Manhole protection and sealing rings for enamelled steel boilers

Initial situation

The enamelling in enamelled reaction and stirring unit containers are shock sensitive.
The enamel layer can easily chip off due to shock or impact which leads to expensive repairs or re-enamelling of the whole boiler.
Especially at risk are the insides of a manhole, filling pieces and sampler nozzles, since shock and impact cannot be excluded during manipulation with open cover.
The construction as per image 1 or similar was used in order to reduce the risk to the container.

Between nozzle opening (1) and cover (2) is an enamelled steel spacer ring (3) which is sealed on either side with seals (4) as per detail "A" against nozzle and lid.
The disadvantage of this design is

  • that the enamelled steel spacer rings are sensitive to the same stresses and may be rendered useless
  • that there is no protection inside the nozzle
  • that the top seal often buckled and became loose when a vacuum was applied
  • that a change of the top seal became necessary more often if the cover was opened often (sampling, adding of ingredients and additives)

IDT offers an intelligent solution to remove the above mentioned disadvantages which works without spacer rings and inserted seals on both sides, yet is fully functionally and provides a high sealing quality.

Problem solution

Integral elements of the new sealing model are a basic body (5) with a circumferential groove at the inner shell and a threaded skirting (6).
Basic body and skirting consist of conducting Hostaflon®-TFM 4220 (with in the molecular chain modified PTFE with excellent sealing properties).
The basic body has a serrated profile to seal off liquid on the top and bottom part. The dovetail grooves on either side are designed to take one sealing O-ring (7) each.
These O-rings are used to achieve gas tightness and are made from a flexible material (FPM) with or without PTFE-shell.
A bandage (8) made from stainless steel suited to the operating conditions guarantees rupture strength for inner pressurisation as per the requirements of the pressure container regulation.

The height of the bandage is 70% of the thickness of the basic body, their thickness is more than 2,5 mm.
The bandage has straps on the outside which fix the seal onto the container sleeve and prevent hence potential leaks due to slipping and also aid the deflection of electrical charges. 
The sealing model can be made both for circular as well as oval nozzles.

Areas of use

  • operating pressure max. 10 bar
  • max. operating temperature approx. 200 °C
  • flange sensitive to stress
  • aggressive and toxic media in gaseous and liquid condition 
  • pharma and chemical industry
  • batch operation (change in temperature and pressure)


  • almost universal resistance against chemicals and solvents
  • sheathed and blow-out tightness as per UVV
  • seals and protects manholes, funnel and sampling openings of enamelled  containers from damage to the sealing surfaces and inside of the sleeve
  • prevents expensive repairs or re-enamelling of the whole boiler, saves the use of  expensive enamelled steel spacer rings and the need to replace seals often
  • has a long service life (2,5 years) as per experience even during rough operating  conditions (opening and closing the cover three times per week)
  • no product contamination, no health hazard
  • conductive (deflection of electric charges)
  • asbestos-free

Installation recommendations

  • install seal between clean, dry and grease-free flanges
  • minimum surface compression 5  N/mm2
  • tighten screws cross-wise in steps up to 50%, 75% and 100% of final tightening torque check bolts frequently and tighten if necessary until all reached the intended  final tightening torque

The tightening and re-tightening recommendations of the enamel container manufacturer have to be adhered to.
The component is subject to the pressure container regulation.
The information is based on today's knowledge and is designed to inform about our products and their range of applications. They are not designed to guarantee certain product properties and their suitability for certain uses.
Potential industrial property rights have to be considered. We guarantee impeccable quality as per our general terms and conditions.

Safety instructions / fire performance

If Hostaflon®-TFM is overheated (above 400 °C) a harmful decomposition product is created mainly as hydrofluoric acid.
Please adhere therefore to the safety instructions (see information sheet “Hostaflon® safety information of raw material types and safety instructions for the processing”, KS 613).
Hostaflon®-TFM is flame resistant.

After the limiting-oxygen-index-test, the LOI-value is 95 (i.e. the material will only start burning in an atmosphere which contains more than 95% oxygen).