Vocational training report format

15 DAYS INDUSTRIAL TRAINING REPORT

ON

HEAT TRANSFER DEVICES

5 JULY 2014

LAXMI ENGINEERING INDUSTRIES PVT. LTD

SUBMITTEDBY

…………………

DEPARTMENT OF MECHANICAL ENGINEERING

IES INSTITUTE OF TECHNOLOGY & MANAGEMENT

15 DAYS INDUSTRIAL TRAINING REPORT

ON

HEAT TRANSFER DEVICES

5 JULY2014

LAXMI ENGINEERING INDUSTRIES PVT. LTD

SUBMITTED IN PARTIAL FULFILLMENT FOR AWARD OF DEGREE OF

BACHELOR OF ENGINEERING

IN

MECHANICAL ENGINEERING

IES INSTITUTE OF TECHNOLOGY & MANAGEMENT

SUBMITTED BY:

……………………………

………………………………

CERTIFICATE

It is to certify that …………………………..student of Mechanical Engineering Department, IES ISTITUTE OF TECHNOLOGY & MANAGEMENT RATIBAD, BHOPAL

has completed the industrial Training at “LAXMI ENGINEERING INDUSTRIES” for the partial fulfillment of

the requirement for the award of Bachelors of Engineering (Mechanical Engineering) Degree of

RGPV, Bhopal .This is a record of student’s own study carried under my supervision & guidance.

This report has been submitted for the award of B.E degree.

Head of Department Principal

(ME)

ACKNOWLEDGEMENT

I take this opportunity to express my profound gratitude and deep regards to my guide for his exemplary guidance, monitoring and

constant encouragement throughout the course of this thesis. The blessing, help and guidance given by him time to time shall carry

me a long way in the journey of life on which I am about to embark.

I also take this opportunity to express a deep sense of gratitude to , ER Jitendra Phulre Laxmi Engineering Industries, for his cordial support, valuable information and guidance, which helped me in

completing this task through various stages.

I am obliged to staff members of Laxmi Engineering Industries, for the valuable information provided by them in their respective

fields. I am grateful for their cooperation during the period of my assignment.

Lastly, I thank almighty, my parents, brother, sisters and friends for their constant encouragement without which this assignment

would not be possible.

ABSTRACT

In our project report, we discuss about the all technical description which we are getting

During our training duration at Laxmi engineering industries, Bhopal.

In our project we discuss about operations of lathe machines, drilling machines, planno machines, welding machines, shell and tube type heat exchangers and surface condensers.

We know that heat exchangers are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment.

A surface condenser is a commonly used term for a water-cooled shell and tube heat exchanger installed on the exhaust steam from a steam turbine in thermal power stations. Surface condensers are also used in applications and industries other than the condensing of steam turbine exhaust in power plants.

The growth of welding is very fast in fabrication industry. It is an alternative method for casting and forging. It is successfully employed in daily use items, automobile vehicles, aircrafts, ships, household appliances, electronic equipments, pressure vessels, tanks, rail and road equipments.

S.NO CONTENT PAGE

NO.

1 COMPANY PROFILE 7-11

(a) PLANT AND MACHINERY

(b) PRODUCTS

(c) CUSTOMER

2 MACHINERY INFORMATION 12-23

3 SHELL AND TUBE HEAT EXCHANGER 24-28

4 SURFACE CONDENSER 29-33

5 DYE PENETRATION TEST 34

6 CONCLUSION 35

COMPANY PROFILE

Laxmi Engineering Industries (Bhopal) Pvt. Ltd., is a SME promoted by technocrat entrepreneur. From a modest beginning in 1987 as a supplier of small heat exchangers to the Central and State Electrical Utilities and BHEL, the company has over the past 20 years, emerged as an accredited supplier of heat transfer equipments to many discerning customers like BHEL, NTPC, Triveni Engineering Industries Ltd., Power machines India Ltd., ALSTOM Projects India Ltd., VOITH Seimens India Ltd., TD Power Systems Ltd., etc. The core competences of the company are thermal & mechanical design, fabrication, machining & assembly and erection & commissioning of heat transfer equipments. The company product range covers all types of heat transfer solutions in power generation and other process plant like refineries, fertilizer, chemical, smelting etc.

A professional with diverse qualifications and proven track record as mentors is the core strength of the company. Recently with the association of doyens of power generation in Madhya Pradesh the company has started the Power Project Division for undertaking renovation and modernization of Power Plants.

