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Liquid Petroleum Gas Injection Tank Design Engineering Essay

For my final year project I will be designing a liquid petroleum gas injection tank in accordance with the Vehicle type approval and ISO certification. This will include approval of things such as materials, operations and third party approvals including fire regulations. The reason for the design on an LPG tank is that it will improve the carbon emissions of any vehicle such as CO2 and hydrocarbons as well as saving companies and people money on their vehicles.

Aims

Objectives

Complete initial research including VCA specifications to establish a design brief and a product design specification.

Detailed research into specific design elements (including: Materials, Impact mechanics, Machinery etc)

A set of conceptual designs

Complete one cycle of controlled convergence using both evaluation matrices and a weighted objectives method. Select three best.

Compare best concepts against VCA specifications.

Repeat controlled convergence on the best concepts using feedback from VCA specifications. Select a single concept to take foreward.

Generate a general arrangement drawing, a set of embodiment drawings, and identify key components and connections.

Create detailed designs using SolidWorks.

Use analysis tools to digitally validate design.

Research and Generate manufacturing data.

Use manufacturing data to create a prototype.

Scope

The scope of my project is sure that my project stays on the right track and within the time limit I have set for myself and my project.

My project is to design a commercial LPG tank which will reduce the levels of carbon omissions released by the vehicles. This will also save companies money which they are paying out for diesel.

I will use VCA specifications to make concept designs on an LPG tank and used evaluation matrices to pick the best design.

Research

For my research I will be looking into why we need LPG tanks for the future and what their advantages and disadvantages are in the industry. I will also research the different materials that can be used and how they can affect the performance.

Liquefied petroleum includes commercial butane, commercial propane and mixtures thereof. At normal atmospheric temperatures and pressures it is a gas, but has the property of being readily liquefied under moderate pressures at ambient temperatures. It can be stored and handled as a liquid under pressures at ambient temperature or partially refrigerated to reduce vapour pressure.

It is supplies against close specifications which include limiting figures for vapour pressure. The two different grades of LPG are usually markets are referred to as commercial butane and propane. They have wide differences in vapour pressures.

Properties and characteristics

Commercial Butane- Is a hydrocarbon mixture consisting predominately of butane or butylenes.

Commercial Propane- Is a hydrocarbon consisting predominately of propane or propylene.

General Characteristics

Lpg at normal atmospheric temperatures and pressures is a gas which is heavier than air, butane in the vapour phase is twice as heavy where as propane is one and a half times as heavy.

Small quantities of lpg vapour in air can form a flammable mixture.

Lpg is non corrosive to steel and generally to copper, copper alloys or aluminium.

Lpg, whether in liquid or vapour phase, is only slightly toxic. The vapour is slightly anaesthetic if it is inhaled in high concentrations.

Pure Lpg is practically odourless, for safety purposes an odorant may be added to the commercial grades.

 NPL can produce LPG (liquefied petroleum gas), LNG (liquefied natural gas) and other liquid hydrocarbon standards in two forms of vessel technology: constant pressure (piston) cylinders or dual-port valve dip-tube cylinders.

      Constant pressure cylinder on the left             Dual-port valve dip-tube cylinder on the right

The constant pressure cylinders employ a piston as a physical barrier maintained by high pressure, which ensures that the composition of the mixture remains. The cylinders also possess an integral mixer that guarantees users draw homogenous samples of constant composition. Cylinders of 300mL, 500mL or 1L volume are available.

The dual-port valve dip-tube cylinders do not have any physical barrier between the gas and the liquid hydrocarbon mixture, however the dual port valve does allow for a overpressure of gas (usually helium) to be maintained. These cylinders have an internal volume of 10L.

Some example liquid hydrocarbon mixtures are shown in the table below.

Component

Amount Fraction (% mol/mol)

Liquefied Petroleum Gas (C3rich)

Liquefied Petroleum Gas (C4rich)

Liquefied Natural Gas

Methane

-

-

80

Ethane

0.5

-

10

Propane

70

17.5

2.5

Propene

15

4.0

-

iso-Butane

2.0

10

2.0

n-Butane

5.0

60

2.0

But-1-ene

1.5

2.5

-

iso-Butene

1.0

2.0

-

trans-2-Butene

-

1.75

-

cis-2-Butene

-

1.25

-

iso-Pentane

-

0.5

1.0

n-Pentane

-

0.5

1.5

n-Hexane

-

-

1.0

Market Research

From only 3,500 at the end of 1998, there were 160,000 vehicles on the road in the UK by the end of 2009.

