Sealing performance test

Sealing Performance Testing Service – Accredited ISO/IEC 17025 Leak‑Tightness and Seal Integrity Assessment for the Croatian Market

Sealing performance is a critical quality parameter that quantifies the ability of gaskets, O‑rings, seals, packings, and sealing materials to prevent the passage of fluids, gases, and contaminants under specified conditions of pressure, temperature, and mechanical stress. This property is essential for ensuring the safety, reliability, and environmental compliance of components used in oil and gas pipelines, hydraulic systems, pneumatic systems, chemical processing, automotive engines, aerospace structures, and medical devices. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Državni inspektorat, the Ministarstvo gospodarstva i održivog razvoja, the Ministarstvo graditeljstva i prostornoga uređenja, 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 sealing performance is essential for product certification, supplier qualification, type testing, quality control in manufacturing, and import‑export processes. Our laboratory offers a comprehensive sealing performance testing service, applying standardized methods such as ASTM F36, ASTM F38, ASTM F112, ASTM F2834, ISO 7483, EN 13555, ASTM E493, and HRN EN 13555 to measure leakage rate, sealing force, compression, recovery, creep relaxation, and resistance to thermal and chemical degradation under controlled 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, gaskets, and seal assemblies for 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, NBR, 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 sealing performance before series production.
• Field‑retrieved sealing components – for failure analysis and remaining life assessment.

Leak Rate Measurement – Evaluating the Seal Tightness under Pressure

Leak rate is the most direct and fundamental measure of sealing performance. Our tests measure the flow of gas or liquid through the sealing interface under controlled temperature and pressure conditions. These tests follow international standards and the requirements of the Croatian oil, gas, chemical, and automotive industries.

• Leak rate test – gas method (EN 13555 / HRN EN 13555 / NTC 5600 – 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 pressurized with a test gas (typically helium or nitrogen) to the specified pressure (e.g., 10 bar, 20 bar, or 100 bar) at a controlled temperature (e.g., 23 °C, 100 °C, or 200 °C). 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 pressure, the test temperature, and the clamping force.
• Helium leak test for hermetic seals (ASTM E493 / NTC 5601 – for high‑sensitivity leak detection) – we use a helium mass spectrometer to measure the leak rate with a sensitivity of up to 10⁻⁶ mbar·L/s. The seal is pressurized with helium, and the helium leak rate is measured. This method is used for hermetically sealed components, medical devices, and electronic enclosures. We report the helium leak rate (in mbar·L/s).
• Liquid leak test – pressure decay method (ASTM D4991 / NTC 5602 – for seals in liquid service) – we pressurize the seal assembly with a liquid (e.g., water, oil, or a process fluid) and monitor the pressure decay over a specified time (e.g., 1 hour). The leak rate is calculated from the pressure drop. We report the pressure drop (in kPa) and the leak rate (in mL/min).
• Leak rate test at different clamping forces (NTC 5603 – 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.
• Leak rate test under thermal cycling (NTC 5604 – for the thermal fatigue assessment) – we subject the sealing assembly to repeated thermal cycles (e.g., from 23 °C to 200 °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.

Compression, Recovery, and Relaxation – Evaluating the Long‑Term Sealing Force

The sealing force is generated by the compression of the seal material. Our tests measure the initial compression, the recovery, and the creep relaxation (the loss of sealing force over time) of the sealing material under sustained compression at elevated temperatures. These properties are essential for predicting the long‑term sealing performance and the service life of the seal.

• Compression and recovery test (ASTM F36 / ISO 7483 / HRN EN ISO 7483 / NTC 5610 – 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, or 200 °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 5611 – 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, or 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.
• Creep relaxation test (ASTM F38 / ISO 7483 / NTC 5612 – 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, or 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.
• Creep relaxation at different temperatures (NTC 5613 – 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 5614 – 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.

Sealing Force and Blow‑Out Resistance – Evaluating the Seal Stability under High Pressure

Blow‑out resistance is the ability of a gasket or seal to withstand the internal pressure without being ejected from the joint. Our tests measure the sealing force and the blow‑out pressure, providing essential data for the design of high‑pressure sealing systems.

• Sealing force measurement (NTC 5620 – for the gasket contact pressure) – we use pressure‑sensitive film (e.g., Fuji Prescale film) or a pressure sensor array to measure the contact pressure distribution on the gasket surface. The average sealing force and the sealing force distribution are determined. We report the average sealing force (in MPa) and the contact pressure map.
• Blow‑out pressure test (EN 13555 / NTC 5621 – for the gasket ejection resistance) – we apply an increasing internal pressure to the gasket joint while maintaining a fixed clamping force. The pressure at which the gasket is ejected (the blow‑out pressure) is recorded. We report the blow‑out pressure (in MPa) and the safety factor.
• Sealing force relaxation under pressure cycling (NTC 5622 – for the dynamic sealing performance) – we subject the sealing assembly to repeated pressure cycles (e.g., from 0 to the maximum operating pressure) and measure the sealing force after each cycle. The change in the sealing force is reported. We report the sealing force after each cycle and the reduction in the sealing force.
• Blow‑out pressure at different temperatures (NTC 5623 – for the thermal effect) – we perform the blow‑out pressure test at elevated temperatures (e.g., 100 °C, 200 °C) to evaluate the effect of temperature on the blow‑out resistance. We report the blow‑out pressure at each temperature.
• Sealing force and blow‑out pressure correlation (NTC 5624 – for the design optimization) – we correlate the sealing force (from the pressure‑sensitive film) with the blow‑out pressure (from the ejection test) to establish the relationship between the contact pressure and the blow‑out resistance. We report the correlation and the recommended minimum sealing force.

