08.06.2015 pressure vessels

7/24/2019 08.06.2015 Pressure Vessels

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TYPE OF PRESSURE VESSEL

PRESSURE VESSEL SIZE AND

ANALYSIS OF PRESSURE VESSEL


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THE EFFECTS THAT PRESSURE AND FORCE HAVE ON A

PRESSURE VESSEL

WHEN A CONTAINER IS PRESSURIZED THEN PRESSURE ISEXERTED AGAINST THE WALLS OF THE VESSEL. PRESSURE ISALWAYS NORMAL [PERPENDICULAR] TO THE SURFACEREGARDLESS OF THE SHAPE.

THE FORCE EXERTED ON THE SURFACE BOWS THE SURFACEOUTWARD. THIS IS WHY PRESSURE VESSELS TEND TO BE ROUND.IN FACT,AN IDEAL PRESSURE VESSEL IS A SPHERE.

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WE EXPRESS PRESSURE IN DIFFERENT WAYS [ENGLISH

UNITS]

POUNDS PER SQUARE INCH or psi

POUNDS PER SQUARE INCH ABSOLUTE or psia

INCHES OF WATER OR MERCURY or inches-H2O; inches- Hg

PRESSURE

PRESSURE IS FORCE DIVIDED BY AREA OR P= FORCE DIVIDEDBY AREA

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Psia DESCRIBES AN ABSOLUTE PRESSURE PER SQUARE INCH THATSTARTS FROM A PERFECT VACUUM .

Psia IS INFLUENCED BY WEATHER AND ELEVATION .

A GOOD FRAME OF REFERENCE IS AT SEA LEVEL . THERE IS 14.7-psia, psi DESCRIBES A RELATIVE PRESSURE THAT STARTS FROMATMOSPHERIC PRESSURE.

THEREFORE IF YOU ARE ON A MOUNTAIN AND THE PRESSURE

VESSEL GAUGE READS 1000 psi AND RELOCATE THE PRESSUREVESSEL TO SEA LEVEL ,THEGAUGEWILL READ 1000 psi.WE CANFURTHER SAY THAT AT SEA LEVEL THERE IS 0 psi.

EXAMPLE, WHEN PURCHASING A NEW GAUGE , PRESSURE GAUGEREADS ZERO. WE CAN NOW SAY psia IS AN ABSOLUTE PRESSUREREADING, AND psi IS A RELATIVE PRESSURE READING. IN MOST

CASES, psiIS USED ON PRESSURE VESSELS.

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THERE IS LITTLE DIFFERENCE EXCEPT THEY HAVE TO BECONVERTED. Inches of H2O IS MORE SENSITIVE THAN inches of HgBECAUSE MERCURY IS HEAVIER THAN WATER.

AT SEA LEVEL THERE IS 407.1 inch H2O AND 29.9 inches Hg

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TWO BASIC TYPES OF PRESSURE VESSELS BASED ON WALLTHICKNESS?

THINNED WALL- THESE PRESSURE VESSELS ARE THE MOSTCATEGORIZED. A THINNED WALLED PRESSURE VESSEL IS ANYCYLINDER [SHELL] RATIO THAT IS 10% OR LESS THE RATIO OFTHE THICKNESS TO THE DIAMETER. ANOTHER WAY OF SAYINGTHIS IS A PRESSURE VESSEL IS THINNED WALLED IF THE

DIAMETER IS 10 TIMES OR MORE THE THICKNESS.

t < 0.1

THICK WALLED- THESE PRESSURE VESSELS ARE THE LEASTCOMMON. A THICK WALLED PRESSURE VESSEL IS ANY CYLINDER

[SHELL] RATIO THAT IS 10% OR MORE THE RATIO OF THETHICKNESS TO THE INSIDE DIAMETER.

t > 0.1

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THIN WALL REFERS TO A VESSEL HAVING AN INNER-RADIUS-TO-WALL-THICKNESS RATIO OF 10OR MORE (R / T 10).

WHEN THE VESSEL WALL IS THIN, STRESS DISTRIBUTIONTHROUGHOUT ITS THICKNESS WILL NOT VARY SIGNIFICANTLY,AND SO WE WILL ASSUME THAT IT IS UNIFORM OR CONSTANT.

