Product Introductions

Substitute Sealants for Refractory
Ceramic Fiber
1. Introduction

has adopted inorganic fibers to replace RCF, as they
are soluble in living organisms, and has developed
products which are both safe and functional. Since

and used as substitutes for asbestos. However, there isthese fibers readily dissolve within the body whenconcern that some of them may be carcinogenic, andinhaled via the respiratory system, they are considered

so regulations have been introduced in each country.

to pose low risks to health and so are not subject toIn Japan, in November 2015, refractory ceramic fiber

legal regulations.

（RCF）was categorized as a Group-2 substance andTable1 shows products subject to RCF substitution.

specified chemical substance to be controlled underThis article introduces substitute products in terms of

the Ordinance on the Prevention of Hazards due tospiral wound gaskets, metal jacketed gaskets, rubber-Specified Chemical Substances（hereafter“Ordinance”）.

coated woven fabric gaskets, and gland packings.

The major regulatory items and management tasks
required in manufacturing are as follows.1）

Table1

Products subject to RCF substitution

Applicable product group

VALQUA part number

Spiral wound gasket

No.8590 series＜Major management tasks＞

Metal jacketed gasket

No. N510, N520, N530, N570, N580,N6520, N6580① Placement of local ventilation

Rubber-coated woven
fabric gasket

No.P-N314

Textile productNo. P-101S, P-102SF, P-102S, P-105S
P-105SN, P-112S, P-112S-N

Gland packing

No. N340G-F, N340M-F② Nomination of an operational chief③ ‌Creation and preservation of notifications andoperation records④ Measurement of operational environment⑤ Medical examinations

2. Spiral wound gasketsAlthough molded products in which binder is used toSpiral wound gaskets are semi-metal gaskets designed

solidify RCF, and products in which RCF is sealed, arefor use under high temperature and high pressure,

not subject to the regulation, when such products are

and also have excellent sealing properties and heatcut or polished, RCF dust can be dispersed. Therefore,resistance. Therefore, they are used in a wide range of

the Ordinance is applied to these products.

applications including general piping and devices, as

RCF is widely used as a refractory material and heatseals for steam and heat media. In a spiral woundinsulator, which can be used at high temperatures ofgasket, a V-shaped metal belt （hoop） and a soft

1,000ºC or higher, at various plants including steel, oil

sealing belt（filler）are wound together. Generally,and chemical plants. Meanwhile, sealants have beenspiral wound gaskets, to which inner and outer metal

widely used in various products including gaskets andrings are attached, are used for various purposes

gland packings because of their excellent heat

depending on the conditions.

resistance. In line with legal regulations, VALQUA

Inorganic paper is one of the fillers used in spiral
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Summer 2018

Various artificial mineral fibers have been developed

No.35

Substitute Sealants for Refractory Ceramic Fiberwound gaskets. In the paper-making process, organic/properties of No. 8596V and No. 8596VL wereinorganic fibers, fillers, and rubber binders are mixedevaluated under the condition of heating the twoand then the mixture is made into paper. Thegaskets while connected to a flange, then cooling themmaximum service temperature is 500ºC. For

to room temperature. Table2 shows the results.

inorganic-paper fillers, RCF used to be used as a“Lined products”is a foamed-carbon filler in which

substitute inorganic fiber for asbestos.

inorganic-paper filler is placed at both ends of theVALQUA developed inorganic-paper filler spiralfiller to prevent oxidation loss of the filler. No leakage

wound gaskets（No. 8590 series）containing biosoluble

occurs in RCF-substitutes; they were confirmed torock wool as a substitute fiber for RCF（Figure1）.

have adequate high-temperature sealing properties.

