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Engineering Reference

Piping Class Chart: 150#–1500# Materials, Fittings, Gaskets

A piping class defines every component in a pressure system—pipe, fittings, flanges, gaskets, bolts, and schedules. This chart shows standard configurations for Class 150 through 1500 in typical oil & gas and petrochemical service.

1. What is a Piping Class?

A piping class (or piping specification) is a complete bill of materials for a pressure-rated system. It specifies:

  • Pipe: Material grade, schedule, and standard (A106, A53, API 5L)
  • Fittings: Material, standard (B16.9, B16.11), and wall thickness matching pipe
  • Flanges: Material, facing type (RF/FF/RTJ), and standard (B16.5, B16.47)
  • Gaskets: Type, material, and thickness
  • Bolts: Stud bolt grade, nut grade, and length

Engineers assign a class number (150#, 300#, etc.) based on the maximum design pressure and temperature. Every component must match or exceed the class rating.

2. Piping Class Chart 150#–1500#

Standard configurations for carbon steel and alloy steel service (A106/A53 pipe):

Class 150#

Max pressure: 285 psi (1.96 MPa)

Pipe

A106 Gr.B / A53 Gr.B

Fittings

A234 WPB

Flanges

A105, RF

Gaskets

Non-asbestos sheet

Bolts

A193 B7 / A194 2H

Schedule

STD / SCH 40

Class 300#

Max pressure: 740 psi (5.10 MPa)

Pipe

A106 Gr.B / A53 Gr.B

Fittings

A234 WPB

Flanges

A105, RF

Gaskets

Spiral wound

Bolts

A193 B7 / A194 2H

Schedule

STD / SCH 40

Class 600#

Max pressure: 1480 psi (10.2 MPa)

Pipe

A106 Gr.B / A335 P11

Fittings

A234 WPB / A234 WP11

Flanges

A105, RF or RTJ

Gaskets

Spiral wound / RTJ

Bolts

A193 B7 / A194 2H

Schedule

SCH 80 / SCH 120

Class 900#

Max pressure: 2220 psi (15.3 MPa)

Pipe

A106 Gr.B / A335 P11/P22

Fittings

A234 WPB / A234 WP22

Flanges

A182 F11/F22, RTJ

Gaskets

RTJ ring

Bolts

A193 B16 / A194 7

Schedule

SCH 120 / SCH 160

Class 1500#

Max pressure: 3705 psi (25.5 MPa)

Pipe

A335 P11/P22 / A335 P91

Fittings

A234 WP22 / A182 F91

Flanges

A182 F22/F91, RTJ

Gaskets

RTJ ring (BX)

Bolts

A193 B16 / A194 7

Schedule

SCH XXS / Double Extra Strong

Note: Actual classes vary by project specification. Always check your project's piping material specification (PMS) before ordering.

3. Pressure-Temperature Ratings

Flange class ratings are based on ASME B16.5 pressure-temperature tables. A Class 300 flange at 100°F handles 740 psi, but at 1000°F it drops to 170 psi. Key factors:

  • Material group: A105 (Group 1.1) vs F304 (Group 2.2) have different ratings
  • Temperature derating: Ratings decrease as temperature increases
  • Creep range: Above 700°F for carbon steel, ratings controlled by creep strength

Example: A105 Carbon Steel Working Pressure (psi)

Temp (°F)150#300#600#900#1500#
-20 to 100285740148022203705
200260675135020253375
300230655131519703280
400200635126519003170
500170600120017952995
600140550109516402735
700110535106516002665

Source: ASME B16.5 Table 2, Group 1.1 (A105). For exact values, consult the standard.

4. Material Selection Logic

As pressure and temperature rise, material requirements become more stringent:

Low Pressure (150#–300#)

Standard carbon steel: A106 Gr.B pipe, A234 WPB fittings, A105 flanges. Cost-effective for water, air, and low-pressure hydrocarbons.

Medium Pressure (600#–900#)

Enhanced carbon or low-alloy: A106 Gr.B or A335 P11 pipe, A234 WPB/WP11 fittings, A105 or A182 F11 flanges. Spiral wound or RTJ gaskets required.

High Pressure (1500#–2500#)

Cr-Mo alloy or stainless: A335 P22/P91 pipe, A234 WP22 or A182 F91 fittings, RTJ flanges with BX rings. B16 studs with 7 nuts mandatory.

5. Special Classes: 2500#, 4500#

Above 1500#, flanges enter ultra-high-pressure territory:

  • Class 2500: Up to 6170 psi at 100°F (A105). Used in high-pressure injection wells and chemical reactors.
  • Class 4500 (API 6A): Wellhead and Christmas tree equipment. Not covered by B16.5—uses API 6A BX flanges.
  • Class 15000–30000: Subsea BOP stacks and fracturing equipment. Specialty designs with metal seals.

6. FAQ

What is the difference between a piping class and a flange class?
Flange class is just the pressure rating of the flange (150#, 300#, etc.). Piping class encompasses the entire system—pipe schedule, fitting material, flange type, gasket, and bolting. A piping class specifies which flange class to use.
Can I mix Class 300 flanges with Class 150 pipe?
No. The flange class must match or exceed the piping class design pressure. Mixing lower-rated flanges creates a weak point. However, you can use higher-class flanges on lower-class pipe if the facing and dimensions match.
What schedule pipe goes with Class 600?
Typically SCH 80 or SCH 120 for NPS 6" and below. Larger sizes may use SCH 40 or STD depending on wall thickness calculations. The schedule must be thick enough to handle the design pressure at the design temperature.
How do I convert flange class to PN (European)?
Approximate equivalents: 150# ≈ PN20, 300# ≈ PN50, 600# ≈ PN100, 900# ≈ PN150, 1500# ≈ PN250. These are not exact—always verify pressure-temperature ratings for your specific material and temperature.

Need Components for a Specific Class?

We supply complete piping packages—pipe, fittings, flanges, gaskets, and bolts—for any class from 150# to 2500#.

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