1 Introduction
Vessels, tanks and pipelines that carry, store or receive fluids are called Pressure vessel.
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
The fluid inside the vessel may undergo a change in state as in case of steam boilers, or may combine
with other reagents as in case of a chemical reactor.
Pressure vessels often have a combination of high pressures together with high temperatures, and in
some cases flammable fluids or highly radioactive materials.
Because of such hazards it is imperative that the design be such that no leakage occurs and these
vessels have to be designed carefully to cope with the operating temperature and pressure.
2 Applications of Pressure vessel in Industries
Pressure vessels are used in a number of industries
 Power generation industry for fossils
 Nuclear power
 Petrochemical industry for storing and processing crude petroleum oil in tank farms as well as
storing gasoline in service station
 Chemical Industry
 Industry plants for storage and manufacturing process
3 Pressure vessel classification
3.1 Based on manufacturing methods





Welded vessels
Forged vessels
Multi wall vessels
Multi wrapped vessels
Band wrapped vessels
3.2 Based on manufacturing materials



Steel vessels
Non ferrous vessels
Non metallic vessels
3.3 Based on geometric shapes




Cylindrical vessels
Spherical vessels
Rectangular vessels
Combined vessels
3.4 Based on installation methods


Horizontal vessels
Vertical vessels
3.5 Based on pressure bearing situation


Internal pressure vessels
External pressure vessels
3.6 Based on wall thickness


Thin wall vessels
Thick wall vessels
3.7 Based on technological processes




Heat exchanger vessel
Separation vessel
Reaction vessel
Storage container vessel
3.8 Based on operating temperatures




Low temperature vessels (less than or equal to -20oC)
Normal temperature vessels (between -20oC to 150oC)
Medium temperature vessels (between 150oC to 450oC)
High temperature vessels (more than or equal to 450oC)
3.9 Based on design pressure




Low pressure vessel (0.1 MPa to 1.6 MPa)
Medium pressure vessel (1.6 MPa to 10 MPa)
High pressure vessel (10 MPa to 100 MPa)
Ultra high pressure vessel (More than 100 MPa)
3.10 Based on usage mode


Fixed pressure vessel
Mobile pressure vessel
4 Pressure vessel types
4.1 Horizontal Pressure vessel
4.2 Vertical Pressure vessel
4.3 Tower (Column)
4.4 Reactor
Reactors are used where chemical reactions of process fluids are required.
4.5 Spherical tank
Spherical tanks are usually used for gas storage under high pressure
5 Components of Pressure Vessel
5.1 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.
There are two different classes of shell
 Thick shell
 Thin shell
A shell is called thin if the maximum valve of the ratio t/r (where r is the radius of the curvature of the
middle surface) can be neglected in comparison with unity.
Max(t/r) ≤ 1/20
Shells for which this inequality is violated are referred to as thick shell.
5.2 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 can also be used inside a vessel. These “intermediate
heads” separate sections of the pressure vessel to permit different design conditions in each section.
5.2.1 Ellipsoidal
This is also called a 2:1 elliptical head. The shape of this head is more economical, because the height
of the head is just a quarter of the diameter. Its radius varies between the major and minor axis.
5.2.2 Torispherical
A Torispherical (or flanged and dished) head is typically somewhat flatter than an elliptical head and
can be the same thickness as an elliptical head for identical design conditions and diameter. The
minimum permitted knuckle radius of a Torispherical head is 6% of the maximum inside crown radius.
The maximum inside crown radius equals the outside diameter of the head.
5.2.3 Hemispherical
A sphere is the ideal shape for a head, because the pressure in the vessel is divided equally across the
surface of the head. The radius (r) of the head equals the radius of the cylindrical part of the vessel.
The required thickness of a hemispherical head is normally one-half the thickness of an elliptical or
Torispherical head for the same design conditions, material, and diameter. Hemispherical heads are
normally fabricated from segmented sections that are welded together, spun, or pressed.
5.2.4 Conical
Tall towers may have sections with different diameters along their length. The transition between the
different diameters is made in a conical section. The most common design for a conical transition does
not have formed knuckles at the ends of the cone. The cylindrical sections of different diameter are
welded to each end of the cone. Formed knuckles are sometimes used at the cone-to-cylinder
transition in order to reduce localized stresses. When knuckles are used, the transition is called
Toriconical. The use of knuckles is 106 mandatory when the cone half-apex angle exceeds 30°.
Knuckles are also sometimes used for smaller angles when there is concern about potentially high
local stresses at the cone-to-cylinder junction. The ASME Code has design procedures for Toriconical
sections.
5.3 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 the following applications: ·