Biosoluble rock wool is a fiber which is not regulated

Table3 shows the results of evaluating steam resistance.

by the Ordinance; it is excluded from the carcinogenic

Generally, loss of fiber strength of biosoluble fibers is a

category by Note Q of Commission Directive 97/69/

concern when the fiber comes in contact with steam

EC“Carcinogenicity categorization and package

or water. To evaluate steam resistance, we evaluateddisplay regarding artificial amorphous fiber.”the sealing properties of the RCF-substitutes using

The performance of RCF-substitute productsnitrogen gas after steam exposure, and deterioration（hereafter“RCF-substitute（product）”）containing

was confirmed. The result shows that no leakage

biosoluble rock wool is shown below. The sealingdeveloped with the RCF-substitutes, and RCFsubstitutes have similar sealing properties to those ofSummer 2018

RCF-containing products.
Regarding design data including m/y values, there
were no changes following the change in fiber; theRCF-substitutes can be used in a similar manner as
conventional products containing RCF.
Table3 Comparison of steam resistance regarding No. 8596VNo.35
Figure1No. 8590 series（RCF-substitute products）

Table2 Comparison‌of high-temperature characteristics
between No. 8596V and No. 8596VL

Sealing-property evaluation, Inner pressure（MPa）
Steam exposure No. 8596V（RCF-containing product） No. 8596V（RCF-substitute）
time
2.0
4.0
2.0
4.0
Pre-exposure No leakage No leakage No leakage No leakage
1 weekNo leakage No leakage No leakage No leakage
3 weeks
No leakage No leakage No leakage No leakage
Note: Test conditions
Exposure fluid：30 K steam（230ºC, 3 MPa）
Tightening force：Bolt-fastening under a contact pressure equivalent to 70 MPa

Heatingtemperature

3. Metal jacketed gaskets
Roomtemperature

Metal jacketed gaskets are semi-metal jacketed

Additional tightening

gaskets in which the outer side of felt（thick plate
made from inorganic materials）is covered with a thin

3Leakage amount（Pa・m /s）
No.8596VL（RCF-substitutelined products）

metal plate. Since complex shapes and narrow sizes

500ºC

600ºC

they are used in towers and tanks as well as heat

No leakage

No leakage

No leakage

1No leakage

No leakage

No leakage

2No leakage

No leakage

No leakage

Specimen

No.8596V（RCF-substitute）

Heating temperature

400ºC0Cycle
numberNote: Test conditions
Internal pressure：4 MPa（400ºC and 500℃）, 1 MPa（600℃）
Tightening
force：Bolt-fastening under a contact pressure equivalent to 70 MPa‌25

can be manufactured using metal jacketed gaskets,exchangers.
Metal jacketed gaskets are often used at temperaturesof 500ºC or higher. Since RCF has excellent heat
resistance, it is used as a core material for felt. Since theProduct Introductions

felt of a metal jacketed gasket is completely coveredwith metal, there is minimal exposure risk, and so the

4. Woven fabric gaskets
Woven fabric gaskets are gaskets using fabric, ribbon,

for even safer use, we developed metal jacketed gaskets

or yarn. In these gaskets, RCF materials are used at（No. N510 and N520）which instead use inorganic fiber,

temperatures of 500ºC or higher. In some woven

which is not subject to the Ordinance（Figure2）.

fabric gaskets, special treatments are applied using

We compared the sealing properties between RCF-rubber-soaked cloth. They are used at places wherecontaining products and RCF-substitute products at aleaking is relatively acceptable, such as in devices’heat cycle of 600ºC. In the comparison, gaskets weremanholes and the flanges of exhaust-gas ducts.

connected to a flange, several thermal cycles wereVALQUA started supplying gaskets that use

applied, and the room-temperature sealing properties

biosoluble fiber（BSF）instead of RCF. BSF remains inwere compared. Figure3 shows the results. According

the body for a shorter time than RCF and is notto the figure, even after the heating cycles, the RCF-

subject to the Ordinance.

substitute products appear to have equivalent or

When making RCF-substitute products, the wovensuperior sealing properties to those of RCF-containing

fabric, which the main material of BSF, is added withproducts.

a small amount of organic fiber and is soaked with

Regarding various design data, the same as in spiralrubber. Through this process, RCF-substitute has

wound gaskets, there were no changes in the metal

improved sealing properties.

jacketed gaskets. Therefore, RCF-substitutes can be

The sealing properties of RCF-containing products areused in a similar manner as RCF-containing products.

compared with those of RCF-substitute products at athermal cycle of 800ºC. Figure4 shows the results.
According to the figure, RCF-substitute products
appear to have equivalent or superior sealing

