Metal O-Rings

Eurosealings metal O-rings have been developed as a secure sealing of gases or liquids. They even can be used in case of extreme conditions. These static and metallic sealing elements can be applied in ranges of ultrahigh vacuum and up to a pressure of 6800 bar. They are suitable in case of continuous temperatures from 269 degrees centigrade below zero up to 980 degrees centigrade above zero and resistant to radioactive radiation, chlorides, corrosion and other aggressive influences. They neither age in use or during storage.

General

Construction - materials - coating - dimensions

Eurosealings metal-O rings are produced of metal tubes or solid wire material. The material is shaped and welded to rings or other figurations. The O-ring consists of stainless steel or other alloys and can be electroplated with silver, cooper, nickel, gold, lead or other metals or can be coated with Teflon*). The flowing of the coating material improves the sealing especially under high pressure and / or vacuum. Eurosealings offers a variety of heat treatments according to material or customer´s specifications, as the resistance to extension and the spring deflection are partially determined by the thermal subsequent treatment. Hollow or solid wire rings can be produced in sizes from 6.4 mm up to 2500 mm outside diameter.

Application and function

The metal O-ring is axially pressed between parallel surfaces, which are arranged at right angles to the flow or to the vessel, as typical application. The sealing is usually placed in an open or closed groove, but can also be installed in a holding device. The working of a groove can be omitted for this reason. The tubing of the seal buckles slightly upon pressing to a predetermined and fixed height. As a result originate two virtual contact widths on the sealing surface and a maximum contact potential between sealing and jointing face. A spring-back effect is obtained, which pursues a positive force, due to the closing of two flanges and the resultant pressing of the O-ring. With the self-energizing performance of metal O-rings, the system pressure increases the sealing force upon the flange facing.

Advantages

With conventional flanged joints many technical data, from which only very few are precisely available during the design state, have to be known for the calculation. Also the values for the rigidity of the flange, the screws etc. have to be available. The consequence are extensive calculations with imprecise or assumed values and the involved disadvantages. There is always a defined initial tension, no setting and smaller flange and screw dimensions with the Eurosealings metal O-rings or lip seals. The proof has not to be furnished with complicated and difficult calculations about unknown quantities but simply by adding the forces of pressure to the operating pressures.

Developed for extreme operating conditions


Standard type

Standard Type

This type is not self-energizing or pressure-filled, produced of different metallic tubings or solid wire and the most reasonable O-ring type for low to moderate pressure or vacuum ratios.

Self-energizing type

Self-energizing type

At the inside or outside diameter the O-ring shows borings and grooves, thereby the same pressure originates in the inside as in the system. They system pressure supports the sealing behavior.

Pressure-filled type

Pressure-filled type

Pressure-filled O-rings have been designed especially for temperatures from 425 degrees centigrade up to 980 degrees centigrade above zero. They are less pressure resistant the self-energizing type, contain a gas filling of approx. 40 bar pressure or more, the gas pressure increases upon higher temperatures and compensates the initial tension deficiency of the flanged joint and increases the sealing force thereby.

Typical applications

Eurosealings metal O-rings are successfully used in vacuum or high-pressure systems as well in critical ranges for hydraulic units and lubricating oils, jet engines and rocket propellants, liquid metals and combustion gases. They yield positive and leakproof seals in tube systems and with production processes for the chemical, petrochemical, petroleum, natural gas and refinery industry. Many manufacturers of reciprocating engines, heat exchangers, gas turbines, pressure vessels, injection units, high-pressure filters and other elements rely on metal O-rings as a permanent and highly stressable seal. Some common applications are illustrated below:

quick release coupling
quick release coupling
screwed flange
screwed flange
heat exchanger /
pressure vessel
heat exchanger/pressure vessel

screwed cover
screwed cover
screwing with external pressure
screwing with external pressure
nuclear power station pressure vessel
nuclear power station pressure vessel

Selection Criterions for metal o-rings

In order to be able to select the appropriate metal O-ring for a particular application the pressure, the temperature and the kind of the media to be sealed in the system have to be known:

O-ring type

The selection of the correct O-ring type depends on the system pressure:

