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How to Read Steel Pipe Specifications and Standards

steel pipe specifications

Table of Contents

A complete steel pipe specification identifies the pipe’s size, wall thickness, material standard, grade, manufacturing method, ends, length, and surface finish.

Consider this example:

ASTM A106 Grade B, NPS 6, SCH 40, SMLS, BE, 12 m

Each element controls a different part of the order:

Element Example Meaning
Material specification ASTM A106 Manufacturing, material, and testing requirements
Grade Grade B Chemical and mechanical properties
Nominal size NPS 6 Standardized pipe size
Wall thickness SCH 40 Nominal wall thickness series
Manufacturing method SMLS Seamless pipe
End preparation BE Beveled ends
Length 12 m Required pipe length

Understanding these elements helps buyers avoid inaccurate quotations, incompatible fittings, failed inspections, and replacement orders.

What Does a Steel Pipe Specification Mean?

A steel pipe specification may reference several types of standards:

Term Example What It Controls
Dimensional standard ASME B36.10M Outside diameter and wall thickness
Product specification ASTM A53, ASTM A106, API 5L Material, manufacture, testing, and marking
Material grade Grade B, X52 Chemical and mechanical properties
Piping code ASME B31.1, ASME B31.3 Design and construction of the piping system
Project specification RFQ or pipe class Additional project and purchasing requirements

These documents are not interchangeable. ASME B36.10M defines standardized pipe dimensions, while ASTM A106 defines requirements for seamless carbon steel pipe. A complete order may need to reference both.

How to Read a Steel Pipe Specification Step by Step

Most steel pipe specifications contain the following information.

Nominal Pipe Size and DN

Nominal Pipe Size, abbreviated as NPS, is the North American system used to identify pipe sizes. The number is a designation, not always the actual outside diameter.

For NPS 1/8 through NPS 12, the actual OD is numerically larger than the nominal size. For example:

  • NPS 2 has an actual OD of 2.375 inches.
  • NPS 4 has an actual OD of 4.500 inches.
  • NPS 6 has an actual OD of 6.625 inches.

From NPS 14 upward, the NPS number and actual OD in inches are numerically equal. An NPS 16 pipe therefore has an OD of 16 inches.

DN, or Diameter Nominal, is the corresponding metric designation. Common equivalents include:

NPS DN Actual OD
NPS 1 DN 25 33.4 mm
NPS 2 DN 50 60.3 mm
NPS 4 DN 100 114.3 mm
NPS 6 DN 150 168.3 mm
NPS 8 DN 200 219.1 mm

The shortcut DN ≈ NPS × 25 works for many common sizes, but it is not an exact conversion. Use a standardized table when confirming dimensions. You can find additional values in our steel pipe sizes and dimensions chart.

Pipe Schedule and Wall Thickness

Pipe Schedule, usually written as SCH or Sch, identifies a nominal wall thickness series. It must always be read together with the NPS.

For the same NPS:

  • The outside diameter remains unchanged.
  • A higher Schedule generally means a thicker wall.
  • A thicker wall reduces the inside diameter.
  • A thicker wall increases the pipe weight.

For example:

Size Outside Diameter Wall Thickness Inside Diameter
NPS 4 SCH 40 4.500 in 0.237 in 4.026 in
NPS 4 SCH 80 4.500 in 0.337 in 3.826 in

SCH 80 is thicker than SCH 40 at this size. However, Schedule is not a pressure rating. Allowable pressure also depends on the material, temperature, applicable piping code, manufacturing tolerance, joint design, and corrosion allowance.

Schedule also does not determine corrosion resistance. SCH 80 carbon steel has more wall thickness than SCH 40, but resistance to a corrosive medium depends mainly on the steel grade, coating, lining, and operating environment.

STD, XS, and XXS Weight Classes

Older drawings may use weight-class designations:

  • STD: Standard Weight
  • XS: Extra Strong
  • XXS: Double Extra Strong

STD has the same nominal wall thickness as SCH 40 through NPS 10. XS matches SCH 80 through NPS 8. At larger sizes, the wall thicknesses differ.

Do not automatically replace STD or XS with a Schedule number. Confirm the required wall thickness from the applicable dimensional table.

Material Specification and Grade

The material specification defines how the pipe must be manufactured, tested, inspected, and marked. The grade defines a particular level of chemical composition and mechanical properties within that specification.

