High-temperature sealing test service

High-Temperature Sealing Testing Service – Accredited ISO/IEC 17025 Thermal and Mechanical Seal Integrity Assessment for the Croatian Market

High-temperature sealing performance is a critical parameter that determines the ability of gaskets, seals, packings, and sealing materials to maintain a leak‑tight barrier under elevated temperature conditions. In industries such as oil and gas, petrochemicals, power generation, aerospace, automotive, and marine engineering, sealing components must withstand extreme thermal and mechanical stresses without degradation, loss of compression, or leakage that could lead to process inefficiencies, environmental hazards, or catastrophic failures. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, and the Carinska uprava enforce strict quality, safety, and environmental standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of high-temperature sealing performance is essential for product certification, supplier qualification, type testing, quality control in manufacturing, and import‑export processes. Our laboratory offers a comprehensive high-temperature sealing testing service, applying standardized methods such as ASTM F36, ASTM F38, ASTM F112, ISO 7483, DIN 3535, EN 13555, and HRN EN 13555 to measure compression, recovery, creep relaxation, leakage rate, and thermal aging resistance under controlled high‑temperature conditions. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, product validation, and market access in Croatia and the European Union.

Sealing Materials and Components We Regularly Test

Our laboratory receives a wide variety of sealing materials and components for high‑temperature sealing performance testing. Typical samples include:

• Gaskets and sealing sheets – non‑asbestos gaskets, compressed fiber gaskets, PTFE gaskets, graphite gaskets, and metallic gaskets (spiral wound, kammprofile, and ring joint).
• O‑rings and elastomeric seals – silicone, FKM (Viton), EPDM, and other high‑temperature elastomers.
• Packing and braided seals – graphite packing, PTFE packing, and carbon fiber packing for valves and pumps.
• Sealants and jointing compounds – liquid gaskets, anaerobic sealants, and high‑temperature silicone sealants.
• Insulating gaskets and flange isolation kits – for cathodic protection and electrical isolation.
• Prototype and new sealing material formulations – submitted by manufacturers for validation of high‑temperature sealing performance before series production.
• Field‑retrieved sealing components – for failure analysis and remaining life assessment.

Compression and Recovery Testing – Evaluating the Sealing Capability

Compression and recovery are fundamental properties of sealing materials that determine their ability to conform to flange surfaces and maintain a seal under load. Our high‑temperature compression and recovery tests measure the deformation of the sealing material under a specified compressive stress and its ability to recover its original thickness after the load is removed. These tests are performed at elevated temperatures to simulate service conditions.

• Compression and recovery test (ASTM F36 / ISO 7483 / HRN EN ISO 7483 / NTC 5600 – for gasket materials) – we measure the thickness of a test specimen under a specified compressive stress (typically 6.9 MPa or 34.5 MPa) at a specified temperature (e.g., 23 °C, 100 °C, 200 °C, or 300 °C). The compression (the percentage of thickness reduction) and the recovery (the percentage of thickness increase after the load is removed) are calculated. We report the compression (in %) and the recovery (in %) at each temperature.
• High‑temperature compression set test (ASTM D395 / ISO 815 / NTC 5601 – for elastomeric seals) – we compress the elastomeric seal specimen to a specified strain (e.g., 25 %) at a specified elevated temperature (e.g., 100 °C, 150 °C, 200 °C) for a specified duration (e.g., 22 hours). The compression set (the permanent deformation) is measured after the load is removed. A low compression set indicates good sealing performance. We report the compression set (in %) and the test conditions.
• Thickness loss after thermal cycling (NTC 5602 – for the thermal stability of the sealing thickness) – we subject the sealing material to repeated thermal cycles (e.g., from 23 °C to 200 °C and back) under a constant compressive stress, and we measure the change in the thickness after each cycle. The thickness loss (in %) is reported. We report the thickness loss and the number of cycles.
• Compression and recovery at different temperatures (NTC 5603 – for the temperature dependence) – we perform the compression and recovery test at multiple temperatures (e.g., 23 °C, 100 °C, 200 °C, 300 °C) to evaluate the temperature dependence of the sealing properties. We report the compression and the recovery at each temperature.
• Effect of the compressive stress on the sealing performance (NTC 5604 – for the stress‑sealing relationship) – we perform the compression test at different compressive stress levels (e.g., 1 MPa, 5 MPa, 10 MPa, 20 MPa) and measure the resulting compression and the sealing effectiveness. We report the compression as a function of the stress.

Creep Relaxation and Stress Decay Testing – Evaluating the Long‑Term Sealing Force

Creep relaxation is the decrease in the sealing stress (the force exerted by the seal on the flange) over time due to the viscoelastic deformation of the sealing material. Our creep relaxation tests measure the loss of sealing force under sustained compression at high temperatures, providing essential data for the prediction of the long‑term sealing performance.

