A Seminar on Design of Pressure Vessel

A Seminar onDesign of Pressure VesselBy: Mayank Nirbhay (10/IME/032)Prashant Tripathi (10/IME/040)Vivek Kumar Gupta (10/IME/059)

Faculty Advisor: Dr. R.K. Mishra

Date: 22/10/2013

Department of Mechanical EngineeringSchool of EngineeringGautam Buddha UniversityGreater Noida (U.P.)Seminar HighlightsIntroduction to Pressure Vessels and its classificationComponents of Pressure VesselsASME Codes Design software and industrial applicationsMaterials SelectionStress in Pressure VesselsDesign of cylindrical shell.Calculation Program1. General Introduction of Pressure Vessel

INTRODUCTION [1]Vessels, tanks, and pipelines that carry, store, or receive fluids are called pressure vessels.A pressure vessel is defined as a container with a pressure differential between inside and outside.The inside pressure is usually higher than the outside, except for some isolated situations.Pressure vessels often have a combination of high pressures together with high temperatures.Because of such hazards it is imperative that the design be such that no leakage can occur. Pressure vessels and tanks are, in fact, essential to the chemical, petroleum, petrochemical and nuclear industries. It is in this class of equipment that the reactions, separations, and storage of raw materials occur.CLASSIFICATION OF PRESSURE VESSEL [3] COMPONENTS OF PRESSURE VESSELSThe main components of pressure vessel are [4] ShellHeadsNozzlesStiffening ringsSupports

Photo courtesy: www.theculminates.comShellThe shell is the primary component that contains the pressure. Pressure vessel shells are welded together to form a structure that has a common rotational axis.Most pressure vessel shells are cylindrical, spherical and conical in shape

HeadAll pressure vessel shells must be closed at the ends by heads (or another shell section). Heads are typically curved rather than flat. Curved configurations are stronger and allow the heads to be thinner, lighter, and less expensive than flat heads. Heads are usually categorized by their shapes.

Fig: Different types of heads. (Modified from ASME Boiler and Pressure Vessel Code, ASME, New York.)SupportThe type of support that is used depends primarily on the size and orientation of the pressure vessel. the pressure vessel support must be adequate for the applied weight, wind, and earthquake loads.Typical kinds of supports are as follow:a. Skirtb. Legc. Saddled. Lug

Photo courtesy: www.pressurevesslesconsulting.comSaddleLegSkirtLug

Figure showing various pressure vessel supports.NozzleA nozzle is a cylindrical component that penetrates the shell or heads of a pressure vessel. The nozzle ends are usually flanged to allow for the necessary connections and to permit easy disassembly for maintenance or access. Nozzles are used for attaching piping for flow into or out of the vessel and attach instrument connections, (e.g., level gauges, thermowells, or pressure gauges).

Stiffener RingsRings made of flat bar or plate or structural shapes welded around the Circumference of the vessel. These rings are installed on vessels operating under external pressure to prevent collapse of the vessel.

Photo courtesy: www.pressurevesslesconsulting.comFollowing parts of ASME Code SECTION VIII DIV-1 are used in design [5]U-1Scope for the design of pressure vesselsUG-16General regarding designUG-20Design temperatureUG-21LoadingsUG-22Maximum allowable stressesUG-23Maximum allowable stressesUG-27Thickness of shells under internal pressureUG-28Thickness of shells under external pressureUG-29Stiffening rings for cylindrical shells under external pressureUG-32Formed heads, pressure on concave sideUG-33Formed heads, pressure on convex side. Graph in Appendix VUG-45Nozzle neck thicknessUW-12Welded Joint efficienciesUG-45Nozzle neck thicknessUW-12Welded Joint efficienciesAppendix VCharts for determining shell thickness of cylindrical and spherical vessels under external pressureDESIGNING A PRESSURE VESSEL IN INDUSTRY

Software used in designing the pressure vessels:Intergraph PV Elite is a complete solution for pressure vessel design, analysis and evaluation. Users of PV Elite have designed equipment for the most extreme uses and have done so quickly, accurately and profitably.

