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7/29/2019 Gasket Tornillos

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PART UG GENERAL REQUIREMENTS Fig. UG-34

ts ts

ts

ts t

ts

tf

d d

d

Yt

t tt

C= 0.17 or

C= 0.10(a)

C= 0.13

(d)

C= 0.33m

Cmin. = 0.20

(i)

C= 0.3[Use Eq. (2) or (5)]

(j)

C= 0.3[Use Eq. (2) or (5)]

(k)

C= 0.33

(h)

C= 0.30

C= 0.25

C= 0.75

C= 0.33 C= 0.33

C= 0.30 C= 0.30

(m)

(p)

(q)

(r) (s)

(n) (o)

(e) (f) (g)

C= 0.33mCmin. = 0.20

(b-2)

Continuationof shelloptional

Sketches (e), (f), and (g) circular covers, C= 0.33m, Cmin. = 0.20

See Fig. UW-13.2 sketches (a) to (g),inclusive, for details of welded joint

tsnot less than 1.25tr

See Fig. UW-13.2 sketches (a) to (g),inclusive, for details of outsidewelded joint

Threaded ring

30 deg min.45 deg max.

Seal weld

When pipe threads are

used, see Table UG-43

0.8tsmin.

3/4tmin.

ormin. t1 = tor tswhichever

is greater

Retainingring

rmin. = 0.375 in. (10 mm)for ts 1

1/2 in. (38 mm)

rmin. = 0.25tsfor ts 1

1/2 in. (38 mm)

but need not be greaterthan 3/4 in. (19 mm)

C= 0.17

(b-1)

Center of weld

Taper

Tangentline

r= 3tmin.

d

Y

tsts

t

ts ts

ts

t1

d

t

hG

ttddd

d

d d d

hG

d

Projectionbeyond weldis optional

Bevel is optional

45 deg max.

tw= 2trmin. nor less than 1.2tsbut need not be greater than t

tfmin. = 2ts

0.7ts0.7ts0.7ts

0.7ts

0.7ts

t

C= 0.30

C= 0.20 or 0.13(c)

Center of lap

Tangentline

r= 3tmin.

r= 3tfmin.

r= 1/4tmin.

t

t t t

ddd

dd

d

ttt

t

t

t

t

t

FIG. UG-34 SOME ACCEPTABLE TYPES OF UNSTAYED FLAT HEADS AND COVERS 01

The Above Illustrations Are Diagrammatic Only. Other Designs That Meet

the Requirements of UG-34 Are Acceptable.

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4.3.6-2 4.3 SHELL-AND- TUBE DESIGN CODES 4.3.6 TEMA Type AJS

(c) Order calculation

For a heat exchanger with a floating tubesheet, assuming

that the tube layout is known, it is advisable to design

the floating-head cover first. This will confirm if there

is sufficient space within the shell and outer tube limit

circle diameter to fit the required gasket. The shell,

channel, and shell cover cylinder thicknesses may then

be calculated. The remaining components may then be

designed at random. For this design, the selected tube

wall thickness is checked, followed by the design of the

flanges and end enclosures. The tubesheets and nozzles

calculations complete the calculations for components

subjected to pressure. Finally, the dimensions of the

nonpressure components are determined.

The units used for pressure are and for material

stresses are as specified in the nomenclature

(1 = 1 newton per square meter).

B. Floating-head cover

(a) Flange and dish

The floating-head cover is a spherically dished cover

designed to UA-6 (4)(b), Fig.

see also Sec. The minimum dish thickness is the

greater of the tube-side or shell-side requirements.

= tube-side corrosion allowance = 3 mm

= shell-side corrosion allowance = 3 mm

For internal pressure (tube side),

where P = = 500 L is the dish corroded inside

radius (mm), and is the maximum allowable stress =

121

Assuming that the shell-to-floating tubesheet,

radial clearance is mm and assuming a gasket width

of 13 mm (TEMA minimum = 12.7 mm), then the

flange corroded inside diameter

B = 635 + 13) = 599 mm

The flange uncorroded inside diameter is

Assume that the dish uncorroded inside radius is 0.75 X

593 = 445 mm; then

L = 445 + = 445 + 3 = 448 m m

Therefore

5 500 448=6X 121

For external pressure (shell side), the rules in

UG-33 apply. A thickness is assumed, and the procedure

appropriate to the shape of the formed end is followed.

From TEMA R-3.13, the minimum allowable corroded

plate thickness is 6.35 mm. Assume that tfhd = mm

and confirm this, using the procedure in

UG-33(c).

0.125 0.125

= maximum allowable design pressure

B ch(3)

From materials chart, Fig. UCS-28.2,

= 14 500 = 14 500 X 6.895

= 99 978

Therefore

a 99 978

This is less than the shell-side design pressure (2 000

therefore assume that 9 mm and repeat the

calculation.

factor A3

factor = 15 200 = 15 200 X 6.895

= 104 804

Therefore

104 804a 105

This is greater than the shell-side design pressure; there-

fore a corroded dish thickness of 9 mm is satisfactory.

