ASME A106/ASTM A106: Seamless Carbon Steel Pipe for High-Temperature Service
Overview
ASME A106, also known as ASTM A106, is a standard specification that covers seamless carbon steel pipe for high-temperature service. It is widely used in process piping systems in oil refineries, petrochemical plants, power plants, and other industrial facilities where fluids and gases are transported at elevated temperatures and pressures. The code is essential for specifying, manufacturing, and verifying seamless carbon steel pipes to ensure safety, reliability, and compliance with engineering standards.
Scope and Application
The standard applies to seamless carbon steel pipes intended for use in high-temperature environments. It covers nominal pipe sizes (NPS) from 1/8 inch to 48 inches, with wall thicknesses as defined by ASME B36.10M. The pipes are suitable for bending, flanging, and similar forming operations, as well as for welding. Typical applications include steam lines, process piping, boiler piping, and heat exchangers.
Grades and Their Applications
ASME A106 specifies three grades:
Grade A: Lower strength, used less frequently.
Grade B: Most commonly used grade, offering a balance of strength and ductility.
Grade C: Higher strength, used where greater mechanical properties are required.
Selection of grade depends on the required mechanical properties and the specific application.
Chemical Composition Requirements
The code specifies strict limits on the chemical composition of the steel to ensure predictable mechanical properties and corrosion resistance.
| Element | Grade A (%) | Grade B (%) | Grade C (%) |
|---|---|---|---|
| Carbon | 0.25 max | 0.30 max | 0.35 max |
| Manganese | 0.27–0.93 | 0.29–1.06 | 0.29–1.06 |
| Phosphorus | 0.035 max | 0.035 max | 0.035 max |
| Sulfur | 0.035 max | 0.035 max | 0.035 max |
| Silicon | 0.10 min | 0.10 min | 0.10 min |
| Copper* | 0.40 max | 0.40 max | 0.40 max |
| Nickel* | 0.40 max | 0.40 max | 0.40 max |
| Chromium* | 0.40 max | 0.40 max | 0.40 max |
| Molybdenum* | 0.15 max | 0.15 max | 0.15 max |
| Vanadium* | 0.08 max | 0.08 max | 0.08 max |
*These elements are considered residuals.
Mechanical Properties
Mechanical properties are critical for ensuring the pipe’s ability to withstand pressure and temperature.
| Property | Grade A | Grade B | Grade C |
|---|---|---|---|
| Tensile Strength | 330 MPa min | 415 MPa min | 485 MPa min |
| Yield Strength | 205 MPa min | 240 MPa min | 275 MPa min |
| Elongation | See Table X2.1 in code (varies by size and thickness, typically 30% or higher) |
Manufacturing Methods
Seamless Pipe: Manufactured by hot working steel, with subsequent cold finishing permitted.
Heat Treatment: Required for pipes that are cold drawn or cold finished. The pipe must be normalized, normalized and tempered, or full-annealed.
Dimensions and Tolerances
Nominal Pipe Size (NPS): 1/8 inch to 48 inches.
Wall Thickness: As per ASME B36.10M (Standard for Welded and Seamless Wrought Steel Pipe).
Outside Diameter Tolerance: ±0.75% for NPS 1 and larger.
Wall Thickness Tolerance: -12.5% minimum permitted.
Testing and Inspection Requirements
Hydrostatic Test
Every pipe must be hydrostatically tested at the mill to ensure it can withstand the required pressure without leakage.
Nondestructive Electric Test (NDE)
As an alternative to hydrostatic testing, pipes may be subjected to nondestructive electric tests to detect imperfections.
Mechanical Tests
Tensile Test: To verify yield and tensile strength.
Bending Test: For NPS ≤ 2, to ensure ductility.
Flattening Test: For larger sizes, to check soundness and ductility.
Visual and Dimensional Inspection
Pipes are inspected for surface defects, dimensions, and markings to ensure compliance with the standard.
Marking and Certification
Each pipe must be clearly marked with:
Manufacturer’s name or trademark
Specification (A106)
Grade (A, B, or C)
Size and schedule
Heat number
Additional markings as required by purchase order
A mill test certificate (MTC) or material test report (MTR) must be provided, confirming compliance with chemical, mechanical, and testing requirements.
Supplementary Requirements
ASME A106 includes optional supplementary requirements for enhanced testing or inspection, such as:
Additional NDE or ultrasonic testing
Stricter dimensional tolerances
Charpy impact testing for low-temperature service
Special surface finish or cleaning
These are applied as specified by the purchaser.
Reference Standards
ASME B36.10M: Pipe dimensions and weights
ASME Section II, Part A: Material specifications
ASME B31.3: Process piping code (for design and installation)
ASTM E213, E309, E570: Nondestructive testing methods
Typical Applications
Steam, water, and air lines at high temperature
Oil and gas transmission
Chemical process piping
Boiler and heat exchanger tubes
Importable Table: Quick Reference for ASME A106
| Feature | Grade A | Grade B | Grade C |
|---|---|---|---|
| Max Carbon (%) | 0.25 | 0.30 | 0.35 |
| Min Yield (MPa) | 205 | 240 | 275 |
| Min Tensile (MPa) | 330 | 415 | 485 |
| Common Use | Rare | Most common | High strength |
| Typical Applications | General | Refineries, Power | High-pressure |
How to Specify and Use ASME A106 Pipe
Determine service conditions: Temperature, pressure, fluid type, and corrosiveness.
Select grade: Grade B is standard; choose A or C as needed for strength.
Specify dimensions: NPS, schedule (wall thickness), and length.
Define end finish: Plain, beveled, or threaded.
Include supplementary requirements: If additional testing or inspection is needed.
Verify compliance: Check MTRs, markings, and test results against the code.
Summary
ASME A106 is the global standard for seamless carbon steel pipe in high-temperature, high-pressure process applications. Understanding its scope, grades, chemical and mechanical requirements, manufacturing, testing, and documentation is essential for safe and reliable piping design and procurement. Always refer to the latest edition of the code and project specifications for precise requirements, and consult with qualified engineers for critical applications