Fig:Screenshot of PV-Elite Software2. Materials SelectionSelection of materials The broad classification of these materials can be done in following categories: 1. Boiler Quality Materials 2. Structural Quality Materials 1. Boiler Quality Materials [5]These are the materials employed for pressure carrying components. a) Carbon Steel Principal element is carbon, generally ranging from 0.2 to 0.4.b) Low Alloy Steel Alloying elements are used, but the total alloy content is limited to generally 5 %.c) High alloy steel heavy alloying is done for example Stainless Steels.Commonly used stainless steels for refinery, petrochemical services are:-Austenitic Stainless Steels Ferritic Stainless Steels.

2. Structural Quality Materials [5]These are the materials employed for very general services and nonpressure services. The Structural quality materials are generally only of Carbon steel.They are very economical .Material testing for Pressure vessel [5]PWHT Post Weld Heat Treatment. Radiographic testing is done of the welding joints according to the pressure vessel.If Vessel is designed according to ASME sec 8 div only spot radiography will be done for ASME sec 8 div 2 full radiographic testing is being done.After this test heat treatment is done on the welding joints to relieve the stresses.Recommended for corrosive services like HS, amine, caustic services etc.

Impact Testing The impact testing of materials is done to take care of low temperature service. This is because the material tend to become more brittle at low temperature. Charpy V notch impact test is the most common type of test used.

3. Stresses in PressureVesselsMainly there are 2 types of stresses involved in a pressure vessel

Primary stressPrimary stresses are generally due to internal or external pressure or produced by sustained external forces and moments.These stresses act over the full cross section of the vessel. They are produced by mechanical loads and are the most hazardous of all types of stress.

Types of primary general stress1.Primary general membrane stress, P : a. Circumferential and longitudinal stress due to pressure.b. Compressive and tensile axial stresses due to wind.2. Local primary membrane stress, PLIt is the combination of primary membrane stress, P, plus secondary membrane stress, Q, produced from sustained loadings.

2. Secondary stressSecondary mean stresses are developed at the junctions of major components of a pressure vessel and are produced by sustained loads other than internal or external pressure. Types of secondary stresses:1. Secondary membrane stress, QThese are the stress which area. Thermal stresses.b. Membrane stress in the knuckle area of the head.c. Membrane stress due to local loads.2. Secondary bending stress, QLThese include :a. Bending stress at a gross structural discontinuity:b. The stress variation of the radial stress due to internal pressure.d. Discontinuity stresses at stiffening or support rings.

STRESS/FAILURE THEORIES [5]

The major theories of failures used to design a pressure vessel are :

Maximum principle stress theory: Both ASME Code, Section VIII, Division 1, and division use the maximum stress theory as a basis for design. While it accurately predict failure in brittle materials, but it is not always accurate for ductile materials.

2. Maximum shear stress theoryThis theory asserts that the breakdown of material depends only on the maximum shear stress attained in an element. It is mainly used for Ductile material

Major Failures associated with pressure vessel can usually be classified as 5 types :1. EXCESSIVE ELASTIC DEFORMATIONIt is a type of expansion of vessel till limit of proportionality.It affects the volume and density of fluid inside the vessel, hence the purpose of the vessel will fail and effect the process. So excessive elastic deformation is undesirable.2. PLASTIC INSTABILITY :Plastic deformations occur in a pressure vessel if the Internal or external pressure becomes so high that resultant stresses acting on the pressure vessel exceeds the yield point.Elastic instability in vessels is usually associated with the use of thin shells.Plastic instability3. BRITTLE RUPTURE :If the material used for the vessel is brittle than instead of plastic or elastic deformation, vessel will ruptured instantly after increasing the slight load after yield point. Hence for brittle material stresses should be kept low below the yield point.

MAJOR FAILURES ASSOCIATED WITH PRESSURE VESSELS [5]4. CREEP:Creep is a failure of material due to constant loading and unloading of material kept at one place for long time. It arises due to periodic loading and loading. It starts initially from grain boundary where abnormal grains are there. It increases to cracks in the material after some time and finally material fails on load much lower than the yield point stress.