PLANT & MACHINERY

Highlights of Production Facilities:

Total Area: 52,000 Sq. Feet

Covered Area (Workshop): 30,000 Sq. Feet (Approx.)

Maximum Span: 50 Feet

Maximum Height: 35 Feet

Administrative Office : 3300 Sq. Feet (First Floor)

Store –I: 3000 Sq. Feet (Ground Floor)

Store –II: 1125 Sq. Feet (Ground Floor)

Open Area: 17,575 Sq. Feet

Manufacturing Facilities

Drilling 100 mm dia. & Depth up to 350 mm (Max.)

Welding MIG / TIG / CO2 & SMAW

Machining Turning & Plaining

Material Handling EOT Crane - 35 M.T. capacity (1 No.)

15 M.T. capacity (1 No.)

10 M.T. capacitiy (3 Nos.)

Mobile Crane – 50 M.T. capacity (Available Locally) PLANT AND MACHINERY

PRODUCTS

SURFACE CONDENSER

HIGH/LOW PRESSURE FEED WAER HEATER

SHELL AND TUBE TYPE HEAT EXCHANGER

SEAL OIL COLLER

TURBINE OIL COLLER

COMPRESSOR OIL COLLER

HEAT EXCHANGER

CONDENSER

EQUIPMENTS FOR HEAT RECOVERY SYSTEMS

TUBULAR AIR PRE HEATER

EXHAUST DIFFUSER

CUSTOMERS

Bharat Heavy Electricals Ltd.

Power Machines India Ltd., N’ Delhi

( Formerly LMZ Energy India Ltd., N’Delhi)

Triveni Engineering & Industries Ltd., Bangalore

Sutlej Textiles & Industries Ltd.,

National Thermal Power Corporation Ltd.,

Indian Oil Corporation Ltd., Mathura Refinery

Paradeep Phosphates Ltd., Paradeep

Rastriya Chemicals & Fertilizers Ltd.,

Fertilizer Corporation of India Ltd.,

Hindustan Insectiside Ltd.,Rashyani

Bharat Pumps & Compressors Ltd., Naini

T.D. Power System Pvt. Ltd., Bangalore

VA TECH Hydro (India) Ltd., Mandideep

ABB Ltd., Vadodara

Alstom Ltd.,

Anfilco Ltd., Gurgaon

National Aluminium Company Ltd.,

Bharat Aluminium Company Ltd.,

MACHINERY INFORMATION

WELDING MACHINE

The process of joining together two pieces of metal so that bonding accompanied by appreciable interatomic

penetration takes place at their original boundary surfaces. The boundaries more or less disappear at the

weld, and integrating crystals develop across them. Welding is carried out by the use of heat or pressure or both and with or without added metal. There are many types of welding including Metal Arc, Atomic Hydrogen,

Submerged Arc, Resistance Butt, Flash, Spot, Stitch, Stud and Projection.

During training we studied about the use of different welding machine for different purpose

MIG (METAL INERT GAS WELDING)

TIG (TUNGSTEN INERT GAS WELDING)

SMAW (SHEILD METAL ARC WELDING)

METAL INERT GAS WELDING (MIG)MIG is also known as SHEILD INERT GAS METAL ARC WELDING (SIGMA) uses a shielded stuck between a bare metal electrode and the work piece. Metal electrode provide in the form of rell. It is fed continuously through the feed

mechanism at the rate at which it is being consumed so as to maintain the welding arc between its end and the base metal. The arc is shielded by an inert gas atmosphere provided by the gas flowing through the nozzle of the holder through which electrode wire also passes. The welding equipment consists of a pistol shaped wire gun, a gas hose with a concentric metallic tube for conveying filler wire , control cables, wire feed system, wire reel, welding power source and the inert gas cylinder.

Equipment

● DC output power source

● Wire feed unit

● Torch

● Work return welding lead

● shielding gas supply, (normally from cylinder)

Power Source

MIG welding is carried out on DC electrode (welding wire) positive polarity (DCEP). However DCEN is used (for higher burn off rate) with certain self- shielding and gas shield cored wires. DC output power sources are of a transformer-rectifier design, with a flat characteristic (constant voltage power source). The most common type of power source used for this process is the switched primary transformer rectifier with constant voltage characteristics from both 3-phase 415V and 1-phase 240V input supplies.

