ASTM C201 Standard Test Method for Thermal Conductivity of Refractories

The ASTM C201 Standard Test Method for the Thermal Conductivity of Refractories, developed by the American Society for Testing and Materials (ASTM) , describes a test method for determining the comparative thermal conductivity of refractories under standard test conditions. This test method is designed for refractories with a conductivity factor not exceeding 28,8 W/m·K and a thickness of 25 mm.

Other detailed ASTM test methods to be used in conjunction with this test method in testing specific types of refractory materials are:

• ASTM C182 Standard test method for thermal conductivity of insulating firebrick
• ASTM C202 Standard test method for thermal conductivity of refractory brick
• ASTM C417 Standard test method for thermal conductivity of unfired monolithic refractories
• ASTM C767 Standard test method for thermal conductivity of carbon refractories

The thermal conductivity of refractories is a necessary property for selecting thermal conductivity properties. Users select refractories that will meet specified heat loss and cold face temperature conditions without exceeding the refractory's temperature limitation. This test method allows testing of refractories' thermal conductivity using a calorimeter.

This test method requires a large thermal gradient and steady-state conditions. Results are based on an average temperature. Data obtained from this test method are suitable for specification acceptance and design of multilayer refractory construction. Use of this data requires consideration of the actual application environment and conditions.

The test specimen should consist of three 228 mm plain bricks and six 228 mm x 64 mm x 57 mm soapstone bricks representative of the material being tested. Additional instructions for sample preparation and placement of the protection brick are provided in the test methods for specific materials. These bricks should be selected for uniformity of structure and bulk density, and should be free of broken corners or edges. One brick should be used as the test specimen, and two other bricks should be used as protection bricks, one on each side of the specimen.

Six soapstone bricks should be placed along the edges of the test sample and the protection brick to prevent heat from flowing sideways. The test sample and protection brick cover an area of ​​approximately 456 mm x 342 mm. A total of nine 228 mm plain bricks can be submitted for testing, six of which are cut to form the soapstone brick.

When preparing the test specimen, the surfaces of three flat bricks (228 mm x 114 mm) and the surfaces of the soap brick (228 mm x 57 mm) should be ground flush and parallel, with a thickness of no more than 60,3 mm. The thickness should not exceed 76 mm and no less than 51 mm. The contact edges should be ground flush and at right angles to the surface of the brick and the surface of the soap brick.

The test specimen shall be dried for 12 hours at a temperature of 105°C to 110°C. At the end of this period, the bulk density shall be determined in pounds per cubic foot (or kilograms per cubic meter) in accordance with ASTM C134. However, thickness measurements shall be made in accordance with these methods.

When performing testing, procedures are used to test specific types of refractory materials described in the following test methods: ASTM C182, ASTM C202, ASTM C417, and ASTM C767 standards.

During the test, the following data is recorded:

• Linear dimensions of the test sample
• The distance between the thermocouple connections on the test sample
• Three sets of temperature readings measured by thermocouples on the test sample
• The average temperature between each thermocouple in the test sample, calculated from the recorded temperatures
• Average temperature increase of water flowing through the calorimeter
• Average flow rate of water passing through the calorimeter
• Heat flow rate through the test sample per unit area

Calculations are made according to the formula given in the standard.

The report to be prepared should include the following information:

• Brand name or other identifying information
• Bulk density of dried test sample
• General description of the test specimen before and after the test in terms of possible structural changes that may occur when exposed to heating chamber temperatures.
• Thermal conductivity data calculated in accordance with this standard at the average temperatures recorded during the 2-hour holding period in the case of constant heat flow and reported at the average of the two temperatures used in the calculation
• A curve showing the actual thermal conductivity values ​​obtained against average temperatures.

When requested, recorded data should be included in the report.

In short, ASTM C201 provides a precise method for determining the thermal conductivity of refractory materials under controlled conditions. This property is crucial for applications in high-temperature environments such as furnaces, ovens, incinerators, and reactors. The primary purpose of this standard is to measure the thermal conductivity of dense and insulating refractories. Thermal conductivity is a key parameter in determining a refractory material's heat transfer performance. Lower thermal conductivity indicates better insulation, which helps increase energy efficiency and reduce heat loss.

The ASTM C201 standard applies to:

• Densely shaped refractories (e.g. firebricks, castables)
• Insulating refractories (e.g. lightweight bricks)
• Monolithic refractories
• Preformed refractory products with various geometries and compositions

Testing is typically conducted at elevated temperatures (from room temperature to approximately 1650 degrees Celsius) to simulate real-world application conditions.

The ASTM C201 test method generally includes the following steps:

• Test setup: A sample is placed in an oven where it is subjected to a controlled temperature gradient. The sample should be of sufficient size to maintain a representative test area.
• Temperature measurement: A platinum resistance thermometer is placed on the test piece to measure the temperature gradient. This thermometer offers high accuracy and stability over a wide temperature range.
• Heat input: A known amount of electrical energy is passed through a heater embedded in or placed near the sample.
• Data collection and calculation: The resulting temperature profile and power input are used to calculate the thermal conductivity of the material.

This standard is important for the following reasons:

• Design and engineering: Helps engineers select appropriate materials for high-temperature applications.
• Energy efficiency: Helps develop energy-efficient thermal systems by identifying materials with optimum insulation properties.
• Quality control: Enables manufacturers to verify material properties and ensure compliance with design specifications during production.
• Research and development: Provides valuable data for developing new refractory materials and improving existing ones.

The limitations of this method are:

• This method is best suited for homogeneous materials and may not provide accurate results for materials with high porosity or non-homogeneous composition.
• The samples must be large enough to accommodate the temperature sensors and heater, which may not always be practical.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the "ASTM C201 Standard Test Method for Thermal Conductivity of Refractories" standard.