We have over 1400 refuelling stations which is one of the highest number compared with the number of vehicles in the world.

Worldwide at the end of 2008 there were over 14 million LPG vehicles with 8.5 million of these in Europe.

Notable markets include:

Wordwide

Korea - 2.321 million - the largest market in the world

Australia - 650,000 - now one of the fastest growing markets following the introduction of grants in 2006

Japan - 289,000 - mostly taxis which are required to run on LPG

Europe

Turkey - 2.240 million

Poland - 1.9 million - the largest market in Europe

Italy - 930,000 - one of the longest established markets and one of two main sources of LPG equipment used in the UK

Netherlands - 240,000 - the other main source of LPG equipment used in the UK

France - 140,000 - our closest neighbour and with one of the best refuelling networks on main routes

Germany - 300,000 - and the fastest growing market in the world following the government freeze on fuel duty to 2018

Auto gas market from 2007-2008

Design Codes

Storage tanks have to be designed, fabricated and tested in accordance with a recognized pressure vessel code such as BS 1515, BS1500 or ASME.

BS EN 589:2008-Automotive fuels. LPG. Requirements and test methods

BS EN 12493:2008-LPG equipment and accessories. Welded steel tanks for liquefied petroleum gas (LPG). Road tankers design and manufacture

BS EN 12817:2010-LPG equipment and accessories. Inspection and requalification of LPG tanks up to and including 13 m3

BS EN 12252:2005+A1:2008: LPG equipment and accessories. Equipping of LPG road tankers

BS EN 12542:2010: LPG equipment and accessories. Static welded steel cylindrical tanks, serially produced for the storage of liquefied petroleum gas (LPG) having a volume not greater than 13 m$u3. Design and manufacture

BS EN 12805:2002: Automotive LPG components. Containers

BS EN 12807:2009: LPG equipment and accessories. Transportable refillable brazed steel cylinders for liquefied petroleum gas (LPG). Design and construction

BS EN 12816:2001: Transportable refillable steel and aluminium LPG cylinders.

ASME Section VIII-Overview- Used worldwide, use minimum requirements for safe construction and operation used in Divisions 1,2 and 3.

The ASME Code Section VIII, Division 1 applies for pressures that exceed 15 psig and through 3,000 psig. At pressures below 15 psig, the ASME Code is not applicable. At pressures above 3,000 psig, additional design rules are required to cover the design and construction requirements that are needed at such high pressures.

The ASME Code is not applicable for piping system components that are attached to pressure vessels. Therefore, at pressure vessel nozzles, ASME Code rules apply only through the first junction that connects to the pipe. This junction may be at the following locations:

· Welded end connection through the first circumferential joint.

· First threaded joint for screwed connections.

· Face of the first flange for bolted, flanged connections.

· First sealing surface for proprietary connections or fittings.

The Code also does not apply to no n pressure-containing parts that are welded, or not welded, to pressure-containing parts. However, the weld that makes the attachment to the pressure part must meet Code rules. Therefore, items such as pressure vessel internal components or external supports do not need to follow Code rules, except for any attachment weld to the vessel.

The scope of Division 2 is identical to that of Division 1; however, Division 2 contains requirements that differ from those that are contained in Division 1. Several areas where the requirements between the two divisions differ are highlighted below.

· Stress. The maximum allowable primary membrane stress for a Division 2 pressure vessel is higher than that of a Division 1 pressure vessel. The Division 2 vessel is thinner and uses less material. A Division 2 vessel compensates for the higher allowable primary membrane stress by being a more stringent

than Division 1 in other respects.

· Stress Calculations. Division 2 uses a complex method of formulas, charts, and design by analysis that results in more precise stress calculations than are required in Division 1.

· Design. Some design details are not permitted in Division 2 that are allowed in Division 1.

· Quality Control. Material quality control is more stringent in Division 2 than in Division 1.

· Fabrication and Inspection. Division 2 has more stringent requirements than Division 1.

The choice between using Division 1 and Division 2 is based on economics. The areas where Division 2 is more conservative than Division 1 add to the cost of a vessel. The lower costs that are associated with the use of less material (because of the higher allowable membrane stress) must exceed the increased costs that are associated with the more conservative Division 2 requirements

in order for the Division 2 design to be economically attractive.

A Division 2 design is more likely to be attractive for vessels that require greater wall thickness, typically over approximately 2 inches thick. The thickness break point is lower for more expensive alloy material than for plain carbon steel, and will also be influenced by current market conditions. A Division 2 design will also be attractive

for very large pressure vessels where a slight reduction in required thickness will greatly reduce shipping weights and foundation load design requirements.

