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Jacketed Piping_ Interview Questions and Answers _ What is Piping

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Common questions asked in Piping stress interv iew
related to Jacketed piping are listed below:
Why Jacketed Piping is used? Ans: It is commonly used to convey very viscous processfluids in an inner pipe, heated by steam/hot water/hot oilor other heating medium between the jacket and corepipe. Vacuum jacketing is also used as an insulator forcryogenic fluids and can be analyzed using the samecalculation method for heated jacketed piping.If water (density=1000Kg/m3) is flowing through the jacket then what is value of density you will enter into
What is Piping
A n attempt to explain process piping engineering basics in detail to help all the process piping engineeringprofessionals around the world.
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Jacketed Piping: Interview questions andanswers
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Caesar spreadsheet? Ans: We have to calculate equivalent density for the same. The following formula can be used Actual jacket fluid equivalent density = [(rj2 - Rc2)/ rj2 ] x dj Where, rj = Inner radius of core Rc = Outer radius of pipe dj = Density of heating medium What are the major stress checks that you will perform while analysing Jacketed Piping system? Ans:· Sustained And Expansion Stress Check Limits of calculated stresses due to sustained loads (primary stresses) and displacement strain due toexpansion (secondary stresses) should be evaluated separately for core and jacket pipe (as per clause302.3.5 of ASME B31.3).· Checking of buckling load. (Manual Calculation):This check will not be performed by Caesar-II as it is not in the code. However it will provide forcecalculated at the junction point (P) between core and jacket. It should be less than Pcr which is given by theformula Pcr = 4π2 *Ec*Ic , For Core L2 Pcr = 4π2 *Ej*Ij , For Jacket L2 Where, P = Force calculated by computer program at junction point Pcr = Critical force Ec, Ej = Modulus of Elasticity of core/ jacket material Ic = Moment of Inertia of Core Ij = Moment of Inertia of Jacket L = Length of pipe between junction of core/ jacket.If P ≤ Pcr then no buckling failure· Weld strength check between jacket and core pipe:P calculated at the junction point between core & jacket pipe compared with allowable load at the weldpoint. P allowed = area of weld * 80% of hot allowable stress of material Area of weld = π D * root of weld D = Diameter of core pipe Root of weld = 0.707 * weld sizeIf P calculated ≤P allowed, then the system is safe· Checking of deflection of jacket:In this case, it is assumed that no spider/spacer is used between core and jacket. Deflection for the jacket with available length has to be computed and should be ensured that it does not create obstruction to the
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flow of hot medium in the jacket. Normally maximum allowed deflection of jacket is T/2, where T is thethickness of jacket.· Checking for External Pressure (By material Group):Sometimes jacket may be subjected to partial vacuum conditions due to failure of steam supply andsubsequent condensation of steam inside the jacket. In such cases, jacket should be checked for vacuumcondition.Like another example in a system the core is at a pressure of 30 psig and the jacket is at a pressure of 180psig, then the core is subjected to an external pressure of 150 psig. For this the core must be investigatedfor collapse or local buckling from the external pressure load (Refer para 304.1.3 of ASME B31.3 and UG-28through UG-30 of ASME BPVC Section-VIII Division-I)· Checking for Axial stress: As per ASME B31.3 calculated displacement stress range (Expansion case stress) isSE = (Sb2 + 4St2)1/2. Code does not take into account the axial forces and consequent axial stress incalculating expansion stresses. This is because for the normal pipe axial forces are normally due tolongitudinal stresses which is already taken care in thickness calculation and sustained stress calculations, but in case of jacketed piping, axial stresses at core-jacket junction point is just not due to longitudinalstresses, but mainly due to differential thermal expansion of core and jacket pipes. Thus calculated stressshould be corrected by adding axial stresses for local analysis of that particular junction point. Thus, Actual StressSEa = SE + Axial Force/ Area Axial force can be obtained from CAESAR output or can be calculated by the equation, Faxial = E x ΔL x Area LOr else, CAESAR also calculates the value of axial stresses which it calculates for operating case. Activatethe option “Add F/A in stress” in configuration file. Axial stress due to thermal differential is added to thecalculated expansion stress and then it should be compared with the allowable loads as per ASME B31.3. What allowable value is considered for welding check at core jacket interconnection? Ans:Two methods are prevalent. You have to consider any one of the following (discuss with the stress lead)a) Consider the 0.6 times of electrode tensile strength (As per AISC code) b) Consider SE=1.25Sc+0.25Sh of electrode as allowable (as per secondary stress generated theory)
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