FRP flange design (Part 1): Necessary strength and optimum ...

GPI Journal Vol. 2, No. 2

187

GPI Standards Committee

GPI7G-039 Published on Dec 27, 2016

Regular Article

Received on Aug 18, 2016.

Revised on Sep 26, 2016.

Accepted on Oct 9, 2016.

Featured Technology

FRP flange design (Part 1): Necessary strength and optimum structure

Yoshinori NISHINO1, Allen S CHIU2, Shinichi TAMURA1,

Masaki NISHINO1, Taiga TATSUMI1 1NBL Technovator Co., Ltd., 2NOV FGS Singapore (Pte) Ltd.

Abstract: Generally from the course of corrosion-resistant FRP pipe has been developed as an alternative material

of the corrosive metal pipe, combination with existing metal flange is required. Basically, by mating surfaces unified,

common commercialization can be achieved. So, after standards of PCD/ hole diameter of the bolt, a flange inner

and outer diameters are defined, from the specifications of unevenness of the flange contact surface, waterproof

function, applied bolts/ number, and the allowable pressure, product design is carried out.

Keywords: corrosion-resistant materials, FRP, flange, strength design of flameproof, sealed

1. Introduction

Fittings necessary to the piping is flange. Flange is made

from a metallic material or FRP (Fiber Reinforced Plastic)

material. The present study, optimal product design research

has been carried out to the reference flange of ASA150 and

ASA300 that the most commonly and frequently used in size

from the product which outer diameter of 25 mm up to about 3

m. As a result, as compared with the conventional FW molding

method or hand-layup molding method, the product was about

50% lighter, the quality was improved about twice. It should be

noted that the product introduced here is the write-once that it

is a pending patent application preparation.

In general flange molding, large compounds that the most

popular is FW molding method. Compression molding, such as

SMC is less than 10 inches of small size are common. This

study describes the optimum design method for flange products

with the latest molding technology of the new centrifugal

molding method (NBL company development called CW

method) and NMC molding method (NBL company

development) that the bulk of the material was compression-

molded.

2. Basic design conditions

Flange design basics bonded mains with the tapered working

surface is selected from the following conditions. (ASA150,

ASA300, JIS10 / 16K, such as international standards apply)

Figure 1 is a flange made in the thick of the hat-shaped called

Vanstone flange.

Its feature is simple and heavy, and shear stress of its

adhesive surface to tube surface shown in the figure will be

concentrated to the end since the rigidity balance of the joint

surface works, its adhesive strength should be weak. Figure 2

is called contact molded flange that plate thickness of its flange

surface is thin.

Its feature is that shear forces should be smoothed and

adhesive strength should be stronger since it is light we 1eight

and the adhesive surface is made of a scarf wrap shape.

Generally, it is said that corrosion resistant FRP pipe [1] have

been developed as a substitute material for corrosive metal tube,

it should be demanded to be used in combination with the

existing metal flange. Basically, the mating surfaces is to

become a possible common commercialized by being

standardized and unified, product design starts from ②③

specification after ① criteria is stipulated.

Ｆｉｇ 1 Vanstone Flange

Y. Nishino et al. / GPI Journal 2(2) (2016) 187-192

Global oil & gas Pipe Institute 188

«Flange Basic Specifications»:

① PCD of bolt · hole diameter, flange ID and OD

② flange contact surface of the irregularities, watertight

function

③ applied bolts and number, allowable breakdown

pressure

«Seal of the flange surface»:

Figure 3 shows a structure for joining using the O-ring on the

inside back-up ring and the groove over blanking the structure

of the new development.

Both have a seat surface seal structure that can be shared with

metal flange. The former is an existing structure, the latter is a

single & double O-ring that can be used in combination glove

was developed to common functions in the various flange

surfaces. A new O-ring seal (patent pending preparation).

Feature is that it can be applied to any flange surface, acceptable

breakdown pressure Max 10MPa of ASA150 / 300 is satisfied.

At the same time the seat surface pressure load is smaller than

a gland packing type, shown in Figure 4. Face seal structure of

the place where the packing over the flange entire surface of a

large bolt load burden for the seal. Small area gland packing of

the inner surface side open glove is small bolt load burden for

the seal.

«Flange of production»:

The system for manufacturing flanges are roughly 3 pattern.

Figure 5 shows an overview in the illustration. There is a most

primitive type hand lay-up molding method to perform, such as

drilling in the secondary processing after lamination of curing

the FRP in hand, in addition, the resin and the short glass fiber

were put in the rotary-type mold and be produced by centrifugal

casting called CW molding method [2, 3], in the filament

winding, there is a method of machining finishing such as hole

in the secondary processing followed by FW molded into a

mold of the outer surface.

