Seamless Pipe Thickness

The thickness of seamless pipe is one of their key parameters, directly affecting their pressure resistance, weight, cost, and ultimate application. In industries such as oil and gas, boilers, power, chemicals, and machinery manufacturing, seamless pipes are often the preferred material for demanding conditions due to their lack of welds, dense structure, and consistent performance. Thickness is a crucial variable in engineering design and procurement decisions.

Thickness Meaning

The thickness of a seamless pipe is typically defined as half the difference between its outer diameter (OD) and inner diameter (ID), i.e., the pipe wall thickness (t).

The basic relationship is: t = (OD − ID) ÷ 2

It has clear measurement standards in production and inspection. Unlike welded pipes, which are formed by rolling and welding sheet metal, seamless pipes are made from solid steel billets through processes such as piercing, rolling, or stretching, without welds. The uniformity and consistency of its thickness are important indicators of quality.

Methods for Measuring Seamless Pipe Thickness

1. Ultrasonic Thickness Measurement

This is the most commonly used and non-destructive testing method. Utilizing the propagation time of ultrasonic waves within the pipe wall allows for rapid detection of wall thickness at various points, particularly suitable for assessing thickness uniformity.

2. Caliper and Micrometer Measurement

For pipe ends or sampling areas, direct measurement with precision measuring instruments is possible, but this method relies on sampling inspection.

3. Weighing Calculation

Given the seamless pipe's length, outer diameter, and steel density, accurate weighing allows for the calculation of the average wall thickness, providing an effective auxiliary verification method.

Seamless Pipe Thickness Chart

Actual tolerances are subject to specific standards (ASTM A106 / EN 10216 / GB 8162, etc.).

Seamless Pipe Thicknesses by Different Processes

1. Hot-rolled Seamless Pipe Thickness

Outer diameter range: ≥ 32 mm

Wall thickness range: Approximately 2.5 mm ~ 75 mm

Hot rolling, through plastic deformation at high temperatures, gives the steel pipe high dimensional stability and good mechanical properties, suitable for applications requiring thicker walls and bearing high pressure.

2. Cold-rolled Seamless Pipe Thickness

Compared to hot-rolled steel pipes, cold-rolled seamless pipes can have smaller outer diameters.

Minimum outer diameter: Up to 6 mm (or even smaller)

Minimum wall thickness: Approximately 0.25 mm

Due to the lower processing temperature, cold rolling produces seamless pipes with higher dimensional accuracy and better surface quality, suitable for applications requiring high dimensional accuracy and surface quality.

Thickness Tolerance of Seamless Pipe

Seamless pipe thickness tolerance refers to the permissible deviation of the actual wall thickness of a manufactured steel pipe from its nominal wall thickness. It is a crucial criterion for determining the quality of a steel pipe.

For example, a steel pipe with a nominal wall thickness of 10mm may have an allowable deviation of ±10% or ±0.5mm (depending on the precision grade and product standard). This means that a qualified steel pipe may have an actual wall thickness between 9mm and 11mm.

ASTM / EN / GB Seamless Pipe Thickness and Tolerance Standards:

ASTM A106: ±12.5%

ASTM A53: ±12.5%

ASTM A179: ±10%

ASTM A192: ±12.5%

EN 10216-2: ±10%

EN 10297-1: ±10% / Agreement

GB/T 8162: ±12.5%

GB/T 8163: ±12.5%

GB 5310: ±10% or more stringent

Thickness Comparison with Other Pipe Materials

1. Seam Pipe vs. Seamless Pipe

Uniformity: High-quality seamless steel pipes generally have better wall thickness uniformity than seam pipes. Seam pipes may exhibit microstructure variations and slight thickness differences in the weld area, especially during bending or machining, where the weld area can become a weak point. Seamless pipes do not have this concern; their circumferential properties are consistent.

Thickness Range: Seamless pipes can be produced in a wide range of sizes, from extremely thin (e.g., capillary tubes) to extremely thick (e.g., thick-walled pipes hundreds of millimeters thick). Seam pipes, limited by the thickness of the sheet metal and the welding process, may be restricted in extremely thick and thin applications, especially in ultra-thick cases, where reliability challenges are greater.

High Pressure Applications: For ultra-high pressure, high temperature, or corrosive harsh environments, even with the same thickness, seamless pipes, due to the absence of weld seams, are often preferred for their safety, reliability, and fatigue resistance.

2. Cast Pipes vs. Seamless Pipes

Density and Strength: Cast pipes (such as some cast iron and cast steel pipes) are formed by casting, and their metal structure density is generally lower than that of seamless pipes that are rolled or forged.

