A Seminar on
Design of Pressure Vessel By: 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 Engineering School of Engineering Gautam Buddha University Greater Noida (U.P.)
Seminar Highlights • • • • • • • •
Introduction to Pressure Vessels and its classification Components of Pressure Vessels ASME Codes Design software and industrial applications Materials Selection Stress in Pressure Vessels Design of cylindrical shell. Calculation Program
1. 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 Pressure vessel Function
Geometry
Construction
Storage tank
Cylindrical
Process vessel
Spherical
Multi Wall
Steam
Heat Exchanger
Conical
Forged
Lethal
Horizontal/Vertical
Monowall
Service
Cryogenic
Fired/Unfired
[3]
COMPONENTS OF PRESSURE VESSELS • The main components of pressure vessel are i. ii. iii. iv. v.
Shell Heads Nozzles Stiffening rings Supports
Photo courtesy: www.theculminates.com
[4]
Shell • The 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 Head • All 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.)
Support • The 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. Skirt b. Leg c. Saddle d. Lug
Leg
Saddle
Figure showing various pressure vessel supports. Photo courtesy: www.pressurevesslesconsulting.com
Lug Skirt
Nozzle • A 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 Rings • Rings 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.com
Following parts of ASME Code SECTION VIII DIV-1 are used in design [5] U-1
Scope for the design of pressure vessels
UG-16
General regarding design
UG-20
Design temperature
UG-21
Loadings
UG-22
Maximum allowable stresses
UG-23
Maximum allowable stresses
UG-27
Thickness of shells under internal pressure
UG-28
Thickness of shells under external pressure
UG-29
Stiffening rings for cylindrical shells under external pressure
UG-32
Formed heads, pressure on concave side
UG-33
Formed heads, pressure on convex side. Graph in Appendix V
UG-45
Nozzle neck thickness
UW-12
Welded Joint efficiencies
UG-45
Nozzle neck thickness
UW-12
Welded Joint efficiencies
Appendix V
Charts for determining shell thickness of cylindrical and spherical vessels under external pressure
DESIGNING A PRESSURE VESSEL IN INDUSTRY
Software used in designing the pressure vessels:
Fig: Screenshot of PV-Elite Software
• 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.
2. Materials Selection
Selection 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 non‐pressure services. • The Structural quality materials are generally only of Carbon steel. • They are very economical .
Material testing for Pressure vessel
[5]
1. 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.
2. 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 Pressure Vessels
Mainly there are 2 types of stresses involved in a pressure vessel 1.
Primary stress Primary 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 stress 1.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, PL It is the combination of primary membrane stress, P, plus secondary membrane stress, Q, produced from sustained loadings.
2. Secondary stress Secondary 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, Q These are the stress which are
a. Thermal stresses. b. Membrane stress in the knuckle area of the head. c. Membrane stress due to local loads. 2. Secondary bending stress, QL These 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 : 1. 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 theory This 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 VESSELS [5] Major Failures associated with pressure vessel can usually be classified as 5 types : 1. EXCESSIVE ELASTIC DEFORMATION • It 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 instability 3. 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.
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 fail • Due 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
VESSEL NOMENCLATURE
E = Joint Efficiency Factor P = 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 material t = thickness of the cylinder (mm) ρ=Density of liquid H=Height of liquid level CA = Corrosion allowance n = number of stiffening rings Leff = Overall effective length of pressure vessel L = Length of pressure vessel σhoop= Hoop or circumferential stresses σlong= Longitudinal stresses Pa, Pa1, Pa2 = Allowable external pressure
Shell Design Basically 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.
Pe
Pi 1
2
SHELL UNDER INTERNAL PRESSURE
HOOP STRESS
Calculate internal design pressure P = Pi + Pliquid level
Classical Equation 𝑃𝑟 𝜎ℎ𝑜𝑜𝑝 = 𝑡 ASME CODE EQUATION
𝒕=
𝑷𝑹𝒊 (𝑺𝑬 − 𝟎. 𝟔𝑷)
LONGITUDINAL STRESS Classical Equation 𝑃𝑟 𝜎𝑙𝑜𝑛𝑔 = 2𝑡 ASME CODE EQUATION
𝒕=
𝑷𝑹𝒊 (𝟐𝑺𝑬 + 𝟎. 𝟒𝑷)
Design of cylindrical shell under external pressure • Designing vessels for external pressure is an iterative procedure • External pressure on cylindrical shells causes compressive forces that could lead to buckling • . In the ASME code, the critical pressure is calculated for two situations, involving the ratio of the outside diameter to the thickness (Do/t). [8].
[9].
1.
𝐷0 𝑡
≥ 10
2.
𝐷0 𝑡
< 10
Case-I: External Pressure for Cylinders with
𝑫𝒐 𝒕
≥ 𝟏𝟎
Steps [9]1) Assume a value of t for the cylinder. 2) Calculate the quantities L/Do and Do/t. 3) Use Fig. with the calculated values of L/Do and Do/t and establish an A value. 4) Use an External Pressure Chart to determine the A value and determine the B value from the appropriate temperature chart. 5) Calculate the allowable external pressure from the equation 𝑃𝑎 =
6)
4𝐵 𝐷 3 𝑜 𝑡
When A falls to the left of the curves, the value of Pa is determined from 𝑃𝑎 =
7)
2𝐴𝐸 𝐷 3 𝑜 𝑡
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]
Case-II: External Pressure for Cylinders with
𝑫𝒐 𝒕
For values of Do/t less than 4, the value of factor A can be calculated using the following formula [9]: 1.1 𝐴= 𝐷𝑜 2 𝑡 For values of A greater than 0.10, use a value of 0.10. When Do/t is less than 10, the allowable external pressure is taken as the smaller of the values determined from the following two equations: 𝑃𝑎1
2.167 = − 0.0833 𝐵 𝐷𝑜 𝑡
Where B is obtained as discussed above.