Shielding Gas

This is a complicated area with many various mixtures available, but the primary purpose of the shielding gas in the MIG process is to protect the molten weld metal and heat affected zone from oxidation and other contamination by the atmosphere. The shielding gas should also have a pronounced effect on the following aspects of the welding operation and the resultant weld.

• Arc Characteristics a basic position or starting point would be

• Mode of Metal Transfer

• Penetration and Weld Head Profile Aluminum - Argon

• Speed of Welding Magnesium - Helium

• Undercutting Tendency Copper Alloys - Argon - Helium Mix

• Cleaning Action Steel - CO2 not commonly used * Weld Metal Mechanical Properties today, Ar-CO2 mix is preferred

TUNGSTEN INERT GAS WELDING (TIG)

The electrode used in this process is made of either tungsten or thoriated tungsten. The process is therefore,

sometimes called Tungsten Inert Gas (TIG) or Gas Tungsten Arc welding (GTAW). Thoriated tungsten

electrode run cooler than plain tungsten electrodes and maintains square arcing ends but arc more expensive.

The inert gas is supplied to the weld area through a water cooled electrode holder It provides a protective shield around the arc. The inert gas generally used is argon though helium or mixture or a mixture of the two may also be used. When required a filler may be added just

like in gas welding. The current source may be either DC or AC depending upon application. DC straight polarity

arc is used in metals other than aluminium and magnesium including copper alloys, cast iron, steel and

stainless steel. It gives good heat concentration and produces weld that are deep and narrow. Welding rates are high and there is less distortion of base metal. DC reverse polarity is generally used because it produces

shallow and wide weld. AC arc is used for welding aluminium, magnesium, cast iron and a number of other

metals.

APPLICATIONAdvantages

The TIG welding process has a very large area of application due to its many advantages, e.g.:

• It provides a concentrated heating of the work piece.

• It provides an effective protection of the weld pool by an inert shielding gas.

• It can be independent of filler material.

• The filler materials do not need to be finely prepared if only the alloying is all right.

• There is no need for after treatment of the weld as no slag or spatter is produced.

Materials for TIG welding

The most important area of application is:

• Welding of thin materials in stainless steels

• Aluminium

• Nickel

• Nickel alloys

The increasing demands to the weld quality has made TIG welding very popular for welding of smaller tube dimensions as well as root runs in both non-alloyed and alloyed materials in heavier plates.

TIG Welding Equipment

ConfigurationIn order to handle the TIG welding process and make it work to its full capability you need equipment consisting of different parts with their own separate function.

The TIG welding equipment chiefly consists of:

• A TIG torch that is the tool the welder uses to control the arc.

• A power source which is capable of providing the necessary welding current.

• A TIG unit with incorporated control systems that make it possible to adjust the welding current, arc initiation etc.

• A shielding gas cylinder with pressure reducing valve and flow meter.

1 Cable for welding current

2 Cable for welding current

3 Control cable for TIG unit

4 Shielding gas

5 Cable for welding cable for TIG torch

6 Control cable for TIG torch

7 Welding cable with +polarity

TIG TorchThe main purpose of the TIG torch is to carry the welding current and shielding gas to the weld. The TIG torch is constructed on the basis of the welding handle and a torch head that is coated with an electrically insulated material

The torch handle is usually fitted with a switch to turn the welding current and the shielding gas on and off.

1. Torch head

2. Handle

3. Control switch

4. Electrode cap

5. Sealing ring

6. Electrode collet

7. Heat shield

8. Collet body

9. Gas nozzle

SHEILD METAL ARC WELDING (SMAW)

The SMAW process is an arc welding process which produces coalescence of metal by heating them with an arc between a covered metal electrode and the work. Sheilding is obtained from decomposition of the electrode covering. Pressure is not used. Filler metal is obtained from the electrode

Typical SMAW setup

1. Welding power source (suitable for work to be performed)

2. Length of suitable welding cable

3. Length of suitable ground cable

4. Suitable electrode holder

5. Suitable ground clamp

6. Covered electrode (matched to base metal)

7. Welding helmet and protective equipment

A constant current type power source is most commonly used: these are available in AC, AC/DC combination or DC output with mechanical, electrical, solid state controls, either static or dynamic. Constant current power sources come in a large variety of output characteristics, capacities and controls. They can be static or dynamic. All AC and AC/DC combination static power sources require single phase input (primary power). The industrial classes are usually reconnect able on different voltages i.e. 230, 460 or 575; while the limited input machines are single voltage connection i.e. 208, 230 or 575. Most of the DC output machines require three phase primary power. These are also normally reconnect able on different voltages.