Summer 2018legal regulations do not apply to such gaskets. However,properties to those of RCF-containing products.
Regarding the design data of rubber-soaked woven
fabric gaskets, there were no changes. Therefore,rubber-soaked woven fabric gaskets can be used in asimilar manner as RCF-containing products. However,when only cloth and ribbon are used as textiles that
No. N510, N520, and others（RCF-substitute products）

Test Condition
Heat-cycle condition：600℃ × 15hours × 5cycles
Tightening force：‌Bolt fastening under a contactpressure equivalent to 70 MPa

No. N520（RCF-containing product）
No. N520（RCF-substitute product）

BeforeheatingCycle number
Figure3 Comparison‌of high-temperature characteristics
regarding No. N520

are not soaked with rubber, care should be taken
No. N314（RCF-containing product） Test Condition
Heating condition：800℃ × 15 hours
No. P-N314（RCF-substitute product） Tightening force：‌Bolt fastening under a contactpressure equivalent to 24.5 MPa

Leakage amount（Pa・m3/s）

Leakage amount（Pa・m3/s）

Figure2

Internal pressure MPa

Figure4‌Comparison of high-temperature characteristics
between No. N314 and P-N314
26No.35

Substitute Sealants for Refractory Ceramic Fiberregarding the maximum service temperature: that ofwoven fabric using the conventional RCF is 1,260ºC,
whereas that of woven fabric using BSF is 1,000ºC.
The temperature difference is due to BSF’s inferior
heat resistance to RCF. One inorganic fiber that canbe used above 1,000ºC is alumina fiber, but it is very
expensive. Thus, challenges remain in this field.

5. Gland packings

Figure6

No. N340M-F（RCF-substitute product）

Gland packings are widely used as sealed packings forSummer 2018

valves, rotary pumps, and various other devices. In aOn the other hand, BSF, which is used as an RCF-

gland packing, fibers are braided into a rope-like

substitute, is biosoluble. Therefore, under highshape. The cross section of a gland packing is square,temperature and dry conditions（dry heat）involving

and so the packing is highly versatile as a sealant andblast furnace gas or exhaust gas, BSF shows similar

is used for parts where some leakage is acceptableperformance as the conventional RCF-containing

but heat resistance is required. Examples include theproducts. However, durability in the presence of

coupling of exhaust-heat ducts of boilers and turbines

steam or hot water（wet heat）is unknown; care isand the fixing parts of manholes.

required.

Gland packings for these purposes are often used at

Although BSF will not break down immediately in thetemperatures above 400ºC, and so heat-resistant RCF

case of slight wetting, usage after adequate drying is

has been used for gland packings. However, RCF

recommended.

became subject to the Ordinance. Therefore, we used

Test Condition
Tightening contact pressure:
Mold cut-off
Fluid：Compressed air
Heating condition：15 hours × 500℃

BSF, which is not subject to the regulation, instead ofRCF, and started supplying the RCF-substitute glandpacking（Figures5 and 6）.
We compared the high-temperature characteristics ofNo. N340M（RCF-containing product）with those of
N340M-F（RCF-substitute product）at 500ºC. Figure7
shows the results. According to the figure, No.
N340M-F（RCF-substitute product）appears to haveequivalent or superior sealing properties to those of
No. N340M（RCF-containing product）.

Leakage amount（Pa・m3/s）

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No. N340M（RCF-containing product）
No. P-N340M-F（RCF-substitute product）

Loading internal pressure（MPa）

Figure7 Comparison of sealing properties at high temperatures

6. Conclusion
Sealants consist of combined materials with varying
characteristics including heat resistance, chemical
resistance, and high intensity to withstand various
challenging conditions. However, international
Figure527

No. N340G-F（RCF-substitute product）

regulations have been tightened to reduce theProduct Introductions

environmental burden and negative impacts on thehuman body, placing increasing restrictions on usable

7. Reference１）‌Japan High Temperature Insulation Wool Association,materials.
As a seal manufacturer, VALQUA will continue toHandling of ceramic-fiber products, revised edition

reduce the environmental burden and develop（January 2016）.

products that do not negatively affect the humanbody, thus contributing to customers’safety.

Masato Hamade
Corporate Research andDevelopment Group
Product Development DivisionⅠ

Summer 2018
No.35

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