Schedule 20 Seamless Steel Pipe

Schedule 20 seamless steel pipe is a carbon steel pipe manufactured without a longitudinal weld and specified with a Schedule 20 wall thickness. It is commonly selected for piping systems where a relatively light wall is suitable for the required service conditions.
The term Schedule 20 describes the pipe's wall thickness in relation to its nominal pipe size (NPS); it does not identify the steel grade or manufacturing process. Seamless pipe can therefore be supplied in Schedule 20 when the selected NPS and applicable dimensional standard provide a Schedule 20 wall thickness.

For carbon steel seamless pipe, common material specifications include ASTM A106/A106M and other project-specific standards. ASTM A106/A106M covers seamless carbon steel pipe for high-temperature service and references ASME B36.10M for nominal wall thickness.

What Is Schedule 20 Seamless Steel Pipe?

Schedule 20 seamless steel pipe is a seamless steel pipe with Schedule 20 dimensions. Unlike welded pipe, seamless pipe is produced from a solid steel billet that is heated and pierced to form a hollow tube, followed by rolling or other sizing operations.
There are three terms that should be distinguished:
Schedule 20 — identifies a standardized wall-thickness designation for a given NPS.
Seamless — describes the manufacturing method and means the pipe does not have a longitudinal weld seam.
Carbon steel — describes the material family.
Therefore, "Schedule 20 seamless steel pipe" combines a dimensional designation with a manufacturing method. The actual material grade still needs to be specified separately.

ASME B36.10 covers dimensions for both welded and seamless wrought steel pipe, while ASTM A106/A106M provides requirements for seamless carbon steel pipe for high-temperature service.

Schedule 20 Seamless Steel Pipe Dimensions

Schedule 20 dimensions vary with nominal pipe size. The outside diameter is determined by the NPS, while the Schedule designation determines the applicable wall thickness for that size.
The following commonly used dimensions are based on ASME B36.10 dimensional data:

NPS	Outside Diameter	Schedule 20 Wall Thickness	Approx. Inside Diameter
8 in.	8.625 in. (219.1 mm)	0.250 in. (6.35 mm)	8.125 in. (206.4 mm)
10 in.	10.750 in. (273.0 mm)	0.250 in. (6.35 mm)	10.250 in. (260.4 mm)
12 in.	12.750 in. (323.8 mm)	0.250 in. (6.35 mm)	12.250 in. (311.2 mm)
14 in.	14.000 in. (355.6 mm)	0.312 in. (7.92 mm)	13.376 in. (339.8 mm)
16 in.	16.000 in. (406.4 mm)	0.312 in. (7.92 mm)	15.376 in. (390.7 mm)
18 in.	18.000 in. (457.0 mm)	0.312 in. (7.92 mm)	17.376 in. (441.3 mm)
20 in.	20.000 in. (508.0 mm)	0.375 in. (9.53 mm)	19.250 in. (488.9 mm)
24 in.	24.000 in. (610.0 mm)	0.375 in. (9.53 mm)	23.250 in. (590.6 mm)
30 in.	30.000 in. (762.0 mm)	0.500 in. (12.70 mm)	29.000 in. (736.6 mm)
36 in.	36.000 in. (914.0 mm)	0.500 in. (12.70 mm)	35.000 in. (889.0 mm)

The table is intended as a quick reference. For procurement, engineering design, or pressure calculations, the applicable edition of the dimensional standard and the actual purchase specification should always be checked.
One important point is that Schedule 20 is not available as a standard wall thickness for every NPS. Schedule designations are size-dependent, so a buyer should confirm the required NPS and wall thickness rather than assuming that every pipe diameter has a Schedule 20 value. ASME B36.10 specifically standardizes dimensions for welded and seamless steel pipe.