Attach piping for flow into or out of the vessel. ·
Attach instrument connections, (e.g., level gauges, thermo-wells, or pressure gauges).
Provide access to the vessel interior at man-ways. ·
Provide for direct attachment of other equipment items, (e.g., a heat exchanger or mixer).
Nozzles are also sometimes extended into the vessel interior for some applications, such as for inlet
flow distribution or to permit the entry of thermo-wells.
5.4 Support
5.4.1 Skirt
Most common methods of supporting vertical pressure vessels are by means of a rolled cylindrical or
conical shell called a skirt. The skirt can be either lap fillet or butt welded directly to the vessel.
This method of support is attractive from the designer’s stand point because it minimizes the local
stresses at the point of attachment, and the direct load is uniformly distributed over the entire
circumference.
The critical line in the skirt support is the weld attaching the vessel to the skirt
5.4.2 Leg
A wide variety of vessels, bins, tanks, and hoppers may be supported on legs. Leg supports should be
equally spaced around the circumference.
Leg supports may be braced or unbraced. Braced legs are those which are reinforced with either cross
bracing or sway bracing. Sway braces are the diagonal members which transfer the horizontal loads,
but unlike cross braces, they operate in tension only. Cross braces are tension and compression
members. Cross braces can be pinned at the centre or unpinned, and transfer their loads to the legs
via wing plated or can be directly welded to the legs.
Bracing is used to reduce the number or size of the legs required by eliminating bending in legs.
5.4.3 Saddle
Horizontal pressure vessels and tanks are supported on two vertical cradles called saddles. A saddle
support spreads the weight load over a large area of the shell to prevent an excessive local stress in
the shell at the support points. The width of the saddle, among other design details, is determined by
the specific size and design conditions of the pressure vessel. The use of more than two saddles should
be avoided. The reason for not using is that it creates an indeterminate structure, both theoretically
and practically. Saddle itself as various parts: the web, base plate, ribs and wears plate. The saddle
itself is normally bolted to a foundation via anchor bolts. The other support is normally free to permit
unrestrained longitudinal thermal expansion of the drum
Saddles may be steel or concrete.
5.4.4 Lug
Lugs that are welded to the pressure vessel shell may also be used to support vertical pressure vessels.
The use of lugs is typically limited to vessels of small to medium diameter (1 to 10 ft.) and moderate
height-to-diameter ratios in the range of 2:1 to 5:1. Lug supports are often used for vessels of this size
that are located above grade within structural steel. The lugs are typically bolted to horizontal
structural members to provide stability against overturning loads; however, the bolt holes are often
slotted to permit free radial thermal expansion of the pressure vessel.
Lugs offer one of the least expensive and most direct ways of supporting pressure vessels. They can
readily absorb diametric expansion by sliding over greased or bronzed plates, are easily attached to
the vessel by minimum amounts of welding, and are easily levelled in the field.
Since lugs are eccentric supports they induce compressive, tensile, and shear forces in the shell wall.
Two or four lug systems are normally used.
6 Design conditions & loading
The mechanical design of a pressure vessel begins with specification of the design pressure and design
temperature. Pressure imposes loads that must be withstood by the individual vessel components.
Temperature affects material strength and, thus, its allowable stress, regardless of the design
pressure. Some pressure vessels have multiple sets of design conditions that correspond to different
modes of operation. For example, during its operating cycle, a reactor may have a high pressure and
moderate temperature during normal operation, but it may operate at a much lower pressure and a
very high temperature during catalyst regeneration. Both sets of design conditions must be specified
because either one or the other may govern the mechanical design. All pressure vessels must be
designed for the most severe conditions of coincident pressure and temperature that are expected
during normal service.
Normal service includes conditions that are associated with
 Startup
 Normal operation
 Deviations from normal operation that can be anticipated (e.g., catalyst regeneration or
process upsets)
 Shutdown
6.1 Different types of loads acting on pressure vessel
6.1.1
Pressure
6.1.1.1 Operating Pressure
The operating pressure must be set based on the maximum internal or external pressure that the
pressure vessel may encounter. The following factors must be considered:
 Ambient temperature effects.
 Normal operational variations. ·
 Pressure variations due to changes in the vapour pressure of the contained fluid.
 Pump or compressor shut-off pressure. ·
 Static head due to the liquid level in the vessel.
 System pressure drop.
 Normal pre-start-up activities or other operating conditions that may occur (e.g., vacuum),
that should be considered in the design.
6.1.1.2 Design Pressure
 Generally, design pressure is the maximum internal pressure (in psig), that is used in the
mechanical design of a pressure vessel.
 For full or partial vacuum conditions, the design pressure is applied externally and is the
maximum pressure difference that can occur between the atmosphere and the inside of the
pressure vessel.
 Some pressure vessels may experience both internal and external pressure conditions at
different times during their operation. The mechanical design of the pressure vessel in this
case is based on which of these is the more severe design condition.