To achieve the same pressure resistance, cast pipes often require thicker walls, resulting in greater weight. Seamless pipes have higher material utilization and can achieve lighter weight while maintaining the same strength.

Precision and Surface Finish: Seamless pipes have high dimensional accuracy, smooth inner walls, and low resistance to fluid flow. Cast pipes typically have a rougher inner wall and lower dimensional accuracy.

3. Solid Bars vs. Seamless Pipes

Weight and Material Efficiency: This is the most direct comparison. When subjected to the same bending or torsional moment, seamless pipes of appropriate thickness save significantly more material and weight than solid round steel. This demonstrates the efficiency advantage of "hollow structures."

Thickness is a key variable in optimizing the design. Engineers calculate the ideal wall thickness that meets strength and stiffness requirements while minimizing material consumption.

4. Plastic Pipes, Composite Pipes vs. Seamless Pipes

Strength and Stiffness: Plastic pipes or fiber-reinforced composite pipes have advantages such as corrosion resistance and light weight, but their elastic modulus and strength are generally much lower than steel.

In high-pressure, high-temperature, or high-structural-stiffness applications, plastic pipes may require very thick walls to barely meet the requirements, or may not be a viable alternative. Seamless pipes can achieve extremely high pressure resistance and support capacity with relatively thin walls.

Temperature and Fire Resistance: Seamless pipes are heat-resistant, non-combustible, and their performance is relatively stable at high temperatures. Many non-metallic pipes have upper temperature limits; their strength drops sharply at high temperatures, restricting their application in boilers, superheated steam pipelines, and other fields.

The Impact of Thickness on Seamless Pipes

1. Pressure Bearing Capacity

This is the most direct impact of thickness. With the same material and outer diameter, a thicker wall allows the pipe to withstand higher internal or external pressures.

2. Structural Strength and Stability

Increasing wall thickness significantly increases the moment of inertia of the cross-section, thereby enhancing the steel pipe's resistance to bending and deformation, making it suitable for mechanical structures such as columns and drive shafts.

3. Weight and Material Cost

Increased thickness means the use of more raw materials, directly leading to increased weight and material costs per pipe.

4. Fluid Flowability

For pipelines transporting fluids, with a fixed outer diameter, increased wall thickness leads to a smaller inner diameter, potentially increasing flow resistance. Pipeline design needs to strike a balance between pressure and flow requirements.

5. Process and Manufacturing Limitations

Hot-rolled seamless pipes can generally be produced with thicker walls, while cold-drawn or cold-rolled processes are better suited for producing high-precision, thin-walled seamless pipes. However, excessively thin or thick walls may exceed the processing capacity of a specific unit.

Applications of Different Thicknesses Seamless Pipes

1. Thin-walled Seamless Pipe (Smaller Wall Thickness/Outer Diameter Ratio)

Commonly used in applications where weight is critical, pressure requirements are not extreme, but high precision is required.

Examples: Hydraulic brake lines and fuel lines in automobiles and motorcycles; pneumatic and hydraulic connection pipes in precision instruments; structural tubes in furniture; drive shaft sleeves in certain light machinery.

2. Medium-thick-walled Seamless Pipe

This is the most widely used category. It includes: general pressure vessel shells; surface gathering and transportation pipelines for oil and natural gas; hydraulic cylinder barrels for engineering machinery; and piping and structural pipes in shipbuilding.

3. Thick-walled and Ultra-thick-walled Seamless Pipe

Mainly used in extreme working conditions. For example: high-temperature and high-pressure steam pipelines in power plant boilers; high-pressure hydrogenation reactors and heat exchanger tubes in the petrochemical industry; drill pipes and casings for deep-sea drilling; and load-bearing spindles and large bearing sleeves for heavy machinery.

FAQ

1. How to quickly determine if the thickness of a seamless pipe is up to standard?

Common methods include:

Ultrasonic thickness measurement (preferred);

Micrometer measurement at the pipe end;

Theoretical weight verification;

Third-party testing reports (SGS/BV/TUV).

2. What sizes do seamless pipes come in?

Seamless steel pipe sizes include: outer diameter, thickness and length.

Outer diameter: 1/2 inch - 36 inch (21.3mm-914.4mm)

Thickness: 2.11mm-60mm ( SCH10, SCH20, SCH40, SCH80, STD, SCH120, SCH160, XXS)

Length: Common sizes are 5.8 m, 6 m, 11.8 m, and 12 m, but custom lengths are also available.

3. Are thick-walled seamless pipes always safer than welded pipes?

Thick-walled seamless pipes are significantly safer in the following situations: high pressure, high temperature, strong corrosion, and cyclic fatigue loads.