to 0.10
Nitrogen (N)	Not specified	Not specified	Not specified	Not specified	Not specified	Not specified	0.03 to 0.07
Aluminum (Al)	Not specified	Not specified	Not specified	Not specified	Not specified	Not specified	0.02 max
Titanium (Ti)	Not specified	Not specified	Not specified	Not specified	Not specified	Not specified	0.01 max
Zirconium (Zr)	Not specified	Not specified	Not specified	Not specified	Not specified	Not specified	0.01 max

Mechanical Properties of Alloy Steel Threaded Flanges

Grade & Class	Tensile Strength, Min (MPa)	Yield Strength, Min (MPa)	Elongation in 2 in. (50 mm), Min (%)	Reduction of Area, Min (%)	Brinell Hardness Range (HBW)
ASTM A182 F5	485	275	20	35	143 to 217
ASTM A182 F9	585	380	20	40	179 to 217
ASTM A182 F11 Class 2	485	275	20	30	143 to 207
ASTM A182 F11 Class 3	515	310	20	30	156 to 207
ASTM A182 F12 Class 2	485	275	20	30	143 to 207
ASTM A182 F22 Class 3	515	310	20	30	156 to 207
ASTM A182 F91	585	415	20	40	190 to 248

Alloy Grades for Threaded Flanges

Grade	Nominal Alloy	Cr %	Mo %	Typical Use
ASTM A182 F5	5Cr 0.5Mo	4.0 to 6.0	0.44 to 0.65	Refinery lines needing sulfidation and oxidation resistance
ASTM A182 F9	9Cr 1Mo	8.0 to 10.0	0.90 to 1.10	Higher temperature refinery and power lines
ASTM A182 F11	1.25Cr 0.5Mo	1.00 to 1.50	0.44 to 0.65	Steam, boiler and general chrome moly service
ASTM A182 F12	1Cr 0.5Mo	0.80 to 1.25	0.44 to 0.65	Steam and process lines at moderate temperature
ASTM A182 F22	2.25Cr 1Mo	2.00 to 2.50	0.87 to 1.13	High temperature steam and hydrogen service
ASTM A182 F91	9Cr 1Mo V Nb N	8.0 to 9.5	0.85 to 1.05	Ultra supercritical steam lines

Dimensions Chart of Alloy Steel Threaded Flanges

Dimension Code	Parameter / Feature	Class 150	Class 300	Class 600	Class 900	Class 1500	Class 2500
A	Hub Diameter at Base (mm)	30.0	38.0	38.0	38.0	38.0	43.0
D	Outside Diameter of Flange (mm)	90.0	95.0	95.0	120.7	120.7	133.4
B (RF)	Flange Thickness - Raised Face (mm)	9.6	12.7	14.3	22.3	22.3	30.2
B (RTJ)	Flange Thickness - Ring Joint (mm)	11.2	14.3	20.7	28.7	28.7	36.6
G	Raised Face Diameter (mm)	34.9	34.9	34.9	34.9	34.9	34.9
K	Bolt Circle Diameter (mm)	60.3	66.7	66.7	82.6	82.6	88.9
H (RF)	Length Through Hub - Raised Face (mm)	14.0	21.0	22.0	32.0	32.0	40.0
H (RTJ)	Length Through Hub - Ring Joint (mm)	15.6	22.6	28.4	38.4	38.4	46.4
—	Number of Bolt Holes	4	4	4	4	4	4
—	Bolt Hole Diameter (mm)	15.9	15.9	15.9	22.2	22.2	22.2

Pressure Rating of Alloy Steel Threaded Flanges

Class	Approx. psig	Approx. bar
150	290	20
300	750	51
600	1500	103
900	2250	155
1500	3750	258

Applications and Industrial Uses of Alloy Steel Threaded Flanges

Instrumentation Lines
Sampling Lines
Auxiliary Utility Manifolds
Steam Drain Lines
Steam Vent Lines
Refinery Auxiliary Lines
Industrial Test Connections

Frequently Asked Questions

1. What are alloy steel threaded flanges?

Forged flanges in ASTM A182 chrome moly grades with an internal tapered thread. They screw onto a matching pipe end, so no welding is needed to make the joint.

2. What is the difference between NPT and BSP threads?

NPT is a 60 degree tapered thread to ASME B1.20.1. BSPT is a 55 degree tapered thread to ISO 7. They do not interchange, so state the type.

3. Which sizes and pressure classes are available?

ASME B16.5 threaded flanges cover a wide size range in the lower classes and small bore only in Class 900 and 1500. Larger sizes are custom.

4. Which alloy grade should I choose?

F11 and F22 suit most auxiliary steam and refinery lines. Operating temperature, thermal cycling and the design code decide the grade. F91 is rarely used for threaded joints.

5. Can alloy steel threaded flanges be seal welded?

Yes, where the design code and approved procedure allow it. Seal welding the first thread reduces leakage but needs welding and heat treatment control.

6. When should I avoid an alloy steel threaded flange?

Avoid them in severe cyclic loading, vibration, thermal shock and high temperature steam service. A weld neck or socket weld flange suits those lines better.

7. How is a threaded flange sealed?

The tapered thread is sealed with a sealant suited to the service temperature, plus a gasket on the flange face. Anti seize helps prevent galling on alloy threads.

8. What details are needed to order?

Give NPS, class, grade and class of grade, thread type, face type, standard, quantity and the certificates needed, such as EN 10204 3.1.

Alloy Steel Threaded Flanges Manufacturer and Supplier in India