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Introduction to thermal performance testing of pressure pipeline materials

Introduction to thermal performance testing of pressure pipeline materials

Thermal performance testing is a method of inspecting product quality by using thermal instruments to determine the thermal properties of products. The thermal characteristics of products mainly include melting point, freezing point, boiling point, heat resistance, thermal conductivity, thermal stability, etc. The thermal properties of materials are closely related to the operating conditions and performance requirements of the products.

Melting Point and Melting Range: The melting point is the temperature at which the solid and liquid phases of a pure substance are in equilibrium under a certain pressure. The melting point range refers to the temperature range from the beginning to the complete melting of the substance measured by the capillary method. Materials can be crystalline or amorphous, with crystalline materials having a definite melting point and amorphous materials having a melting point range. The melting point is determined using the capillary method, with the melting point tester as the measuring instrument.

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Freezing Point: The freezing point is the temperature at which crystalline substances solidify, which is the temperature at which the vapor pressure of the liquid is equal to that of the solid under a certain pressure. Different crystals have different freezing points. The freezing point testing method uses the supercooling method, with the self-cooling freezing point tester as the measuring instrument.

Boiling Point: The boiling point is the temperature at which a liquid turns into a gas when heated. It is the temperature at which the liquid and its vapor are in equilibrium. Generally, the lower the boiling point, the greater the volatility. The boiling point testing method uses the constant method or the micro method, with the boiling point tester as the measuring instrument.

Thermal Conductivity: Thermal conductivity, also known as “thermal conductivity coefficient,” is a measure of the thermal conductivity of a substance. It is the amount of heat transferred per unit time through a unit horizontal cross-sectional area when the temperature gradient perpendicular to the heat conduction direction is 1°C/m. The thermal conductivity testing methods include steady-state heat flow calorimetry, guard plate method, dynamic method, laser flash method, etc., with instruments such as high-temperature thermal conductivity coefficient testing system, guard plate method thermal conductivity meter, thermal conductivity meter (hot wire method), laser flash method thermal conductivity measurement system, etc.

Coefficient of Linear Expansion: The coefficient of linear (or volume) expansion refers to the relative increase in length (or volume) of an object when the temperature rises by 1 K. Thermal expansion usually refers to the increase in volume when the temperature rises, under constant external pressure, most substances increase in volume when the temperature rises, and decrease in volume when the temperature decreases. Thermal expansion is related to temperature, specific heat, bonding energy, and melting point. The main factors affecting the expansion properties of materials are phase change, material composition and structure, and anisotropy. The measurement methods for thermal expansion include optical method, electric measurement method, and mechanical method.

Heat Deflection Temperature: Heat deflection temperature, Vicat softening point, and Martens heat resistance temperature are indicators of evaluating the heat resistance of plastic products, among which the heat deflection temperature is the most commonly used. The heat deflection temperature is the parameter expressing the relationship between heating and deformation of the tested object. It is the temperature corresponding to a certain deformation when a certain load is applied to the polymer, and is a measure of the thermal resistance of the polymer or polymer material. The heat deflection temperature testing method is the loaded heat deflection temperature test method, and the heat deflection temperature tester is used as the measuring instrument.

Vicat Softening Point: The Vicat softening point is a method for evaluating the high-temperature deformation trend of thermoplastic materials. It is the temperature at which a flat needle with a specified load and a cross-sectional area of 1 mm² is inserted into the sample to a depth of 1 mm. The typical test instrument is the Vicat softening point temperature tester.

Martens Heat Resistance Temperature: Martens heat resistance, also known as Martens heat stability, is an index for evaluating the heat resistance of plastics. During the test, the sample is subjected to a specified temperature and bending stress, and the temperature at which it reaches a certain bending deformation is measured. The Martens heat resistance temperature is the highest temperature that the plastic product may reach during use, and it is the temperature below which the physical and mechanical properties of the plastic will not change substantially. The test is conducted in a Martens heat resistance oven. The testing instrument is the Martens heat resistance tester.

Glass Transition Temperature: The glass transition temperature (Tg) is the temperature at which an amorphous polymer changes from a high elastic state to a glassy state. It is the lowest temperature at which the molecular chains of amorphous polymers are freely movable, usually expressed as Tg. The glass transition temperature is an important process index for polymers. Above this temperature, polymers exhibit elasticity, and below it, they exhibit brittleness. The glass transition temperature testing methods include thermal mechanical analysis (TMA), differential thermal analysis (DTA), differential scanning calorimetry (DSC), etc. The testing instruments are TMA thermal mechanical analyzers, DSC differential scanning calorimeters, etc.

Oxidative Induction Time: The oxidative induction time (OIT) is the time it takes for a sample to start catalytic oxidation under high temperature (200°C) oxygen conditions. It is an indicator of the heat resistance degradation ability of materials during molding, storage, welding, and use. The oxidative induction period (OIT) method is a method of testing the accelerated aging degree of plastics in high-temperature oxygen by using differential thermal analysis (DTA) based on the exothermic reaction when the plastic molecular chains are broken. The oxidative induction time testing instrument is a differential thermal analyzer.

Melt Flow Rate: The melt flow rate (MFR), also known as the melt index (MI), is the weight of resin melt that flows out of a standard capillary in a standard melt flow rate instrument at a certain temperature and pressure within a certain time (usually 10 minutes). It is an important reference for selecting plastic processing materials and grades, which can better adapt the selected raw materials to the requirements of the processing technology and improve the reliability and quality of the products in the molding process. The melt flow rate testing instrument is a melt flow rate tester.