Studies carried out on a wide range of storage installations showed
the need for more efficiently in seal performance.
It has been
shown that Secondary Seals in combination with Primary Seals are
necessary to combat the effect of wind generated suction above the
rim. This effect creates a serious loss in product, with associated
influence on the environment.
in vapour loss created by fitting a secondary seal depends on many
factors such as the product stored, tank location and climatic conditions,
but in every case there are measurable savings in vapour loss.
seals have been developed to replace and to be used as an alternative
to metallic and fabric seals combined with secondary seals.
These seals offer enhanced efficiency and are probably the most
cost effective seals produced to date.
this seal design combines the advantages of long service life, ease
of maintenance and safety in use aspects of the Nayflex Secondary
Seal with a specially adapted Primary Seal.
these seals, Motherwell Nayler Petroseals have not only taken account
of increased efficiency but also the service life, ease of maintenance
and safety in use aspects have been taken into consideration.
The Nayflex range of seals consist of a seal tip of composite material
attached to a ring of flexible steel compression plates bolted to
the top of the roof rim.
The plates are pre-formed and specially shaped in such a way to
utilise the elastic strength of the steel to provide positive pressure
to the seal tip over a range of rim gap variations. This action
produces an extremely effective and flexible seal which can accommodate
a degree of local shell deformation.
plates are fixed to the roof rim with bolts and clamping channels,
thus ensuring a firm connection to develop the positive pressure
exerted on the seal tip. The illustrations on the previous page
show the seal attached to a vertical lip on the roof rim, but the
connection can be designed for other configurations.
gasket is used between the overlap in the plates to permit relative
movement while maintaining a gas-tight seal. As an alternative option,
a continuous flexible vapour barrier can be provided which is attached
to the tip and the roof rim.
particular conditions, these seals can show improvements in sealing
efficiency of 95% or more over other sealing systems.
Since the seal is attached only at the top of the roof rim it is
easily installed working from the top of the roof and may be carried
out with the tank in service.
is simple, and should it be necessary, it is possible to renew the
tip without dismantling the seal.
The specially compounded tip material is highly resistant to chemical
attack and abrasion and, depending on the working environment, should
last on average 10 to 12 years.
Galvanised steel is used for the compression plates as standard,
but where the atmospheric or service conditions can cause serious
corrosion it is recommended that stainless steel is used.
have an excellent service record. Some have been in use for 12 years
without the need of any major maintenance or renewal.
To provide electrical continuity, stainless steel grounding shunts
are attached to the edge of the compression plates and make sliding
contact with the tank shell.
have been tested in rim fire simulations and have shown excellent
performance in not only containing the effects of the fire, but
also helping to extinguish the fire by excluding the supply of oxygen
to the flames.
As an option,
integral foam dams can be provided which will meet NFPA requirements.
Nayflex Seal Tips
Three forms of seal tip have been developed made from polymer materials
which are highly resistant to chemical and atmospheric attack.
can be produced with anti-static properties.
suitable for butt welded
Gives positive contact with the tank shell.
suitable for butt welded tank shells.
Used where shell is distorted or welds are rough.
Gives double contact with the tank shell.
suitable for riveted tank shells.
Gives optimum contact with the tank shell over rivet
and plate laps.