6.1.2
The specified design pressure is based on the maximum operating pressure at the top of the
vessel, plus the margin that the process design engineer determines is suitable for the
particular application.
The hydrostatic pressure that is exerted by the liquid must be considered in the design of
vessel components upon which it acts. Therefore, the pressure that is used to design a vessel
component is equal to the design pressure at the top of the vessel, plus the hydrostatic
pressure of the liquid in the vessel that is above the point being designed
Temperature
6.1.2.1 Operating Temperature
The operating temperature must be set based on the maximum and minimum metal temperatures
that the pressure vessel may encounter.
6.1.2.2 Design Temperature
The design temperature of a pressure vessel is the maximum fluid temperature that occurs under
normal operating conditions, plus an allowance for variations that occur during operation.
6.1.2.3 Critical Exposure Temperature
The CET must also be specified for pressure vessel design to ensure that materials that have adequate
fracture toughness are selected for construction (i.e., MDMT ≤CET).
6.1.3
Other Design Loadings
 Internal or external design pressure.
 Weight of the vessel and its normal contents under operating or test conditions. ·
 Superimposed static reactions from the weight of attached equipment (e.g., motors,
machinery, other vessels, piping, linings, insulation).
 Loads at attached of internal components or vessel supports.
 Wind, snow, and seismic reactions.
 Cyclic and dynamic reactions that are caused by pressure or thermal variations, or by
equipment that is mounted on a vessel, and mechanical loadings.
 Test pressure combined with hydrostatic weight.
 Impact reactions such as those that are caused by fluid shock.
 Temperature gradients within a vessel component and differential thermal expansion
between vessel components.
7 Pressure vessel design codes and standards
There are standards and codes laid down by approved regulatory bodies for the design,
construction, welding, testing, marking, operation, inspection, and repair of any pressure vessel,
which provides fundamental safeguards and good safety practices.