Division 3, Alternative Rules For Construction of High

Pressure Vessels

Division 3 applies to the design, fabrication, inspection, testing, and certification of unfired or fired pressure vessels operating at internal or external pressures generally above 10,000 psi. This pressure may be obtained from an external source, a process reaction, by the application of heat, or any combination thereof. Division 3 does not

establish maximum pressure limits for either Divisions 1 or 2, nor minimum pressure limits for Division 3.

The design stress should include an allowance to enable the thank to withstand shocks normally encountered by movements on the road. If the tank is self supporting the tank design should provide carrying for the additional stresses normally carroed by the chassis frame. Alos provisions should be made for distrubing the localized stresses from attachements to the tank.

The tank and all attachements to the tank should be protected against accidental damage which may result from a collision or an operational cause.

Design Pressure

The design pressure of the tank should not be less than the vapoir pressure of the actual LPG to be stored, at the highest temperature that the contents will reach in service.

Tanks should not be designed for a pressure of less than 30psig.

Tank Fittings

Each tank should be provided with at least one of the fittings, which all should be suitable for use with LPG ata pressure not less than the design pressure of the tank in which they are fitted. The fittings are:

Pressure relief valve connected directly to the vapour space.

Drain

Means of determing liquid level.

Pressure gauge connected to the vapour space

Means of measuring the temperature of the contents of the tank.

Tank Connections

Each connections should be designed and attached to the tank in accordance with the requirements of the design codes expected for butt welded connections, if screwed connections are used they have to adhere to BS3799 or equivelent. Also that the screwed connections are limitied to a 2inch nominal size or smaller.

All connections should be designed to withstand the most serve combined stresses to which they may be subjected by the pressure of the LPG, then pumping pressures and shock loadings caused by transport conditions.

Pressure Relief Valves

One or more pressure relief valves should be fitted to the tank connected to the vapour space. Relief valves should preferably be spring loaded, and in no circumstances should weight loaded relief valves be used. Relief valves should be constructed so that the break-age of any part will not obstruct the free discharge of vapour under pressure. The discharge from the pressure relief valves should be vented away from the tank upwards and unobstructed to the open air, so as to avoid any impingement of the espacing vapour on your tank. The operating mechanism of the valves should preferably be within the tank. The valves should also marked with the start to discharge and the certified capacity in terms of air and pressure. The valves should be tested more than once every five years.

Emergency Shut off Valves

All apertures in the tank which are in excess of 0.055 inch in diameter, other than those for pressure releif valves and those permanently fitted with blank flanges should be fitted with emergency shut off valves, preferably internally mounted which should be designed to to prevent excessive LPG escape. The emergency shut off valves should be operated automatically.

Gauges

The tank should be provided with at least of one of the following gauages:

Determining liquid level of LPG

A pressure gauage

All gauages should be designed to operate in the range of temperatures and pressures for which the tank is designed to withstand normal road shocks. The gauage should also be placed so it can be read from ground level.

Filling Capacity

The maximum quantity of LPG which should be filled into tank should be such that the tank will not become liquid full due to expansion of the contents with rise of temperature to the highest temperature the contant will reach in service. This requirement should be applied irrespective of the ambient temperatrure or product temperature at the time of filling.

Protection of Valves and Accessories

All valves and accessories should be safeguarded against accidentally damage or interference, they should also be mounted and protected away in such a way that the risk of accidental rupture of the branch to which the valve or accessory is connected in minimized. The valves or accessories situated at the rear of a road tanker should be protected by the rear cross member of the chassis.

Tank Painting

Each tank should be adequately painted externally to prevent corrosion and should have reflecting surface.

Marking of Tanks

Each tank should be conspicuously and permanently marked to include the following:

The pressure vessel code to which it is made

The manufactures name and serial number

The water capacity in uk gallons or litres

The maximum safety working pressure

The year in which it was made.

All the markings should remain visible after assembly.

Tank Equipment

Piping, Fittings, Pumps, Meters

Piping valves and fittings should be designed to withstand the most serve combined stresses imposed by the following:

Vapour pressure of product in service

Pumping pressure

Shock loadings caused by road movement

The materials used for the equipment should be sufficiently ductile to withstand rough usage and accidental damage. Brittle materials such as cast iron should not be used.

