External Pressure Applied Case of KEPIC/ASME Code Applied Case of KEPIC/ASME Code KEPIC/ASME Joint...

External Pressure Evaluation Criteria and Applied Case of KEPIC/ASME Code

KEPIC/ASME Joint Seminar Jeju, Korea

September 5, 2017

Nuclear Business Group

Tae-Jung Park

Table of Contents

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I. Introduction

II. Requirements of MNB-3100 & 3200

III. Evaluation of Allowable External Pressure

IV. Discussion of KEPIC MNB-3221.4

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The rules of KEPIC MNB cover the requirements for strength and pressure

integrity of items in the Safety Class 1 component, the failure of which would

violate the pressure retaining boundary.

Since most of detailed requirements mainly focus on the internal pressure

loading which the pressure vessel withstands, the design criteria for external

pressure loading might be not well established as much as internal pressure

loading.

For example, allowable limit only for test condition provides an alternative

criteria for external pressure such like lower bound both by collapse and elastic

instability pressure.

The application case of alternative criteria is presented and discussed.

I. Introduction

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3100 GENERAL DESIGN

3110 LOADING CRITERIA

3120 SPECIAL CONSIDERATIONS

3130 GENERAL DESIGN RULES

3131 Scope

3132 Dimensional Standards for Standard Products

3133 Components Under External Pressure

Applicable to all kinds of component. The design Sub-article for the specific

component provides rules applicable to that particular component.

In case of conflict between MNB-3130 and the design rules for a particular component, the component design rules govern.

Rules are given for determining the stresses under external pressure loading in spherical and cylindrical shells with or without stiffening rings, and tubular products consisting of pipes, tubes, and fittings.

The design of cylindrical shells and tubular products subjected to loadings that produce longitudinal compressive stresses.

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3200 DESIGN BY ANALYSIS

3210 DESIGN CRITERIA

3220 STRESS LIMITS FOR OTHER THAN BOLTS

3230 STRESS LIMITS FOR BOLTS

3221 Design Loadings

3222~3 Level A, B Service Limits

3224 Level C Service Limits

3225 Level D Service Limits

3226 Testing Limits

3221.4 External Pressure MNB-3133 apply

No Requirement

3224.2 External Pressure - The permissible external pressure shall be taken as 120% of MNB-3133.

The permissible external pressure is 150% of MNB-3133 [Appendix F-1331.5(b)].

3226(4): The external pressure shall not exceed 135% of the MNB-3133.

Alternatively, applied up to 80% of the lower of the collapse or elastic instability pressures.

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MNB-3228 Applications of Plastic Analysis

Code Description of Requirements

MNB-3228.1 Limit

Analysis

If the loadings do not exceed two-thirds of the lower

bound collapse load, the limits on General Membrane

Stress Intensity (MNB-3221.1), Local Membrane Stress

Intensity (MNB-3221.2), and Primary Membrane Plus

Primary Bending Stress Intensity (MNB-3221.3) need not be

satisfied.

MNB-3228.2 Experimental

Analysis

If the loadings do not exceed two-thirds of the test

collapse load, the limits on General Membrane Stress

Intensity, Local Membrane Stress Intensity, and Primary

Membrane Plus Primary Bending Stress Intensity need not

be satisfied.

MNB-3228.3 Plastic

Analysis

If the loadings do not exceed two-thirds of the plastic

analysis collapse load, the limits on General Membrane

Stress Intensity, Local Membrane Stress Intensity, and

Primary Membrane Plus Primary Bending Stress Intensity

need not be satisfied.

For primary stress limits

caused by such as design

condition loadings,

applications of plastic

analysis and experiment

is allowed.

Primary stress limits may

be defined by lower

bound collapse load, test

collapse load, and plastic

analysis collapse load.

Safety factor is 1.5 for

primary stress limits by

application of plastic

analysis and experiment.

