whats the difference b/w primary n Secondary stresses .................. y one is self limiting n other is not ............ can any 1 explain with example.........?
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whats the difference b/w primary n Secondary stresses .................. y one is self limiting n other is not ............ can any 1 explain with example.........?
[B][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][LEFT]WHAT IS STRESS ANALYSIS?[/LEFT]
[/B][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Times New Roman][LEFT]Piping Stress analysis is a term applied to calculations, which address the static and dynamic loading
resulting from the effects of gravity, temperature changes, internal and external pressures, changes in fluid
flow rate and seismic activity. Codes and standards establish the minimum requirements of stress
analysis.[/LEFT]
[/FONT][B][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][LEFT]PURPOSE OF PIPING STRESS ANALYSIS[/LEFT]
[/B][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Times New Roman][LEFT]Purpose of piping stress analysis is to ensure:[/LEFT]
[/FONT][FONT=TT1E54o00][LEFT][/FONT][FONT=Times New Roman]Safety of piping and piping components.[/LEFT]
[/FONT][FONT=TT1E54o00][LEFT][/FONT][FONT=Times New Roman]Safety of connected equipment and supporting structure.[/LEFT]
[/FONT][FONT=TT1E54o00][LEFT][/FONT][FONT=Times New Roman]Piping deflections are within the limits.[/LEFT]
[/FONT][B][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][LEFT]HOW PIPING AND COMPONENTS FAIL (MODES OF FAILURES)[/LEFT]
[/B][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Times New Roman][SIZE=2][FONT=Times New Roman][SIZE=2][LEFT]There are various failure modes, which could affect a piping system. The piping engineers can provide protection against some
of these failure modes by performing stress analysis according to piping codes.[/LEFT]
[/SIZE][/FONT][/SIZE][/FONT][FONT=TT1E58o00][LEFT] [/FONT][B][I][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]FAILURE BY GERNRAL YIELDING[/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][SIZE=5][FONT=Times New Roman][SIZE=5]: [/B][/I][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman]Failure is due to excessive plastic deformation.[/LEFT]
[/FONT][FONT=TT1E5Do00][SIZE=1][FONT=TT1E5Do00][SIZE=1][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Yielding at Sub Elevated temperature: [/B][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][SIZE=3]Body undergoes plastic deformation under slip action[/SIZE]
of grains.[/LEFT]
[/FONT][FONT=TT1E5Do00][SIZE=1][FONT=TT1E5Do00][SIZE=1][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Yielding at Elevated temperature: [/B][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][SIZE=3]After slippage, material re-crystallizes and hence yielding[/SIZE]
continues without increasing load. This phenomenon is known as creep.[/LEFT]
[/FONT][FONT=TT1E58o00][LEFT] [/FONT][B][I][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]FAILURE BY FRACTURE: [/B][/I][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman]Body fails without undergoing yielding.[/LEFT]
[/FONT][FONT=TT1E5Do00][SIZE=1][FONT=TT1E5Do00][SIZE=1][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Brittle fracture: [/B][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][SIZE=3]Occurs in brittle materials.[/SIZE][/LEFT]
[/FONT][FONT=TT1E5Do00][SIZE=1][FONT=TT1E5Do00][SIZE=1][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Fatigue: [/B][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][SIZE=3]Due to cyclic loading initially a small ----- is developed which grows after each cycle and[/SIZE]
results in sudden failure.[/LEFT]
[/FONT][B][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][LEFT]WHEN PIPING AND COMPONENTS FAIL (THEORIES OF FAILURE)[/LEFT]
[/B][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Arial][LEFT]Various theories of failure have been proposed, their purpose being to establish the point at
which failure will occur under any type of combined loading.
The failure theories most commonly used in describing the strength of piping systems are:[/LEFT]
[/FONT][FONT=TT1E61o00][SIZE=4][FONT=TT1E61o00][SIZE=4][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][I][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Maximum principal stress theory[/LEFT]
[/B][/I][/SIZE][/FONT][/SIZE][/FONT][FONT=Arial][LEFT]This theory states that yielding in a piping component occurs when the magnitude of any of the
three mutually perpendicular principle stresses exceeds the yield point strength of the material.[/LEFT]
[/FONT][FONT=TT1E61o00][SIZE=4][FONT=TT1E61o00][SIZE=4][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][I][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Maximum shear stress theory[/LEFT]
[/B][/I][/SIZE][/FONT][/SIZE][/FONT][FONT=Arial][LEFT]This theory states that failure of a piping component occurs when the maximum shear stress
exceeds the shear stress at the yield point in a tensile test.
