How to Improve the Safety of Steel Pipes Under High Temperature and High Pressure Environments?

In many core areas of modern industry, such as power, petrochemicals, nuclear energy, and aerospace, the transportation and reaction of media often need to be carried out under extreme high temperature and high pressure conditions. At this time, the safety and reliability of steel pipes, as key equipment bearing these harsh conditions, are particularly important. High temperature and high pressure environments pose enormous challenges to the steel pipe material itself and its service performance. Failure can lead to serious accidents, causing huge economic losses and safety threats.

So, facing the "dual test" of high temperature and high pressure, how should we improve the safety of steel pipes and ensure their long-term stable and reliable operation?

The Severe Challenges of High Temperature and High Pressure Environments to Steel Pipes:

High temperature and high pressure are not simply two stresses superimposed; they often bring more complex and destructive synergistic effects:

Material Performance Degradation:

1. High Temperature Effects: High temperatures lead to a decrease in the yield strength and tensile strength of steel. Prolonged operation at high temperatures will cause creep, that is, the slow plastic deformation of the material under continuous stress, which may eventually lead to fracture. Graphitization and Reduced Toughness in Some Steels: High temperatures can cause structural changes such as graphitization in some steels, reducing their toughness.

2. High Pressure Effects: High pressure primarily generates significant circumferential and longitudinal stresses, requiring steel pipes to possess sufficient strength and resistance to deformation. High pressure can also exacerbate the risk of crack propagation. Seamless steel pipes are commonly used in high-pressure environments, and alloying elements can be added depending on the harshness of the environment.

3. High Temperature and High Pressure Synergy:The decrease in strength at high temperatures makes materials more susceptible to creep or plastic deformation under high pressure. High-pressure media penetration can induce hydrogen-induced cracking (such as high-temperature hydrogen corrosion, HTHA) in high-strength steels.


Corrosion and Environmental Degradation:

1. High Temperature Accelerated Corrosion: The rate of most chemical reactions (including corrosion) increases with increasing temperature. High temperatures can lead to more severe forms of corrosion such as oxidation, sulfidation, and chloride corrosion. At this point, stainless steel or alloy steel pipe materials can be selected.

2.High-Pressure Media Effects: Under high pressure, the solubility and corrosiveness of media (such as high-temperature steam and acidic gases H2S/CO2) increase, resulting in a higher risk of internal corrosion.

3. High-Temperature and High-Pressure Corrosion: In high-temperature, high-pressure, hydrogen-rich environments, high-temperature hydrogen corrosion (HTHA) may occur. Hydrogen atoms penetrate into the steel and react with carbon to form methane, leading to internal cracks and performance degradation.


Thermal Stress and Thermal Fatigue:

During pipeline start-up and shutdown or when operating conditions fluctuate, temperature changes cause thermal expansion and contraction in the steel pipe, resulting in thermal stress.

Repeated temperature cycling and corresponding thermal stress can lead to the initiation and propagation of thermal fatigue cracks.

Structural Stability and Connection Issues:

Creep and softening at high temperatures can affect the overall stability of the pipeline, especially at support points and bends.

Flanges, welds, and other connections are weak points under high temperature and pressure, prone to leakage or failure.

These challenges require special measures throughout the entire lifecycle of the pipeline, including design, material selection, manufacturing, installation, operation, and maintenance, to ensure the safety of the steel pipes.

Key Strategies for Improving the Safety of Steel Pipes Under High Temperature and High Pressure Environments:

Ensuring the safety of high-temperature and high-pressure steel pipes is a systematic project requiring comprehensive measures from multiple aspects:

1. Optimizing High-Performance Materials

High-Temperature Resistant Steel: To address the issues of high-temperature creep and decreased thermal strength, heat-resistant steels, such as chromium-molybdenum steel (Cr-Mo steel), are commonly selected. Different chromium-molybdenum content steels are suitable for different temperature ranges (e.g., ASTM A335 P11/P22 is suitable for medium- and high-temperature steam pipes, and P91/P92 is suitable for ultra-critical (supercritical) units). These steels exhibit better creep strength and oxidation resistance at high temperatures.

High-Strength Steel: To address high-pressure stress, high-strength steels with higher yield strength and tensile strength are required, while ensuring sufficient toughness to prevent brittle fracture.

Corrosion-resistant alloys (CRAs): For environments containing high-temperature corrosive media (such as high-temperature, high-pressure oil and gas with high H2S/CO2 content, or high-temperature acidic chemicals), pure steel may not be sufficient to resist corrosion. Higher-grade alloys are required, such as duplex stainless steel, super duplex stainless steel, or nickel-based alloys (such as Inconel and Hastelloy series), or even composite pipes or corrosion-resistant linings.

Understanding material behavior: When selecting materials, their long-term performance data under specific high-temperature, high-pressure conditions must be fully considered, such as creep curves, fatigue life data, and high-temperature corrosion rates.

2. Optimizing engineering design

Wall thickness design: Based on working pressure, temperature, allowable material stress, and various safety factors, a reasonable pipe wall thickness is calculated and determined. At high temperatures, the allowable material stress decreases, typically requiring a thicker wall.

Stress analysis: A comprehensive stress analysis is performed, including internal pressure stress, thermal stress caused by temperature changes, external loads (such as weight, wind load, and seismic load), and the cumulative effects between them. Special attention should be paid to stress concentration areas (such as elbows, tees, reducers, and pipe support connections).

Fatigue Analysis: Conduct fatigue life assessments for pipeline start-up and shutdown, and fluctuations in operating conditions to ensure that fatigue-induced failure does not occur within the design life.

Structural Support and Flexible Design: Properly design pipe supports and hangers to manage displacement and stress caused by thermal expansion and contraction. Expansion joints or flexible pipeline designs may be necessary.

Connection Design: Flange and welded connections require rigorous design and selection to ensure sealing and strength under high temperature and pressure. Material selection for flanges and gaskets, and bolt preload are all critical.

3. Strictly control manufacturing and installation quality: base material quality, welding quality, heat treatment, and non-destructive testing.
4. Effectively control corrosion and material degradation: monitor internal and external corrosion and material condition.
5. Implement a comprehensive monitoring and testing plan: online monitoring, periodic testing, intelligent testing technology, data analysis, and evaluation.

Read more: Seamless Steel Pipes for High Temperature and High Pressure or Seamless Pipe vs. Welded Pipe