WELDING DEFECTSUndercuttingUndercutting is one of the more severe welding defects. It is essentially an unfilled groove along the edge of the weld (see Figure 2). The causes are usually associated with incorrect electrode angles, incorrect weaving technique, excessive current and travel speed. Undercutting can be avoided with careful attention to detail during preparation of the weld and by improving the welding process. It can be repaired in most cases by welding up the resultant groove with a smaller electrode.

Concave and Convex Welds Misshaped welds are caused by a combination of incorrect electrode current and speed. Excessive concavity (lack of reinforcement), results in insufficient throat thickness in relation to the nominated weld size. Excessive convexity results in poor weld contour. In multilayer welds this can give rise to slag inclusions, while in the finished weld it provides a poor stress pattern and a local notch effect at the toe of the weld. They can be avoided by using an appropriate electrode size, current and weaving pattern. Repair by either filling with further weld material or by grinding back to the base metal on each side of the weld and re-welding.

Cracking Cracks and planar discontinuities are some of the most dangerous especially if they are subject to fatigue loading conditions. There are several different type of cracks and none are desired. They must be removed by grinding back (if superficial) or repaired by welding. Cracks can occur in the weld itself, the base metal, or the heat affected

Holes (Porosity) Porosity can be caused by one or more of: contamination of weld surfaces or filler metals, improper electrode selection, inadequate shielding, unstable arc, too short or too long an arc length, too high a travel speed, and generally poor welding technique. The effect of porosity on weld performance will depend on the number, location, and size of the holes. Porosity cannot be repaired by welding overtop of the problem. Grind out to remove the porosity, then re-weld

DRILLINGDrilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross-section in solid materials. The drill bit is a rotary cutting tool, often multipoint. The bit is pressed against the work piece and rotated at rates from hundreds to thousands of revolutions per minute. This forces the cutting edge against the work piece, cutting off chips (swarf) from the hole as it is drilled.

PROCESS

o Establishing a centering mark or feature before drilling, such as by:

o Casting, molding, or forging a mark into the work piece

o Center punching

o Spot drilling (i.e., center drilling)

o Spot facing, which is facing a certain area on a rough casting or forging to establish, essentially, an island of precisely known surface in a sea of imprecisely known surface

o Constraining the position of the drill bit using a drill jig with drill bushings

Surface finish in drilling may range from 32 to 500 microinches. Finish cuts will generate surfaces near 32 microinches, and roughing will be near 500 microinches.

Cutting fluid is commonly used to cool the drill bit, increase tool life, increase speeds and feeds, increase the surface finish, and aid in ejecting chips. Application of these fluids is usually done by flooding the workpiece or by applying a spray mist.

In deciding which drill(s) to use it is important to consider the task at hand and evaluate which drill would best accomplish the task. There are a variety of drill styles that each serve a different purpose. The subland drill is capable of drilling more than one diameter. The spade drill is used to drill larger hole sizes. The indexable drill is useful in managing chips

LATHE MACHINEA lathe is a machine tool which turns cylindrical material, touches a cutting tool to it, and cuts the material. The lathe is one of the machine tools most well used by machining .

Material is firmly fixed to the chuck of a lathe. The lathe is switched on and the chuck is rotated. And since the table which fixed the byte can be moved in the vertical direction, and the right-and-left direction by operating some handles shown in Fig. 3. It touches a byte's tip into the material by the operation, and make a mechanical part.

Operations of Lathe Machine:

(i) Facing: This operation is almost essential for all works. In this operation, as shown in fig., the work piece is held in the chuck and the facing tool is fed from the center of the work piece towards the outer surface or from the outer surface to the center, with the help of a cross-slide.

(ii) Plane Turning: It is an operation of removing excess amount of material from the surface the surface of the cylinder work piece. In this operation, shown in fig., the work is held either in the chuck or between centers & the longitudinal feed is given to the tool either by hand or power.

(iii) Step Turning: It is an operation of producing various steps of different diameters of in the work piece as shown in fig. This operation is carried out in the similar way as plain turning.

(iv) Drilling : It is an operation of making a hole in a work piece with the help of a drill. In this case as shown in fig., the work piece, by rotating the tail stock hand wheel. The drill is fed normally, into the rotating work piece, by rotating the tail stock hand wheel.