In the tensile test, at yield, S[/FONT][FONT=Arial][SIZE=1][FONT=Arial][SIZE=1]1[/SIZE][/FONT][/SIZE][/FONT][FONT=Arial]=Sy (yield stress), S[/FONT][FONT=Arial][SIZE=1][FONT=Arial][SIZE=1]2[/SIZE][/FONT][/SIZE][/FONT][FONT=Arial]=S[/FONT][FONT=Arial][SIZE=1][FONT=Arial][SIZE=1]3[/SIZE][/FONT][/SIZE][/FONT][FONT=Arial]=0.So yielding in the components occurs
when
Maximum Shear stress =[/FONT][FONT=Symbol]τ[/FONT][FONT=Arial][SIZE=1][FONT=Arial][SIZE=1]max[/SIZE][/FONT][/SIZE][/FONT][FONT=Arial]=S[/FONT][FONT=Arial][SIZE=1][FONT=Arial][SIZE=1]1[/SIZE][/FONT][/SIZE][/FONT][FONT=Arial]-S[/FONT][FONT=Arial][SIZE=1][FONT=Arial][SIZE=1]2 [/SIZE][/FONT][/SIZE][/FONT][FONT=Arial]/ 2=Sy / 2[/FONT]
[FONT=Arial]
The maximum principal stress theory forms the basis for piping systems governed by ASME B31.3.
Note: maximum or minimum normal stress is called principal stress.[/LEFT]
[/FONT][B][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][LEFT]STRESS CATEGORIES[/LEFT]
[/B][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Times New Roman][LEFT]The major stress categories are primary, Secondary and peak.[/LEFT]
[/FONT][B][I][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4][LEFT]PRIMARY STRESSES:[/LEFT]
[/B][/I][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][LEFT]These are developed by the imposed loading and are necessary to satisfy the equilibrium between external
and internal forces and moments of the piping system. [/FONT][B][FONT=Times New Roman]Primary stresses are not self-limiting.[/LEFT]
[/FONT][I][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4][LEFT]SECONDARY STRESSES:[/LEFT]
[/B][/I][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][LEFT]These are developed by the constraint of displacements of a structure. These displacements can be caused
either by thermal expansion or by outwardly imposed restraint and anchor point movements. [/FONT][B][FONT=Times New Roman]Secondary
stresses are self-limiting[/B][/FONT][FONT=Times New Roman].[/LEFT]
[/FONT][B][I][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4][LEFT]PEAK STRESSES:[/LEFT]
[/B][/I][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][LEFT]Unlike loading condition of secondary stress which cause distortion, peak stresses cause no significant
distortion. Peak stresses are the highest stresses in the region under consideration and are responsible for
causing fatigue failure.[/LEFT]
[/FONT][B][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][FONT=Times New Roman][SIZE=4][COLOR=#0000ff][LEFT]CLASSCIFICATION OF LOADS[/LEFT]
[/B][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=TT1E61o00][SIZE=4][FONT=TT1E61o00][SIZE=4][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Primary loads:[/LEFT]
[/B][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][LEFT]These can be divided into two categories based on the duration of loading.[/LEFT]
[/FONT][FONT=TT1E5Do00][SIZE=1][FONT=TT1E5Do00][SIZE=1][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Sustained loads[/LEFT]
[/B][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][LEFT]These loads are expected to be present through out the plant operation. e,g. pressure and weight.[/LEFT]
[/FONT][FONT=TT1E5Do00][SIZE=1][FONT=TT1E5Do00][SIZE=1][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4]Occasional loads[/B][/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][SIZE=4][FONT=Times New Roman][SIZE=4].[/LEFT]