Schedule 20 Seamless Pipe Wall Thickness

The wall thickness of Schedule 20 pipe changes according to NPS.
For example, an NPS 8 Schedule 20 pipe has an outside diameter of 8.625 inches and a nominal wall thickness of 0.250 inch. An NPS 20 pipe has an outside diameter of 20 inches and a Schedule 20 wall thickness of 0.375 inch.
This means that Schedule 20 should not be interpreted as a fixed 20 mm or 20% wall thickness.
The basic relationship is:
Inside Diameter ≈ Outside Diameter − 2 × Wall Thickness
Actual dimensions should be taken from the applicable standard because manufacturing tolerances can affect the measured dimensions of individual pipes.

Schedule 20 Seamless Steel Pipe Standards

The dimensional and material standards should be considered separately when specifying seamless pipe.

ASME B36.10M
ASME B36.10M is the principal dimensional reference for welded and seamless wrought steel pipe. It standardizes nominal pipe sizes, outside diameters and wall-thickness designations used in common industrial piping systems.

ASTM A106/A106M
ASTM A106/A106M covers seamless carbon steel pipe intended for high-temperature service. The specification includes NPS 1/8 through NPS 48 and uses nominal wall thicknesses associated with ASME B36.10M.
ASTM A106 is commonly specified as:
ASTM A106 Grade A
ASTM A106 Grade B
ASTM A106 Grade C
The correct grade depends on the mechanical, temperature and service requirements of the project.

ASTM A53
ASTM A53 is another commonly encountered carbon steel pipe specification. However, the purchaser should not assume that an ASTM A53 pipe and an ASTM A106 pipe are interchangeable simply because they have the same NPS and Schedule.

The applicable material specification should be selected according to the design code, service conditions and project requirements.

Common Materials for Schedule 20 Seamless Pipe

Schedule 20 is a dimensional designation, so the material grade must be specified separately.
Common carbon steel seamless pipe grades may include:

Material Standard	Typical Grade	General Use
ASTM A106/A106M	Grade A, B, C	High-temperature service
ASTM A53	Grade A, B	General mechanical and pressure applications
API 5L	Grade B and selected grades	Oil and gas pipeline service
Project-specific standards	As specified	Special industrial applications

Not every grade is appropriate for every application. The final selection should consider temperature, pressure, fluid, corrosion conditions, welding requirements and applicable design codes.

How Is Schedule 20 Seamless Steel Pipe Manufactured?

Seamless steel pipe is produced without forming a longitudinal welded joint.
A typical manufacturing sequence includes:
1.Steel billet preparation
A solid round billet is prepared according to the required steel grade.
2.Heating
The billet is heated to a suitable temperature for piercing and forming.
3.Piercing
A rotary piercing process creates the initial hollow shell.
4.Rolling and sizing
The hollow shell is rolled and sized to approach the specified outside diameter and wall thickness.
5.Heat treatment
Heat treatment is applied when required by the material specification and grade.
6.Straightening and finishing
The pipe is straightened, cut to length and finished according to the purchase requirements.
7.Inspection and testing
The pipe is inspected and tested according to the applicable product specification.
For ASTM A106 pipe, the specification includes mechanical and other inspection requirements such as tensile, bending, flattening, hydrostatic and nondestructive electric testing as applicable.

Schedule 20 Seamless vsWelded Steel Pipe

The major difference is the manufacturing method, not the Schedule designation.

Feature	Schedule 20 Seamless Pipe	Schedule 20 Welded Pipe
Manufacturing	Formed from a solid billet	Formed from steel plate/coil and welded
Longitudinal weld	No	Yes
Schedule	Schedule 20	Schedule 20
Dimensional standard	Commonly ASME B36.10M	Commonly ASME B36.10M
Material options	Depends on specification	Depends on specification
Typical selection factor	Seamless construction and service requirements	Cost, size availability and project requirements

Both welded and seamless steel pipe can be dimensioned according to ASME B36.10M. Therefore, Schedule 20 does not mean seamless, and "seamless" does not automatically mean a particular Schedule.