< 𝟏𝟎
SUMMARY OF DESIGN PROCEDURE FOR SHELL Step-1: Calculate the total internal design pressure (P).
Total internal pressure, P = pressure inside the vessel+ pressure due to liquid Pressure due to liquid level =
𝜌×𝐻 𝑘𝑔/𝑐𝑚2 6 10
Where ρ=Density of liquid H=Height of liquid level
Step-2: Calculate the minimum shell thickness considering hoop or circumferential stress when the shell is under internal pressure. 𝑃𝑅𝑖 𝑡= , 𝑤𝑒𝑛 𝑡 < 0.5𝑅𝑖 𝑜𝑟 𝑃 < 0.385𝑆𝐸 (𝑆𝐸 − 0.6𝑃) 𝑤𝑒𝑟𝑒,
𝑅𝑖 = 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑟𝑎𝑑𝑖𝑢𝑠 + 𝑐𝑜𝑟𝑟𝑜𝑠𝑖𝑜𝑛 𝑎𝑙𝑙𝑜𝑤𝑎𝑛𝑐𝑒 (𝐶𝐴) 𝑓𝑖𝑛𝑎𝑙 𝑡𝑖𝑐𝑘𝑛𝑒𝑠𝑠 𝑜𝑓 𝑠𝑒𝑙𝑙 = 𝑡 + 𝐶. 𝐴.
SUMMARY OF DESIGN PROCEDURE FOR SHELL Step-3: Calculate the minimum shell thickness considering longitudinal stress when the shell is under internal pressure. 𝑡=
𝑃𝑅𝑖 , (2𝑆𝐸 + 0.4𝑃)
𝑤𝑒𝑟𝑒,
𝑤𝑒𝑛 𝑡 < 0.5𝑅𝑖 𝑜𝑟 𝑃 < 1.25𝑆𝐸
𝑅𝑖 = 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑟𝑎𝑑𝑖𝑢𝑠 + 𝑐𝑜𝑟𝑟𝑜𝑠𝑖𝑜𝑛 𝑎𝑙𝑙𝑜𝑤𝑎𝑛𝑐𝑒 (𝐶𝐴)
𝑓𝑖𝑛𝑎𝑙 𝑡𝑖𝑐𝑘𝑛𝑒𝑠𝑠 𝑜𝑓 𝑠𝑒𝑙𝑙 = 𝑡 + 𝐶. 𝐴. Step-4: Select the maximum thickness as obtained from the step-1 & 2. t = maximum (thoop ,tlong)
SUMMARY OF DESIGN PROCEDURE FOR SHELL Step-5: Calculate the allowable external pressure when the shell is under external pressure. Calculate the ratio Do/t assuming the thickness obtained in step 4. Then consider one of the case from below conditions. Case-I: External Pressure for Cylinders with Case-II: External Pressure for Cylinders with
𝐷0 𝑡 𝐷0 𝑡
≥ 10 < 10
Follow the steps as described in the section design of cylindrical shell under external pressure.
SUMMARY OF DESIGN PROCEDURE FOR SHELL Step-6: Select the assumed thickness if Pallowable > Pexternal .
But if Pallowable < Pexternal Either (a) select a new thickness and start the procedure from the beginning to satisfy the design. or (b) Elect to use stiffening rings to reduce the L dimension. Step-6(a) Select a new thickness and repeat step-4 to 6 for calculating allowable pressure Step-6(b) Calculation for the use of stiffening rings i) Taking number of stiffening rings = n ii) Now, 𝐿 =
𝐿𝑒𝑓𝑓 𝑛+1
iii) Repeat step-4 to 6 for calculating allowable pressure using new value of L.
Fig: 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 COVER
• • • • •
Design of Stiffening rings Design of Heads Design of Nozzles Design of various types of supports Programming the various design procedure and calculation involved. • Sample data results, comparison and validation • Conclusion
References 1.
Nitant M. Tandel, Jigneshkumar M. Parmar, A Review on Pressure Vessel Design and Analysis, Paripex - Indian Journal Of Research, May 2013
2.
J. Philip Ellenberger PE, Robert Chuse, Bryce E. Carson Sr., Pressure Vessels – The ASME code simplified, 8th edition, Mc Graw- Hill Professional Engineering
3.
B.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.
4.
Ghader Ghanbari, Mohammad Ali Liaghat, Ali Sadeghian, “Pressure Vessel Design, Guides & Procedures”
5.
Dennis R. Moss, Pressure Vessel Design Manual, 3rd Edition-2004, Gulf Professional Publishing (An imprint of Elsevier)
6.
Dr. R. K. Bansal, A Textbook of Strength of Materials, 4th Edition-2009.
7.
Somnath Chattopadhyay, Pressure Vessel Design and Practice, CRC Press.
8.
Henry H. Bednar, Pressure Vessel Design Handbook, 2nd Edition-1991. Krigerer Publishing company
9.
James R. Farr and Maan H. Jawad, Guidebook for the design of ASME Section VIII pressure vessels, 2nd Edition-2001, ASME Press New York.
10.
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