For example:

ASTM A106 Grade B

ASTM A106 is the product specification, while Grade B is the material grade.

Similar grade names are not necessarily equivalent. ASTM A53 Grade B, ASTM A106 Grade B, and API 5L Grade B have different scopes and requirements. They should only be substituted when the project permits it and the Mill Test Certificate confirms compliance.

Manufacturing Method

The manufacturing method may be shown through abbreviations:

Abbreviation Meaning
SMLS Seamless
ERW Electric Resistance Welded
HFW High-Frequency Welded
SAWL or LSAW Longitudinal Submerged Arc Welded
SAWH or SSAW Helical or Spiral Submerged Arc Welded

Some specifications also use type designations. ASTM A53 Type E identifies electric-resistance-welded pipe, while Type S identifies seamless pipe.

The manufacturing method should follow the project specification. Seamless pipe is not automatically required for every high-pressure or industrial application. Read our comparison of seamless vs. welded steel pipes for more information.

Ends, Length, and Surface Finish

A complete specification should also define how the pipe will be delivered.

Common end preparations include:

  • PE: Plain End
  • BE: Beveled End
  • T&C: Threaded and Coupled
  • Grooved End: Roll-grooved or cut-grooved connection

Length may be fixed, single random, double random, 6 meters, or 12 meters.

Surface requirements may include black finish, mill varnish, hot-dip galvanizing, red paint, epoxy, FBE, 3LPE, or 3LPP coating.

These details affect production, installation, packing, freight, and price. They should be stated before the supplier prepares the quotation.

steel pipe specifications

Major Steel Pipe Standards

The following standards are commonly found in steel pipe specifications:

Standard Main Scope Typical Application
ASME B36.10M Steel pipe dimensions and wall thicknesses Carbon and alloy steel piping
ASME B36.19M Stainless steel pipe dimensions Stainless steel piping
ASTM A53/A53M Black and galvanized welded or seamless pipe Mechanical and pressure service
ASTM A106/A106M Seamless carbon steel pipe High-temperature service
ASTM A795/A795M Black and galvanized welded or seamless pipe Fire protection systems
API Specification 5L Seamless and welded line pipe Pipeline transportation
ASTM A500/A500M Structural tubing in rounds and shapes Buildings and structural fabrication

ASTM A53 Pipe

ASTM A53 covers black and hot-dip galvanized welded and seamless steel pipe. It is commonly used for mechanical and pressure applications and for ordinary steam, water, gas, and air lines.

Because the standard permits different types and grades, an order should identify the required grade, type, size, Schedule, finish, and ends. See our ASTM A53 pipe guide for more details.

ASTM A106 Pipe

ASTM A106 covers seamless carbon steel pipe for high-temperature service. It is commonly specified for refineries, power plants, boilers, and process piping.

Grades A, B, and C are available, with Grade B widely used. BAOLAI supplies seamless steel pipes with specified dimensions, grades, testing, and documentation.

ASTM A795 Fire Sprinkler Pipe

ASTM A795 covers black and hot-dip galvanized welded and seamless pipe intended for fire protection systems.

A fire sprinkler pipe order may also need to specify:

  • Schedule or listed wall thickness
  • Black, galvanized, or painted finish
  • Grooved, threaded, welded, or plain ends
  • UL Listing or FM Approval
  • Required inspection documents

The standard alone does not confirm acceptance for every project. Contractors should also verify the approved product listing and local project requirements. Explore BAOLAI’s fire sprinkler pipes for available options.

API 5L Line Pipe

API Specification 5L covers seamless and welded line pipe for pipeline transportation systems. It includes two Product Specification Levels:

  • PSL 1 provides standard manufacturing and testing requirements.
  • PSL 2 adds stricter requirements for areas such as chemistry, toughness, traceability, and testing.

Common grades include Grade B, X42, X52, X60, X65, and X70. API 5L pipe is often ordered by actual OD and wall thickness instead of NPS and Schedule.

See the API 5L line pipe guide for more information.

Steel Pipe Specification Examples

ASTM A53 ERW Pipe

ASTM A53/A53M Grade B, Type E, NPS 4, SCH 40, black, BE, 6 m

This describes an electric-resistance-welded ASTM A53 Grade B pipe with a black finish, beveled ends, and a fixed 6-meter length.