Thermal and Chemical Degradation – Evaluating the Long‑Term Stability of the Seal

The sealing performance of materials can degrade over time due to thermal aging, chemical attack, and environmental exposure. Our tests simulate these conditions and evaluate the long‑term stability of the sealing properties, ensuring the reliability of the seal over its service life in the diverse Croatian climate (coastal, continental, and mountainous).

• Thermal aging and its effect on sealing performance (ASTM D573 / ISO 188 / NTC 5630 – for the heat‑aged seals) – 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 leak rate, the compression, and the recovery. We report the leak rate, the compression, and the recovery after aging, and the change (in %).
• Chemical exposure and its effect on sealing performance (ASTM D471 / ISO 1817 / NTC 5631 – for the fluid compatibility) – we immerse the sealing material in the process fluid (or a simulant) at a specified temperature for a specified duration (e.g., 7, 14, or 28 days). After the immersion, we re‑measure the mass, the dimensions, the hardness, and the sealing performance. We report the mass change, the dimensional change, the hardness change, and the change in the sealing performance.
• Ozone aging and its effect on sealing performance (ASTM D1149 / ISO 1431‑1 / NTC 5632 – for the ozone resistance) – we expose the sealing material to a specified ozone concentration (e.g., 50 ppb, 100 ppb) at a specified temperature (e.g., 40 °C) for a specified duration (e.g., 48 hours, 168 hours). We inspect the material for cracks and re‑measure the sealing performance. We report the crack rating and the change in the sealing performance.
• Humidity and moisture effect (ASTM D570 / NTC 5633 – for the moisture‑exposed seals) – we condition the sealing material at a high‑humidity environment (e.g., 40 °C, 95 % RH) for a specified duration (e.g., 7 days) and then re‑measure the sealing performance. We report the sealing performance after humidity exposure and the moisture uptake.
• Thermal cycling and sealing stability (NTC 5634 – for the thermal fatigue) – we subject the sealing material to repeated thermal cycles (e.g., from 23 °C to 300 °C) while under a constant clamping pressure, and we measure the leak rate at each cycle. The change in the leak rate is reported. We report the leak rate vs. the number of cycles.

Environmental and Aging Effects – Evaluating the Long‑Term Sealing Durability

The sealing performance of materials can change over time due to environmental exposure, mechanical stress, and aging. Our environmental and aging tests evaluate the long‑term durability of the sealing properties, ensuring the reliability of the seal over its service life.

• Environmental exposure test (NTC 5640 – for the outdoor and coastal applications) – we expose the sealing material to a simulated outdoor environment (UV radiation, humidity, and temperature cycling) for a specified duration (e.g., 500 hours) and then re‑measure the sealing performance. We report the sealing performance after the environmental exposure and the change.
• Mechanical wear and abrasion effect (NTC 5641 – for the mechanically worn seals) – we subject the sealing surface to a specified number of wear cycles (e.g., by rubbing or sliding against a mating surface) and then re‑measure the sealing performance. We report the sealing performance after wear and the wear depth.
• Fatigue and cyclic loading effect (NTC 5642 – for the fatigue‑tested seals) – we apply a cyclic mechanical load (e.g., compression or flexing) to the sealing material for a specified number of cycles (e.g., 10,000 cycles, 100,000 cycles) and then re‑measure the sealing performance. We report the sealing performance after fatigue and the fatigue life.
• Storage stability and shelf‑life assessment (NTC 5643 – for the aged‑in‑storage seals) – we store the sealing material under controlled conditions (temperature, humidity, and light) for a specified duration (e.g., 1 year) and then re‑measure the sealing performance. We report the sealing performance after storage and the shelf‑life rating.
• Corrosion effect on metallic seals (NTC 5644 – for the corrosion‑resistant seals) – we expose the metallic sealing components to a corrosive environment (e.g., salt spray, acidic solution) and then re‑measure the sealing performance. We report the sealing performance after corrosion and the corrosion rating.

Complementary Tests – Material Characterization and Physical Property Evaluation

To fully understand the sealing performance and to correlate it with the material's properties, we perform complementary tests, including material identification, hardness testing, and microstructural examination.

• Material identification (FTIR, TGA – NTC 5650 – 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 5651 – 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 5652 – for the elastomeric seals) – we measure the tensile strength (in MPa) and the elongation at break (in %) of the 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 5653 – 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 5654 – 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 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: leak rate (mbar·L/s), compression (%), recovery (%), compression set (%), stress relaxation (%), blow‑out pressure (MPa), 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 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, by the Ministarstvo graditeljstva i prostornoga uređenja for building materials approval, 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 sealing materials with high performance, 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.