Pressure O-Ring Type
vacuum up to 6.8 bar standard type
6.8 bar and above self-energizing
vacuum to approx. 20 bar pressure-filled

O-ring material

The selection of the correct O-ring material depends on the used temperature:

O-ring material

Ring diameter and tube wall thickness

The tube profile section is determined by means of the outside diameter of the rings, the desired force of pressure and the available space. The wall thickness thus has to be selected that an adequate force of pressure accrues upon the appropriate deformation. The following data comprehend the common wall thicknesses, which can be applied for each diameter. With electroplated surfaces, seals with a tube wall thickness 3.2 mm diameter and load of approx. 72 N/mm peripheral length lead to a plastic deformation of the electroplating. For tubing with a diameter 3.2 mm a pressing of 140 N/mm peripheral length is required. Teflon*) coatings on rings are plastically deformed with a load of 18 N/mm peripheral length.

Ring diameter and tube wall thickness

Groove dimensions

The correct dimension and quality of finish of the groove are as important as the O-ring itself for the use of the seal. The following recommended groove dimensions for internal and external pressure applications are to be understood as general recommendations for the preparation of sealing faces. The dimensions in the list refer to rings, which are not electroplated. Groove depths for rings with a profile section of 0.9 mm are increased by the double of the coating thickness. Groove depths for electroplated or coated rings with a tube diameter of 1.6 mm or more are not increased.

Groove dimensions

Coating or electroplating

By means of coating or electroplating of the metal O-ring a higher adhesion and a more ductile (softer) surface is obtained, so that an adaptation to microscopic irregularities in the groove or flange can be enabled. Based upon the following formula the leakage of liquids can be determined approximately for non electroplated seals:

Coating or electroplating

When the calculated leakage is > 10-3 to < 10-4 cm3/s, the effective leakage may possibly be zero owing to the surface tension. When leakage occurs it should be proportional to the sealing diameter and correspond to the value of the above equation multiplied by D/2 (D= sealing diameter). The effective leakage probably will be under the calculated value. Even helium impermeable connections may be prduced upon practical selected O-rings, coating or electroplating. The results range at a pressure difference of 1 bar and a leakage between 10-6 to 10-12 mbar.l/s.

Also uncoated rings and customized performances are additionally available to the following indicated coating materials:

Material Order Code
Silver S
PTFE T
Copper C
Lead P
Nickel N
Gold G
Coating Thickness
0,15 - 0,30 1
0,30-050 2
0,50-0,80 3
According to specifications X

Temperature limit for coatings:

Coating Order Code Temperature Limit
Lead P 150°C
PTFE T 250°C
Copper C 500°C
Silver S 800°C
Gold G 850°C
Nickel N 980°C

Quality of finish

Recommended qualities of finish of the groove and the jointing face of the flange:

  • 0.4 µm Ra (N5) - for uncoated rings
  • 0.8 to 2,54 µm Ra (N6-N8) - for electroplated or coated rings
  • 0.4 µm Ra (N5) - for gases, vacuum or liquids of low viscosity (water)
  • 0.8 µm Ra (N6) - for medium

Ghost lines on the groove surface or flange facing have to be free of dirt, grinding dust or other impurities.

The following surface roughnesses are usual in practical operation:

Sealing load or required force of pressure

The following graphic chart shows the required force of pressure referring to the diameter of the sealing ring for different tube outside diameters and wall thick-nesses of the stainless tubing. For tubing made of Inconel 600 the indicated values have or be multiplied with factor 1.1 and for Inconel X-750 with factor 1.4.

Sealing specification - order code key

The order example describes above "MOR-332-096,80-PFS1" refers to a metal O-ring of:
Inox 321, with tube outside diameter of 2.4 mm, a wall thickness of 0.25 mm, a ring outside diameter of 96.80 mm (without coating thickness), pressure-filled and silver coated with an extra coating thickness from 0.15 to 0.30.

Should you require any further instructions or recommendations, please supply us the following information:
application, ranges of temperature and pressure, available space, material, medium to be sealed, available force of pressure, drawing of the installation position.

Our competent and experienced team will always assist you consultative.

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