EN 13555:2021 – A Comprehensive Standard for Gasket Testing

In today’s rapidly evolving industrial landscape, there is a growing emphasis on environmental sustainability and the reduction of harmful emissions. Fugitive emissions, which refers to the unintended release of gases or vapors from industrial processes, pose significant challenges to environmental preservation. To address this issue, industries are increasingly adopting more rigorous controls to minimize fugitive emissions and ensure compliance with stringent environmental regulations. Over the years, various sectors have made a significant commitment to addressing this issue through the implementation of enhanced monitoring systems, improved maintenance practices, updated sealing technologies, employee training, regulatory compliance, and technology integration reducing the occurrence of fugitive emissions.

By Francisco Duque, Applications Engineer, Teadit

Providing a reliable sealing mechanism to prevent leaks and minimize fugitive emissions is crucial as industries strive to enhance their environmental sustain­ability and meet stringent regulatory requirements. There is an increasing focus on upgrading sealing technolo­gies by adopting advanced gaskets and seals. Industries can achieve more rig­orous control over fugitive emissions, ensuring operational efficiency while minimizing environmental impact.

Gaskets are essential components used in industrial equipment to provide a seal between two surfaces and prevent leakage of fluids or gases. As such, the performance of gaskets is critical to ensuring the safety and reliability of in­dustrial operations. However, assessing gasket performance can be challenging due to the complex operating condi­tions under which gaskets operate.

One such industry standard that guides the selection and performance of gaskets is EN 13555. Developed by the European Committee for Stan­dardization (CEN), EN 13555 provides guidelines for the classification and testing of gaskets, ensuring their re­liability and efficiency in controlling fugitive emissions. In this article, we will elaborate on the highlights to give an understanding of the standard.

The standard defines all parameters involved in studying gasket behavior in flanged joints, which are later used in calculation definitions in EN 1591-1 which provides a comprehensive al­gorithm that explains the operation of joints, considering various factors such as the elastic deformation of the joint, as well as both elastic and plastic defor­mations of the sealing material.

From a gasket selection point of view, the EN 13555 standard defines several parameters crucial in determining the suitable gasket for a specific applica­tion. These parameters, outlined in the standard, help ensure optimal sealing performance and compliance with industry requirements. According to the EN 13555 standard, some key pa­rameters defined for gasket selection include:

– QSmax: Maximum surface pressure that may be imposed on the gasket at the indicated temperatures without col­lapse or ‘crash.’

– EG: Unloading modulus of elasticity determined from the thickness recov­ery of the gasket between the initial compression surface pressure and un­loading to a third of this initial surface pressure (modulus of elasticity).

– PQR: Factor allowing for the effect on the imposed load of the relaxation of the gasket between the completion of bolt up and long-term experience ser­vice temperature.

– ΔeGC: Additional change in thickness of the gasket under the service condi­tions of temperature and gasket surface pressure in the axial direction.

– LN: Tightness classes that denotes maximum limit of defined leak rates. This is shown in Table 1.

– Qmin: Minimum gasket surface pres­sure on assembly required at the ambi­ent temperature to seat the gasket into the flange facing roughness and close internal leakage channels, ensuring the tightness class is at the required level L for the internal test pressure.

– QSmin: Minimum gasket surface pressure required under the service pressure conditions (i.e., after off-load­ing and at the service temperature) to maintain the required tightness class L for the internal test pressure.

The standard provides more detailed guidance on test preparation and evaluation. EN 13555 specifies the required instrumentation and mea­surement procedures, including the use of calibrated equipment to en­sure accurate and reliable results. It also provides clear guidelines on the evaluation of test results, including the calculation of maximum leakage rate, total leakage volume, and time to reach a specified leakage rate. This guidance helps ensure that test results are consistent and reliable across dif­ferent testing laboratories and allows for better comparison of gasket perfor­mance across different manufacturers and products.

EN 13555 provides detailed guidance on sample preparation, storage, and conditioning. The standard specifies the size and shape of the samples and how they should be stored and conditioned before testing. These guidelines help ensure that test results are consistent and accurate, reducing the risk of errors and variability in test results.

Test Method

The fundamental importance of a gas­ket lies in its ability to establish and sustain a reliable seal. It is notewor­thy that the data obtained from these tests not only serve as valuable input for the calculation method defined in the standard but also proves beneficial for advancing the development of im­proved gaskets.