• Creep relaxation test (ASTM F38 / ISO 7483 / NTC 5610 – for gasket materials) – we compress the gasket specimen to a specified stress at a specified temperature (e.g., 200 °C, 300 °C) and measure the decay of the stress over a specified duration (e.g., 100 hours, 500 hours, 1000 hours). The stress relaxation (the percentage of the initial stress that is lost) is calculated. We report the initial stress, the residual stress, the stress relaxation (in %), and the relaxation curve.
• Stress relaxation test for elastomeric seals (ASTM D6147 / NTC 5611 – for O‑rings and rubber seals) – we compress the elastomeric seal to a specified strain at a specified temperature and measure the decay of the sealing force over time. The force relaxation (in %) is reported. We report the force relaxation and the relaxation curve.
• Creep relaxation at different temperatures (NTC 5612 – for the temperature dependence) – we perform the creep relaxation test at multiple temperatures (e.g., 100 °C, 200 °C, 300 °C) to evaluate the temperature dependence of the stress relaxation. The activation energy of the relaxation is calculated. We report the stress relaxation at each temperature and the activation energy.
• Creep relaxation under cyclic temperature and pressure (NTC 5613 – for the service condition simulation) – we subject the sealing material to repeated cycles of temperature (e.g., from 23 °C to 200 °C) and pressure (e.g., from 0 to 10 bar) while measuring the sealing force. The residual sealing force after the cycles is reported. We report the residual sealing force and the number of cycles.
• Creep relaxation and leak rate correlation (NTC 5614 – for the performance‑based assessment) – we correlate the measured creep relaxation (the loss of sealing force) with the leak rate of the seal. The correlation is used to establish the acceptable limit for the stress relaxation. We report the correlation and the recommended limit.

High‑Temperature Leak Rate Testing – Evaluating the Seal Tightness

The leak rate is the ultimate measure of the sealing performance. Our high‑temperature leak rate tests measure the flow of gas through the sealing interface under controlled temperature and pressure conditions, providing a direct measure of the seal integrity and its ability to meet the emission requirements.

• Leak rate test (EN 13555 / HRN EN 13555 / NTC 5620 – for gasket flange joints) – we mount the gasket in a test flange assembly and apply a specified clamping force (the bolt load). The assembly is heated to the specified temperature (e.g., 200 °C, 300 °C) and pressurized with a test gas (e.g., helium or nitrogen) to the specified pressure (e.g., 10 bar, 20 bar). The leak rate (in mbar·L/s or cm³/min) is measured using a mass flow meter or a helium leak detector. We report the leak rate, the test temperature, the test pressure, and the clamping force.
• Helium leak test for high‑temperature seals (ASTM E493 / NTC 5621 – for the high‑sensitivity detection) – we use a helium mass spectrometer to measure the leak rate of the seal at high temperatures, with a sensitivity of up to 10⁻⁶ mbar·L/s. The seal is pressurized with helium, and the helium leak rate is measured. We report the helium leak rate (in mbar·L/s).
• Thermal cycling leak rate test (NTC 5622 – for the thermal fatigue assessment) – we subject the sealing assembly to repeated thermal cycles (e.g., from 23 °C to 300 °C and back) while under pressure, and we measure the leak rate at each temperature. The leak rate is recorded as a function of the temperature and the number of cycles. We report the leak rate vs. temperature and the number of cycles.
• Leak rate under pressure cycling (NTC 5623 – for the pressure fluctuation assessment) – we apply repeated pressure cycles (e.g., from 0 to 20 bar) at a constant high temperature, and we measure the leak rate at each pressure. The leak rate vs. pressure curve is plotted. We report the leak rate vs. pressure curve.
• Leak rate under different clamping forces (NTC 5624 – for the bolt load optimization) – we perform the leak rate test at different clamping forces (e.g., from 0.5 × the recommended bolt load to 1.5 × the recommended bolt load) to determine the optimal clamping force for the sealing performance. We report the leak rate as a function of the clamping force.

Thermal Aging and Degradation Testing – Evaluating the Long‑Term Stability

Thermal aging can cause the degradation of sealing materials, leading to a loss of compression, an increase in the leak rate, and a reduction in the service life. Our thermal aging tests simulate the long‑term service conditions and evaluate the stability of the sealing properties over time.