ASME Boilers and Pressure Vessel Codes
API Standards
PD5500
British Standards
European Codes and Standards
Other International Codes
The standards and codes that are commonly used codes for pressure vessels are:




























ASME Boiler and pressure vessel code: Section VIII, div 1 and div2
ASME B16.9 Factory made wrought steel butt welding fittings : 1978
ASME B16.11 Forged steel fittings socket-welded and threaded : 1980
ASME Boiler and Pressure Code Part X, Fiberglass Reinforced Plastic Pressure Vessels (1992).
BS
1500:
1958
Fusion
Welded
Pressure
Vessels
for
General
Purposes.
BS 5500 replaced this conventional code in the UK in 1976.
BS 1515: 1965 - Fusion Welded Pressure Vessels for Use in the Chemical, Petroleum and Allied
Industries.
BS 5500 : Specification for Unfired Fusion Welded pressure Vessels
BS EN 286-1:1991. Simple unfired pressure vessels designed to contain air or nitrogen.
BS 1501: 1970 - Steels for Pressure Purposes:
Part 1 (1990) - Specification for carbon and carbon manganese steels
Part
2
(1988)
Specification
for
alloy
steels
Part 3 (1990) - Specification for corrosion and heat resisting steels
BS 1502: 1990 - Specification for steels for fired and unfired pressure vessels: sections and bars
BS 1503: 1989 - Specification for steel forgings for pressure purposes
BS 1504: 1984 - Specification for steel castings for pressure purposes
BS 1506: 1990 - Specification for carbon, low alloy and stainless bars and billets for bolting material to
be used in pressure retaining applications.
BS 2594: 1975 - Specification for carbon steel welded horizontal cylindrical storage tanks.
BS 2654: 1989 - Specification for vertical steel welded non-refrigerated storage tanks with butt-welded
shells for the petroleum industry
BS 2790: 1992 - Specification for design and manufacture of shell boilers of welded construction
BS 5276: 1977 - Pressure Vessel details (dimensions)
BS 5387: 1976 - Specification for vertical cylindrical welded steel storage tanks for low temperature
service: double wall tanks for temperatures down to -196°C.
BS 4994: 1987 - Specification for Design and Construction of Vessels and Tanks in Reinforced Plastics.
BS 6374: 1984 - Lining of equipment with polymeric materials for the process industries.
API 510 Pressure vessel inspection code: Maintenance inspection, rating, repair, and alteration
API RP 572 Inspection of pressure vessels
API Standard 653 Tank inspection, repair, alteration and reconstruction.
API RP 520 Sizing, selection, and installation of pressure relieving devices in refineries
ISO R831: Recommendations for Stationary Boilers which is applicable to pressure vessels.
Pressure Vessels: Non-metallic materials of construction
ASTM D 4021-86 Standard Specification for Contact Moulded Glass-fiber-reinforced Thermosetting
Resin Underground Petroleum Storage Tanks.
ASTM D 4097-88 Standard Specification for Contact Moulded Glass-fiber-reinforced Thermosetting
Resin Chemical Resistant Tanks.
Other Vessels (including Storage Tanks)





API Std 620 Design and construction of large, welded, low-pressure storage tanks, American
Petroleum Institute, 1990.
API Std 650 Welded steel tanks for oil storage, American Petroleum Institute, 1988.
API Std 653 Tank inspection, repair, alteration, and reconstruction, American Petroleum Institute,
1991.
API 12B - Bolted Production Tanks.
API 12D - Large Welded Production Tanks.


API 12F - Small Welded Production Tanks.
API Std 2000 venting atmospheric and low pressure storage tanks: Nonrefrigerated and
refrigerated, American Petroleum Institute, 1998.
Heat Exchangers
 BS 3274: 1960- Tubular Heat Exchangers for General Purposes.
 American Tubular Heat Exchanger Manufacturers Association (TEMA standards).
 The TEMA standards cover three classes of heat exchanger:
 Class R - generally severe duties in the petroleum and related industries;
 Class C - moderate duties in commercial and general process applications;
 Class B - exchangers for use in the chemical process industries.
 API Standard 660: 1987 - `Shell and Tube heat Exchangers for General Refinery Services'
supplements both the TEMA standards and the ASME code.
 API Standard 661: 1992 - Air Cooled Heat Exchangers for General Refinery Services.
8 Pressure Vessel failure
It is important to identify the potential failure modes and mechanism in the pressure vessel. Different
failure modes should be related to possible safety and economic consequences. It is necessary to focus
evaluation on those failure scenarios which are having highest rate of occurrence.
The failure modes are identified below.