Protection of Piping and Equipment

All piping and equipment should be adequately protected to minimize accidental damage including rough usage, collision or overturning. Any equipment or section of piping in which liquid may be trapped should be protected against excessive pressure caused by thermal expansion of the contents.

Road Tank Design Considerations

The tank should be either a component of the chassis of the vehicle or securely attached to the chassis. Also if the tank is removable it should be securely fastened to a cradle in which it can be taking away from.

Design Safety Requirements

The engine needs to be a an internal combustion type of engine, the fuel system needs to have a cut off valve which is easy accessible and clearly marked position. The engine and exhaust system together with any all electrical generators, motors, batteries and fuses need to be effiecently screened from the tank. The maximum weight of LPG should not exceed the difference in weight between the unladen weight of the vehicle and the maximum gross weight permitted for that class of transport.

Fire Safety/Protection

The possibility of a major fire outbreak leading to direct flame impingement on the vehicle can be minimized by sound engineering, good operating practices and proper education and training of personnel on both routine operations and on actions to be taken in emergency.

Two serviceable fire extinguishers of suitable size and type should be provided on each vehicle, although foam extinguishers are not suitable for LPG fires. Also while on or near a vehicle carrying LPG a person should not smoke or use lighters or matches.

Gas Leakage Without Fire

In event of a gas leak close any valves where possible which will stop the gas flow, if this is not possible considerations should be given to removing the vehicle to a safe place, providing that doesn’t expose the tank to any further damage or endangering the public or property. If the vehicle can’t be moved use all available means to disperse LPG vapours as well as evacuating the area and removing all sources of ignition.

Gas Leakage with Fire

Apply large quantities of water by jet or spray to the tank to keep it cool. This will allow controlled burning of the gas without the fear of the tank failure. However an effort should be made to remove the source of the flame impingement by cutting off the gas supply.

If sufficient water is not available and an increase in noise or flame will indicate a rise in pressure then evacuate the surrounding area with immediate effect. Except in cases of the flame impingement no attempted should be made to extinguish the flame unless the leakage can be properly stopped or reduced to innocuous proportions.

Inspection and Maintenance of Tank

Check should be made on the vehicle to ensure that at all times it is roadworthy and that it is in fit condition to take on a road journey and all the stress which will be included in that journey. Routine examinations should be carried out by competent staff at regular intervals. Drivers and staff should be selected carefully and be given the appropriate training in the safe handling of LPG.

Material Research Needed!!!!!!!!!!!!!!!!!!!!! Book Engineering Materials

Performance Attributes

Recyclability, safety, corrosion resistance in methanol fuels, and weight

Manufacturing Issues

Cost, formability/shape flexibility, weldability

Steel

Terne-Coated Steel

Advantages: Low cost at high volumes, recyclable, materials cost, and permeability

Disadvantages: Shape flexibility, ineffective corrosion protection from methanol fuel, lead-containing coating

Electrocoated Zn-Ni and Galvanneal

Advantages: Low cost at high volumes, recyclable, effective inside and outside corrosion protection, material cost, and permeability

Disadvantages: Weld ability and shape flexibility

Hot-Dipped Tin

Advantages: Low cost at high volumes, recyclable, effective inside and outside corrosion protection, material cost, permeability, and weld ability

Disadvantage: Shape flexibility

Stainless Steel

Advantages: Corrosion, recycable, and permeability

Disadvantages: Cost at all volumes, formability, and join ability (Alvarado, 1981)

Mechanical Properties Code Requirements

Tensile Requirements

SA 533

22NiMoCr37

SA508

Tensile Strength (N mm-2)

552-689

590-740

550-725

Plastics

Plastic high-density polyethylene (HDPE) fuel tanks made by blow molding. This technology is increasingly used as it now shows its capacity to obtain very low emissions of fuel (see Partial zero-emissions vehicle). HDPE can also take complex shapes, allowing the tank to be mounted directly over the rear axle, saving space and improving crash safety. Initially there were concerns over the low fracture toughness of HDPE, when compared to steel or aluminum. Concern for safety and long term ability to function should be considered and monitored.

After looking into this research I feel that the material which would be more beneficial to use for my design would be stainless steel which will obviously cost more but due to safety factors that are needed when the product will be in use I feel this would be the best material to use.

Theory

Problem identified

The problem that I have identified throughout all my research is that currently there is no products on the market which makes LPG an alternative option for commercial vehicles, mostly all commercial vehicles are currently using diesel when filling up. The cost of diesel is high at the moment and it would be beneficial to the companies to given a cheap option, it would also benefit the world as less gases would be being produced if every commercial vehicle was using an LPG system on the vehicles.

