Steel Casing Pipe Wall Thickness

In engineering construction and pipeline transportation, steel casing pipe serves as a crucial component for protecting pipelines and cables or providing structural support. Its thickness requirements are directly related to safety, durability, and cost-effectiveness. Depending on the application, media characteristics, and natural conditions, steel casing pipe thickness must comply with different standards and specifications. The following is an analysis of general standards, application areas, and key influencing factors.

General Standards and Basic Thickness Requirements

1. API 5L Standard

Chemical transportation casing has higher requirements. For example, the thickness of steel casing pipe for DN100 pipelines is typically 5-7mm, but can increase to 8-10mm in high-pressure environments.

2. ASTM A53/A106

According to US material standards, the thickness of DN50 (standard grade) steel casing pipe is 3.9mm, while Sch 80 (extended grade) reaches 5.5mm, suitable for high-temperature and high-pressure conditions.

3. Chinese Standard (GB/T 3091-2015)

For welded pipes for general fluid transportation (such as Q235 material), the thickness of steel casing pipe for nominal diameters (DN) 15-150mm is generally 1.8-4.5mm; for pipes DN200 and above, the thickness can be 6.0mm or greater. For applications in corrosive environments or high pressure, a corrosion allowance (typically 0.5-2mm) is required.

Steel Casing Pipe Thickness for Different Applications

1. Municipal Engineering (Cable/Optical Cable Protection)

Buried cable casings generally use DN80-DN200 welded pipes with a thickness of 1.5-3.0mm to meet mechanical protection requirements. For applications crossing roads or lightly loaded areas, the thickness should be increased to 4-6mm to withstand pressure.

2. Petrochemical Industry

Oil pipeline casings should take into account media corrosion and external loads. For example, DN300 20# steel casing pipe in acidic environments must be ≥8mm thick and feature an epoxy coal tar coating.

3. Building Water Supply and Drainage

The thickness of fireproof steel casing pipe (e.g., DN150) must be at least 3.550mm, and general drainage casing can be reduced to 2.75mm.

4. Special Environments

Due to water pressure and impact, submarine pipeline casings can be up to 12-20mm thick and utilize a double-sided welding process.

Factors Affecting Thickness

1. Mechanical Properties

Internal Pressure Calculation

Determine the required pressure using the formula: t = P (2S) (P = pressure, D = diameter, and S = allowable stress).

External Loads

Finite element analysis is required to analyze deformations such as soil pressure and vehicle dynamic loads.

2. Corrosion and Damage

In acidic soils or sandy media, the thickness should be increased by 1-2 mm to allow for corrosion, or stainless steel (such as 304/316L) should be used instead of carbon steel.

3. Economy and Lifespan

Excessive thickness increases costs, while excessive thinness shortens service life. For example, in municipal engineering, galvanized steel casing pipe has a design life of 30 years and should be 0.5 mm thicker than bare steel pipe.

4. Installation Process

Due to the complex load conditions, the steel casing pipe thickness for pipe jacking projects should be 10%-15% thicker than for direct burial.

Criteria for Selecting Steel Casing Pipe Thickness

1. National Standards and Regulations

The thickness of steel casing pipe must first be determined in accordance with national standards. These standards detail the recommended wall thickness for different sizes of steel casing pipe, providing an important basis for engineering design. For example, the standard wall thickness for DN50 rigid waterproof casing is 3.9 mm, while the wall thickness for DN100 is 5-7 mm.

2. Operating Environment and Conditions

The operating environment and conditions of steel casing pipe are also key factors in determining its thickness. In highly corrosive environments, extremely high temperatures, or high pressures, thicker steel casing pipe is required to ensure resistance to corrosion, wear, and thermal deformation.

3. Material Selection

In addition to environmental and pressure factors, the material of steel casing pipe also influences its thickness selection. High-quality steel offers better corrosion resistance and surface smoothness, making it suitable for protecting pipelines in high-pressure and harsh environments. Therefore, when selecting materials, the compatibility of material and thickness should be comprehensively considered.

Summary

The thickness requirement for steel casing pipe is a complex and important issue. In practical applications, it is necessary to comprehensively consider the specific operating conditions and safety standards to ensure that the casing can operate safely and stably in various environments.