Schedule 20 Seamless vs Schedule 40 Seamless Pipe

The main difference between Schedule 20 and Schedule 40 is wall thickness.
For the same NPS, a Schedule 40 pipe generally has a thicker wall than a Schedule 20 pipe. This normally means greater pipe weight and a smaller internal diameter, while the actual allowable pressure must be determined from the applicable material, design code, temperature, corrosion allowance and other engineering factors.

Item	Schedule 20	Schedule 40
Wall thickness	Generally lighter	Generally thicker
Pipe weight	Lower for the same NPS	Higher for the same NPS
Internal diameter	Generally larger	Generally smaller
Material consumption	Lower	Higher
Pressure suitability	Depends on design	Depends on design
Typical selection	When lighter wall is acceptable	When greater wall thickness is required

A thicker Schedule should not be selected solely because it is "stronger." Pipe selection should be based on the actual design conditions and applicable engineering code.

What Should You Check When Buying Schedule 20 Seamless Steel Pipe?

A purchase description should contain more information than simply "Schedule 20 seamless pipe."
At minimum, confirm:
Nominal pipe size (NPS)
Schedule: SCH 20
Material specification
Steel grade
Outside diameter and wall thickness
Pipe length
Pipe ends: plain, beveled or threaded
Surface condition
Heat treatment requirements
Inspection and testing requirements
Applicable dimensional standard
Mill Test Certificate (MTC) requirements
For a project order, the specification should also identify the applicable design code and any supplementary testing requirements.

Schedule 20 Seamless Steel Pipe Weight

Pipe weight depends on the outside diameter, wall thickness and steel density.For a quick estimate of carbon steel pipe weight, a commonly used metric formula is:
Weight (kg/m) ≈ 0.02466 × T × (OD − T)
Where:
OD = outside diameter in mm
T = wall thickness in mm
For Schedule 20 seamless pipe, the applicable OD and wall thickness should first be obtained from the relevant dimensional standard.

The calculated value is an estimate. Actual delivered weight can vary according to dimensional tolerances, length and the applicable product specification.

FAQ About Schedule 20 Seamless Steel Pipe

What is Schedule 20 seamless steel pipe?
Schedule 20 seamless steel pipe is a seamless steel pipe manufactured without a longitudinal weld and supplied with a Schedule 20 wall thickness for the applicable nominal pipe size.
Is Schedule 20 pipe seamless?
No. Schedule 20 describes the dimensional wall-thickness designation, not the manufacturing process. Both welded and seamless steel pipe can use Schedule 20 dimensions where the applicable standard provides them.
What is the difference between Schedule 20 and Schedule 40 seamless pipe?
Schedule 40 generally has a thicker wall than Schedule 20 for the same NPS. This usually results in greater weight and a smaller internal diameter. The appropriate Schedule should be selected according to the actual design conditions.
Is Schedule 20 seamless pipe suitable for high pressure?
Not necessarily. Schedule alone does not establish a universal pressure rating. Allowable pressure depends on pipe size, material grade, temperature, design code, wall thickness, corrosion allowance and other factors.
What is the standard for Schedule 20 seamless steel pipe dimensions?

ASME B36.10M is the principal dimensional standard for welded and seamless wrought steel pipe.

Conclusion

Schedule 20 seamless steel pipe combines a standardized pipe dimension with seamless manufacturing. Schedule 20 identifies the wall-thickness designation; seamless identifies how the pipe is manufactured; the material grade must be specified separately.For buyers, the most important considerations are NPS, Schedule 20 wall thickness, material specification, grade, operating pressure and temperature, corrosion allowance, testing requirements and applicable design standards.
For projects requiring carbon steel seamless pipe, ASTM A106/A106M is one commonly specified material standard for high-temperature service, while ASME B36.10M provides the dimensional framework for welded and seamless steel pipe.For an accurate quotation, provide the NPS, SCH 20, material grade, length, pipe ends, quantity and applicable standard to the steel pipe supplier.