Design hypothesis

I will be designing a liquid petroleum gas tank for use on commercial vehicles. The reason for design is because if all commercial vehicles use LPG it will reduce the harmful emission such as CO2 and hydrocarbons as well as saving companies money and the fuel bill.

Supporting theory for design hypothesis

Material properties

Benefits of Stainless Steel

Corrosion resistance

Lower alloyed grades resist corrosion in atmospheric and pure water environments, while high-alloyed grades can resist corrosion in most acids, alkaline solutions, and chlorine bearing environments, properties which are utilized in process plants.

Fire and heat resistance

Special high chromium and nickel-alloyed grades resist scaling and retain strength at high temperatures.

Hygiene

The easy cleaning ability of stainless makes it the first choice for strict hygiene conditions, such as hospitals, kitchens, abattoirs and other food processing plants.

Aesthetic appearance

The bright, easily maintained surface of stainless steel provides a modern and attractive appearance.

Strength-to-weight advantage

The work-hardening property of austenitic grades, that results in a significant strengthening of the material from cold-working alone, and the high strength duplex grades, allow reduced material thickness over conventional grades, therefore cost savings.

Ease of fabrication

Modern steel-making techniques mean that stainless can be cut, welded, formed, machined, and fabricated as readily as traditional steels.

Impact resistance

The austenitic microstructure of the 300 series provides high toughness, from elevated temperatures to far below freezing, making these steels particularly suited to cryogenic applications.

Long term value

When the total life cycle costs are considered, stainless is often the least expensive material option.

 Chemical compositions for selected stainless steel grades

Chemical composition (% by mass)

Element

Steel Designation (Number)

1.4301 (304)

1.4401 (316)

1.4462 (2205)

Carbon (C)

⩽0.07

⩽0.07

⩽0.030

Chromium (Cr)

17.00–19.50

16.50–18.50

21.00–23.00

Nickel (Ni)

8.00–10.50

10.00–13.00

4.50–6.50

Molybdenum (Mo)

2.00–2.50

2.50–3.50

Manganese (Mn)

⩽2.00

⩽2.00

⩽2.00

Silicon (Si)

⩽1.00

⩽1.00

⩽1.00

Phosphorus (P)

⩽0.045

⩽0.045

⩽0.035

Sulphur (S)

⩽0.015

⩽0.015

⩽0.015

Nitrogen (N)

⩽0.11

⩽0.11

0.10–0.22

Titanium (Ti)

5 × C–0.70

5 × C–0.70

Tungsten (W)

 

 

0.50–1.00

Impact and guidelines

Required Thickness for Internal Pressure

Determine the minimum required thickness for the cylindrical shell and heads of

the following pressure vessel:

· Inside Diameter - 10 - 6

· Design Pressure - 650 psig

· Design Temperature - 750°F

· Shell & Head Material - SA-516 Grade 70

· Corrosion Allowance - 0.125

· 2:1 Semi-Elliptical heads, seamless

· 100% radiography of cylindrical shell welds

· The vessel is in an all vapor service (i.e., no liquid loading)

Testing For Tank

ASME Code and Brittle-Fracture Evaluation

The following pressure vessel components must be considered

in brittle fracture evaluations:

· Shells

· Manways

· Heads

· Reinforcing pads

· Nozzles

· Tubesheets

· Flanges

· Flat cover plates

· Backing strips that remain in place

· Attachments that are essential to the structural integrity of the vessel when welded to pressure-containing components (e.g., vessel supports)

The Minimum Design Metal Temperature (MDMT) is the lowest temperature at which the component is designed to have adequate fracture toughness. It is a function of the component’s material specification and thickness. The Critical Exposure Temperature (CET) is the minimum metal temperature that can occur at the same time as a significant membrane stress in the vessel (e.g., at a pressure that is greater than 25% of the design pressure). The CET is determined by either ambient conditions or process conditions, whichever results in the lowest metal temperature. While the terms MDMT and CET are often used interchangeably, they are separate parameters.

Each component must be evaluated separately for impact test requirements based on its material, thickness, and MDMT. In all cases, the MDMT must be no greater than the CET.

Concept Designs

Brush pens- check internet on how to use

Scan sketches

Design selection

Look up books on design selection

Embodying design

Solidworks

Prototype

Bibliography

Alvarado, P. J. (1981). Steel vs. Plastics: The Competition for Light-Vehicle Fuel Tanks.

Detailed design

Engineering drawings

Discussion/Conclusions/Recommendations

References

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