SHELL AND TUBE HEAT EXCHANGER

Heat exchangers are devices used to transfer heat between two or more fluid streamsat different temperatures. Heat exchangers find widespread use in power generation,

Shell and tube heat exchangers are widely used as power condensers, oil coolers,preheaters, and steam generators. They consist of many tubes mounted parallel toeach other in a cylindrical shell. Flow may be parallel, counter, or cross flow and insome cases combinations of these flow arrangements as a result of baffeling

It finds application in a variety of industries and is, without doubt, one of the most widely used exchangers. It has a series of tubes which is enclosed by a shell. One fluid flows inside the tubes while the other liquid flows over the outside walls of the tubes which, basically, is the shell. It's highly recommended for places where there's a need for high heat transfer coefficient as the number of tubes can be increased depending on the need. Due to its unique shape, it finds use in high pressure applications

HEAT EXCHANGER

CONSTRUCTION

SHELL

1. Material correlation with TC.

2. Marketing of items, and identification punching [Mo No, Item No, and Heat No.] accordingly.

3. Before F/C Items marking checked [shop QC].

4. F/C grinding and edge preparation to be done.

5. After rolling each shell parts to be checked on layout and provide bracing inside diameter of the shell.

6. ‘C’ seam and ‘L’ seam fit up together [applicable for rolled shell ].

7. Fit up inspection [shop QC].

8. Welding

a. Root Run Welding- where ever is possible ‘TIG’ welding it is to be done, avoid the back chipping.

b. Root Run cleaning and D.P. Tested, before final welding.

c. Final welding and grinding.

d. After final welding and grinding, shell inside dia to be checked with dummy. Dummy not passed easily to shell inside. Shell to be Re-rolling and check the ovelity.

MACHINING

9. Machining as per drawing-

a. Tube plate machining

b. Baffles outer dia machining

c. End flange, nozzle flange machining

10. Tube holes marking on tube plate.

11.After marking inspection[shop QC].

12.Mock up if required, it is to be made and inspect dimension recorded before starting the tube plate drilling.

13. Pilot drilling [tube plate] and transfer the holes on baffle bundle.

FINAL DRILLING AND REAMING-

a.1st three, four holes drilling and remaining to be done and checked holes size, quality of holes and finishing, found the holes OK then start drilling and reaming same method.

b. Each and every 10 holes drilling, it must be checked hole size, ovality and finishing, if it is found ‘NOT OK’, Tool will be changed.

c. After completion of drilling, reaming, deburing shop inspection to be carried out. 100 percent holes are checked with ‘GO’ and ‘NO GO’ gauges.

FIT UP OF I/O AND R/E WATER BOX.

14. Marking on vertical and horizontal center line on cylinder, and nozzles position to be marked F/C and grinding to be done.

15. Fit up of cylinder [shell] with end flanged and dished end.

16. Fit up the inspection [QC].

17.’C’ seam joints root run welding by ‘TIG’ and other root run welding of shell with flange by electrode.

18. Root run cleaning and D.P. tested.

19 .FINAL WELDING- Cleaning and grinding.

20. NDT-As per drawing/QAP.

TUBE BUNDLE ASSEMBLY

a. Tube inspection [correlation with TC] one no. tube plate.

b. Plate setting on fixture vertically and clamped with fixture.

c. Then tie rod tight with tube plate, setting the baffles and spare tube, inserting the tubes carcly.

d. After completion of tubing, setting on the other side tube plate and maintain the ‘LBTP’ as per drawing. Dimension and locked with tube plate and tube.

e. Tube bundle insert the shell , and bolted with shell and tube bundle.

TUBE EXPANSION-

LEI Product standard M/S/03/Rev.00 to be followed after tube expansion tube bundle remove from the shell.

SAND BLASTING-

Shell and water box to be sand blasted and one coat of primer point apply.

21. HYDRAULIC TEST

a. Shell hydraulically checked separately if any leakage found it is to be rectified and Re-checked.

b. After cleared the hydraulic pressure test, insert the tube bundle to shell and bolted with shell.

HYDRAULIC TEST SHELL SIDE-

a. Inspection

b After hydraulic testing of the shell, shell inside must be dried up.

HYDRAULIC TEST TUBE SIDE/WATER BOX SIDE-

a .All opening blanked properly before filling the water.

b. 1 kg sodium nitrate + 1 liter soap solution mixing with every 200 liter water for avoid the resting of inside shell and tube.

c. LEI product standard M/S/03/Rev.00 to be followed.