• Thermal aging test (ASTM D573 / ISO 188 / NTC 5630 – for the heat‑aged materials) – we age the sealing material in an oven at a specified temperature (e.g., 200 °C, 300 °C) for a specified duration (e.g., 7, 14, 28, or 56 days). After the aging, we re‑measure the compression, the recovery, and the leak rate. We report the compression, the recovery, and the leak rate after aging, and the change (in %).
• Thermal aging with cyclic temperature (NTC 5631 – for the thermal fatigue) – we subject the sealing material to repeated thermal cycles (e.g., from 23 °C to 300 °C) for a specified number of cycles (e.g., 10, 50, or 100 cycles) and then we re‑measure the sealing properties. We report the sealing properties after the thermal cycles and the change.
• Oxidation and weight loss analysis (NTC 5632 – for the thermal stability evaluation) – we measure the weight loss of the sealing material after thermal aging (using thermogravimetric analysis, TGA) and we analyze the oxidation products (using FTIR spectroscopy). The weight loss is correlated with the degradation of the sealing performance. We report the weight loss (in %) and the oxidation products.
• Microstructural examination after aging (SEM – ASTM E1508 / NTC 5633 – for the degradation analysis) – we use scanning electron microscopy (SEM) to examine the microstructure of the sealing material after thermal aging, to detect any cracks, voids, or phase changes that could affect the sealing performance. We report the SEM images and the microstructural changes.
• Thermal aging and leak rate correlation (NTC 5634 – for the life prediction) – we correlate the thermal aging time with the measured leak rate to predict the service life of the seal at the service temperature. The life prediction is based on the Arrhenius model. We report the predicted service life (in years) and the acceleration factor.

Complementary Tests – Material Identification, Hardness, and Surface Characterization

To fully understand the high‑temperature sealing performance and to identify the factors that influence the sealing properties, we perform complementary tests, including material identification, hardness testing, and surface characterization.

• Material identification (FTIR, TGA – NTC 5640 – for the polymer and filler identification) – we use Fourier‑transform infrared spectroscopy (FTIR) to identify the chemical composition of the sealing material (the polymer type, the fillers, and the additives) and thermogravimetric analysis (TGA) to determine the thermal stability. We report the material identification and the thermal stability.
• Hardness testing (ASTM D2240 / NTC 5641 – Shore A or Shore D for elastomers) – we measure the Shore A or Shore D hardness of the sealing material. The hardness is correlated with the compression and the sealing force. We report the hardness and the correlation.
• Tensile strength and elongation (ASTM D412 / ISO 37 / NTC 5642 – for the elastomeric seals) – we measure the tensile strength (in MPa) and the elongation at break (in %) of the elastomeric sealing material. The tensile properties are correlated with the durability and the resistance to tear. We report the tensile strength and the elongation.
• Surface roughness and texture (ASTM D7127 / NTC 5643 – for the sealing surface characterization) – we measure the surface roughness (Ra, Rz) of the sealing surface (the flange surface) using a profilometer. The surface roughness is correlated with the leak rate. We report the roughness values and the correlation.
• Water absorption and chemical resistance (ASTM D471 / NTC 5644 – for the fluid compatibility) – we immerse the sealing material in the process fluid (or a simulant) at a specified temperature for a specified duration, and we measure the change in the mass, the dimensions, and the hardness. The compatibility is correlated with the sealing performance. We report the compatibility and the change in the properties.

Test Report and Recognition in the Croatian Industrial, Energy, and Petrochemical Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (universal testing machines, creep relaxation testers, leak testers, and thermal chambers) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the sealing material (manufacturer, material type, dimensions, and intended application).
• Detailed description of the test methods applied (ASTM/ISO/EN/HRN EN/NTC standards, test conditions, temperature, pressure, and duration).
• Numerical results: compression (%), recovery (%), compression set (%), stress relaxation (%), leak rate (mbar·L/s), weight loss (%), hardness (Shore), and property retention after aging (%).
• Graphical data: stress relaxation curves, leak rate vs. temperature curves, and thermal aging degradation curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ASTM F36, ASTM F38, EN 13555, HRN EN 13555, and the requirements of the HZN, Ministarstvo gospodarstva, and Državni inspektorat).
• Photographs and micrographs (SEM) of the sealing material before and after the tests.
• Recommendations for material selection, gasket design, and bolt load optimization to achieve the required high‑temperature sealing performance.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98‑3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo gospodarstva i održivog razvoja for industrial and energy compliance, by the Državni inspektorat for market surveillance, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of sealing materials and gaskets. Additionally, we offer consulting services for the selection of high‑temperature sealing materials, the design of leak‑tight flange connections, and the implementation of sealing integrity programs, contributing to the safety, reliability, and environmental compliance of industrial operations in the diverse and growing Croatian market, from the refineries and power plants to the chemical and petrochemical facilities.