In this study, we describe

CW molding method which is

most productive such as

possible one piece per one hour

(1-type) in the large flange with

fully automatic, which is

shown in Figure 6. In addition,

this is to report on the outcomes

of performing product design,

which was the basic O-ring

specification of contact flange

that material cost is inexpensive.

3. Basic design of the flange

Figure 7 is a flow diagram of a flange design. Since flange

provided in the conduit, performs enhancement layer design to

ensure acceptable distortion design of the corrosion-resistant

layer and corrosion-resistant layer needed to ensure the cost and

pipe design and durability further reduce the necessary

functions from quality assurance.

New 0-ring seal

Back up ring 0-ring seal

Ｆｉｇ 3 ０-ring seal flange

Grand packing seal New groove grand packing seal

Fig 5 ASA 150/Maxφ3.5m－300/Ｍａｘφ１m,

Production System

Fig.６ Contact molded

flange


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Furthermore, for the total cost reduction, it is necessary to

adhere to the design conditions of 4 items shown in Figure 7.

From design basic conditions, for example standard flange

such as ASA150 is applied tube ID and flange OD and bolts

have been established. Therefore, it should be started from

structural design to reduce the load on the flange bolts required

to seal the flange surface in order to increase the first

performance.

3.1 O-ring seal design

Figure 8 is a significant seal theory of the smallest O-ring of

the load. O-ring, if added to sealing pressure Pci the seat surface

required initially, by automatically own deformation required

seal surface pressure Pc (about 1.5Ps fold pressure load) in

proportion to the pressure load Ps, it is maintained. Then, O-

ring and gasket is a theory of history that stability is obtained in

the seat surface seal of the small area on the same principle.

Since the only drawback is made from the material is weak

rubber, short-term maximum pressure is about 20MPa and low.

However, it is necessary and sufficient for the pipe flange.

3.2 Flange strength design

Load applied by the internal pressure load P1 of the flange,

in the axial direction shown in Figure 9, axial force Fs generated

by a seal that acts on the tube by the clamping force F and the

internal pressure by the flange bolts and each stress of axial

force F-Fs acting on the tube by the internal pressure is

generated.

Bolt maximum load F requires a stress relief, such as a bolt

washer equal to or less than the allowable compressive stress

200MPa of FRP flange.

Various stress generated in the flange structural member,

the axial pulling force on the tube via a junction surface

between the bolt load, the tensile force in the circumferential

direction due to internal pressure, resulting from the combined

load due to compression force in the thickness direction.

Adhesive shear stress is generated on the weakest member of

joining surface. This shear stress is precisely consists frictional

force between the laminated and the adhesive shearing force

Ｆｉｇ 4 ＧｒａｎｄｐａｃｋｉｎｇＳｅａｌｆｉａｎｇｅ

Ｆｉｇ 7 Strength of Flange Design System４）

Ｆｉｇ 8 Basic Mechanism Design of Rubber Seal4）

Ｆｉｇ 9 Strength Design of Flange

Ｆｉｇ 10 Adhesive Strength of Joint System &

Adhesive Length7）



between materials. Figure 10 shows the characteristics.

Effective bonding length is eight times the length of the tube

thickness at the scarf wrap connection structure in the 1/16 taper

is ideal bonding length. Subject of the other member is a

bending stress. From the fact that these analysis and theoretical

calculation method has already become apparent to by GPI

technology standard by the author, the details will be omitted.

Formulas required for strength design is shown in Figures 9 and

12.

3.3 Inner surface peeling (prevention of corrosion

degradation)

Structural considerations of the bonding flange, shown in

Figure 11, since the secondary bonding or the like thin

laminated resin (Mylar) there is a peeling of the laminate by the

high-speed running water. The flow rate of the Mylar peeling

prevention is usually not more than 3m / s, cavitation, erosion,

where corrosion environment deteriorates, the lamination

structure shown in Figure 13 is antiaging. The thickness of the

case corrosion-resistant layer criteria PS-15-69 is valid.

Mylar is due to decrease by incomplete curing and in

strength of the bonding portion. If these measures are cleared,

allowable flow rate is applied to 6 m / sec. Incidentally, Figure

13 shows the relationship between the allowable flow rate and

the laminated thickness of the resin. They are already published

written by authors that details of technology standard that got

from a lot of experience will be omitted.

3.4 Stress calculation

Performing stress calculation flange structural member is

shown in Figure 9. Figure 11 shows a theoretical calculation

formula for the mechanical properties to be used in the design

of the laminated material usable in CW molding. It can be used

for the simulation of the laminate strength design of the

materials used. In other words, it can be calculated allowable

strength of the laminate material to the design of the selected

material. Since it is significant theoretical formula that has

already been published by authors, omitted in this paper. Figure

Ｆｉｇ 11 Position and Mechanism of Internal7）

Delamination for Transfer Line

Fig 12 Approximate equations for material constant applied for the design of reinforced layer6）

Ｆｉｇ 13 Delamination Characteristics of

Secondary Lamination and Design for Delamination

Prevention7）


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14 is an approximate theoretical formula and the approximate

stress analysis model of the flange structure. Allowable strength

of the design laminate material according to Figure 11 to select

the calculated value of the generated stress shown in Figure 9,

optimal choice value of commodity durability performance

(AWWA: Sf; 5 times, GPI: Life 10 year (Sf: 3 times), Life 40

year (Sf: 5 times)) is obtained.