[/SIZE][/FONT][/SIZE][/FONT][FONT=Times New Roman][LEFT]These loads are present at infrequent intervals during plant operation. e,g. earthquake, wind, etc.[/LEFT]
[/FONT][FONT=TT1E61o00][SIZE=4][FONT=TT1E61o00][SIZE=4][LEFT] [/SIZE][/FONT][/SIZE][/FONT][B][SIZE=4][SIZE=4][FONT=Times New Roman]Expansion loads:[/FONT][/LEFT]
[/B][/SIZE][/SIZE][LEFT][FONT=Times New Roman]These are loads due to displacements of piping. e,g .thermal expansion, seismic anchor movements, and[/FONT]
[FONT=Times New Roman]building settlement.[/FONT][/LEFT]
[B][SIZE=4][COLOR=#0000ff][SIZE=4][COLOR=#0000ff][SIZE=4][COLOR=#0000ff][LEFT][FONT=Times New Roman]REQUIRMENTS OF ASME B31.3 (PROCESS PIPING CODE)[/FONT][/LEFT]
[/B][/COLOR][/SIZE][/COLOR][/SIZE][/COLOR][/SIZE][LEFT][FONT=Times New Roman]This code governs all piping within the property limits of facilities engaged in the processing or handling[/FONT]
[FONT=Times New Roman]of chemical, petroleum or related products. Examples are a chemical plant, petroleum refinery, loading[/FONT]
[FONT=Times New Roman]terminal, natural gas processing plant, bulk plant, compounding plant and tank farm.[/FONT]
[FONT=Times New Roman]The loadings required to be considered are pressure, weight (live and dead loads), impact, wind,[/FONT]
[FONT=Times New Roman]earthquake-induced horizontal forces, vibration discharge reactions, thermal expansion and contraction,[/FONT]
[FONT=Times New Roman]temperature gradients, anchor movements.[/FONT]
[FONT=Times New Roman]The governing equations are as follows:[/FONT][/LEFT]
[B][LEFT][FONT=Times New Roman]1.Stresses due to sustained loads.[/FONT][/LEFT]
[/B][LEFT][FONT=Times New Roman]S[SIZE=1][SIZE=1]L [/SIZE][/SIZE]< S[SIZE=1][SIZE=1]h[/LEFT]
[/SIZE][/SIZE][/FONT][LEFT][FONT=Times New Roman]S[SIZE=1][SIZE=1]L [/SIZE][/SIZE]= (PD/4t) + S[SIZE=1][SIZE=1]b[/LEFT]
[/SIZE][/SIZE][/FONT][LEFT][FONT=Times New Roman]S[SIZE=1][SIZE=1]h [/SIZE][/SIZE]= Basic allowable stress at maximum metal temperature.[/FONT]
[FONT=Times New Roman]The thickness of the pipe used in calculating S[SIZE=1][SIZE=1]L [/SIZE][/SIZE]shall be the nominal thickness minus mechanical,[/FONT]
[FONT=Times New Roman]corrosion, and erosion allowance.[/FONT][/LEFT]
[B][LEFT][FONT=Times New Roman]2.Stresses due to occasional loads.[/FONT][/LEFT]
[/B][LEFT][FONT=Times New Roman]The sum of the longitudinal loads due pressure, weight and other sustained loads and of stresses produced[/FONT]
[FONT=Times New Roman]by occasional loads such as earthquake or wind shall not exceed 1.33Sh.[/FONT][/LEFT]
[B][LEFT][FONT=Times New Roman]3.Stress range due to expansion loads.[/FONT][/LEFT]
[/B][LEFT][FONT=Times New Roman]The displacement stress range S[SIZE=1][SIZE=1]E [/SIZE][/SIZE]shall not exceed S[SIZE=1][SIZE=1]A[/SIZE][/SIZE]:[/FONT]
[FONT=Times New Roman]S[SIZE=1][SIZE=1]E [/SIZE][/SIZE]< S[SIZE=1][SIZE=1]A[/LEFT]
[/SIZE][/SIZE][/FONT][LEFT][FONT=Times New Roman]WHERE[/FONT][/LEFT]
[B][LEFT][FONT=Times New Roman]S[SIZE=1][SIZE=1]E [/SIZE][/SIZE]= (S[/FONT][SIZE=1][SIZE=1][FONT=Times New Roman]b[/FONT]
[FONT=Times New Roman]2 [/FONT][/SIZE][/SIZE][FONT=Times New Roman][SIZE=3]+ 4S[/SIZE][/FONT][SIZE=1][SIZE=1][FONT=Times New Roman]t[/FONT]
[FONT=Times New Roman]2[/FONT][/SIZE][/SIZE][FONT=Times New Roman][SIZE=3]) [/SIZE][SIZE=1][SIZE=1]½[/LEFT]
[/B][/SIZE][/SIZE][/FONT][LEFT][FONT=Times New Roman]S[SIZE=1][SIZE=1]b [/SIZE][/SIZE]= resultant bending stress,psi[/FONT]
[FONT=Times New Roman]= [(IiMi)2 + (IoMo)2] / Z[/FONT]
