What Is The Difference Between Hydraulic Tube and Boiler Tube?

Hydraulic tube and boiler tube are two common seamless steel pipes used in the industrial sector. Although they appear similar and are both manufactured using seamless processes, they differ significantly in material properties, application scenarios, and technical standards. The following analyzes the differences between the two from five perspectives:

Core Function Differences

1. Seamless Hydraulic Tube

Seamless hydraulic tube is designed specifically for hydraulic transmission systems, primarily transporting high-pressure fluids (typically operating pressures of 20-50 MPa).

Typical applications include hydraulic cylinders for construction machinery and hydraulic stations for machine tools, requiring the pipe to remain stable under pulsating pressure.

2. Seamless Boiler Tube

Seamless boiler tube generally refers to pipes used in thermal equipment and is commonly used in the manufacture of various types of boilers, high-pressure pipes, steam pipes, and heating pipes.

Because these pipes must withstand high temperatures and high pressures, stringent requirements are imposed on the steel pipe's thickness, strength, corrosion resistance, and stability.

Chemical Composition Comparison

Hydraulic tubes are enhanced by the addition of alloying elements such as Cr and Mo, while boiler tubes prioritize weldability and control carbon content.

Mechanical Property Comparison

1. Tensile Strength

Hydraulic tubes are generally ≥930 MPa (e.g., ASTM A519 standard), while boiler tubes are typically 410-550 MPa (GB3087 standard).

2. Impact Toughness

Low-Temperature Impact Energy at -20°C: Hydraulic tubes require ≥54J (to prevent brittle cracking), while boiler tubes are typically ≥35J.

Special Manufacturing Process Requirements

1. Cold Working Process

Hydraulic steel tubes are mostly cold-drawn and finish-rolled (dimensional accuracy reaches H9); boiler tubes are primarily hot-rolled (accuracy reaches H11).

2. Heat Treatment

Hydraulic tubes require quenching and tempering (quenching and high-temperature tempering), while boiler tubes are typically normalized.

Comparison of Inspection Standard Systems

1. Key Inspection Points for Hydraulic Tubes

100% eddy current testing;

High-pressure burst testing (up to 1.5 times the working pressure);

Pulse fatigue testing (over 500,000 cycles);

Surface treatment typically includes phosphating or chrome plating to enhance wear resistance.

2. Key Inspection Points for Boiler Tubes

Ultrasonic testing;

Expansion test (expansion ratio ≥ 12%);

High-temperature endurance strength test (500°C/1000h);

Grain size typically must reach grades 5-8.

Comparison of Applications

1. Typical Applications for Hydraulic Tubes

Engineering machinery

For example, the hydraulic cylinders of excavators require pipes to withstand frequent pulse pressure without fatigue cracking.

Aerospace

Hydraulic control system pipes must meet -50°C low-temperature impact resistance.

Injection Molding Machine

High-pressure injection molding systems require the inner surface of steel pipes to be mirror-polished (Ra ≤ 0.4μm).

2. Typical Applications of Boiler Tubes

Power plant boilers

Economizers, superheaters, and other components must withstand long-term corrosion from 400°C steam.

Chemical Equipment

Waste heat recovery systems require materials to resist sulfide stress corrosion.

Food Industry

Steam sterilization piping must comply with the hygiene standards of GB 150.2-2011.

FAQ

1. Common Failures of Hydraulic Steel Tubes?

Fatigue cracking caused by pulse pressure and pitting corrosion caused by acidic media (the corrosion rate accelerates three times when the pH value is <5).

2. What are Typical Problems with Boiler Steel Tubes?

Graphitization and perforation due to oxygen corrosion caused by long-term overheating.

Summary

In general, although hydraulic tubes and boiler tubes are both types of seamless steel pipe, their manufacturing processes, applications, and performance differ significantly. When purchasing, you need to choose the appropriate type of steel pipe according to actual needs to ensure the quality and safety of the entire project.