The “rating” of a reducer mainly refers to its pressure rating (pressure-bearing capacity) and wall thickness rating (directly related to pressure). Two major systems are widely used globally: the metric system (PN) and the American standard system (Class / Sch). For some plastic reducers, the SDR rating is adopted (indirectly related to pressure). The detailed classification and corresponding relationships are as follows:
I. Pressure Rating
(Core rating indicator that directly reflects pressure-bearing capacity)
1. Metric Pressure Rating (PN, GB/T Standard)
- Definition: Nominal Pressure (PN), in MPa, representing the rated pressure-bearing capacity of the reducer at ambient temperature.
- Common ratings (ascending order):PN0.25, PN0.6, PN1.0, PN1.6, PN2.5, PN4.0, PN6.3, PN10.0, PN16.0, PN25.0, PN40.0.
- Application scenarios:
- PN ≤ 1.6 MPa: Low-pressure pipelines (civil water supply/drainage, household gas, farmland irrigation).
- PN2.5 ~ 6.3 MPa: Medium-pressure pipelines (urban gas mains, chemical process pipelines).
- PN ≥ 10.0 MPa: High-pressure pipelines (long-distance oil pipelines, power plant steam pipelines).
2. American Standard Pressure Rating (Class, ASME Standard)
- Definition: Class Rating, unitless; actual pressure resistance must be converted using a temperature-pressure table.
- Common ratings (ascending order):Class150, Class300, Class600, Class900, Class1500, Class2500.
- Approximate equivalent to metric PN (carbon steel at ambient temperature):
- Class150 ≈ PN2.0 MPa
- Class300 ≈ PN5.0 MPa
- Class600 ≈ PN10.0 MPa
- Class900 ≈ PN15.0 MPa
- Class1500 ≈ PN25.0 MPa
- Class2500 ≈ PN42.0 MPa
- Application scenarios:
- Class150: Low-pressure civil / general industrial pipelines.
- Class300 ~ 600: Medium and high-pressure chemical / petroleum pipelines.
- Class900 ~ 2500: Ultra-high-pressure oil and gas exploitation / power plant pipelines.
II. Wall Thickness Rating
(Indirectly reflects pressure rating; thicker wall means higher pressure resistance)
1. American Standard Wall Thickness Rating (Sch, ASME B36.10 / B36.19)
- Definition: Schedule number; a higher value indicates a thicker wall.
- Common ratings:Sch10, Sch20, Sch40 (STD, standard wall thickness), Sch80 (XS, extra strong), Sch160, XXS (double extra strong).
- Relationship with pressure rating (same diameter and material):Higher Sch rating corresponds to higher Class / PN rating.(e.g., DN100 Sch40 reducer matches Class150; Sch80 matches Class300).
- Typical wall thickness (DN100 carbon steel reducer):
- Sch40: 6.02 mm (Class150)
- Sch80: 8.56 mm (Class300)
- Sch160: 13.49 mm (Class600)
2. Metric Wall Thickness Rating (Integrated with PN, GB/T 12459)
No independent Sch marking; wall thickness is directly determined by PN rating and pipe diameter:
- Same PN rating: larger diameter → thicker wall.
- Same diameter: higher PN rating → thicker wall.
III. Rating System for Plastic Reducers (SDR)
- Definition: Standard Dimension Ratio (SDR = outer diameter / wall thickness).Smaller SDR means thicker wall and higher pressure resistance.
- Common ratings: SDR11, SDR17, SDR21, SDR26, SDR33.
- Corresponding pressure ratings (PE100 material):
- SDR11 ≈ PN1.6 MPa
- SDR17 ≈ PN1.0 MPa
- SDR26 ≈ PN0.6 MPa
- Application: PE / PVC plastic reducers (buried gas / water supply pipelines).
IV. Core Rules for Rating Selection
- Pressure matching: Reducer pressure rating ≥ design pressure of the piping system.
- Temperature correction: At high temperatures, pressure capacity decreases; a higher rating is required.
- Diameter correlation: For the same rating, large-diameter reducers have thicker walls.
- Material correlation: For the same rating, stainless steel reducers may have slightly thinner walls than carbon steel due to higher strength.
- Standard consistency: Reducer rating must match that of connected pipes.
V. Typical Rating Marking Examples
- Metric: DN200×DN150 PN4.0 20# carbon steel reducer
- American standard: 4″×2″ Class300 Sch80 ASTM A234 WPB reducer
- Plastic: De110×De75 SDR11 PE100 reducer
