Technical Papers

Unsuitable Usage Conditions ofGaskets and Countermeasures
1. Introduction

suggest that the phenomenon might be caused
through the following mechanism: monomeric fluid
permeates the inside of a gasket; the permeating fluidof a gasket to resist corrosive fluids including acidic andcauses polymerization inside the gasket; thealkaline fluids. It also sometimes refers to countermeasurespolymerization results in volume expansion; and thefor events that could occur with given fluids. To address

expansion causes the gasket to break.

such events, not only seal materials themselves, but also

To address these problems, it is recommended toproper selection and application of seal materials arechange to a spiral wound gasket（No. 7596V）, which

important. This report introduces examples of such

does not break when fluid permeates and polymerizes,events and countermeasures.

and to use gaskets made of PTFE only which are lesslikely to cause permeation. Also, inadequate tightening

2. Examples of Troubles andCountermeasures

is possible o cause permeation, so proper tightening２-1）Blooming phenomenon of resin-type gaskets２-2）Chemical degradation of a core joint sheet

caused by polymerizable monomers

can be a countermeasure in some cases.

caused by permeation of strong acids into

The phenomenon of blooming occasionally occurs in

the PTFE jacket of the N 7030 series

the fluororesin jacketed gasket: No. N 7030 series andBecause of PTFE jackets, PTFE jacket gaskets are

the filler-added fluororesin gaskets: No. 7020, No. 7026,

superior in chemical resistance to joint sheets.

and No. GF300 series. Chemical reaction between theHowever, PTFE could permeate some chemicals whenconstituent materials and fluid is not considered toa PTFE jacket gasket is used for a long period. Thecause this phenomenon. In addition, the results ofPTFE may occasionally allow fluid, especiallyanalyzing affected gaskets, which revealed thehydrochloride, to permeate the gasket's core andinvolvement of a material not contained in theaffect the core. If that happens, the following events

gaskets, and the morphology of affected gaskets,

may occur: fluids accumulate into the inside of thePTFE jacket and the inner core; traces of permeation
including discoloration are observed; and fluid
contents are detected by analyzing the inside of thecore. As countermeasures, it is recommended toincrease the thickness of the PTFE jacket and tochange the gasket material（for example, to use thePTFE blended gasket No. MF300 and the spiralwound gasket containing PTFE filler）.

Figure1

Blooming phenomena of a resin-type gasket
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Summer 2017

The term "gasket corrosion resistance" means the ability

No.33

Unsuitable Usage Conditions of Gaskets and Countermeasures２-3）Decomposition of expanded graphitesmoothly and efficiently. It means they are easy tocaused by oxidation using the gasket

permeate into gaskets. In general, expanded graphite

above the recommended temperature

itself shows lower coefficient of thermal expansion andAs a seal material, expanded graphite has ideal

thermal stability, and could be highly suitable material

properties including excellent chemical resistance andfor seal. However, expanded graphite shows relatively

low creep relaxation, but when the temperature ispoor resistance in permeation and sometimes it results

450ºC or higher, its oxidation reaction with oxygen in

in leakage through the sheet gaskets.

the air usually causes gasification, which transforms

In general, permeation through materials could be

the content into carbon monoxide, carbon dioxide, etc.,

decreased with increasing density by compression, soresulting in fade-out. Therefore, recommended ranges

it could be a countermeasure to generate tighteningof temperature are maximum 400ºC for the graphiteload to suitable for sealing. For trustworthy sealing,

sheet gaskets: No. VF-30 and No. VF-35E, which arechanging to spiral wound gaskets containing

comprised of carbon only and are significantly

expanded graphite filler such as the No. 6590 series isaffected by temperature, and maximum 450ºC evenrecommended.

for the spiral wound gasket containing expandedgraphite filler of the No. 6590 series because of theSummer 2017
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２-5）Chemical degradation of a joint sheet

structural advantage. When those gaskets are used atgasket in applying to solvent（acid/temperatures above the recommended range, leakage

alkaline）process line

occurs due to loss of the constituent material in a

When a gasket is used for a fluid for which it does notrelatively short time. In the case of spiral woundhave enough resistance, the resulting fade-out or

gaskets, placing non-asbestos filler or mica filler along

dissolution of some constituent materials make thethe inner and outer periphery blocks oxygen contact,gasket more fragile and softer, leading to reduce

inhibits oxidation decomposition, and maintains sealing

tightening stress and other phenomena. These eventsfunctions at 450ºC or higher. Although non-asbestos

can readily be determined by analyzing usedfiller loses organic constituents at high temperatures,products. In these problems, it is especially dangerous

usually, inorganic constituents will not change.

that a gasket breaks so markedly that it does not

Therefore, during non-asbestos filler remains withinkeep its original shape.

hoops, it prevent expanded graphite from oxidation

As a countermeasure, it is recommended to change tobecause of oxygen shielding effects.

gaskets, such as No. UF300, which have moreresistant to fluid.
２-6）Erosion of soft gaskets caused by slurry fluid
When a gasket looks severely broken in appearance
but has no tightening problems, and an analysis of aused product shows no chemical deterioration causedby fluid and heat, even if it is very rare case, physicalfracture by erosion from fast-moving powder crashing

Figure2 O
 xidation loss of expanded graphite from a spiralwound gasket

against the gasket could be considered. Although thefluid's properties and the channel's design influence
the erosion, erosion usually occurs in slurry fluids２-4）Leakage of heat transfer oil through gasket

which contain fine particles.

Oils and fats used as heat media are generally

As a countermeasure, it is effective to placedesigned to have a low viscosity so as to flow

constituent materials that have adequate resistance3

Technical Papers

against erosion inner side of gasket such as spiralwound gasket with inner ring or sheet gasket withgrommet.

3. Conclusion
We introduced a part of cases of gasket corrosion
troubles and countermeasures. We hope this reportwill help you to select and determine seal products tosolve leakage problems and achieve the requiredsealing.

Figure3

Erosion of a soft gasket

Sales Group

Summer 2017

Toshihiko Enishi
Technical Solution Division

No.33

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