ASTM A106 Seamless Pipe

ASTM A106/A106M Grade B, NPS 6, SCH 80, SMLS, BE, 12 m, MTC EN 10204 3.1

This describes a seamless ASTM A106 Grade B pipe with SCH 80 wall thickness, beveled ends, a 12-meter length, and a Type 3.1 inspection document.

API 5L Line Pipe

API Spec 5L, Grade X52, PSL 2, 12.750 in OD × 0.375 in WT, SAWL, BE, 3LPE coated

This describes PSL 2 longitudinal submerged arc welded line pipe with a specified OD, wall thickness, beveled ends, and a three-layer polyethylene coating.

How to Read Steel Pipe Markings and the MTC

Pipe markings normally identify the manufacturer, standard, grade, dimensions, manufacturing method, and traceability number.

A typical marking may look like:

BAOLAI – ASTM A53 GR. B TYPE E – NPS 4 SCH 40 – ERW – HEAT 123456

During receiving inspection, compare the marking with the purchase order and Mill Test Certificate. Check:

  1. Manufacturer
  2. Product standard and grade
  3. Manufacturing method
  4. NPS, OD, and wall thickness
  5. Heat number
  6. Chemical composition
  7. Mechanical properties
  8. Required test results
  9. Coating and end preparation
  10. Inspection document type

The heat number should connect the delivered pipe to its material records. A batch number may identify a later production or inspection group and is not necessarily the same as the heat number.

Read Pipe Heat Number vs Batch Number for a detailed explanation.

steel pipe specifications

How to Write a Complete Steel Pipe RFQ

An inquiry that says only “6-inch carbon steel pipe” does not provide enough information for an accurate quotation.

Use this format:

Standard + grade + manufacturing method + size + wall thickness + length + ends + finish + testing + documentation + quantity

For example:

ASTM A106/A106M Grade B seamless steel pipe, NPS 6, SCH 40, 12 m fixed length, beveled ends, black finish, hydrostatically tested, MTC EN 10204 3.1, total quantity 100 metric tons.

For international orders, also state the required standard edition, destination, packing method, inspection requirements, coating system, and delivery date.

Common Steel Pipe Specification Mistakes

Avoid these common purchasing errors:

  • Treating NPS as the actual OD
  • Specifying Schedule without NPS
  • Treating Schedule as a pressure rating
  • Assuming SCH 80 is corrosion-resistant
  • Confusing dimensional and material standards
  • Assuming similar grades are interchangeable
  • Omitting the manufacturing method
  • Forgetting ends, lengths, coatings, or documents
  • Accepting an MTC without checking heat-number traceability

Correcting these details before production is usually faster and less expensive than resolving them during inspection or installation.

FAQs About Steel Pipe Specifications

What information is included in a steel pipe specification?

A complete specification normally includes the product standard, grade, manufacturing method, NPS or OD, Schedule or wall thickness, length, ends, finish, testing, documents, and quantity.

What is the difference between a pipe standard and a pipe specification?

A standard is a technical document published by an organization such as ASTM, ASME, or API. A project specification identifies which standards and additional purchasing requirements apply to a particular pipe order.

Does pipe Schedule indicate the pressure rating?

No. Schedule identifies a wall thickness series. Allowable pressure also depends on the material, temperature, dimensions, piping code, corrosion allowance, and joint design.

How do you read an ASTM pipe designation?

In “ASTM A53 Grade B Type E,” A53 identifies the product specification, Grade B identifies the material grade, and Type E identifies electric-resistance-welded manufacture. Size, Schedule, ends, and length must be stated separately.

How can you verify that delivered pipe matches the specification?

Compare the pipe marking, dimensions, purchase order, and Mill Test Certificate. Confirm the standard, grade, manufacturing method, heat number, chemical composition, mechanical properties, test results, and required documentation.

About Baolai Pipes

Founded in 1991, Baolai manufactures steel pipes and structural hollow sections for international projects. Visit Baolai Pipes to explore our products or request a quotation.

Conclusion

Reading steel pipe specifications requires more than identifying NPS, Schedule, and material grade. Buyers must also check the manufacturing method, ends, length, finish, testing, and traceability requirements.

Before requesting a quotation, make sure each part of the pipe callout is complete. Before accepting delivery, match the pipe markings and measurements with the purchase order and Mill Test Certificate.

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