= dish uncorroded thickness

15mm

= dish uncorroded inside radius

(b) Flange design

The flange design thickness is the greatest thickness of

that required for gasket seating, tube-side pressure, and

shell-side pressure, or from geometric considerations to

allow for sufficient crossover flow area. The positioning

of the dish relative to the flange centroid is an important

part of the design calculations; there are numerous

methods of approach. For this example the procedure

used is as follows.

1983 Hemisphere Publishing Corporation


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4.3.6-4 4.3 SHE LL- AND- TUB E DESI GN CODE S 4.3.6 TEMA Type AJS

18374Nm and = 121

18 374 X 702 + 599t==121 X 599 702 - 5 9 9

For crossover flow area, from TEMA R-8.12 the actual

crossover flow area is to be at least 1.3 times the flow

area through one tube pass. There are 468 tubes,

19.05 mm OD X 2.11 mm wall thickness, arranged infour tube passes.

Flow area/tube pass = (19.05 2 X 2.1

The total required crossover area is

The segmental area of the dish = 46 012

If the effect of the pass partition plates is neglected,

the area available under the dish for crossover flow per

pass is

46 012 X 0.5 = 23 006

If the dish is excluded, the depth of flange required

for crossover flow area per pass is

593 x 0.5

Obviously, even allowing for the dish, the gasket seat-

ing will require a greater thickness than that for cross-

over flow area.

Assume a corroded flange thickness of 57 mm and

position the dish at the back of the flange; check the

thickness for internal and external pressures.For internal pressure (tube side):

121

where

500 X X X

8 X 599)

121 X 599 702 599= 415.64

For external pressure (shell side):

S = = 121

where

2 000 X X X 8

8 X 599)

=121 X 599 702

1 566.62599

t = 8.00 + + 1 566.62 = 48.38 mm

Therefore, with the dish positioned at the back of

the flange, a corroded flange thickness of 57 mm is

satisfactory. The cover will have a pass partition plate

13 mm thick, tapered at one end to 10 mm to suit the

gasket web; see TEMA R-8.13. The flange will be re-

cessed to confine the gasket. The cover dimensions

are given in Fig. and a summary of the flange dimen-

sions is given in Table 11 (flange no. 6).

(c) Floating-head backing device

The backing device clamps the floating-head cover to

the tubesheet. There are various types; for this design

a single split ring is used, designed to UG-53(a).

The split ring is designed as if it were a solid flange

(without splits) using 200% of the greater of or

calculated in the mating flange design. From Tableis greater than for either the tube-side or

side operating conditions.

The effective thickness,

(7)

Shape constant,

B 599

Hence

Y = 12.31 from Fig. UA-5 1

18374Nm from Table 1

121 B = 599 m m

12.31 X 18 374 X 2=

121 x 599 x

There will be a recess (5 mm) deep to locate the spit

ring on the tubesheet. The dimensions of the backing

ring are given in Table 11 (flange no. and in Fig. 1.

C. Cylindrical shells

The minimum allowable wall thickness for cylindrical

shells is the greater of the or TEMA require-

ments; see also Sec.

The minimum thickness, exclusive of corrosion

allowance will be the greater thickness from the for-

mulas in UG-27.

For circumferential stress (longitudinal joints):

1983 Hemisphere Publishing Corporation


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4.3 SHELL-AND -TUBE DESIGN CODES 4.3.6 TEMA Type AJS 4 . 3 . 6 - S

2244

H

HOOLLEESS2244DDIIAA

Figure 1 Floating-head cover and backing device.

For longitudinal stress (circumferential joints):

For this example the weld examination is spot

throughout, thus the joint efficiency E = 0.85 for all

welded joints (see UW-12); Eq. (9) can therefore

be neglected. The calculations of cylinder thickness are

summarized in Table 2.

In practice, the selected plate thickness is not

necessarily the minimum allowable thickness rounded

up to the nearest millimeter. The availability of material

may be the deciding factor, or the designer may select

a thicker wall to increase the area available for reinforce-

ment at the nozzle locations. The channel will have pass

partition plates, of the same material, 13 mm thick,tapered at both ends to 10 mm thick to suit the webs of

the gaskets.

D. Tubes

The minimum allowable wall thickness is determined

from UG-31; see also Sec. The tube

dimensions are specified by the thermal designer. The

1983 Hemisphere I Corporation

wall thickness is usually the preferred gauge from TEMA

Table R, C, or B, -2.21. The tube length plays an im-

portant part in the thermal performance of the ex-

changer, so the length should not be altered without

the agreement of the thermal designer.

= tube outside diameter = 19.05 mm

tube wall thickness = 2.11 mm

= tube-side (internal) pressure = 500

= shell-side (external) pressure = 2 000

S = maximum allowable stress = 121

E = joint efficiency = 1

= tube inside radius = 2 X 2.11)

= 7.415 mm

For internal pressure the minimum allowable thick-ness is calculated using Eq. (8):

- - = 5 0 0 x

X 7.415= 0.031 mm

121 X 1.00 -0.6 X 500 X

For external pressure the rules in UG-28 are

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