Analysis of Life of Pressure Vessel

GRD Journals- Global Research and Development Journal for Engineering | Volume 4 | Issue 5 | April 2019 ISSN: 2455-5703

Analysis of Life of Pressure Vessel S. Elangovan Student Department of Mechanical Engineering Bharath Institute of Higher Education and Research, (BIHER) Chennai, India S. Karthikeyan Assistant Professor Department of Mechanical Engineering Bharath Institute of Higher Education and Research, (BIHER) Chennai, India

Rajesh Head - EHS Department of Environmental & Health Chennai

Abstract Pressure Vessels are storage tanks which were constructed to keep liquids, vapors, or gases at very high pressures, usually over 15 psig. Few Examples of general pressure storage tanks used in the petro refining and chemically processing companies include, but are not limited to, containers, boilers, and heat exchangers. Each storage tank has its own operating limits construct in by design that it is to work in the, referred to as its designed pressure and designed temperature. Operating outside of these type of limits could damage the equipments, potentially lead to loss of containment as otherwise catastrophic failure. Because of they working with in immense pressures and a ruptured pressure vessel could be incredibly high dangerous and leading to poison gas leaks, fires, and even explosions can happen. For these reasons, pressure vessel safety is high imperative. There are several standards and practices that cover the construction, maintenance, and inspection of pressure vessels. The Chief among these standards are ASME Section VIII and API 510. Corrosion forming over the life of a storage tank is catered for by a corrosion limit, the design value of which depends upon the storage tank duty and the corrosiveness of its content.

Keywords- Pressure Vessel, Pressure Vessel Types, Horizontal Pressure Vessel, Vertical Pressure Vessel, Tower, Reactor, Spherical Tank

I. INTRODUCTION Pressure storage tanks are compressed gas storage tanks designed to hold gases as otherwise liquids at a pressure substantially differ from the ambient pressure. They are having many variety of applications in companies, including in oil refineries, nuclear reactors, gas reservoirs, etc. An aircraft fuselage, a gas cylinder and a soda can, all are pressure vessels which must be designed to meet very specific requirements of integrity.

The human arteries maintaining pressure in the circulatory manner like a balloon maintains pressure on the air within the system. The arteries therefore work as pressure tanks by maintaining pressure. Pressure vessels could be any shape, but shapes made of sections of spheres and cylinders were usually employed. A common design factor is a cylinder with end caps called heads. Head shapes are frequently hemispherical or dish.

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Analysis of Life of Pressure Vessel (GRDJE/ Volume 4 / Issue 5 / 002)

II. FUNCTIONAL BLOCKS

Block Diagram 1: Functional Block Diagram

A. – – – – –

Pressure Storage Tank (or) Air Receivers are used in a Number of Companies Power generation companies for fossils Nuclear power stations Petrochemical company for storing and processing of crude petroleum oil in the storage cylinder forms as like as storing gasoline in the service station Chemical companies Industry plants for storing and manufacturing process

Fig. 1: Pressure vessel

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Analysis of Life of Pressure Vessel (GRDJE/ Volume 4 / Issue 5 / 002)

III. PRESSURE VESSEL TYPES

Fig. 2: Horizontal Pressure vessel

Fig. 3: Vertical Pressure vessel

Fig. 4: Tower (Column)

Fig. 5: Reactor: Reactors are used where chemical reactions of process fluids are required

Fig. 6: Spherical tank: Spherical tanks are usually used for gas storage under high pressure

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Analysis of Life of Pressure Vessel (GRDJE/ Volume 4 / Issue 5 / 002)

IV. DESIGN CONDITIONS A. Different Types of Load Acting on a Pressure Storage Tank 1) Working (Operating) Pressure The operating pressure should be set based on the maximum internal or external pressure that the pressure vessel may encounter.

The following factors must be considered: – Ambient temperatures effects.

– Normal operational variation.

– Pressure variation due to change in the vapour pressure of the contained fluids.

– Pump or compressor shut-off pressures.

– Static head due to the liquid level in the storage tank.

– System pressure drops.

– Normal pre-start-up activity or other operating condition that may occur (e.g., vacuum), that must be considered in the design.

