A steam boiler seal is small in comparison to the entire system, but it performs a crucial function. If the wrong seal is fitted, the sealing surface is damaged or the bolted joint is tightened unevenly, a routine maintenance task can quickly a persistent leakage problem. In high-pressure steam applications, it is therefore not enough to select a gasket based solely on pressure rating or temperature. The seal design, surface roughness, gasket material and installation conditions must also be taken into account. This guide explains what is important when it comes to steam boiler gaskets for high-pressure flanges , when a gasket should be replaced and what points are important during installation.
Why steam boiler gaskets are important in high-pressure applications
Steam boilers operate under demanding pressure and temperature conditions. In particular, handhole, headhole and manhole closures require a gasket that reliably seals between the contact surfaces. Thoenes Solutions manufactures steam boiler gaskets for heating and steam boilers, process steam generators and apparatus. The seals are specifically designed to meet the demanding requirements of handholes, head holes and manholes . They are suitable for steam and hot water at high temperatures and pressures. The seal is always part of an overall sealing system. The closure, sealing surfaces and bolted connection must all fit together. Selecting a reliable steam boiler gasket therefore begins with an analysis of the actual operating conditions.
How do you select flange gaskets for steam boilers?
The question ‘How do you select flange gaskets?’ cannot be answered by referring to a single material. First of all, the technical conditions of the application should be examined.
Key selection criteria are:
- Operating pressure
- Operating temperature
- Medium
- Design of the flange or closure
- Seal gap
- Surface roughness
- Dimensions and shape of the seal
- Condition of the existing system
- Installation requirements
A seal should therefore not be selected solely on the basis of a specified maximum pressure or temperature value. The decisive factor is whether its design is suitable for the application as a whole.
With Thoenes steam boiler seals, for example, the surface roughness of the ring and cover, as well as the existing sealing gap, play an important role in selecting the seal type.
Selecting a steam boiler seal: Type 1 or Type 2?
Thoenes offers two different types of steam boiler seals. The choice depends on the specific closure and installation situation.
Type 1 steam boiler gaskets
The Thoenes Type 1 steam boiler gasket consists of a corrugated stainless steel carrier made of 1.4571 with a graphite lining on both sides. Depending on the version, the graphite lining may be reinforced with smooth sheet metal or have a thickness of 0.5 mm. The carrier profile and the linings are designed such that the crests of the corrugations remain covered by the lining material when the seal is installed and under load.
Type 1 is suitable for various steam boiler closures with a surface roughness of the ring and cover of < 12.5 µm and, according to Thoenes, is primarily intended for plants already in operation . The seals are specified for temperatures up to 250 °C and pressures up to 40 bar . They are available in round, square, oval and stadium-oval shapes, including for handhole, headhole and manhole closures.
Type 2 steam boiler gaskets
Type 2 consists of expanded graphite with a purity of at least 98 per cent and a stainless steel or perforated stainless steel insert. A distinctive feature of this design is its certification for an increased sealing gap of 4.5 mm.
It is suitable for closures with surface roughnesses of the ring and cover between 6.3 and 12.5 µm and, according to Thoenes, is primarily intended for new installations. Type 2 is also various forms for handhole, headhole and manhole closures . The product documentation specifies a permissible operating pressure of 40 bar and a permissible operating temperature of 250 °C.
When should high-pressure seals be replaced?
The question ‘When should high-pressure gaskets be replaced?’ is particularly relevant for maintenance and servicing teams.
A gasket should always be inspected whenever a boiler closure has been opened. If the existing gasket is damaged, deformed or no longer suitable for the intended operating conditions, it should be replaced with a suitable new gasket.
Replacement is particularly advisable if:
- a leak has been detected,
- the seal is damaged,
- the sealing gap has changed,
- the sealing surfaces have been machined or repaired,
- the operating conditions have changed,
- a different seal design is required,
- the valve has been opened as part of maintenance.
A recurring leak should not simply be rectified by tightening the screw connection more firmly. Instead, the seal, sealing surfaces, valve and assembly should all be checked together.
Complete guide to fitting screw connections
The correct seal is only one part of a reliable seal. The assembly of the screw connection also influences the result.
