GASKET RUBBER

The cost of leaky joints in industry today is staggering. Out-of-pocket costs run into billions of dollars annually in lost production, waste of energy, loss of product and, most recently, impact on the environment. These
problems are increasing, not decreasing. It behooves all of us to consolidate our knowledge and experience to solve or at least minimize these problems. This publication is being produced because we, as gasket
manufacturers and suppliers, are constantly called upon to solve sealing problems after the fact. Toooften we find insufficienttime and attention has been given to:
. proper design of flanged joint
. installation procedures and
. selection of the optimum gasket material required to solve a particular sealing problem.
Wewill endeavor to outline in this publication those areas we believe to be essential in a properly designed, installed and m"aintainedgasketed joint.
We believe most people involved with the design, installation, and maintenance of gasketed joints realize that no such thing as "zero" leakage can be achieved. Whether or not ajoint is "tight" depends on the sophistication
of the methods used to measure leakage. In certain applications the degree of leakage may be perfectly acceptable if one drop of water per minute is noted at the gasketed joint. Other requirements are that no
bubbles would be observed if the gasketed joint was subjected to an air or gas test underwater and a still more stringent inspection would require passing a mass spectrometer test. The rigidity of the test method would be determined by:
. the hazard of the material being confined
. loss of critical materials in a process flow
. impact on the environment should a particular fluid escape into the atmosphere
. danger of fire or of personal injury
All of these factors dictate proper attention must be given to:
. design of flange joints or closures
. proper selection of gasket type . proper gasket material
. proper installation procedures
Care in these areas will ensure that the best technology goes into the total package and will minimize operating costs, pollution of the environment and hazards to employees and the general public.
WHY GASKETS ARE USED
Gaskets are used to create a static seal between two stationary members of a mechanical assembly and to
maintain that seal under operating conditions which may vary dependent upon changes in pressures and
temperatures. If it were possible to have perfectly mated flanges and if it were possible to maintain an intimate
contact of these perfectly mated flanges throughout the extremes of operating conditions, a gasket would
not be required. This is virtually an impossibility either because of . the size of the vessel and/or the flanges . the difficulty in maintaining such extremely smooth flange finishes during handling and assembly
. corrosion and erosion of the flange surfaces during operations.
As a consequence, relatively inexpensive gaskets are used to provide the sealing element in these mechanical
assemblies. In most cases, the gasket provides a seal by external forces flowing the gasket material into the
imperfections between the mating surfaces. It follows then that in a properly designed gasket closure, three
major considerations must be taken into account in order for a satisfactory seal to be achieved.
. Sufficientforce must be available to initially seat the gasket. Stating this another way, adequate means
must be provided to flow the gasket into the imperfections in the gasket seating surfaces. . Sufficient forces must be available to maintain a residualstresson the gasket under operating conditions
to ensure that the gasket will be in intimate contact with the gasket seating surfaces to prevent
blow-by or leakage. . The selection of the gasket material must be such that it will withstand the pressures exerted against the gasket, satisfactorily resist the entire temperature range to which the closure will be exposed and withstand corrosive attack of the confined medium.
EFFECTING A SEAL
A seal is affected by compressing the gasket material and causing it to flow into the imperfections on the
gasket seating surfaces so that intimate contact ismade between the gasket and the gasket seating surfaces
preventing the escape of the confined fluid. Basically there are four differentmethods that may be used either
singly or incombination to achieve this unbroken barrier. . Compression (Figure 1). This is by far the most
common method of effecting a seal on a flange joint and the compression force is normally applied by
bolting. . Attrition (Figure 2). Attrition is a combination of a dragging action combined with compression such
as in a spark plug gasket where the spark plug is turned down on a gasket that is both compressed
and screwed into the flange
By heat, such as in the case of sealing a bell and spigot joint on cast iron pipe by means of molten
lead. Note, however, that after the molten lead is poured, it is tamped into place using a tamping tool
and a hammer.
. Gasket lip expansion. This is a phenomenon that would occur due to edge swelling when the gasket
would be affected by confined fluid, as in the case of elastomeric compounds affected by the confined
fluids, such as solvents, causing the gasket material to swell and increase the interaction of the gasket
against the flange faces.
Generally, gaskets are called upon to effect a seal across the faces of contact with the flanges. Permeation
of the media through the body of the gasket is also a possibility depending on material, confined media,
and acceptable leakage rate.
GASKET SEATING
There are two major factors to be considered with regard to gasket seating.The first is the gasket material itself. 'The ASME Unfired Pressure Vessel Code Section VIII, Division 1
defines minimum design seating stresses for a variety of gasket materials. These design seating stresses range
from zero psi for so-called self-sealing gasket types such as low durometer elastomers and O-rings to
26,000 psi to properly seat solid flat metal gaskets.
Between these two extremes there are a multitude of materials available to the designer enabling himto make
a selection based uponthe specific operating conditions under investigation. Table No.1 indicates the more
popular types of gaskets covered by ASME Unfired Pressure Vessel Code.
If you need our products please contact us at:Tel: +62 31 72179064Fax: +62 31 8535442Mobile: +62 858 50837808Email: sales.javatech @ gmail.com