Edge-welded metal bellows mechanical seals have earned a reputation in today’s fluid sealing marketplace due to their reliability and broad range of applications.
Bellows seals are problem solvers for many industries, providing an answer to common challenges such as harsh applications or pump alignment issues. This article explores the key features of edge-welded metal bellows seals and explains why they are well suited to many applications.
What are edge-welded metal bellows seals?
Edge-welded metal bellows are mechanical seals with the ability to flex in one or more directions. With high-level stroke capability and more accurate spring rates than formed bellows, edge-welded metal bellows are used to address common challenges such as harsh applications, high heat or pressure situations, and installation issues.
Understanding the manufacturing process and other critical elements that influence edge-welded bellows design is essential when selecting the correct bellows option. The right manufacturer will have the engineering expertise and production capabilities to apply key principles such as seal balance, materials selection, operating length, and spring rates to meet the specific requirements of an application.
Formed vs edge-welded bellows
Formed bellows – including cold-formed, hydroformed, and electroformed variants – are typically manufactured from seamless or welded tubing using automated processes. While cost-effective for high-volume production, they are limited in material selection and tend to have thicker walls, higher spring rates, and less precise load control.
Electroformed bellows are created by electroplating metal onto an aluminium mandrel. After this process, the aluminium portion is dissolved using chemicals. Historically, the ranges of mechanical strength and operating temperatures are much narrower than those of edge-welded bellows.
Edge-welded metal bellows are manufactured by microscopically welding the interior diameters of individual, stamped metal diaphragms into two-piece convolutions, then welding a series of those convolutions together on the outer diameters to form a welded bellows core. The bellows core can then be microscopically welded to end fittings that correspond to the final application.
Advantages of edge-welded metal bellows
Wide operating temperature range
One of the major advantages of edge welded metal bellows seals – and a feature which makes them effective in many different industries – is the wide range of available operating temperatures. Flexaseal designs and manufactures bellows suitable for operating parameters as high as 800°F (425°C) to -350°F (-212°C for cryogenic applications).
Hydraulically balanced
Seal face balance is typically expressed as a percentage of the hydraulic closing area relative to the contacting seal face area. Bellows seals are inherently balanced due to their mean effective diameter location.
The balance line “cuts” through the bellows insert, meaning only part of the seal face area is exposed to hydraulic pressure. This results in less force acting on the two mating faces compared to unbalanced mechanical seals. Reducing friction at these faces improves seal performance and prolongs seal life.
Excessive heat generation in the sealing area can lead to:
- Failure of elastomers if they are not compatible with higher temperatures
- Ineffective face lubrication due to changes in product viscosity, which can lead to “flashing” or dry-running
Diverse materials of construction
Edge-welded metal bellows cores and end fittings can be manufactured from a wide range of metallurgies, from different grades of stainless steel to Inconel®, Hastelloy™ and other specialised alloys. Flexaseal also applies heat treatment processes that allow bellows to retain strength and spring rate at elevated temperatures.
Metallurgy, along with sealing faces and elastomers, should be selected based on application parameters including temperature, pressure, and RPM.
No dynamic O-ring
This feature provides the following advantages over a pusher-style component seal:
- The bellows seal is less likely to take a set or hang up from heat or chemical attack
- No O-ring hang-up caused by material build-up on the shaft
- Greater tolerance to axial movement and vibration, helping eliminate fretting
Effective replacement for pusher-style seals
Facilities operating under API Standard 682 or ISO Standard 21049 – which require cartridge seals to utilise balanced designs – can benefit from standardising on hydraulically balanced, edge-welded bellows seals. This approach supports longer run-times and reduced seal maintenance across rotating equipment.
The manufacturing process makes all the difference
The defining feature of edge-welded bellows lies in the manufacturing process. While the overall approach is consistent across manufacturers, specific techniques and refinements are often proprietary and play a significant role in final product performance.
In general, the process involves stamping diaphragm plates (male and female) from rolls of foil stock, which are then ultrasonically cleaned and dried to remove contaminants. These diaphragms are paired and welded along the inside diameter (ID) to form individual convolutions. Multiple convolutions are then welded together on the outer diameters (OD) to create the bellows core.
Precision welding methods – typically TIG or plasma – ensure structural integrity and uniform spacing. The completed bellows core is then welded to end fittings and subjected to rigorous pressure testing to confirm leak-tight performance. This test is performed using water or gas, depending on the application specifications. If the final assembly receives an inserted face, the bellows unit is also tested after insertion to ensure a leak-tight seal.
Key design factors
The performance of an edge-welded bellows assembly is determined by several key design factors:
- Diaphragm plate thickness: thinner plates produce lower spring rates and reduced face loading
- Convolution geometry: nesting ripple designs can maximise flexibility and fatigue life
- Spring rate: directly influences heat generation, face wear, and seal longevity
- Vibration control: integrated dampening features help protect against operational instability
Careful optimisation of these variables ensures the seal performs reliably under real-world operating conditions.
Industries using edge-welded metal bellows
Edge-welded bellows assemblies are used across almost every major industrial sector worldwide, where the adaptability and accuracy of welded metal bellows provide advantages in specialised equipment.
Key industries include:
- Chemical processing facilities including a wide range of production equipment such as filters, dryers, centrifuges, extractors, reactors, and evaporators.
- Food and beverage industries also have equipment which utilise bellows sealing options including commercial tanks, agitators, mixers, and blenders.
- Upstream oil and gas exploration and drilling including artificial (downhole) lift.
- Mid-stream oil and gas processing, storage and transportation including hydrocarbon processing.
- Downstream oil and gas including oil refining and distribution.
- Pharmaceutical production includes clean rooms, dryers and distillers, extruders, raw material pumps, and wastewater processing.
- Pulp and paper equipment includes screens, refiners, mixers, pulpers, and agitators as well as mechanical pumps.
Common applications
Edge-welded bellows are particularly effective where consistent face loading and stable operation are critical in the presence of temperature variation, pressure fluctuation, chemical attack, or abrasive media.
Typical applications include:
- Cryogenic liquid transportation and storage.
- Heat transfer fluids and high temperature media as found in oil and gas refining operations.
- Product purity and compliance in food and beverage production extending from raw material processes to final packaging.
- Emission control for gases such as hexane and sulfur dioxide discharged during various industrial applications.
- Caustic and corrosive products like chlorine dioxide used in the paper bleaching process and sodium hydroxide in hydrocarbon streams.
- Products with high concentrations of abrasives such as boiler feed water, industrial wastewater, various paper pulp liquor processes
Edge-welded metal bellows seals provide a highly engineered solution to complex sealing challenges. Their balanced design, precise spring control, and ability to perform across extreme operating conditions make them a strong alternative to conventional pusher-style seals.
When reliability and long-term performance are critical, working with an experienced designer and manufacturer ensures each bellows assembly is correctly specified and optimised for its application. With decades of engineering expertise, Flexaseal continues to set the benchmark in edge-welded bellows technology.
Discover more here or contact Flexaseal for Australian sales and service at sales_aus@flexasealau.com or 1300 762 548.