Small crack
Local corrosion/Wall thinning
Excessive distortion
Leaking through wall
Through wall corrosion
Excessive leakage
Fracture rupture
Degradation if not detected and repaired will ultimately lead to catastrophic failure.
In some cases, concerns may be limited to catastrophic ruptures that would present the greatest
threat to workers or to the general public. In other cases, evaluations may have a broader objective
that considers unexpected degradation (corrosion, cracking, etc.) that would require repairs or
replacements of components and thereby have an economic impact associated with repair costs
and/or the loss of the productive use of the component. The consequences of small leaks can be very
different depending on the situation. For a water storage vessel, the loss of a small volume of water
could be of little concern; whereas, small leaks in vessels containing toxic or flammable materials could
result in a large number of fatalities.
Small Crack – Degradation is sometimes detected in the form of a crack that does not fully penetrate
the wall of the vessel or piping component.
Local Corrosion and Wall Thinning – While design methods usually specify a wall thickness that
includes some allowance for corrosion over the life of the vessel, the actual operating conditions may
produce local rates of corrosion that exceed the expected rates.
Excessive Distortion – A failure mode of concern may not involve penetration of the component wall,
but may rather degrade the function of the component because of excessive deflection or distortion.
For example, seating surfaces may become sufficiently misaligned to the degree that gasket leakage
results.
Leaking Through-Wall Crack – In some cases, even a small amount of leakage can have significant
safety consequences, especially if the leaking fluid is highly toxic or flammable. In other cases, the
release of otherwise non-hazardous fluids could impact the operation of nearby critical equipment by
causing corrosion or electrical malfunctions.
Through-Wall Corrosion/Wall Thinning – As for cracking, leakage even at relatively small rates can
present significant safety or economic consequences.
Excessive Leakage – Leakage rates can over time increase to levels that impact the function of a
system or component. For example, a leak could eventually depressurize a critical system to the extent
that it could no longer perform its intended function. In other cases, the leakage could create a water
spray that could cause damage in the area adjacent to the leak
Fracture/Catastrophic Rupture – This most severe of consequences comes from sudden fracture or
ruptures, which can occur without any prior leakage to give any warning of impending failure. The
consequences of concern can be related to loss of function of the rupture component itself (e.g., loss
of cooling water to process equipment) or can come from the extreme energy of the rupture event
(e.g., high velocity missiles, blast waves, release of hot fluids, etc)
Rupture
Cracking
Local buckling & Crack
Vacuum Hazard
Failure Mechanisms
Many failures come from gradual material degradation (e.g., corrosion, fatigue cracking, wear, etc.)
that occurs over time spans of many years before it advances to a stage sufficient to cause a structural
failure (leak or rupture event). Metal fatigue is one common failure mechanism. Small-diameter piping
is often subject to vibration stresses that cause cracking. Fatigue failures of larger sizes of vessels and
piping are more likely to come from cyclic thermal stresses such as at locations exposed to cyclic
exposures to hot and cold fluids. Corrosion mechanisms are a particularly common cause of failures
both in the form of widespread loss material (wall thinning) or as local attack such as pitting or
cracking. In other cases, a single short-term event (e.g., overpressure, extreme overheating, water
hammer, etc.) can cause a sudden failure. Some loading events are natural occurrences such as
earthquake loadings; whereas, other events come from human errors in operating and maintaining
the facility such as from improper repairs and operation at pressures or temperatures over design
limits. Pressurized systems are usually protected from excess pressures and temperatures by safety
devices, but these devices can fail to function due to time-related degradation or improper installation
or maintenance.
The main causes of failure of a pressure vessel are as follows:
 Faulty Design
 Operator error or poor maintenance
 Operation above max allowable working pressures
 Change of service condition
 Over temperature
 Safety valve
 Improper installation
 Corrosion
 Cracking
 Welding problems
 Erosion
 Fatigue
 Stress
 Improper selection of materials or defects
 Low –water condition
 Improper repair of leakage
 Burner failure
 Fabrication error
 Over pressurisation
 Failure to inspect frequently enough
 Erosion
 Creep
 Embrittlement
 Unsafe modifications or alteration
 Unknown or under investigation
9 Pressure vessel qualification: Design by analysis (finite element
analysis)
Before 1963, all Pressure Vessels were designed using a systematic Design by Formula Approach which
was based on experience and simple mechanics. What was mostly described was how to keep hoop
stress low with respect to yield and how to use ductile material to accommodate local peak stresses.
In the Design by formula, the vessel geometry and major dimensions such as radius, length, etc. are
specified and the required thickness is then calculated for a given load using equations and graphical
data. With the development of the nuclear technology in the 1950s, pressure vessel design
requirements needed to be improved in order to permit the use of higher allowable stresses without
reduction in Safety.
This required changing the philosophy of Code design by formula. It is also worth to note that advances
in mechanics theory and analysis methods provided new and more scientific methods for the pressure
vessel design.
In 1963, ASME published the B&PV Code Section III: Nuclear Vessels based on the principles of limit
analysis (Shakedown analysis, Fatigue Analysis) and Stress Analysis was used to determine higher
allowable loads and more consistent margins of safety.
This New code permitted two approaches for design:


Improved design by formula, providing more accurate formula for sizing common components
and higher allowable stresses, was intended for standard configurations
Design by Analysis, in which designer performs stress analysis and evaluates results against
code limits, was intended for configurations not covered by the Design By Formula
The main guidelines of the Design by Analysis are to prevent the gross plastic deformation or ductile
burst under static load, the incremental plastic collapse under repeated or cyclic load and the fatigue
under cyclic load. Elastic buckling, creep, brittle fracture, stress corrosion, etc. also have to be
considered…
10 Case studies
10.1 Case study 1: Qualification of mounted butane storage bullet of
2053MT capacity by PD5500, EEMUA-190 using finite element analysis
10.1.1 Introduction
The mounded bullets are used to store highly inflammable, toxic and pressurized gases such as
Butane/Propane/LPG & it is of prime challenging task and there is a need to design storage facilities
for such gases with safety of the personal in and around, the locations, where it is situated. The safety
is of prime importance, because it not only leads to the loss to the industry but also to the lives of the
people.
10.1.2 Objective
The objective of this is “Design validation of Mounded Butane storage bullet as per PD-5500, EEMUA190”
10.1.3 Sequence of activities
 3D cad model generation
 Discretization

FRS generation
3
2.5
2
1.5
1
0.5
0
0
50
100
150







Material modelling
Applying loads & Boundary conditions
o Loads & load combinations as per PD 5500
FE Analysis
Post processing the results
Qualification of the mounded bullets using PD5500
Report & Documentation
Approval from customer
10.1.4 Complexities involved
 Identification of SCL locations
 Calculation of Pressure due to mound at Dome & Shell region of the Mounded Bullet
 Calculation of Elastic foundation stiffness
 Understanding the requirement of “UNEVEN” supports i.e. Midsoft & End soft
conditions
 FRS generation.
 Stress categorization
10.1.5 Approach to resolve complexities
 SCL locations are identified based on the critical regions of the component & on the
previous experience.
 Pressure due to mound is calculated as per A.4.2.5 of EEMUA-190.
 Elastic foundation stiffness is calculated as per EEMUA-190
 ProSIM has previous experience of generating FRS using IS-1893. This helped us to
generate the FRS for this project.
 Good understanding of PD5500 standard helped us to categorize the stress based on the
code annexure.
10.1.6 Qualification criteria & Results
 The accountable stresses on the components meshed with solid elements shall be
extracted from stress linearization method. Since for shell elements we shall get the
membrane and bending
 The qualification of components is based on the membrane and Membrane + Bending
stresses.
 Stress categorization is mandatory requirement to qualify the component as per PD 5500
S
Results: Membrane and membrane + bending stresses are calculated. The stresses are compared
with allowable as mentioned in the PD5500.
10.1.7 Benefits to customer
 The expertise of ProSIM in both finite element analysis and code understanding helped the
customer to validate his equipment and get qualified by the approval authority.
 The simulation of the equipment helped the customer to understand the stressed regions.
 The simulation also helped to understand the factor of safety (FOS) for different components