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MNB-3133 Components Under External Pressure

2. Read the value of factor A.

3. Read the value of factor B.

4. Calculate the Allowable External Pressure

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3 /a

o

BP

D T

1. Determining the Ratios.

, o

o

L D

D T

Determining the stresses under external pressure loading in spherical and cylindrical shells, and tubular products.

Charts for determining the stresses are given in KEPIC-MDP, Appendix VIII.


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* The collapse pressure stands for the lower bound limit load based on limit theorem. ** Elastic instability pressure represents elastic buckling load for hollow cylinder.

MNB-3226(4) Testing Limits

Classification Detailed Description

Fundamental The external pressure shall not exceed 135% of

the value determined by the rules of MNB-3133.

Alternative

Alternatively, an external hydrostatic test

pressure may be applied up to a maximum of

80% of the lower of the collapse* or elastic

instability pressures** determined by analysis or

experimental procedures (MNB-3228 and MNZ

Appendix II) including consideration of allowable

tolerances. If a collapse analysis is performed, it

shall be a lower bound limit analysis assuming

ideally elastic-plastic material ~.

MNB-3226(4) consists

of two independent

parts; fundamental and

alternative.

Alternative rule

provides the guideline

of external test

pressure limit by a

lower bound limit load.

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MNB-3226(4) Alternative Requirement

2(1 )

o

y

D E

t

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MNB-3226(4) Fundamental Requirement

•Determining the factor A - Enter Fig. G in KEPIC-MDP, App. VIII at the values of L/Do and Do/t - A = 0.003

STEP 2

•Determining the factor B (Sy=35 ksi) - Using the value of A, enter the Figure 4 in KEPIC-MDP, App. VIII - B= 11.0 ksi

STEP 3

•Calculate the maximum allowable external pressure.

STEP 4

1.35 41030

3 /a

BP psi

Do t

STEP 1

•Assume a value for t (t = 0.039 in) •Determine the ratios - L/Do>> 50, Do/t = 19.2

B = 11.0 ksi

Sy = 35 ksi

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Load Multiplier

λ=10515 λ=10730 .. λ=27407 ..

Elastic Instability

Pressure (psi) 10515 psi 10730 psi .. 27407 psi ..

Shape of Tube

.. ..

Min. Elastic Instability Pressure = 10515 psi.

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3% Ovality 2409 psi

Ovality Max. δ (inch)

Ovality Max. δ (inch)

1 % 0.00172 5 % 0.00442

2 % 0.00250 8 % 0.00475

3 % 0.00330 10 % 0.00523

1% Ovality 3168 psi

8% Ovality 1640 psi

10% Ovality 1444 psi

2% Ovality 2746 psi

5% Ovality 2042 psi

Low

er

Bound C

ollapse

Pre

ssure

(p

si)

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* Offshore Standard, DNV-OS-F101, Submarine Pipeline Systems, October 2010, Det Norske Veritas

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@3% Ovality Tube

1000 psi 1840psi

Lower bound collapse pressure is less

than the elastic instability pressure.

Consequently the alternative allowable

limit is 1927 psi.

Lower bound collapse pressure = 2409 psi under statically-equilibrium condition.

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IV. Discussion of KEPIC MNB-3221.4

Current Requirement Proposed Requirement

The provisions of MNB-3133 apply.

The provisions of MNB-3133 apply. External design

pressure may be alternatively applied up to a maximum

of two-thirds of the lower of the collapse or elastic

instability pressures determined by analysis or

experimental procedures including consideration of

allowable tolerances. If a collapse analysis is performed, it

shall be a lower bound limit analysis assuming ideally

elastic-plastic material ~.

MNB-3133 gives a conservative allowable external pressure for such geometry of low D/t. In addition, it is unreasonable considering the dominant failure mode.

For allowable external pressure, the requirement for test condition only includes the alternative limit by application of MNB-3228.1 but the allowable external pressure for design condition shall be determined only by MNB-3133.

For design condition, it would be reasonable to allow the identical approach to test condition.

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Thank you

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