5. CORROSION:If excessive corrosion occurs than material thickness will decrease constantly and after a certain limit the material will failDue to this the vessels are provided with corrosion allowance thickness. Generally taken 3mm at inside boundary layer. At outside some corrosion resistant material are used to prevent the rusting.

4. Design of Shell

E = Joint Efficiency FactorP = internal pressure (kg/cm2).Ri, Ro = inside and outside radius with corrosion allowance. (in)Di, Do = inside and outside diameter.S = allowable stress in the materialt = thickness of the cylinder (mm)=Density of liquid H=Height of liquid levelCA = Corrosion allowancen = number of stiffening ringsLeff = Overall effective length of pressure vesselL = Length of pressure vesselhoop= Hoop or circumferential stresseslong= Longitudinal stressesPa, Pa1, Pa2 = Allowable external pressureVESSEL NOMENCLATUREShell DesignBasically the design of shell consists of following steps-Design of shell under internal pressure.Minimum thickness is calculated using ASME Boiler and Pressure Vessel Code, Section VIII Division 1, UG-27. Design of shell under external pressure.For a optimum thickness the pressure vessel under external pressure is analyzed for satisfying the design using ASME BPV Code, Sec. VIII Div. 1, UG-28. Or for the optimum thickness no. of stiffening rings is calculated.12PiPeDesign of cylindrical shell under external pressureSteps [9]-Assume a value of t for the cylinder.Calculate the quantities L/Do and Do/t.Use Fig. with the calculated values of L/Do and Do/t and establish an A value.Use an External Pressure Chart to determine the A value and determine the B value from the appropriate temperature chart.Calculate the allowable external pressure from the equation

When A falls to the left of the curves, the value of Pa is determined from

Compare the calculated value of Pa (Allowable Pressure) obtained in Steps 6 or 7 with P. If Pa is smaller than P, select the thickness. if Pa > P assumed thickness is optimum

FACTOR A CHART [5]FACTOR B CHART [5]

SUMMARY OF DESIGN PROCEDURE FOR SHELL

SUMMARY OF DESIGN PROCEDURE FOR SHELLStep-4: Select the maximum thickness as obtained from the step-1 & 2. t = maximum (thoop ,tlong) SUMMARY OF DESIGN PROCEDURE FOR SHELLSUMMARY OF DESIGN PROCEDURE FOR SHELLFig: A pressure vessel with the use of stiffening rings. [8]

Calculation Program using Mathcad.Program 1: Design of shell under internal pressure.

Program 2: Design of shell under external pressure

POST SEMINAR PROSPECT WILL COVERDesign of Stiffening ringsDesign of Heads Design of NozzlesDesign of various types of supportsProgramming the various design procedure and calculation involved.Sample data results, comparison and validationConclusionReferencesNitant M. Tandel, Jigneshkumar M. Parmar, A Review on Pressure Vessel Design and Analysis, Paripex - Indian Journal Of Research, May 2013J. Philip Ellenberger PE, Robert Chuse, Bryce E. Carson Sr., Pressure Vessels The ASME code simplified, 8th edition, Mc Graw- Hill Professional EngineeringB.S.Thakkar, S.A.Thakkar, DESIGN OF PRESSURE VESSEL USING ASME CODE, SECTION VII DIVISON 1, International Journal of Advanced Engineering Research and Studies, 2012.Ghader Ghanbari, Mohammad Ali Liaghat, Ali Sadeghian, Pressure Vessel Design, Guides & ProceduresDennis R. Moss, Pressure Vessel Design Manual, 3rd Edition-2004, Gulf Professional Publishing (An imprint of Elsevier)Dr. R. K. Bansal, A Textbook of Strength of Materials, 4th Edition-2009.Somnath Chattopadhyay, Pressure Vessel Design and Practice, CRC Press.Henry H. Bednar, Pressure Vessel Design Handbook, 2nd Edition-1991. Krigerer Publishing companyJames R. Farr and Maan H. Jawad, Guidebook for the design of ASME Section VIII pressure vessels, 2nd Edition-2001, ASME Press New York.An international code 2010 ASME Boiler & Pressure Vessel Code, 2010 Edition, VII Section VIII, Div.1, Rules for Construction of Pressure Vessels, ASME New York

Thank You