The standard describes two different scenarios: one for determining the val­ues of Qmin(L) and QSmin(L) related to leakage and another for determining QSmax, EG, PQR, ΔeGC, and μG related to gasket behavior. The first set of pa­rameters relates to leakage, while the second set relates to gasket behavior.

For gasket behavior, the test proce­dure involves increasing the tem­perature of the gasket to the desired level while applying an initial surface pressure. Subsequently, cyclic com­pression and recovery loadings are applied to the gasket, gradually in­creasing the surface pressures until reaching the point where the gasket collapses or the maximum load of the test machine or the maximum spec­ified surface pressure by the manu­facturer is reached. Throughout each loading cycle, the reduction in thick­ness per unit of surface pressure in­crement is measured and recorded.

The surface pressure value observed in the cycle immediately before the collapse is considered as QSmax for that particular temperature. The test procedure, visually depicted in Figure 1 of the standard, is presented below for reference.

These unloading cycles, represented in the figure, allow the generation of val­ues for EG as described in the standard.

The PQR factor is determined by com­paring the residual load to the original load obtained from a relaxation test conducted on a compression press with a known stiffness. The ΔeGC fac­tor measures the additional change of the gasket thickness associated with load loss during the controlled stiff­ness relaxation test. The stiffness of the rig used for the test varies depend­ing on the flange designation, it is set as 500 kN/mm for an EN 1514 DN 40/ PN 40 gasket and 1,500 kN/mm for an EN12560 4” Class 300 gasket.

For the scenario corresponding to Leakage Data, the standard defines the test procedure in a loading and unloading cycle manner on the gasket, with measurement of the leakage rate at the effective surface pressure with internal gas pressure; gas is marked to be Helium. Figure 1 shows an expand­ed PTFE gasket to provide an under­standing of its data.

The thicker line represents the loading curve, blue arrows show the direction in how the load curve is read. The thinnest line corresponds to the unloading curve of the test, green arrows show the direc­tion in how the unloading curve is read. Each black dot on these curves corre­sponds to the applied surface pressure and the measured leakage point. Data between those dots are interpolations for diagram representation. The yellow dots, called Qmin or QSmin, represent the assembly or operational stress re­quired to comply with the tightness class obtained through interpolation.

Figure 1.

One way to use this information is to verify the amount of gasket stress that remains on the gasket after it has been adjusted to the flange surface and has undergone relaxation. Assuming a gasket stress of 30 MPa during instal­lation and considering a PQR of 0.5, the gasket stress after relaxation would be 15 MPa. The image below illustrates these values and indicates their posi­tion in relation to leakage levels. This value suggests compliance with tight­ening class L0.01. If the application re­quirements demand compliance with a higher class, it will be necessary to increase the assembly gasket stress to above 40 MPa.

The test method provides a representation of the perfor­mance of gaskets under actual operating conditions and is appropriate for evaluating the suitability of gaskets for specif­ic applications. From cyclic compression and recovery load­ings to relaxation tests, the procedures outlined in EN 13555 offer a comprehensive approach to assessing gasket behavior under various operating conditions.


In summary, EN 13555 serves as a comprehensive and re­liable framework for the testing and selection of gaskets in industrial applications. By defining key parameters and providing detailed testing procedures, the standard ensures that gaskets meet stringent performance requirements and contribute to the reduction of fugitive emissions. The adop­tion of leakage test standards enables industries to achieve optimal sealing performance, operational efficiency, and environmental sustainability. It is important to mention that no one standard covers all aspects of sealing, however com­bining EN 13555 with other common industry standards, for example, ASME B16.20 or proprietary methods on leader companies, the industry can confidently continue to priori­tize environmental stewardship and regulatory compliance, these tests methodologies play a vital role in promoting the development of improved gaskets and enhancing the overall reliability and safety of industrial operations. By adhering to these standards, companies can confidently select and imple­ment gaskets that provide reliable sealing, minimize leakage, and contribute to a greener and more sustainable future.

ABOUT THE AUTHOR: Francisco Duque is a degreed Mechanical Engineer who serves in the Applications Engineering Department at Teadit North America in Pasadena, Texas. Francisco has been with the Teadit Group for four years providing customer technical support for gaskets and packing, specializing in heat exchangers and packing applications.
Previous articleFugitive Emissions: The Industrial Equivalent of Spilling a Beer
Next articleIdentifying Emissions Using Cooled and Uncooled OGI Camera Technology