4. Structure of optimal FRP flange

Optimum FRP flanges are required to share with metal

flanges which is frequently used, such as ASA150 / 300,

JIS16K. Contact flange is better that its bolt length is short from

the cost and the amount of material is less. Single & double ring

of the new O-ring system that the seat surface can be shared

with the metal flange is recommended to seal format that is the

least the seat ring area, less bolt burden of the necessary load.

Since stress that occurs is a multi-directional to join the radial

direction from the load bending the circumferential direction

and the axial direction, to the laminated material consulting

these flanges, the glass fiber to be applied in the short-fiber,

high-strength multi-end roving of 7 to 25 mm are suitable.

In other words, this shows the new O-ring system shown

in Figure 3. The flange of these selected design structure with

the exception of the grinding processing of secondary adhesive

surface, for all that can be integrally molded is a centrifugal

casting method using a centrifugal molding. Using the fast

curing vinyl ester resin matrix resin, contact flanges optimally

designed can be produced at the fastest.

On the other hand, here it is omitted the description of the

detailed design result, if flange bolts to be used by the general

steel (yield point is 200MPa) to use, for example, in the

ASA150 standard flange, and to apply the AWWA durability

criteria, apply pressure application diameter 3MPa can design

up to about 3.5 m. In ASA300 standard applied pressure can

design application diameter 5MPa up to about 1m. Furthermore,

by using about twice the high-strength bolt, is also allowable

breakdown pressure is doubled in proportion, more high tensile

bolt is not applicable to exceed an allowable compressive

strength of the FRP laminate material.

5. Conclusion

The results obtained in this study, the standard in the FRP

flange ASA150 class of the pipe flange standard about 3.5 m,

in the 300 class can be designed up to about 1 m. Optimal design

results is O-ring seal of contact type flange. Fit production

method is suitable is produced by centrifugal casting. However,

small diameter (about 400 ㎜ below) the combination of the

compression molding method is effective. Use material is glass

fiber and fast curing of the vinyl ester resin of short fiber is

suitable, the epoxy resin is also possible. If you change the

flange bolts in high tension, breakdown pressure of the same

materials used in the same design conditions can be designed

up to 2 times at the maximum. The results of this research

conventional design, as compared to products made in the

manufacturing process, it is possible to obtain about 50% less

product weight(material cost) about twice the allowable

breakdown pressure (performance), and the production rate it

became clear that take about 10 times higher.

In the second report, we will describe in detail the specific

design and development products. .

References

[1] Allen S. Chiu, Performance Requirements of FRP

Tubular for Oil & Gas Production, Japan Reinforced

Plastics, Vol. 33, No. 3, pp. 97-103 (1987)

[2] Masaki Uhara, Taiga Tatsumi, Masaki Nishino, Shinichi

Tamura, Yoshinori Nishino, Study on the production of

the flange by the centrifugal forming method (Part 1),

GPI Journal Vol. 1, No. 2, pp. 262-267 (2015).

[3] Masaki Uhara, Taiga Tatsumi, Masaki Nishino,

Shinichi Tamura, Yoshinori Nishino, Study on the

production of the flange by the centrifugal forming

method (Part 2), GPI Journal Vol. 1, No. 2, pp. 268-273

(2015).

[4] Yoshinori Nishino, Merits of and design method for

long-distance FRP piping, The Piping Engineering,

H10‐01A．Vol. 30, No. 5．Pp. 131-138 (1988).

[5] Takashi Shimosakon, Shinichi Tamura, Yoshinori

Nishino，GPI standard Corrosion FRP High Pressure

Pipes for Oil & Gas Well (Design standard of GPI

standard Piping Joint，The Piping Engineering，Vol. 56,

Ｆｉｇ 14 Calculation of Flange thickness２）



No.9，pp. 17-25 (2014).

[6] Takashi Shimosakon, Masaki Uhara, Taiga Tatsumi,

Shinichi Tamura, Yoshinori Nishino, Design Method of

FRP Pipe for Oil Well Frontier. International Journal of

Oil, Gas and Coal Engineering. Vol. 3, No. 1, pp. 1-12

(2015).

[7] Yoshinori Nishino, Construction method of secondary

bonding joint of fiber reinforced plastic pipe, Adv.,

Composite Material, Vol. 1, No. 4, pp. 277-290 (1991)ʾ

ⓒVSP1991

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