High temperature alloys in industrial applications: Inconel, Hastelloy and their MRO implications

Introduction

High-temperature alloys are critical for ensuring the reliability and durability of industrial equipment, especially under conditions of aggressive environments, high temperatures and corrosive loads. In this regard, choosing the right material for components that perform functions in high temperature conditions is one of the most important tasks for operational and technical services. The article discusses the main high-temperature alloys — Inconel and Hastelloy, their properties, standards, requirements for selection and installation, as well as their impact on MRO (Maintenance, Repair, Operations) in industrial installations of Ukraine.

Fundamental principles

High-temperature alloys are made on the basis of copper, nickel and chromium, which provides them with high thermal resistance, high corrosion resistance and mechanical strength. They are used in conditions where the temperature can exceed 800°C, as well as in environments with a high content of nitrogen, sulfur, salt solutions, or open fire. The main properties of these alloys include:

• High thermal stability;
• High corrosion resistance;
• High viscosity;
• Low fatigue strength;
• High wear resistance.

The fundamental mechanical properties of high-temperature alloys are determined using standard tests such as the tensile test (ISO 6892-1), the impact strength test (ISO 148-1), and the corrosion resistance test (ASTM G59).

Technical specifications and standards

High temperature alloys Inconel and Hastelloy have defined standards that establish their properties and requirements for use. Below are the main standards and requirements:

• Inconel 600 — conforms to the ASTM B163 standard, ISO 15515, DIN 17432. Operating environment temperature: up to 1200°C. Maximum wall thickness: 10 mm.
• Inconel 625 — conforms to the ASTM B564 standard, ISO 5855, DIN 17433. Operating environment temperature: up to 1100°C. Maximum wall thickness: 8 mm.
• Hastelloy C-276 — conforms to ASTM B564, ISO 5855, DIN 17433. Working medium temperature: up to 1000°C. Maximum wall thickness: 7 mm.
• Hastelloy X — conforms to the ASTM B564 standard, ISO 5855, DIN 17433. Operating environment temperature: up to 1100°C. Maximum wall thickness: 10 mm.
• ISO 281: Defines requirements for viscosity tests at high temperatures.
• DIN 51825: Establishes requirements for corrosion resistance tests in various environments.
• IEC 60947-2: Establishes requirements for electrical devices used in high temperature environments.

Selection and calculation

The choice of high-temperature alloy depends on specific operating conditions, requirements for thermal and corrosion resistance, and calculation of mechanical loads. Below is an example of calculating the wall thickness and choosing the material for the pipeline:

Formula for calculating pipe wall thickness:

δ = (P * D) / (2 * σ * η)

where:

• δ — wall thickness, mm;
• P - internal pressure, bar;
• D — outer diameter, mm;
• σ is the permissible stress, MPa;
• η is the reliability margin factor (usually 1.5–2).

Table 1: Alloy selection for different conditions

Practical recommendations for installation and debugging

Proper installation and adjustment of high-temperature alloy components affects their durability and performance. Basic recommendations:

• Use special tools for working with high-temperature materials;
• Provide ventilation and temperature reduction in the work area;
• Perform a control calculation for viscosity and corrosion resistance before installation;
• Use connections that meet the requirements of the ISO 281 standard;
• Perform regular tests for viscosity and corrosion resistance.

During installation, it is necessary to take into account temperature deformations and use special flanges that comply with the DIN 51825. standard

Failure causes and root cause analysis

The main causes of failure of high-temperature components include:

• Corrosion due to high content of sulfur or salts;
• Thermal fatigue at constant high temperatures;
• Excessive load that causes a fatigue crack;
• Incorrect installation, which leads to deformation;
• Insufficient viscosity calculation.

Visual signs of failure:

• Occurrence of cracks on the surface;
• A change in the color of the material (for example, the appearance of a dark shade due to corrosion);
• Decrease in wall thickness;
• Increase in surface temperature;
• A change in material properties (for example, a decrease in viscosity).

Predictive maintenance and condition monitoring

Predictive maintenance and condition monitoring of high-temperature components reduces repair costs and increases service life. The main control methods:

• Temperature measurement: Use temperature sensors with a high level of accuracy (ISO 281).
• Measurement of viscosity: Use tensile test and impact test (ISO 148-1).
• Corrosion Control: Use corrosion resistance test methods (ASTM G59).
• Visual inspection: Check regularly for cracks, discoloration and changes in wall thickness.
• Acoustic Control: Use acoustic emission techniques to detect fatigue cracks.

Comparison table

Table 2: Comparison of high temperature alloys

Conclusion

High temperature alloys such as Inconel and Hastelloy are indispensable in industrial applications where high thermal and corrosion resistance is required. Choosing the right material, performing the correct calculations and following the standards ensures the durability and efficiency of the equipment. For your high temperature alloy component needs, contact UNITEC-D GmbH. Our components meet DSTU, EN, ISO standards, and also have CE, UkrSEPRO certificates. You can find a wide selection of components in our e-catalogue:

https://www.unitecd.com/e-catalog/

List of references

• ISO — Establishing standards for high-temperature alloys.
• DIN — Requirements for corrosion resistance tests.
• IEC — Requirements for electrical devices in high temperature conditions.
• ASTM — Requirements for tests for viscosity and corrosion resistance.
• UNITEC-D GmbH - Material and Certification Reference.