ASTM A106 B seamless tubes, with their excellent high-temperature resistance and stable quality, are widely used in key industries such as petroleum and natural gas, chemical engineering, power generation, boilers and ships. Durability directly determines the safety and economy of pipeline operation. This study aims to systematically analyze the influencing factors of its durability performance and propose optimization strategies.

Overview of Material Properties

Chemical composition

Main: carbon (0.30 0.35%), manganese (0.29 1.06%), silicon (~ 0.10-0.50%)

Trace: Phosphorus, sulfur ≤ 0.035%; Fine-tuning of alloying elements (Cr, Ni, Cu, Mo) enhances corrosion resistance and high-temperature strength

Mechanical indicators

Tensile strength: 290-415 MPa

Yield strength: starting from 205 MPa

Elongation: ≥ 30%

The impact toughness and hardness were verified by standard tensile, hardness and impact tests

Organizational structure

Grain size, phase distribution and microcracks were characterized by means of optical microscopy, SEM, TEM, etc

Refining the grains and homogenizing the phase distribution are helpful to improve the comprehensive mechanical and fatigue resistance performance

Influencing factors of durability

Environmental media: High temperature, humidity, acids, alkalis and salt spray accelerate surface and grain boundary corrosion.

Working condition load: Periodic pressure fluctuations and vibrations cause fatigue cracks;

Surface condition: Roughness is directly related to the integrity of the coating and the anti-corrosion effect.

Stress concentration: Local weaknesses are prone to occur in the heat-affected zone of welding, elbows and connectors.

Test and evaluation methods

Corrosion performance

The corrosion rate was determined by salt spray test, chemical immersion and electrochemical polarization curve

Mechanical testing

Standard tensile, Charpy impact and fatigue life (high cycle/low cycle) tests

Comparison of organizations before and after

Microstructure observations were conducted respectively before and after the test to track grain growth, changes in precipitated phases and the initiation positions of cracks

Main results and analysis

Component-performance correlation: The addition of trace amounts of Mo and Cu can enhance tensile strength and high-temperature creep resistance by approximately 10%.

Environmental sensitivity: The pitting corrosion rate in the Marine atmosphere without protection is significantly higher than that in a neutral salt spray environment.

Fatigue failure characteristics: Cracks usually originate from the heat-affected zone of the weld seam or machining marks, and the propagation rate is positively correlated with the stress amplitude.

Optimization suggestions

Component adjustment

It is recommended that C ≤ 0.32%, Mn be controlled at 0.40% - 0.70%, and Mo be appropriately added at 0.05-0.10%

Surface protection

For Marine and chemical environments, the dual process of hot-dip galvanizing and epoxy powder coating is preferred

Welding and Installation

Low heat input welding was adopted, post-weld stress relief treatment was carried out, and the weld seam was ground and inspected for integrity

Monitoring and Maintenance

Regular online ultrasonic detection of corrosion rate and cracks, and timely repair of coatings and replacement of weak sections

Conclusion

Through systematic analysis of chemical composition and microstructure, as well as comparison of environmental and mechanical tests, this study clarified the main degradation mechanism and weak links of ASTM A106 B seamless tubes under harsh conditions, and proposed targeted formulation and process optimization schemes. Combining online monitoring and maintenance will effectively extend the service life of pipelines, reduce operational risks and costs.