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Due to increasing requirements on bolted flange

connections with view to the environment it hasbecome necessary to take into consideration not

only the leak rate of a flange connection but also a

fire. Where fire safe gaskets are required not onlythe gasket itself but also all parts of the flangeconnection must be taken into account.

In case of fire in the vicinity of a flanged connection

flanges - and especially bolts - may be influenced by

the heat and weakend. For this reason British Stan-dard 6755 part 2 (1987) insists on fire tests forvalves.

In Germany the authorities require the same

conditions also for the flange connections of valvesand pipework if inflammable liquids or gases (ofgreat density) are handled and if no total outer

insulation is provided.

Because the latter is a logic conclusion, werecommend to apply this safety philosophy on allbolted flange connections which must be protected

against fire attack.

Remarks on outer insulationThis type of fire protection is safe in case of fire. It has

disadvantages if the flange joint is leaking in servicebefore fire. In this case the inflammable liquid will be

absorbed by the porous insulation material. Theabsorbed inflammable liquid will lead to an extremelydangerous situation which could give rise to fire or

explosion.

Fire safe flange connectionsFire safe flange connections have the following

characteristics:

G The parts, flanges, bolts and gaskets of fire safe

flange joints are not combustible at

650 C. The stability of these parts in ambient air

at 650 C for 30 minutes is given and oxidation aswell as thermal cracking in this time is negligible.

G The fire safe design enables the flange connection

to maintain for thirty minutes a residual surface

pressure, which is high enough to limit theleakage to the allowed maximum in accordance

to BS 6755 part 2.

The problem

The simplest solution would be to design the flangeconnection for 650 C or a higher applicationtemperature. For economical and technical reasons

this is out of question. The economic reason is self-explanatory. The technical reason is that only metal

gaskets can be used at such high temperatures.

The choice is limited to metal gaskets (flat or profile)

and weld type gaskets. The first makes only sense

at high pressures, the latter are not easy to separateand to reweld.

figure 1

figure 2

Fire safe Flange Connection

Gaskets Packings Expansion Joints Rubber and Plastic Parts

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Solution

The way out of this problem is to compromise, as inmany technical solutions. For example, the flangeconnection is designed for 300 C and the used

gasket has a metal support e. g. Kempchen profileB45A with layers of expanded graphite. This

combination withstands temperatures of 650 C for

30 minutes, though its service temperature is limitedto 550 C.

CONVEX-gaskets profile B45A as shown in figure4 in accordance to Work Standard WN 145 for DIN

flanges and WN 146 and WN 147 for ANSIrespectively MSS - SP 44 flanges enable the designer

to determine a fire safe flange joint. One of theadvantageous features is the nearly constant

remaining sealing diameter, even when flangesrotate, and this will obviously happen at temperatures

of about 650 C.

The dimensions of these gaskets are optimized, sothat each gasket seals on the smallest possible

sealing diameter. With this optimization flange

rotation is initiated by the bolting up procedure. Thedegree of rotation will scarcely increase with

increasing pressure and temperature. Therefore thesmall and constant sealing diameter leads to constant

bolt load and maximum residual stress.

MaterialsFor flange connections with fire safe requirements

metal gaskets or gaskets composed of metal andgraphite are useable. In some cases metal gaskets

are not suitable for instance with flanges of low

nominal pressure rate. In cases where a contactbetween the medium and graphite is to avoid gasketswith an inner metal eyelet are recommended.

If extremely tight and clean sealing is required the

inner part of the layers may be made of PTFE, seefigure 4. With this design the medium will be free ofimpurities. The increase of tightness is related to the

factor 100. The PTFE may be destroyed in case of

fire but the graphite part of the layers ensures thatthe joint will be tight.

kempchenfire safe supplement

The latest development in this field are gaskets withouter rings and layers of intumescenting material onboth sides (fig. 1). This compound blows up at about

300 C and turns into an unburnable, porous heatinsulating foam (fig. 2). The space between the

flanges especially between the outside diameter of

flanges and the bolts is filled with the insulating foamand this protects the bolts against heat transmitted

by convection or radiation. This is the best guarantee

for a constant residual gasket surface pressure.

Fire Safe Flange Connections

Gaskets Packings Expansion Joints Rubber and Plastic Parts

kempchen & Co. GmbH

Alleestr. 4 D - 46049 Oberhausen

Tel.: ++49 208 8482-0 Telefax ++49 208 8482-285

E-mail: info@kempchen.de

URL: www.kempchen.de

132e/1201000X

graphite

PTFE

stainless steelfigure 2

T>= 650 0C, 30 min

test valve through-seat external

position leakage leakage[mL/in/min] [mL/in/min]

highpressure closed

low

pressure closedhigh fullypressure open

test requirements accordingBS 6755 : Part 2 : Section three : 1987

figure 3

400 100

40 20

200

All information and technical descriptions contained in this brochure correspond to our state of knowledge at the time of the printing. They are intended as information about our

products and their various applications.Therefore, we will only guarantee certain attributes described in the brochure or the suitability for actual intended purposes according to a written express warranty in the actual individual case. Any industrial proprietary rights must be observed. Orders will only be accepted and completed under our standard terms and conditions, which we will make available on request.