SURFACE CONDENSER

Surface condenser is the commonly used term for a water cooled shell and tube heat exchanger installed on the exhaust steam from a steam turbine in thermal power stations.  These condensers are heat exchangers which convert steam from its gaseous to its liquid state at a pressure below atmosphericpressure. Where cooling water is  in  short supply, an air-cooled condenser is often used. An air-cooled condenser is however significantly more expensive and cannot achieve as low a steamturbine exhaust pressure as a  surface condenser.Surface condensers are also used in applications and industries other than  the condensing of steam turbine exhaust in power plants.

Purpose

In thermal power plants, the primary purpose of a surfacecondenser is to condense the exhaust steam from a steam turbineto obtain maximum efficiency and also to convert the turbine exhaust steam into pure water (referred to as steam condensate)so that it may be reused in the  steam generator or boiler as boiler feed water.

Why is it required?

The steam turbine itself is a device to convert the heat in steam to mechanical power. The  difference between the heat of steam per unit weight at the inlet to the turbine and the heat of  steam per unit weight at the outlet to the turbine represents the heat which is converted to  mechanical power. Therefore, the more the conversion of heat per pound or kilogram of steam to mechanical power in the turbine, the better is its efficiency. By condensing the exhaust steam of a turbine at a pressure below atmosphericpressure, the steam pressure  drop between the inlet and exhaust of the turbine is increased, which increases the amount of heat available for conversion to mechanical power. Most of the heat liberated due to condensation of the exhaust steam is carried away by the cooling medium (water or air) used by the surface condenser.

Diagram of water-cooled surface condenser

The adjacent diagram depicts a typical watercooled surfacecondenser as used in power stations to condense the exhauststeam from a steam turbine driving an electrical generator as well in other applications. There are many fabrication design variations depending on the manufacturer, the size of the steam turbine, andother site-specific conditions.

Shell

The shell is the condenser's outermost body and contains the heatexchanger tubes. The shell is fabricated from carbonsteel platesand is stiffened as needed to provide rigidity for the shell.  Whenrequired by the selected design, intermediate plates are installedto serve as baffle plates  that provide the desired flow path of thecondensing steam. The plates also provide support that help prevent sagging of long tube lengths.

At the bottom of the shell, where the condensate collects, anoutlet is installed. In some designs, a sump (often referred to asthe hotwell) is provided. Condensate is pumped from the outlet orthe hotwell for reuse as boiler feedwater.

For most water-cooled surface condensers, the shell is undervacuum during normal operating conditions.

Vacuum system

For water-cooled surface condensers, the shell's internal vacuumis most commonly supplied by and  maintained by an external steam jetejector system. Such an ejector system uses steam asthe motive fluid to remove any non-condensible gases that maybe present in the surface condenser. The  Venturieffect, which is a particular case of Bernoulli's principle, applies to the operation of steam jet ejectors.

Motor driven mechanical vacuum pumps, such as liquid ring typevacuum pumps, are also popular for this service.

Tube sheets

At each end of the shell, a sheet of sufficient thickness usually made of stainless

steel is provided, with holes for the tubes to beinserted and rolled. The inlet end of each tube is also bell mouthed for streamlined entry of water. This is to avoid eddies at the inlet of each tube giving rise to erosion, and to reduce flow friction.Some makers also recommend  plastic inserts at the entry of tubes to avoid eddies eroding the inlet end. In smaller units some manufacturers use ferrules to seal the tube ends instead of rolling. To take care of length wise  expansion of  tubes some designs have expansion joint between the shell and the tube sheet allowing the latter to move longitudinally. In smaller units some sag is given tothe tubes to take care of tube expansion with both end waterboxes fixed rigidly to the shell.

Tubes

Generally the tubes are made of stainless steel, copper alloys such as brass or bronze, cupro nickel, or titanium depending on severalselection criteria. The use of copper bearing alloys such as brassor cupro nickel is rare in new plants, due to environmental concerns of toxic  copper alloys. Also depending on the steamcycle water treatment for the boiler, it may be  desirable to avoidtube materials containing copper. Titanium condenser tubes areusually the  best technical choice, however the use of titaniumcondenser tubes has been virtually eliminated by the sharpincreases in the costs for this material. The tube lengths range toabout 55 ft (17)  for modern power plants, depending on the sizeof the condenser. The size chosen is based on  transportability from the manufacturers’ site and ease of erection at theinstallation site. The  outer diameter of condenser tubes typicallyranges from 3/4 inch to 11/4 inch, based on condenser coolingwater friction considerations and overall condenser size.

