ASTM A991/A991M - Conducting Temperature Uniformity Surveys of Furnaces Used to Heat Treat Steel Products
Ensuring Temperature Uniformity in Furnaces for Steel Heat Treatment
Introduction
The effectiveness of heat treatment of steel products is significantly influenced by the temperature uniformity within the furnace. Ensuring consistent and appropriate heat distribution is paramount in achieving desired material properties. ASTM A991/A991M outlines the standard test method for conducting temperature uniformity surveys of furnaces employed in the heat treatment of steel products.
Scope
The standard is applicable to various types of heat treat furnaces, including continuous or semi-continuous conveyance furnaces, batch furnaces, and fluidized beds. It details procedures for determining temperature variations within the furnace, establishes documentation requirements, and outlines the process of identifying the furnace’s working zone, ensuring compliance with specified temperature variations.
Test Procedure
Equipment Preparation:
Utilize metal sheathed thermocouples compliant with Specification E608/E608M.
Ensure the calibration of all measuring devices is traceable to national standards and completed within three months prior to the survey.
Selection of Test Conditions and Frequency:
Determine the set point temperature(s), which should be typical for the furnace's normal operating range.
Primary surveys should be conducted within twelve months prior to first production or after major modifications.
Secondary surveys should be conducted annually, maintaining similar conditions as primary surveys.
Placement of Thermocouples:
Position the thermocouples at the center and outer extremities of the proposed working zone, and in areas of expected temperature variability.
For working zones less than 12 in. height, monitoring the center height location is sufficient; for zones 12 in. or above, monitor both top and bottom extremities.
Data Collection:
For continuous and semi-continuous conveyance furnaces, convey test sensors through the furnace at a rate representative of normal operations, recording temperature at frequent intervals.
In batch and batch liquid media furnaces, initiate readings when the control instrument is within 200°F of the set point temperature, continuing throughout the hold cycle.
Data Analysis:
Evaluate the collected data to assess the temperature uniformity within the furnace.
Identify any recurrent temperature profiles and variations from the test temperature range.
Working Zone Establishment:
Based on the data, identify and document the maximum volume and location within the furnace that meets the permissible temperature variation requirements.
Safety Considerations
Users of this standard must be vigilant in establishing appropriate safety and health practices. It is essential to understand the applicable regulatory limitations and safety concerns associated with the use of heat treat furnaces and the conduct of temperature uniformity surveys.
Conclusion
Ensuring temperature uniformity in heat treat furnaces is critical in achieving optimal steel product properties. Adhering to the ASTM A991/A991M standard ensures that furnaces operate within specified temperature variations, promoting the integrity, safety, and quality of heat-treated steel products. The outlined test procedure serves as a comprehensive guide for effectively conducting temperature uniformity surveys, ensuring that the heat treatment processes yield consistent and high-quality results.