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Table of Contents
Applications of O-rings in heat exchangers within power plants
Placement and function of O-rings
Heat exchangers in power plants handle water, oil, glycol and condensate at varying temperatures. O-rings are located in inspection covers, sensor connections, drain plugs, flange transitions and piping systems. Their primary task: to separate fluids without leakage or contamination, even under repeated thermal expansion and cooling. In plate heat exchangers (PHE), O-rings are often installed in end caps, piping sets and measuring points. They must withstand hot water, glycol and cleaning agents. EPDM is preferred here due to its excellent resistance to water and steam. In systems with oil-containing circuits or higher temperatures, FKM (Viton®) can deliver better performance.
PHE and S&T: differences in loading
In shell-and-tube heat exchangers (S&T), O-rings are located in end covers, tube bundle seals and instrumentation ports. The pressure levels here can be considerable, so harder compounds (80–90 Shore A) are often used. These are combined with PTFE back-up rings to prevent extrusion under high pressure. In both types of heat exchangers, the seals must withstand thermal cycles and pressure variations without losing their elastic properties.
Material selection: EPDM, FKM (Viton®) and FFKM in heat exchangers
Properties of the main compounds
The choice of material largely determines the service life and reliability of O-rings in heat exchangers. Each elastomer has specific advantages and disadvantages depending on the medium, temperature and cleaning method. EPDM is highly resistant to hot water, demineralized water and steam. It remains elastic up to around 150 °C and offers good resistance to oxidation and ozone. FKM (Viton®) is ideal for oil circuits, lubricating oil coolers and systems with chemically aggressive media. It remains stable up to about 200 °C but is less suitable for long-term steam applications. FFKM is the premium choice for extreme temperatures and aggressive chemicals. It combines the chemical inertness of PTFE with the elasticity of rubber but is more expensive.
Compatibility with process media
Water and steam cause NBR to age rapidly, making EPDM often the first choice in water-side circuits. In oil-cooled heat exchangers or closed hydraulic systems, FKM (Viton®) performs better. FFKM is mainly used in critical instrumentation circuits or test facilities where absolute leak-tightness and cleanliness are required. The correct material selection ensures that the O-ring is resistant not only to chemical influences but also to repeated compression and expansion during operation.
Technical design: groove dimensions, tolerances and PTFE back-up rings
Groove design and tolerances according to ISO 3601
Even the best material will fail with poor design. Correct groove geometry, coordination of squeeze and stretch, and the proper use of support rings determine whether an O-ring maintains its function. The ISO 3601 standard defines the tolerances for O-ring dimensions, groove depths and compression percentages. A correctly designed groove according to ISO 3601 ensures that O-rings in heat exchangers retain their sealing properties even under prolonged pressure fluctuations and temperature changes. For static applications, a squeeze of 15–25% and a groove fill of about 80% are generally applied. Excessive compression causes deformation and shortens service life, while insufficient compression can lead to leakage. The surface roughness of the sealing face must be such that micro-leakages are prevented without increasing friction. A surface that is too rough or too smooth may cause O-rings in heat exchangers to seal poorly, especially when pressure and temperature continuously vary.
Application of PTFE back-up rings
At higher system pressures or with larger gap clearances, PTFE back-up rings are used. These rigid rings support the O-ring and prevent the elastomer from being forced into the gap (extrusion). Under demanding operating conditions, such designs prevent O-rings in heat exchangers from premature wear or extrusion damage, significantly extending service life. In shell-and-tube heat exchangers this is essential, especially with the thermal expansion of metal components. A correct fit according to ISO 3601 also prevents the back-up ring from hindering the seal or deforming as temperature rises.
Quality, maintenance and service life in power plants
Maintenance strategy and inspection
A sealing design is only effective if the maintenance process is also carefully organized. Power plants follow strict inspection and replacement schedules to prevent unplanned downtime. Due to their constant exposure to pressure and temperature variations, O-rings in heat exchangers require a controlled maintenance regime to maintain sealing integrity. During planned shutdowns, O-rings are visually inspected for compression set, cracking or hardening. Replacement is carried out preventively after a predetermined operating period, depending on the medium and temperature.
Compounds such as EPDM generally retain their properties longer in water-side circuits, whereas FKM (Viton®) or FFKM perform better in oil circuits or chemical environments. A carefully planned replacement interval prevents O-rings in heat exchangers from aging beyond their elastic limit, which can cause leakage or performance loss.
Quality assurance and traceability
During replacement, traceability is important: material type, hardness, standard size and production date are recorded. Suppliers such as O-Ring-Stocks provide O-rings that comply with ISO 3601 quality classes and originate from certified compounders. This ensures consistency in dimensions, compression and chemical resistance, which is crucial for long-term reliability in any heat exchanger. By using only certified O-rings in heat exchangers according to ISO 3601, sealing performance and dimensional consistency remain guaranteed, even under high loads.
FAQ: O-rings in heat exchangers
They prevent leakage between different process streams and ensure energy efficiency and safety.
EPDM is the most suitable, due to its excellent resistance to water, steam and oxidation. Especially in installations with hot water and steam, O-rings in heat exchangers made from EPDM compound retain their elasticity and leak-tightness even after thousands of operating hours.
FKM (Viton®) is used at high temperatures and with oils; FFKM for extreme chemical exposure or very high temperatures. In practice, O-rings in heat exchangers with FKM compound are often used in oil circuits, while FFKM is preferred in chemically aggressive installations where maximum resistance is required.
It prevents the O-ring from being forced into the gap under high pressure or temperature, preventing leakage.
The international standard ISO 3601 defines dimensions, tolerances and quality levels.
That depends on the medium, temperature and cycles. In many installations they are replaced at every planned maintenance shutdown to avoid downtime. In continuously operating plants, such as baseload power stations, O-rings in heat exchangers are often replaced annually to prevent unexpected outages and ensure consistent efficiency.