The wall thickness classification of reducers is mainly designed to meet pressure resistance requirements. There are three mainstream systems worldwide: metric (tied to PN), American standard (Sch series), and plastic (SDR series). These systems differ significantly in classification logic, marking methods and applicable scenarios, as detailed below:
I. American Standard Wall Thickness Schedules (Sch Series, ASME B36.10/B36.19)
This is the most widely used wall thickness system for industrial metal reducers, marked as Sch + number. The higher the number, the thicker the wall thickness, corresponding to American standard pressure classes (Class).
1. Key Rules
- For the same nominal size, a higher Sch schedule means a thicker wall (e.g., DN100 reducer: Sch40 wall thickness 6.02 mm, Sch80 8.56 mm, Sch160 13.49 mm).
- The wall thickness at the large end of a reducer ≥ that at the small end (due to the larger pressure-bearing area requiring higher strength).
- Stainless steel reducers share the same Sch wall thicknesses as carbon steel, but provide higher actual pressure resistance (stainless steel has superior strength to carbon steel).
2. Applicable Scenarios
- Sch40: urban gas mains, medium-pressure chemical process piping;
- Sch80: long-distance petroleum pipelines, sub-high pressure power station pipelines;
- Sch160/XXS: high-pressure oil and gas production pipelines, ultra-high pressure boiler pipelines.
II. Metric Wall Thickness Schedules (Tied to PN, GB/T 12459)
The metric system has no independent wall thickness marking. Wall thickness is directly determined by nominal pressure (PN) + nominal diameter (DN). The core logic is: higher pressure and larger diameter result in thicker walls.
Key Rules
- Under the same PN class, a larger DN means a thicker wall (e.g., PN1.6: DN50 wall thickness 4.0 mm, DN200 6.0 mm).
- For the same DN, a higher PN means a thicker wall (e.g., DN100: PN1.6 wall thickness 4.5 mm, PN10.0 14.0 mm).
- Due to high-temperature strength requirements, alloy steel reducers have slightly thicker walls than carbon steel at the same PN/DN (e.g., PN10.0 DN100 alloy steel reducer wall thickness 16 mm vs. carbon steel 14 mm).
III. Wall Thickness Schedules for Plastic Reducers (SDR Series, GB/T 10002.2/18742.2)
Plastic reducers use the Standard Dimension Ratio (SDR = outside diameter / wall thickness). A smaller SDR value indicates a thicker wall, indirectly corresponding to the pressure rating (PN).
Key Rules
- For the same outside diameter, a smaller SDR means a thicker wall (e.g., De110 PE reducer: SDR33 wall thickness 3.3 mm, SDR11 10.0 mm).
- The PN corresponding to SDR varies with plastic material (e.g., SDR11: PN1.6 MPa for PE100, PN2.0 MPa for PPR).
- Wall thickness of plastic reducers must be uniform without local thin spots (thin spot thickness ≥ 90% of design wall thickness).
IV. Core Basis for Wall Thickness Schedule Selection
- Pressure matching: The pressure rating corresponding to the wall thickness schedule ≥ design pressure of the piping system (e.g., select Sch80/PN2.5/SDR11 for a design pressure of 2.5 MPa).
- Temperature correction: For high-temperature pipelines (>200℃), increase the wall thickness schedule (e.g., for carbon steel piping at 250℃, select wall thickness per PN6.3 instead of PN4.0).
- Medium characteristics: For piping with corrosive media or solid particles, add corrosion or wear allowance (e.g., slurry pipe wall thickness = design wall thickness + 2 mm wear allowance).
- Standard consistency: Within the same piping system, reducers must match the wall thickness schedule of pipes and valves (e.g., Sch40 pipes with Sch40 reducers).
