C2 CAU Express B31.3

CAESAR II

Recent changes in ASME B31.3

and their implementation in

CAESAR II

Recent B31.3 Updates

� Cyclic factor in allowed expansion stress range

� Longitudinal stress due to sustained loads

� Allowed stress for occasional loads

� Appendix P

� Appendix S

� Weld joint strength reduction

� B31E

� Unless indicated otherwise all ASME B31.3 references are to the 2010 Edition

A Note on the Code Edition and

the Current CAESAR II Version

� CAESAR II Version 2011 was released on November 22, 2010

� ASME B31.3 – 2010 Edition was issued on March 31, 2011

� CAESAR II 2011 does not directly reference B31.3 – 2010

Expansion Stress Range

� Expansion stress range must be less than SA

� SA is defined in equations (1a) & (1b)

� SA is a function of the cyclic factor f


� The definition of f has changed

A Plot of f


� Changes to high and low cycle factors – f

� Equations put in and simplified table removed

� f factors extended from 2,000,000 cycles to an unlimited number of cycles

� f factors of greater than 1 permitted for less than 7,000 cycles

Extension to Lower Cycles

� An increase in f , up to 1.2 is permitted

� This is the margin between the allowable displacement stress range and twice yield1.2*1.25(Sc+Sh)=1.5*[2/3(Syc)+2/3(Syh)]

=Syc+Syh

� Shakedown behavior is preserved

� Not permitted for temperatures in the creep regime

� Not permitted for some materials where the existing rules may be non-conservative

Extension to Higher Cycles

� An endurance limit stress range was calculated based on ASME OM-3*, which provides guidelines for evaluation of nuclear power plant piping vibration

� An f factor of 0.15 gives an endurance limit stress range for typical carbon steel material

� The factor of 0.15 is conservative for austenitic stainless steel material

* ASME OM-3: Pre-operational and Initial Startup Vibration

Testing of Nuclear Power Plant Piping Systems

High Cycle Fatigue

� Recent work (Hinnant and Paulin) has shown the original fatigue curves developed by Marklare flatter than they should be

� This makes them potentially unconservative at high cycles

� Work is underway to develop a new appendix (proposed as Appendix W) to provide improved rules for high cycle fatigue

� Expect f=6N-0.2 to become f=17N-0.32

CAESAR II Implementation

To simplify this exercise,use Equation (1a):SA=f(1.25Sc+0.25Sh)

N


f=6N-0.2

Maximum=1.0


SA=f(1.25Sc+0.25Sh)=f*100MPa

f=6N-0.2

Maximum=1.2

An Equation for Longitudinal

Stress Due to Sustained Loads

Previous Editions: 302.3.5(c) –

The sum of longitudinal stresses, SL, in any component in a piping system, due to sustained loads such as pressure and weight, shall not

exceed Sh.

An Equation for Longitudinal

Stress Due to Sustained Loads

� Until 2010, the Base Code provided verbal description for limits on longitudinal stress due to sustained loads

� Includes stress due to axial load and bending moment

� Use wall thickness minus allowances

� States that loads are usually calculated based on nominal thickness and stress resulting from those

loads are based on thickness less allowances

(corrosion/erosion/mechanical)

� Does not address torsion

� Does not address stress indices

New Paragraph 320

� Provides a specific equation for calculating longitudinal stress due to sustained loads

� Previously presented in Code Case 178

� Stress due to torsion is specifically included

� Stress indices are included

Stress Indices

� 0.75i included as a stress index for calculating bending stress due to sustained loads

� Applicability of 0.75 for components other than elbows is questionable, but the benefits of having a consistent approach led to incorporation

� 0.75 factor same as B31.1

Stress Due to Axial Load

� Axial force term now specifically includes axial force due to internal pressure, the pressure stress is no longer added as PD/4t (CAESAR II, by default, uses PAin/Axs)

� As such, equation is always correct, considering the potential effect of expansion joints


� B31.3- 2010 paragraph 3.20 can be applied now by setting the Code Case 178 switch to TRUE in the Configuration file

� This does notincorporate axial and torsion stress indices

Allowable Stress for

Occasional Loads

Alternative Allowable for

Occasional Loads

� For temperatures above 800ºF (427ºC), the sumof the longitudinal stresses due to pressure, weight, other sustained loadings, and stresses produced by occasional loads, SL, must not exceed 90% of the yield strength at temperature times a strength reduction factor.

� SL ≤≤≤≤ 0.90(Syt)(X)(Ec); Ec is casting quality factor

� Where the strength reduction factor X = 1.0 for austenitic stainless steels and 0.8 for other materials

� This alternative may not be used for materials with non-ductile behavior.


� CAESAR II does not identify basic allowable stresses controlled by creep

� This adjustment to the allowed stress limit for sustained plus occasional loads remains the responsibility of the user.

Appendix P

Alternative Flexibility

Analysis Rules in Appendix P

� They are alternative rules

� Either the Base Code or Appendix P may be used for evaluating expansion stress range

� If either is satisfied, the system is Code compliant – it may fail one and pass the other, but both are conservative

Operating Conditions

� A more complete fatigue analysis, looking at differences between operating conditions, rather than displacement stress only

� Nonlinear effects are inherently included, as are shifts in support effort

� There is no ambiguity related to the inclusion of SL in the allowable stress, as in the Base Code. (SL can change based on active, nonlinear support configuration.)