Waterboxes

The tube sheet at each end with tube ends rolled, for each end ofthe condenser is closed by a  fabricated box cover known as awaterbox, with flanged connection to the tube sheet or  condenser

shell. The waterbox is usually provided with man holes on hinged covers to allow  inspection and cleaning.These waterboxes on inlet side will also have flanged connections for  cooling water inlet butterfly valves, small vent pipe with hand valve for air venting at higher level, and hand operated drainvalve at bottom to drain the waterbox for maintenance. Similarlyon the outlet waterbox the cooling water connection will have large flanges, butterfly valves, vent connection also at higher level and drain connections at lower level. Similarly thermometer pockets are located at inlet and outlet pipes for local measurements of cooling  water temperature.In smaller units, some manufacturers make the condenser shell aswell as  waterboxes of cast iron.

Corrosion

On the cooling water side of the condenser:

The tubes, the tube sheets and the water boxes may be made upof materials having different  compositions and are always incontact with circulating water. This water, depending on its chemical composition, will act as an electrolyte between themetallic composition of tubes and water boxes. This will give rise to electrolytic corrosion which will start from more anodic materials first.Sea water based condensers, in particular when sea water has added chemical  pollutants, have the worst corrosioncharacteristics. River water with pollutants are also  undesirable forcondenser cooling water.The corrosive effect of sea or river water has  to be tolerated and remedial methods have to be adopted.

On the steam (shell) side of the condenser:

The concentration of undissolved gases is high over air zonetubes. Therefore these tubes are  exposed to higher corrosionrates. Some times these tubes are affected by stress corrosion cracking, if originally stress is not fully relieved duringmanufacture. To overc

ome these effects of corrosion some manufacturers provide higher corrosive resistant tubes in this area.

Effects of corrosion

As the tube ends get corroded there is the possibility of coolingwater leakage to the steam side  contaminating the condensed steam or condensate, which is harmful to steam generators. The other parts of water boxes may also get affected in the long run requiring repairs or replacements involving long duration shut-downs.

Protection from corrosion

Cathodic protection is typically employed to overcome thisproblem. Sacrificialanodes of zinc (being  cheapest) plates are mounted at suitable places inside the water boxes. Thesezinc plates will  get corroded first being in the lowest range ofanodes. Hence these zinc anodes require periodic inspection  and replacements. This involves comparatively less downtime. Thewater boxes  made  of steel plates are also protected  inside by epoxy paint.

DYE PENETRATION TESTDye Penetrant Inspection (DPI) also called as Liquid Penetrant Inspection (LPI) or Penetrant Test ( PT) is fast, economical and widely used non destructive test method to detect surface-breaking discontinuities in all non-porous materials (metals, plastics, or ceramics).

Penetrant test is based upon the principles of capillary action where liquid penetrates into a cavity. Penetrant test is performed by cleaning the test surface thoroughly, applying coloured or fluorescent penetrant, allowing penetration time, removal of excess penetrant followed by application of developer (dry or liquid form).

The developer assists to draw penetrant out from the surface breaking discontinuities. After developer dwelling the test surface is examined for bleed out under natural light or black (UV) light (depending on the type of penetrant). Fluorescent Dye Penetrant Inspection (FDPI) is the most sensitive test method.

Dye penetrant Inspection (DPI) is predominantly used on non-ferrous materials in aerospace industries, shipping and offshore, petrochemical industries and stainless industry. Some of the common parts tested are stainless steel welded joints, aluminium alloys joints, turbine blades, stainless steel fittings, castings and forgings, weld overlays (satellite), aerospace engine parts, etc.

CONCLUSIONOur two weeks industrial attachment with Laxmi engineering industries has been one of the most interesting, productive and instructive experience in my life. Through this training, we have gained new insight and more comprehensive understanding about the real industrial working condition and practice, it also improved my soft and functional skills. All these valuable experiences and knowledge’s that we have gained were not only acquired through the direct involvement in task but also through other aspects of training such as : work observation, interaction with collogues, supervisors and other people related to the field. We are sure that industrial training program has achieved its primary objectives. As result of this training we are more confident to build our future career.