1. Check the sealing surfaces
Before installation, the sealing surfaces must be clean and free from residues . Visible damage, corrosion or irregularities should be checked. Surface roughness is particularly important, as Thoenes distinguishes between the various types of steam boiler seals, amongst other things, on the basis of the roughness values of the ring and cover.
2. Check the new seal
Before fitting, check that the seal is in the correct
- shape,
- dimensions,
- seal type,
- material composition and
- operating conditions
suitable for the intended application. A seal should not be used simply because it fits mechanically into the opening.
3. Position the seal correctly
The seal must be carefully positioned on the intended sealing surface . It must not be twisted, damaged or forced into place . Correct positioning ensures that the available sealing surface is utilised as intended.
4. Align the closure
Before tightening the screw connection, the fastener should be correctly aligned. The screws should not be used to compensate for significant misalignment of the fastener.
5. Tighten the screw connection evenly
The screw connection should be tightened in accordance with the installation instructions provided for the respective boiler and closure.
Where specific tightening torques or a prescribed tightening sequence are specified, these should be adhered to. The aim is to ensure as even a load on the seal as possible, rather than placing excessive stress on individual areas.
6. Carry out a final inspection
After assembly, the closure should be checked before the system is put back into operation. For critical applications, the system operator’s specified test and acceptance procedures must also be observed.
Common causes of problems with high-pressure seals
Even a seal that is fundamentally suitable can cause problems if installed or operated under incorrect conditions.
Common causes include:
- incorrect seal type,
- inappropriate seal dimensions,
- damaged sealing surfaces,
- surface roughness not taken into account,
- excessive sealing gap,
- uneven tightening of bolts,
- incorrect positioning,
- unsuitable operating conditions.
Thoenes’ technical specifications show that factors such as seal design, seal gap and surface conditions must be taken into account when making a selection.
Bespoke solutions for high-pressure seals
Not every steam boiler closure corresponds to a standard design. Different designs, dimensions and operating conditions may require a custom-made seal. Thoenes has particular expertise in the manufacture of steam boiler seals and corrugated ring seals.
Among other things, the company manufactures handhole, headhole and manhole seals in round, oval, stadium-oval and square shapes. Customised production based on drawings, samples or customer-specific requirements is also possible. This allows the seal to be specifically tailored to the existing closure design and the relevant requirements .
Checklist for selecting steam boiler gaskets
Before ordering a gasket for a high-pressure steam boiler, the following points should be clarified:
- What are the operating pressure and temperature?
- What medium is to be sealed?
- What is the valve design?
- How wide is the existing sealing gap?
- What is the surface roughness of the ring and the cover?
- Which type of seal is suitable for the application?
- What shape and dimensions are required?
- What assembly specifications apply to the bolted joint?
- Is this an existing system or a new installation?
- Is a custom-made seal required?
The more precise this information is, the easier it is to identify a suitable high-pressure sealing solution.
Conclusion
Reliable sealing in steam boilers starts with choosing the right gasket. For steam boiler seals on high-pressure flanges , pressure and temperature are important factors, but not the only ones. The flange design, surface roughness, sealing gap, seal construction and installation must also be taken into account.
Thoenes offers Type 1 and Type 2 steam boiler seals for different closure conditions. The seals are available for handhole, headhole and manhole closures and can be manufactured in various shapes. For demanding applications, it is therefore more sensible to select a system-specific seal than to use just any standard seal. The technical data for the respective seal type and the conditions of the boiler closure should always be considered together.
FAQs
Which gasket is used for high-pressure steam boilers?
This depends on the specific closure design, the operating pressure, the temperature, the sealing gap and the surface roughness. Thoenes offers, amongst others, Type 1 and Type 2 steam boiler gaskets for this purpose.
How do you select a flange gasket for a steam boiler?
When making a selection, the operating pressure, temperature, medium, closure design, seal gap, surface roughness, dimensions and seal construction should be taken into account.
When should high-pressure gaskets be replaced?
A gasket should be inspected, particularly during maintenance work and after opening a closure. In the event of damage, leakage or changed operating conditions, a suitable new gasket should be fitted.
What is the difference between Thoenes Type 1 and Type 2?
Type 1 consists of a corrugated stainless steel backing with a graphite facing and is, according to Thoenes, primarily intended for systems already in operation . Type 2 consists of expanded graphite with a stainless steel insert and is certified for an increased sealing gap of 4.5 mm and is primarily intended for new installations.