� (1b): SA=f[1.25(Sc+Sh-SL)]

Appendix P

� Fatigue analysis based on differences of combined load states, as it would be in a detailed fatigue analysis such as per Section VIII, Div 2.

� The stress range is computed and compared to the allowable of 1.25f(Sc+Sh)

� SL is not included in the allowable, prevention of ratchet is handled in a different fashion

Appendix P

� Shut down at ambient temperature is one of the operating conditions (so the range from that to other operating conditions is considered)

� Stresses due to axial loads are always included, so that they are included if they are significant (which is a Base Code requirement)

Appendix P

� Stress intensification factors provided for axial loads based on committee judgment

� The higher, out-plane sif for bending is used as the

axial sif, except for elbows

� Since axial load on an elbow creates bending on the other side of the elbow, no additional sif on axial load

is included

� Basically considers axial load as an equivalent bending

Control of Ratchet

� Ratchet is prevented by also limiting maximum operating stress

� This limit effectively reduces the allowable displacement stress range as the stress due to sustained loads increases

� Maximum operating stress limited to 1.5(Sc+Sh)



For this job, f=1.2


Appendix S

Appendix S

� Example flexibility analysis problems now provided in Appendix S

� Demonstrate Code intent for flexibility analysis

� A simple case

� A case illustrating a nonlinear support, with the pipe

lifting off of a support

� A case with moment reversal


� CAESAR II results were included in these examples

� Default Configuration was NOT used




Weld Joint

Strength Reduction Factor

� The creep strength of welds may be lower than the creep strength of the base material

� Mandatory consideration in membrane stress

� Optional in bending stress

Weld Joint Factor

Weld Joint Factor in Wall

Thickness Calculation

“The failure of this 30 inch diameter steam line, operating at 900 psi and 1000 degF, shutdown the Mohave, California power plant. The failure occurred along a longitudinal weld in the pipe.

BEAR engineers determined that although the weld metal was stronger than the pipe steel at room temperature, the creep, or

high temperature deformation rate of the weld metal was 10 times greater than the pipe's base metal. This mismatch led to failure after 10 years of operation. The ASME Piping Codes have

been changed to prevent this type of failure based in part on analysis work performed by BEAR on this failure and others.”- http://www.bearinc.com/projects/refinerypowerplants.html

Weld Joint Strength

Reduction Factors

� Introduced in the 2004 edition

� Task Force formed to include them in B31.1 and Section I developed a consensus that has led to some changes in the 2008 edition of B31.3

� Applies in the creep regime, starting at a temperature 50oF below the temperature, Tcr, at which creep properties govern when establishing the allowable

� Recognizes that many weldments have creep strength less than the base material

Weld Joint Factor

� Factor, W, applies in pressure design

� Factor W did apply to girth welds for longitudinal stress due to sustained loads but this was changed as a compromise to get consistent rules between Codes

� Code now states that application of W for evaluation of longitudinal stresses due to sustained loads is the responsibility of the designer

Weld Joint Factor

� Factor, W, does not apply for stress due to occasional loads because of their short duration

� Factor, W, does not apply to thermal expansion type stress since these stresses relax in the creep regime and are not sustained

� Values may be developed by creep tests

Weld Joint Factors

� Single curve for all materials now replaced with material specific curves

� Start temperature depends upon start temperature at which creep governs the allowable stress

� Slope of factor versus temperature is generally the same as the prior B31.3 curve

� Creep Strength Enhanced Ferritics assigned a factor of 0.5 in the creep regime if the PWHT is Subcritical

Weld Joint Factors

� Autogenous welds in austenitic stainless steel assigned a factor of 1.0

� Section III, Subsection NH referenced for alternative factors for 304 SS welded with 316 SS rod


� In CAESAR II,Wlreferences the longitudinal welds

� Here, a value of 0.85 is entered for 304 stainless steel at 600C


� By default, circumferential welds are not checked


� In CAESAR II, Wc references the value specified for girth welds

� Here, the value of 0.85 is entered


� Some CAESAR II materials have W specified

� You can add your own data as well

ASME B31E

� New standard for evaluation of piping systems for earthquake loads

� Intended to be referenced by all B31 Codes

� Provides design by rule for most systems

� Requires detailed analysis for only critical larger diameter systems

� Provides a new allowable stress for seismic loads

ASME B31E

� Currently ASME B31.3 does not explicitly reference B31E:

� Both documents reference the US Building Code ASCE 7

B31.3 B31E

B31E

� B31E defines allowable stress for sustained plus seismic load

� Minimum of:

� 2.4S

� 1.5SY

� 60ksi (408MPa)

� AND, an allowed limit for forces produced by seismic anchor movement

B31E - 2010

� The 2010 Edition defines ASCE 7 terms for setting seismic load.


� There are unresolved issues with using the seismic demand requirements of the ASCE 7 building code for piping.

� ASD v LRFD (0.7 factor in LRFD gives ASD)

� Value for R for piping

� CAESAR II does not presently address B31E.

In Conclusion

� Over the last few B31.3 Editions there have been several changes that reflect the improved analytical capabilities beyond the slide rule for which the Code was originally designed.

� CAESAR II has kept pace with these changes and has participated in this development.

Thank You for Your Attention

� Any Questions?

Documents

C2 CAU Express B31.3