[FONT=Times New Roman]Mi = in-plane bending moment, in.lb[/FONT]
[FONT=Times New Roman]Mo = out-plane bending moment, in.lb[/FONT]
[FONT=Times New Roman]Ii = in- plane stress intensification factor obtained from appendix of B31.3[/FONT]
[FONT=Times New Roman]Io = out- plane stress intensification factor obtained from appendix of B31.3[/FONT]
[FONT=Times New Roman]St = Torsional stress ,psi[/FONT]
[FONT=Times New Roman]= Mt / (2Z)[/FONT]
[FONT=Times New Roman]Mt = Torsional moment, in.lb[/FONT][/LEFT]
[B][LEFT][FONT=Times New Roman]S[SIZE=1][SIZE=1]A [/SIZE][/SIZE]= Allowable displacement stress range:[/FONT][/LEFT]
[/B][LEFT][FONT=Times New Roman](Allowable stress) [SIZE=1][SIZE=1]cold [/SIZE][/SIZE]= S[SIZE=1][SIZE=1]c [/SIZE][/SIZE]= (2 / 3) Sy[SIZE=1][SIZE=1]c [/SIZE][/SIZE]⇒ Sy[SIZE=1][SIZE=1]c [/SIZE][/SIZE]= (3/2)S[SIZE=1][SIZE=1]c[/LEFT]
[/SIZE][/SIZE][/FONT][LEFT][FONT=Times New Roman](Allowable stress) [SIZE=1][SIZE=1]hot [/SIZE][/SIZE]= S[SIZE=1][SIZE=1]h [/SIZE][/SIZE]= (2 / 3) Sy[SIZE=1][SIZE=1]h [/SIZE][/SIZE]⇒ Sy[SIZE=1][SIZE=1]h [/SIZE][/SIZE]= (3/2) S[SIZE=1][SIZE=1]h[/LEFT]
[/SIZE][/SIZE][/FONT][LEFT][FONT=Times New Roman]Sy[SIZE=1][SIZE=1]c [/SIZE][/SIZE]= yield point stress at cold temperature[/FONT]
[FONT=Times New Roman]Sy[SIZE=1][SIZE=1]h [/SIZE][/SIZE]= yield point stress at hot temperature[/FONT]
[FONT=Times New Roman]Allowable stress =Sy[SIZE=1][SIZE=1]c [/SIZE][/SIZE]+ Sy[SIZE=1][SIZE=1]h[/LEFT]
[/SIZE][/SIZE][/FONT][LEFT][FONT=Times New Roman]=3/2 (S[SIZE=1][SIZE=1]c [/SIZE][/SIZE]+ S[SIZE=1][SIZE=1]h [/SIZE][/SIZE])[/FONT]
[FONT=Times New Roman]= 1.5 (S[SIZE=1][SIZE=1]c [/SIZE][/SIZE]+ S[SIZE=1][SIZE=1]h [/SIZE][/SIZE])[/FONT]
[FONT=Times New Roman]= 1.25(S[SIZE=1][SIZE=1]c [/SIZE][/SIZE]+ S[SIZE=1][SIZE=1]h [/SIZE][/SIZE])---- after dividing with F.O.S[/FONT]
[FONT=Times New Roman]Final allowable stress = [(1.25(S[SIZE=1][SIZE=1]c [/SIZE][/SIZE]+ S[SIZE=1][SIZE=1]h[/SIZE][/SIZE]) – S[SIZE=1][SIZE=1]L[/SIZE][/SIZE]][/FONT][/LEFT]
[B][LEFT][FONT=Times New Roman]S[SIZE=1][SIZE=1]A [/SIZE][/SIZE]= f [(1.25(S[SIZE=1][SIZE=1]c [/SIZE][/SIZE]+ S[SIZE=1][SIZE=1]h[/SIZE][/SIZE]) – S[SIZE=1][SIZE=1]L[/SIZE][/SIZE]][/FONT][/LEFT]
[/B][LEFT][FONT=Times New Roman]S[SIZE=1][SIZE=1]c [/SIZE][/SIZE]= basic allowable stress at minimum metal temperature[/FONT][/LEFT]
[FONT=Times New Roman]f = stress range reduction factor from table 302.2.5 of B31.3[/FONT]
thnx @ Cobraaa ..... that was answer in detail .............. Sir can i find book on "Pipe Stress Engg " by L.C Peng.............??
faisal99,
LC Peng book can be purchased of the net - just google for it!!!
Cobraaa,
Absolute excellent copy and paste there mate!!!
Its first 3 chapters are available in pdf format but rest of the chapters are not available............... from where i can find pdf of that ............some body who have it must share......... so that knowledge should spread.................?
find here
[url]http://www.pipingdesign.com/stressanalysis.pdf[/url]
regard
JH
find here also
[url]http://www.adwaitjoshi.com/misc/psa.pdf[/url]
[url]http://www.adwaitjoshi.com/misc/psa.pdf[/url]
Regards
JH
Gives error......................................?
Although this book is very good ....... but other books are also good which are shared on this forum................ But y only three chapters of this book are available .......not rest of the chapters.....................................?