Schedule 20 vs Schedule 40 Steel Pipe: Wall Thickness Comparison and Application Guide

Selecting the correct pipe schedule is crucial for ensuring optimal performance in various industrial applications. This comprehensive guide examines the key differences between Schedule 20 and Schedule 40 steel pipes, focusing on wall thickness specifications, pressure ratings, and appropriate use cases for each type.

Understanding Pipe Schedules in Steel Pipe Manufacturing

In the steel pipe industry, the schedule number refers to a standardized system that indicates the wall thickness of the pipe relative to its diameter. This designation is critical for engineers and procurement specialists when selecting materials for specific applications, whether for line pipe systems, structural supports, or fluid transmission.

Schedule designations follow standards set by ASME B36.10M and ASME B36.19M, which are referenced in various industry specifications including ASTM A53, ASTM A106, and API 5L for carbon steel pipe products.

Key Characteristics of Schedule 20 Steel Pipe

• Thinner wall construction compared to Schedule 40

• Designed for low to moderate pressure applications

• Significantly lighter weight per foot

• Cost-effective for non-critical service conditions

• Generally available in larger diameter ranges (2" and above)

Key Characteristics of Schedule 40 Steel Pipe

• Thicker wall construction providing enhanced durability

• Higher pressure tolerance for demanding applications

• Greater mechanical strength and structural integrity

• Available in the full range of nominal pipe sizes (from 1/8" up)

• Standard choice for most industrial and commercial applications

Wall Thickness Comparison Chart: Schedule 20 vs Schedule 40

The following comprehensive chart highlights the critical differences in wall thickness, outside diameter (OD), and weight per foot between Schedule 20 and Schedule 40 pipes across various nominal sizes. These specifications conform to ASME standards for seamless and welded pipe manufacturing.

Small Diameter Pipe Specifications (1/8" to 2")

1/8-inch Nominal Pipe Size

• Schedule 40: OD = 0.405" (10.3 mm) | Wall Thickness = 0.068" (1.73 mm) | Weight = 0.24 lb/ft (0.37 kg/m)

• Schedule 20: Not standardly manufactured in this size

1/2-inch Nominal Pipe Size

• Schedule 40: OD = 0.840" (21.3 mm) | Wall Thickness = 0.109" (2.77 mm) | Weight = 0.85 lb/ft (1.27 kg/m)

• Schedule 20: Not standardly manufactured in this size

2-inch Nominal Pipe Size

• Schedule 40: OD = 2.375" (60.3 mm) | Wall Thickness = 0.154" (3.91 mm) | Weight = 3.65 lb/ft (5.44 kg/m)

• Schedule 20: OD = 2.375" (60.3 mm) | Wall Thickness = 0.065" (1.65 mm) | Weight = 1.80 lb/ft (2.68 kg/m)

Medium Diameter Pipe Specifications (8" to 12")

8-inch Nominal Pipe Size

• Schedule 40: OD = 8.625" (219.1 mm) | Wall Thickness = 0.322" (8.18 mm) | Weight = 28.55 lb/ft (42.55 kg/m)

• Schedule 20: OD = 8.625" (219.1 mm) | Wall Thickness = 0.250" (6.35 mm) | Weight = 22.36 lb/ft (33.31 kg/m)

12-inch Nominal Pipe Size

• Schedule 40: OD = 12.750" (323.8 mm) | Wall Thickness = 0.406" (10.31 mm) | Weight = 53.52 lb/ft (79.73 kg/m)

• Schedule 20: OD = 12.750" (323.8 mm) | Wall Thickness = 0.250" (6.35 mm) | Weight = 33.38 lb/ft (49.73 kg/m)

Large Diameter Pipe Specifications (24" to 32")

24-inch Nominal Pipe Size

• Schedule 40: OD = 24.000" (610.0 mm) | Wall Thickness = 0.688" (17.48 mm) | Weight = 171.29 lb/ft (255.41 kg/m)

• Schedule 20: OD = 24.000" (610.0 mm) | Wall Thickness = 0.375" (9.53 mm) | Weight = 94.62 lb/ft (141.12 kg/m)

32-inch Nominal Pipe Size

• Schedule 40: OD = 32.000" (813.0 mm) | Wall Thickness = 0.688" (17.48 mm) | Weight = 230.08 lb/ft (342.91 kg/m)

• Schedule 20: OD = 32.000" (813.0 mm) | Wall Thickness = 0.500" (12.70 mm) | Weight = 168.21 lb/ft (250.64 kg/m)

Application Considerations and Industry Usage

Schedule 20 Pipe Applications

Schedule 20 steel pipe is optimized for applications where weight reduction is beneficial and pressure requirements are moderate. Common applications include:

• Low-pressure fire protection systems (when permitted by local codes)

• General purpose water transmission in non-critical systems

• Gravity flow drainage systems and venting

• Structural supports where load requirements are minimal

• Agricultural irrigation systems

• Large diameter HVAC ducting conversions

Schedule 40 Pipe Applications

Schedule 40 steel pipe is the industry standard for most commercial and industrial applications requiring moderate to high pressure ratings. Typical applications include:

• Natural gas and petroleum transmission (conforming to API 5L specifications)

• Industrial process piping systems (per ASTM A53 or ASTM A106)

• High-pressure water distribution networks

• Fire protection sprinkler systems (NFPA compliant)

• Steam and condensate return lines

• Structural components requiring significant load-bearing capacity

• HVAC systems requiring pressure tolerance and durability

Selection Factors for Engineering and Procurement

When determining whether Schedule 20 or Schedule 40 pipe is appropriate for your application, consider these critical factors:

• Operating Pressure: Schedule 40 offers significantly higher pressure ratings than Schedule 20

• Mechanical Stresses: Schedule 40 provides greater resistance to external forces and bending moments

• Weight Considerations: Schedule 20 can reduce overall system weight by 30-45% compared to Schedule 40

• Cost Efficiency: Schedule 20 typically requires less material, potentially reducing project costs

• Corrosion Allowance: Schedule 40 provides additional material thickness that can accommodate more corrosion over time

• Code Compliance: Verify that your selected schedule meets applicable industry standards (ASME, API, ASTM) and local codes

Conclusion

The selection between Schedule 20 and Schedule 40 steel pipe requires careful consideration of application requirements, pressure ratings, mechanical stresses, and relevant industry standards. Schedule 40 provides greater wall thickness, pressure capacity, and durability, making it suitable for most industrial applications. Schedule 20 offers a lighter-weight, more economical alternative for less demanding applications where pressure requirements are moderate.

Always consult applicable industry standards and engineering specifications when selecting pipe schedules for critical applications, and ensure compliance with relevant codes including ASME B31.1, ASME B31.3, API 5L, ASTM A53, and other application-specific requirements.