ASME Section VIII div 2 2010. ASME Boiler and Pressure Vessel Code. Alternative Rules

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2010 SECTION VIII, DIVISION 2

4-265

4.13.11 Vent Holes

4.13.11.1 Vent holes shall be provided to detect leakage of the inner shell and to prevent buildup of

pressure within the layers as follows.

4.13.11.2 In each shell course or head segment, a layer may be made up of one or more plates. Each

layer plate shall have at least two vent holes 6 mm (0.25 in.) minimum diameter. Holes may be drilled radially

through the multiple layers or may be staggered in individual layer plates.

4.13.11.3 For continuous coil wrapped layers, each layered section shall have at least four vent holes 6 mm

(0.25 in.) minimum diameter. Two of these vent holes shall be located near each end of the section and

spaced approximately 180 deg apart.

4.13.11.4 The minimum requirement for spirally wound strip layered construction shall be 6 mm (0.25 in.)

minimum diameter vent holes drilled near both edges of the strip. They shall be spaced for the full length of

the strip and shall be located a distance of approximately

/tanR

from each other (where

is the mean

radius of the shell and

is the acute angle of spiral wrap measured from the longitudinal centerline, deg).

4.13.11.5 If a strip weld covers a vent hole, partially or totally, an additional vent hole shall be drilled on

each side of the obstructed hole.

4.13.11.6 In addition to the above, holes may be drilled radially through the multiple layers.

4.13.11.7 Vent holes shall not be obstructed. If a monitoring system is used, it shall be designed to prevent

buildup of pressure within the layers.

4.13.12 Shell Tolerances

4.13.12.1 Contact Between Layers

The following requirements shall be satisfied.

a) Category A weld joints shall be ground to ensure contact between the weld area and the succeeding

layer, before application of the layer.

b) Category A weld joints of layered shell sections shall be in an offset pattern so that the centers of the

welded longitudinal joints of adjacent layers are separated circumferentially by a distance of at least five

times the layer thickness.

c) Category A weld joints in layered heads may be in an offset pattern; if offset, the joints of adjacent layers

shall be separated by a distance of at least five times the layer thickness.

d) After weld preparation and before welding circumferential seams, the height of the radial gaps between

any two adjacent layers shall be measured at the ends of the layered shell section or layered head

section at right angles to the vessel axis, and also the length of the relevant radial gap in inches shall be

measured (neglecting radial gaps of less than 0.25 mm (0.010 in.) as non relevant). The gap area,

A ,

shall not exceed the thickness of a layer expressed in square inches. An approximation of the area of

the gap shall be calculated using Equation (4.13.2). The maximum length of any gap shall not exceed

the

inside diameter of the vessel. Where more than one gap exists between any two adjacent layers, the

sum of the gap lengths shall not exceed the inside diameter of the vessel. The maximum height of any

gap shall not exceed 4.8 mm (0.1875 in.). It is recognized that there may be vessels of dimensions

wherein it would be desirable to calculate a maximum permissible gap area, and also when cyclical

service conditions require it. This procedure is provided in paragraph 4.13.12.2 and may be used in lieu

of the maximum gap area given above, (see Figure 4.13.11).

2010 SECTION VIII, DIVISION 2

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Abh= (4.13.2)

e) In the case of layered spheres or layered heads, if the gaps cannot be measured as required in

paragraph 4.13.12.1.d, measurement of gap heights shall be taken through vent holes in each layer

course to assure that the height of layer gaps between any two layers does not exceed the gap

permitted in paragraph 4.13.12.1.d. The spacing of the vent holes shall be such that gap lengths can be

determined. In the event an excessive gap height is measured through a vent hole, additional vent holes

shall be drilled as required to determine the gap length. There shall be at least one vent hole per layer

segment.

4.13.12.2 Alternative to Measuring Contact between Layers During Construction

As an alternative to paragraph 4.13.12.1.d, the following measurements shall be taken at the time of the

hydrostatic test to check on the contact between successive layers, and the effect of gaps which may or may

not be present between layers.

a) The circumference shall be measured at the midpoint between adjacent circumferential joints, or

between a circumferential joint and any nozzle in a shell course. Measurements shall be taken at zero

pressure and, following application of hydrostatic test pressure, at the design pressure. The difference

in measurements shall be averaged for each course in the vessel and the results recorded as average

middle circumferential expansion,

e .

b) The theoretical circumferential expansion of a solid vessel of the same dimensions and materials as the

layered vessel shall be calculated from Equation (4.13.3). The acceptance criterion for circumferential

expansion at the design pressure is:

0.5

mth

ee≥ .