– – – – –

2) Design Pressures Commonly, design pressure was the maximum internal pressure (in psig), that was used in the mechanical design of a pressure vessel.

For full or partial vacuum conditions the design pressure was applied externally and was the maximum pressure differences that can occur between the atmosphere and the inside of the pressure storage tank.

Some pressure storage tanks may experience both internal and external pressure condition at different times during their operation. The mechanical design of the pressure storage tank in this case is based on which of these is the more severe design conditions.

The specified design pressure was based on the maximum operating pressure at the top of the vessel, plus the margin that the process design engineer determines was suitable for the particular application.

The hydrostatic pressure that was 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 was equal to the design pressure at the top of the storage tank, plus the hydrostatic pressure of the liquid in the vessel that is above the point being designed.

3) Temperature a) Working (operating) Temperature The operating temperature should be set based on the maximum and minimum metal temperature that the pressure storage tank may encounter. b) Design Temperatures The design temperature of a pressure storage tank was the maximum fluid temperature that occurs under normal operating conditions, plus an allowance for variations that occur during operation. c) Critical Exposure Temperature The CET should also be specified for pressure storage tank design to ensure that materials that have adequate fracture toughness were selected for construction (i.e., MDMT ≤CET).

– – – – – – – – –

4) Other Design Loadings Internal or external design pressures.

Weight of the storage tank and its normal contents under operating or test conditions.

Superimposed static reactions from the weight of attached equipments (e.g., motors, machinery, other storage tank, piping, linings, and insulation).

Load at attached of internal components or storage tank supports.

Snow, wind and seismic reaction.

Cyclic and dynamic reaction that were caused by pressure and thermal variations, or by equipment that is mounted on a storage tank, and mechanical loadings.

Test pressures combined with hydrostatic weight.

Impact reaction such as those that are formed by fluid shock.

Temperature gradient within a storage tank component and differential thermal expansion between vessel components.

5) Pressure Vessel Design Codes and Standards There are standards and codes by approved authority bodies for the design, construction, welding, testing, marking, inspection, operation and repair of any pressure tanks, which are provides fundamental for safeguards and satisfactory safety practices.

ASME Boilers and Pressure storage tanks Codes and practices – API Standards Pressure storage tanks – P D 5500

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Analysis of Life of Pressure Vessel (GRDJE/ Volume 4 / Issue 5 / 002)

– –

British council Standards European Codes and Standards for Pressure storage tanks

– – – – – – – – – – – – – – – – – –

6) The Main Cause of Failures of a Pressure Storage Tank are as Follows: Worst installations Unsafe modifications or alteration Cracking on the welding joints Welding problem Cracking on the tank Embrittlement on the vessel Improper selection of material or defect Erosions on the vessel Corrosions for outer side vessels Fatigue strength Stress due to pressure Very Low water conditions Improper repairs of leakages The Burner failures Fabrication mistake High pressurization Failure to inspect frequently enough Unknown or under investigation of the tank

V. PROTECTION OF PRESSURE VESSELS A pressure vessel is ideally designed to hold liquids and gases at a much higher pressure than the normal atmospheric pressure.

Industrial pressure vessels can be extremely large and pose the threat of fatal accidents. Therefore, the design of pressure vessels is strongly regulated around the world, especially in high-risk industries. Corrosion can be a real problem in industrial pressure vessels; affecting its performance and compromising the strength of its outer shell, which can pose a health and safety risk.

A. Inert Construction Materials High quality pressure vessels use improved materials that decrease the chance and rate of corrosion by a noticeable margin. The use of stainless steel is common to improve the anti-corrosion performance of a pressure vessel. However, it may not always be feasible or affordable to use a corrosion resistant material, especially where small margins may mean the difference between a successful or unprofitable business ventures.

Some cheaper vessels therefore use materials that are more susceptible to corrosion than others. In a lot of cases this is a false economy, increasing the risk associated with the vessel and increasing your maintenance costs. However, when choosing a material, consider the level of corrosion the vessel will be exposed to. This will depend on the environment and whether the vessel is sited indoors or outdoors, as well as the process fluids used. Your vessel is at a greater risk from corrosion when acidic gases or fluids are present, especially at high temperatures and pressures.