and regions, which will help him in optimize the equipment – strength the region of lesser FOS
and save the material in the region of higher FOS.
10.2 Case study 2: Qualification of blow egg vessel of 22m3 capacity by
ASME sec VIII, Div2, using finite element analysis
10.2.1 Introduction
10.2.2 Objective
The objective was to validate the blow egg vessel as per ASME sec VIII div 2. The scope of work
involves qualification of blow egg vessel by performing stress and fatigue analysis. The ASME sec VII I
div 2 needs the vessel to be qualified based on the stresses generated and the fatigue life of the
equipment.
10.2.3 Sequence of activities
 3D cad model generation

Discretization


Material modelling
Applying loads & Boundary conditions
o Loads & load combinations as per ASME sec VIII div 2
FE Analysis
Post processing the results
Fatigue analysis







Post processing the results
Qualification of the blow egg vessel using ASME sec VIII div 2
Report & Documentation
Approval from customer
10.2.4 Complexities involved
The geometry of the blow egg vessel was intricate. The discretization became complex because of the
geometry. The hexahedral meshing involves detailed planning and approach towards the
discretization and also the quality to be maintained.
Identifying the Stress Classification Lines (SCL) locations
To extract stresses at SCL locations, the mesh needs to as much as possible symmetric in nature and
also have defined mesh flow. To have this in such a complicated model was a challenge.
Identifying zero pressure height and reference pressure height in the assembly to analyze the vessel
for hydrotest analysis
10.2.5 Approach to resolve complexities
The detailed approach note was defined as how to mesh the model and an experience engineer who
has worked on similar complex project was assigned the work.
Well established methods to mesh the complex equipments helped us to maintain the desired
quality parameters and criteria’s.
The understanding of ASME section VIII, div 2 helped us to identify the stress classification lines
(SCL).
10.2.6 Qualification criteria & Results
 The accountable stresses on the components meshed with solid elements shall be
extracted from stress linearization method. Since for shell elements we shall get the
membrane and bending
 The qualification of components is based on the membrane and Membrane + Bending
stresses.
 Stress categorization is mandatory requirement to qualify the component as per PD 5500
S
Results: Membrane and membrane + bending stresses are calculated. The stresses are
compared with allowable as mentioned in the ASME section VIII, Div 2. The fatigue life
calculations were performed using FESAFE software and compared with the life
calculations using ASME sec VIII, Div 2.
10.2.7 Benefits to customer
 The equipment was not qualifying as per ASME sec VIII, div 2. ProSIM expertise in design
analysis helped customer in providing the engineering solution and made sure the equipment
satisfies all the criteria’s as per ASME sec VIII, div 2.
 The expertise of ProSIM in both finite element analysis and code understanding helped the
customer to validate his equipment and get qualified by the approval authority.
 The simulation of the equipment helped the customer to understand the stressed regions.
 The simulation also helped to understand the factor of safety (FOS) for different components
and regions, which will help him in optimize the equipment – strength the region of lesser FOS
and save the material in the region of higher FOS.