()()

1.7 2 2

ms ms

yms

PR t R t

ERt

−+

(4.13.3)

4.13.12.3 Rules for Calculating Maximum Permissible Gaps

The maximum number and size of gaps permitted in any cross section of a layered vessel shall be limited by

paragraphs 4.13.12.3.a and 4.13.12.3.b.

a) Maximum gap between any two layers shall not exceed the value of

h given by Equation (4.13.4):

0.55 0.5

⎛⎞

=−−

⎜⎟

⎝⎠

(4.13.4)

where,

3N for infinite cycles= (4.13.5)

N for a specified number of cycles

⎛⎞

⎜⎟

⎝⎠

(4.13.6)

with,

0.25 0.5

=+−

(4.13.7)

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2010 SECTION VIII, DIVISION 2

4-267

b) Maximum permissible number of gaps and their corresponding arc lengths at any cross section of a

layered vessel shall be calculated as follows.

1) Measure each gap and its corresponding length throughout the cross section.

2) Calculate the value of

F for each of the gaps using the following equation:

0.109

⎛⎞

⎜⎟

⎝⎠

(4.13.8)

3) The total sum of the calculated

F values shall not exceed the quantity

yoi

FNS

ERR

⎛⎞

−

=−

⎜⎟

−

⎝⎠

(4.13.9)

4.13.13 Nomenclature

A gap area.

b length of the gap between any two layers.

C equal to 3 mm (0.125 in.) radial clearance between the nozzle neck and vessel opening

finished opening in the wall

e theoretical circumferential expansion.

e average middle recorded circumferential expansion.

F gap value.

F total permissible gap value.

E Modulus of Elasticity for the layer material from Part 3 .

h gap between any two layers.

Poisson's ratio.

P design pressure of the vessel.

outside radius of the layer above where the gap is located.

inside radius of the vessel.

mean radius of the vessel.

outside radius of the vessel.

S stress amplitude from the applicable fatigue curve for the layer material from Annex 3.F .

S allowable stress for the layers from Annex 3.A at the design temperature.

S allowable stress for the inner layer from Annex 3.A at the design temperature.

S allowable stress for the layer material from Annex 3.A at the design temperature.

r equal to

(

)

min 0.25 ,3 0.125

tmm in⎡⎤

⎣⎦

r equal to 6 mm (0.25 in.) minimum

r equal to

(

)

min 0.25 ,19 0.75

tmm in⎡⎤

⎣⎦

t actual thickness of the head or tubesheet or for nozzle details equal to

[

]

min , 19 (0.75 .)

tmm in, as applicable.

2010 SECTION VIII, DIVISION 2

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act

t actual thickness of inner shell or inner head.

t equal to the larger of 6 mm (0.25 in.) or

[

]

0.7 min , 19 (0.75 .)

tmm in

eff

t effective thickness of inner shell or inner head.

t thickness of the head at the head-to-cylinder joint.

t thickness of the layer.

t nominal thickness of the nozzle wall less corrosion allowance

t total wall thickness of the layered vessel.

Y offset.

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2010 SECTION VIII, DIVISION 2

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4.13.14 Figures

(a) Concentric Wrapped

Note (1)

Note (3)

Note (2)

(b) Coil Wound

Note (1)

Note (3)

Note (2)

Note (1)

Note (3)

Note (2)

(d) Spiral Wrapped

Note (1)

Note (4)

Note (2)

Note (5)

Note (6)

Notes:

1. Inner shell

2. Dummy layer (if used)

3. Layers

4. Shell layer (tapered)

5. Balance of layers

6. Gap

Figure 4.13.1 – Some Acceptable Layered Shell Types

2010 SECTION VIII, DIVISION 2

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Note (1)

Segmental

Note (2)

Note (3)

Note (1)

Note (2)

Note (3)

(a)

Press Fit

(c)

(b)

Note (1)

Note (2)

Note (3)

(b)

(d)

Note (1)

Note (2)

Note (3)

Notes:

1. Inner head

2. Dummy layer (if used)

3. Head layers

Figure 4.13.2 – Some Acceptable Layered Head Types

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2010 SECTION VIII, DIVISION 2

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Details Of Taper For Layers 16 mm

(0.625 in.) Or Less In Thickness

(b)

Weld Line (Category B)

For Layers Over 16 mm (0.625 in.)

