This reference provides a practical dimensional overview of 18 inch Schedule 20 pipe, also identified as NPS 18 and DN450. Use the table and quick-reference data below when checking piping layouts, estimating material quantities, coordinating supports, or preparing fabrication and CAD documentation.
The dimensional values are presented as a reference for steel pipe work. Before using them in a design, confirm the applicable project specification, material requirements, connection details, and engineering design basis.
Schedule 20 pipe 18 inch (DN450) is a standard large-diameter steel pipe size commonly used in piping design, drafting, fabrication, estimation, and industrial layout work. This page provides the standard dimensions, wall thickness, inside diameter, and weight per meter for NPS 18 Schedule 20 pipe based on ASME B36.10.
For engineers, designers, estimators, and CAD users, quick access to accurate pipe data helps improve piping layout, support planning, weight checks, material takeoff, and fabrication coordination during project development.
18 Inch Schedule 20 Pipe Dimensions
- Nominal Pipe Size (NPS): 18 inch
- Diameter Nominal (DN): DN450
- Outside Diameter (OD): 457 mm
- Wall Thickness: 7.92 mm
- Inside Diameter (ID): 441.16 mm
- Pipe Weight: 87.71 kg/m
- Pipe Weight Including Water: 240.48 kg/m
- Standard: ASME B36.10
Schedule 20 Pipe 18 Inch Data Table
| NPS | DN | Outside Diameter (OD) | Wall Thickness | Inside Diameter (ID) | Weight |
|---|---|---|---|---|---|
| 18 inch | DN450 | 457 mm | 7.92 mm | 441.16 mm | 87.71 kg/m |
Understanding 18 Inch Schedule 20 Pipe
18 inch Schedule 20 pipe is a standard steel pipe size used as a reference in industrial piping layouts, water lines, utility systems, process design studies, and CAD drafting. With an outside diameter of 457 mm and a wall thickness of 7.92 mm, this pipe size is useful where a large flow path is needed while keeping the wall lighter than heavier schedules.
What Does Schedule 20 Mean?
Schedule 20 refers to the wall thickness series of the pipe. For NPS 18, Schedule 20 gives a wall thickness of 7.92 mm. The schedule affects the inside diameter, pipe weight, fabrication requirements, and dimensional coordination with fittings, supports, and layout clearances.
Why These Pipe Dimensions Matter
Accurate pipe dimension data is important for piping layouts, spool drawings, support design, structural load review, and material takeoff. Knowing that this pipe weighs 87.71 kg/m helps with transport estimates, lifting plans, and support loading. If the pipe is filled with water, the total weight increases to 240.48 kg/m, which is also useful for operating load calculations.
Common Uses of DN450 Schedule 20 Pipe
DN450 Schedule 20 pipe may be referenced in industrial utility systems, water transfer lines, plant layout studies, process piping documentation, and engineering design work. It is also commonly used by piping designers, CAD users, estimators, and procurement teams who need fast access to standard steel pipe dimensions.
Difference Between NPS 18 and DN450
NPS 18 is the inch-based nominal pipe size designation, while DN450 is the metric nominal diameter reference. Both refer to the same pipe size category on this page. The actual standard outside diameter for this size is 457 mm.
How to Use This Data
You can use this page to quickly check:
- pipe outside diameter for layout and clearance
- inside diameter for flow reference
- wall thickness for schedule comparison
- weight per meter for estimation and transport planning
- water-filled weight for support and structural load review
Quick Reference for Schedule 20 Pipe 18 Inch
- Pipe Size: 18 inch
- DN: DN450
- OD: 457 mm
- ID: 441.16 mm
- Wall Thickness: 7.92 mm
- Weight: 87.71 kg/m
- Weight Including Water: 240.48 kg/m
- Reference Standard: ASME B36.10
Related Pipe Size Pages
Conclusion
Schedule 20 Pipe 18 Inch (DN450) is an important steel pipe reference for piping design, drafting, estimation, and fabrication work. With its 457 mm outside diameter, 7.92 mm wall thickness, and 87.71 kg/m pipe weight, it provides useful dimensional data for engineers and designers who need fast and accurate pipe information.
Note: NPS = Nominal Pipe Size, DN = Diameter Nominal. Dimensions and weights shown here are based on ASME B36.10 steel pipe data.
How to Read the 18 Inch Schedule 20 Pipe Data
The outside diameter is the principal envelope dimension for layout, clearance checks, clamps, sleeves, and support interfaces. The inside diameter describes the available internal passage and can be used as a dimensional reference for flow studies. The listed wall thickness identifies the Schedule 20 dimensional series for this nominal size.
NPS, DN, and actual diameter
NPS 18 and DN450 are nominal designations rather than direct statements of the measured pipe diameter. For coordination work, use the listed outside diameter instead of treating the nominal size as the physical envelope.
Using the weight information
The dry pipe weight is useful for material takeoffs, handling studies, transport planning, and preliminary support-load reviews. The water-filled value represents a different operating condition and should not be confused with the bare-pipe weight. A complete design review may also need to consider contents, insulation, coatings, valves, fittings, supports, and other attached items when those loads apply.
What Schedule 20 does—and does not—specify
Schedule 20 identifies a pipe wall-thickness series for the listed nominal size. It does not, by itself, establish the allowable pressure, material grade, corrosion allowance, design temperature, joining method, or suitability for a particular service. Those decisions require the governing project specifications and engineering checks.
CAD and drafting workflow
For drafting, begin with the listed outside diameter and wall thickness when creating a pipe representation or checking an existing model. Coordinate the pipe envelope with fittings, flanges, supports, access zones, and nearby equipment. The downloadable DWG can support reference work, but the project drawing should still be checked against the approved piping and fabrication requirements.
Selection and Verification Checklist
- Confirm that NPS 18 and DN450 match the project piping specification.
- Use the listed outside diameter for physical layout and clearance coordination.
- Use the listed wall thickness and inside diameter when checking the pipe section represented by this page.
- Separate bare-pipe weight from the water-filled operating condition.
- Verify material, pressure, temperature, corrosion, and connection requirements before procurement or construction.
Related Size Comparisons
For a nearby nominal-size comparison, review the linked 16 inch DN400 Schedule 20 pipe reference and 20 inch DN500 Schedule 20 pipe reference. Comparing adjacent size pages can help with preliminary layout studies and size-selection discussions, but final selection remains a project engineering responsibility.
Frequently Asked Questions
What is 18 inch Schedule 20 pipe called in metric terminology?
It is commonly identified as DN450. The page also uses the inch-based designation NPS 18; both labels refer to the same nominal pipe size category shown in this reference.
What dimension should be used for layout clearance?
Use the listed outside diameter when checking the pipe envelope, clearances, supports, sleeves, and nearby components. Nominal size designations should not be treated as the physical outside diameter.
Is the listed pipe weight the operating load?
The listed bare-pipe weight and the water-filled weight describe different conditions. Operating-load calculations may also require contents, insulation, coatings, fittings, valves, and other project-specific items.
Does Schedule 20 alone determine the pipe pressure rating?
No. Schedule 20 describes the dimensional wall-thickness series. Pressure capability depends on additional factors such as material, design temperature, code requirements, corrosion allowance, manufacturing requirements, and engineering evaluation.
Can this data be used for a CAD drawing?
Yes, the dimensions can be used as a reference for layout and drafting, and the page includes a DWG download. Review the resulting drawing against the approved project specification and the required fittings, connections, supports, and fabrication details.