Using KHK to Analyze Seismic Conditions - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II Version
12

KHK is the High Pressure Gas Safety Institute of Japan, an independent organization. KHK creates and issues technical standards for designing plant infrastructure against seismic loading.

CAESAR II addresses KHK standards within the Seismic Wizard in the piping input. You can use the Seismic Wizard to calculate a seismic load, which is expressed in units of acceleration due to gravity (g).

When analyzing seismic conditions, you should calculate the support movement and ground liquefaction according to KHK seismic standards and the support configuration and define those values into the software.

KHK Level 1

Level 1 assesses conditions in the likelihood of a probable strong earthquake during the life of equipment. The goal is for the plant or facilities to remain safe without plastic deformation and without leakage.

KHK Level 1 evaluation requires the following stress types

K1P

The K1P stress type defines the primary longitudinal stress for the HPGSL and JPI piping codes. The longitudinal stress is due to pressure, weight, and design seismic force (g-load on piping).

For the equations and allowables for K1P, see International Code Stresses in the CAESAR II Quick Reference Guide.

CAESAR II treats the K1P stress type as an occasional (OCC) stress type for other piping codes.

K1SR

The K1SR stress type defines the secondary cyclic stress range for the HPGSL and JPI piping codes. The cyclic stress range is due to the design seismic force (g-load on piping) and support movement.

For the equations and allowables for K1SR, see International Code Stresses in the CAESAR II Quick Reference Guide.

CAESAR II treats the K1SR stress type as an expansion (EXP) stress type for other piping codes.

KHK Level 1 Example

Load Case

Stress
Type

Combination
Method

Condition

L1

W+T1+P1

OPE

NA

Typical operating load case

L2

W+P1

SUS

NA

Sustained load case

L3

W+T1+P1+U1

OPE

NA

Operating condition with inertial seismic force (g)

L4

W+T1+P1+U1+D1

OPE

NA

Operating condition with inertial seismic force (g) + relative support movement

L5

L3-L1

OCC

Algebraic

Inertial seismic force (g)

L6

L4-L1

OCC

Algebraic

Inertial seismic force (g) + relative support displacement

L7

L2+L5

K1P

Scalar

Sustained condition + inertial seismic force (g)

L8

2L6

K1SR

Algebraic

Stress range including inertial seismic force(g) + relative support movement

Different loading directions may require more elaborate load cases.

KHK Level 2

Level 2 assesses the strongest possible earthquake during the life of that equipment. This earthquake has an extremely low probability of occurrence. The goal is for the plant or facilities to remain safe without any leakage, but with plastic deformation of piping allowed. KHK Level 2 requires consideration of ground distortion by possible soil liquefaction, in addition to ground acceleration and support displacement.

In a piping system under extreme earthquake conditions (such as defined by KHK Level 2), the pipe bends go into the plastic range before the straight pipe becomes plastic. Level 2 incorporates the bend plasticity in the solution process by applying equivalent elastic flexibilities. This solution is performed in an iterative way, with the opening or closing of each bend evaluated at the end of each iteration. If the bend angle changes more than the prescribed limit, the analysis modifies the bend stiffness to simulate plasticity and reanalyzes for that particular iteration. This process continues until the solution converges for that load case. The converged bend angle is then compared to the allowable bend angle to check failure criteria. The software reports this data in a special bend report.

Due to the iterative solution required to address bend plasticization, the software limits the KHK 2 load cases to basic load combinations.

KHK Level 2 evaluation requires the following stress types. You may need to construct multiple load cases to implement these conditions.

K2P

The K2P stress type defines the primary longitudinal stress for the HPGSL and JPI piping codes. The longitudinal stress is due to internal pressure, weight, and seismic force (g-load on piping).

For the equations and allowables for K2P, see International Code Stresses in the CAESAR II Quick Reference Guide.

CAESAR II treats the K2P stress type as an occasional (OCC) stress type for other piping codes. The software sets the allowable to 0 for other piping codes due to the extreme nature of the loading.

K2SA

The K2SA stress type defines secondary cyclic stress amplitude for the HPGSL and JPI piping codes. The stress amplitude is due to seismic force (g-load on piping) and support movement. You should use K2SA for secondary amplitude load cases.

For the equations and allowables for K2SA, see International Code Stresses in the CAESAR II Quick Reference Guide.

CAESAR II treats the K2SA stress type as an expansion (EXP) stress type for other piping codes. The software sets the allowable to 0 for other piping codes due to the extreme nature of the loading.

K2SR

The K2SR stress type defines the secondary cyclic stress range for the HPGSL and JPI piping codes. The cyclic stress range is due to seismic force (g-load on piping) and response displacement. You should use K2SR for secondary range load cases.

For the equations and allowables for K2SR, see International Code Stresses in the CAESAR II Quick Reference Guide.

CAESAR II treats the K2SR stress type as an expansion (EXP) stress type for other piping codes. The software sets the allowable to 0 for other piping codes due to the extreme nature of the loading.

K2L

The K2L stress type defines liquefaction for the HPGSL and JPI piping codes. Liquefaction causes the angular displacement corresponding to a maximum equivalent plastic strain of 5% (in degrees).

For the equations and allowables for K2L, see International Code Stresses in the CAESAR II Quick Reference Guide.

CAESAR II treats the K2L stress type as an expansion (EXP) stress type for other piping codes. The software sets the allowable to 0 for other piping codes due to the extreme nature of the loading.

Summary of Stresses and Allowables for KHK Level 2

Stress Type

OPE

Earthquake

Allowable

P

W

T

U

D

K2P

ü

ü

ü
(Inertia)

Bend: qa=1.14/h0.46

Others: 2S

K2SA

ü
(Inertia)

ü
(Support Structure)

Amplitude: Plasticity-2%

Bend: qa=1.14/h0.46

Others: 2Sy

K2SR

ü
(Inertia)

ü
(Support Structure)

Range: Plasticity-4%

Bend: qa= 2x1.14/h0.46

Others: 2x2Sy

K2L

ü
(Ground Displacement/
Liquefaction)

Range: Plasticity-5%

Bend: qa=2.43/h0.46

Others: 4Sy

KHK Level 2 Example

Load Case

Stress
Type

Condition

L1

W+T1+P1

OPE

Typical operating load case

L2

W+P1

SUS

Sustained load case

L3

W+T1+P1+U1

K2P

Operating condition with inertial seismic force (g)

L4

U1+D1

K2SA

Stress amplitude including inertial seismic force (g) + & relative support displacement

L5

D2

K2L

Ground displacement (liquefaction)

You can also construct a range case to use the K2SR stress type, as shown in following example. In this example, the range is twice the load amplitude. You can add this load case to the load case set in the previous example.

Load Case

Stress
Type

Condition

L6

2U1+2D1

K2SR

Secondary stress range including inertial seismic force (g) + & relative support displacement

Different loading directions may require more elaborate load cases.