Thickness

(a)

Taper Line

min.

Weld Optional

0.7 t

min.

Weld Line (Category B)

Optional Weld Line (Category B)

For Layers 16 mm (0.625 in.) Or Less

In Thickness

(d)

For Layers Over 16 mm (0.625 in.)

Thickness

(c)

For Layers 16 mm (0.625 in.) Or Less

In Thickness

(f)

For Layers Over 16 mm (0.625 in.)

Thickness

(e)

Weld Optional

2/3 t

Min.

or Y

3:1 Taper Min. See Detail

Sketch (b)

3:1 Taper. See Sketch (b)

Note: Taper May Be Inside

Or Outside Or Both.

3:1 Taper Min.3:1 Taper Min.

Notes:

3aY≥ where a is the required length of the taper and Y is the offset.

2. The length of the required taper may include the width of the weld.

3. The transition may be on either or both sides.

Figure 4.13.3 – Transitions of Layered Shell Sections

2010 SECTION VIII, DIVISION 2

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Tack Weld

Backing Strip

(g) Butt Girth Welds

Tack Weld

Backing Strip

(e)

(f)

(d)

(c)

Dummy Layer

(b)

(a)

Dummy Insert

Figure 4.13.4 – Some Acceptable Welded Joints of Layered-To-Layered and Layered-To-Solid

Sections

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2010 SECTION VIII, DIVISION 2

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a > 3 Y

0.7 t

min.

3 t

Min.

Hemispherical

Heads Only

Taper Line

Tangent Line

Details Of Taper For

Layers 22 mm (0.875 in.) Or Less In

Thickness

(b-1)

For Layers 16 mm (0.625 in.)

Thickness

(a)

Weld

Butt Weld Line

(Category A)

2/3 t

Min. For

Chamfered Layers

Details Of Taper For

Layers 16 mm (0.625 in.) Or Less In

Thickness

(b-3)

Details Of Taper For

Layers 22 mm (0.875 in.) Or Less

In Thickness

(b-2)

0.7 t

min.

3 t

Min.

Taper Line

a > 3 Y

Butt Weld Line

(Category A)

Tangent Line

Hemispherical

Heads Only

0.7 t

min.

3 t

Min.

Taper Line

Figure 4.13.5 – Some Acceptable Solid Head Attachments to Layered Shell Sections

2010 SECTION VIII, DIVISION 2

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0.7 t

min.

3 t

Min.

Butt Weld Line May Be At Or Below

Tangent Line Depending On Code

Requirement For Type Of Head And Weld

a > 3 Y

Tangent Line

For Layers Over 16 mm (0.625 in.)

Thickness

(c)

Details Of Taper For Layers Over

16 mm (0.625 in.) Thickness

(d-1)

Inside

Inner Shell

For Layers Of Any Thickness

(f)

a > 3 Y

Butt Weld Line May Be At Or Below

Tangent Line Depending On Code

Requirements For Type Of Head

And Weld

Tangent Line

a > 3 Y

For Layers 16 mm (0.625 in.) Or Less In

Thickness

(e)

Permissible For Layers

22 mm (0.875 In.) Or Less In Thickness

(d-2)

Weld Line

Welds Optional

Taper Line

a > 3 Y

2/3 t

Min.

Welds Optional

Notes:

In Sketch (e),

Yt≤ shall be satisfied, in Sketch (f), 0.5

≤

shall be satisfied

2. In all cases, 3aY≥ shall be satisfied. The shell centerline may be on either side of the head centerline

by a maximum distance of

()

0.5

tt− . The length of the required taper may include the width of the

weld.

3. The actual thickness shall not be less than the theoretical head thickness.

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