B. Cathodic Protection Cathodic protection is a method of erosion prevention that adds a more reactive material to the surface of the pressure vessel. This is a cheaper option than using a completely inert material to construct the outer shell. The protection barrier corrodes in place of the vessel material itself, avoiding damage to the vessel, but necessitating replacement every few months to offer continuous protection. Iron vessels are frequently treated with hot zinc (galvanisation) for this purpose.

C. Vessel Coatings A coating is any layer that is placed over the metal surface of the pressure vessel to protect it from the surrounding environment.

There are several different options available for this protection system. Below, we discussed some of the most common coatings that you can apply at the manufacturing stage to protect your industrial pressure vessel.

D. Ceramic Coatings The most commonly used coatings to protect steel tanks and containers are fashioned from ceramic. These coatings are excellent at protecting metallic surfaces from corrosive fluids, and so are used on the inside of a pressure vessels that utilise acidic fluids or gases. A ceramic coating insulates the steel structure with an alkaline surface layer.

This slows down the rate of corrosion, with the level of protection depending on the presence of free acidic radicals.

Ceramic coatings are inorganic and extremely non-reactive, making them perfect for use in a variety of conditions. A ceramic coating will need to be checked and replaced occasionally as part of routine maintenance.

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Analysis of Life of Pressure Vessel (GRDJE/ Volume 4 / Issue 5 / 002)

E. Inhibitor Coatings Inhibitors are compounds that chemically reduce the reactiveness of the surface of the pressure vessel. Zinc oxide excellent for this purpose. It is ideal for use with large iron vessels as it provides a strong cathodic protection. This inhibitor creates a hermetic seal that ensures the substances present in the vessel cannot reach the iron surface.

F. Organic Coatings Recently, a range of organic coatings have become available, especially for aluminum-based pressure vessels. Aluminum is chemically different from other commonly used metals and therefore, needs protection from water, free ions and oxygen. If water persistently remains present on the external layer of the pressure vessel, it may create a microscopic blister, which increases the rate of corrosion in aluminum. This poses a problem for pressure vessels used in outdoor environments, due to the effects of rain, sea spray and snow.

An organic coating is perfect in this regard, because the natural reactivity of aluminum renders other coatings - such as zinc oxide – useless. In extreme environments where unusually high or low pressures are used, or when a highly corrosive process fluid is used, it may not be enough to just use a coating.

VI. RESULT AND DISCUSSION Ceramic coatings are used on the inside of a pressure vessels that utilize acidic fluids or gases. A ceramic coating insulates the steel structure with an alkaline surface layer.

This slows down the rate of corrosion, with the level of protection depending on the presence of free acidic radicals.

Ceramic coatings are inorganic and extremely non-reactive, making them perfect for use in a variety of conditions. A ceramic coating will need to be checked and replaced occasionally as part of routine maintenance.

A. Air Receiver (Vertical) Periodical Maintenance Checklist Chart MONTHS Safety relief valve Pressure gauge Shut down button Auto drainer Accurate working Pr., Inlet valve/outlet valve Flanges/joints leakages Fasteners condition Near welding joints corrosion rust Vessel pressure high Vessel temp., high Frequently changing Pr Abnormality if any

1 ok ok ok ok ok ok ok -ok ok ok ok In Control In Control In Control --

2 ok ok ok ok ok ok ok -ok ok ok ok In Control In Control In Control --

3 ok ok ok ok ok ok ok -ok ok ok ok In Control In Control In Control --

4 ok ok ok ok ok ok ok -ok ok ok ok In Control In Control In Control --

5 ok ok ok ok ok ok ok -ok ok ok ok In Control In Control In Control --

6 ok ok ok ok ok ok ok -ok ok ok ok In Control In Control In Control --

VII. CONCLUSION In this project, an attempt has been made to find ways of decreasing corrosiveness/rust of the pressure vessel accordingly increasing the life of pressure vessel” by applying coatings to the pressure vessels.

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Analysis of Life of Pressure Vessel (GRDJE/ Volume 4 / Issue 5 / 002) [10] Boiler, A. S. M. E. "Pressure Vessel Code Section XI." Rules for inservice inspection of nuclear power plant components (1995).

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