FOLLOWING THIS ASSUMPTION, ANALYSIS OF THIN WALLEDCYLINDRICAL AND SPHERICAL PRESSURE VESSEL WILL BECARRIED OUT.

IN BOTH CASES, THE PRESSURE IN THE VESSEL WILL BECONSIDERED TO BE THE GAUGE PRESSURE, SINCE IT MEASURE

THE PRESSURE ABOVE ATMOSPHERIC PRESSURE EXISTING ATINSIDE AND OUTSIDE THE VESSELSWALLS.

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ABOVE ANALYSIS INDICATES THAT AN ELEMENT OF MATERIALTAKEN FROM EITHER CYLINDRICAL OR SPHERICAL PRESSURE

VESSEL IS SUBJECTED TO BI-AXIAL STRESS, I.E. NORMAL STRESSEXISTING IN ONLY TWO DIRECTIONS.

ACTUALLY MATERIAL OF THE VESSEL IS ALSO SUBJECTED TO ARADIAL STRESS, 3, WHICH ACTS ALONG A RADIAL LINE. THISSTRESS HAS A MAX. VALUE EQUAL TO THE PRESSURE P AT THE

INTERIOR WALL AND DECREASES THROUGH THE WALL TO ZEROAT THE EXTERIOR SURFACE OF THE VESSEL, SINCE THE GAUGEPRESSURE THERE IS ZERO.

FOR THIN WALLED VESSELS, HOWEVER, RADIAL STRESSCOMPONENTS ARE IGNORED BECAUSE r / t = 10 RESULTS IN 1 &

2 BEING, RESPECTIVELY, 5 & 10 TIMES HIGHER THAN THE MAX.RADIAL STRESS, (3)max = p

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IT MUST BE EMPHASIZED THAT THE FORMULA DERIVED FOR THINWALLED PRESSURE VESSELS SHOULD BE USED ONLY FOR CASESOF INTERNAL PRESSURE.

IF A VESSEL IS TO BE DESIGNED FOR EXTERNAL PRESSURE AS INTHE CASE OF VACUUM TANK, OR SUBMARINE, INSTABILITY(BUCKLING) OF THE WALL MAY OCCUR & STRESS CALCULATIONS

BASED ON THE FORMULA DERIVED CAN BE MEANINGLESS.

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STORAGE TANKS- STORAGE TANKS ARE A CATEGORY OF THINWALLED PRESSURE VESSELSEXCEPT THAT ARE TYPICALLY UNDER

15 psi AND ARE SUPER THIN WHEN COMPARED TO THE RATIOABOVE.

TRANSPORTABLE CONTAINERS - THESE ARE THE MOSTCOMMON PRESSURE VESSEL AND POTENTIALLY THE MOST

IGNORED. THESE ARE MASS PRODUCED AND REQUIRE TESTINGEVERY 10 YEARS FOR PROPANE GAS ETC.

PROPANE BOTTLES - FORK TRUCKS, BARBECUES, GASCYLINDERS - CO2, O2,...

OTHER- CONTAINERS, GAS CANES, BUBBLERS ETC.

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A PRESSURE VESSEL HAS TO RETAIN THE PRESSURE. IN DOINGSO, PRESSURE APPLIES TWO TYPES OF STRESSES IN A PRESSURE

VESSEL. THEY ARE CIRCUMFERENTIAL AND LONGITUDINAL

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WHAT IS IMPORTANT TO REMEMBER IS LONGITUDINAL STRESSES

ARE HALF AS MUCH AS THE CIRCUMFERENTIAL STRESSES.THEREFORE, WE CAN SAY THAT LONGITUDINAL STRENGTH ISTWICE AS STRONG AS CIRCUMFERENTIAL STRENGTH.

THIS IS ONLY TRUE FOR ILLUSTRATION PURPOSES.

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CALCULATIONS

THIN-WALLED PRESSURE VESSEL

GENERAL FORMULA FOR PRESSURE VESSELS[THIN WALLED PRESSURE VESSELS]

STRESS IN LONGITUDINAL DIRECTION = P x R / 2 x t

R = MEAN RADIUS

t =THICKNESS

STRESS IN CIRCUMFERENTIAL DIRECTION = P x R / t

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PURPOSE OF A FACTOR OF SAFETY

FACTORS OF SAFETY ARE USED BECAUSE NO MANUFACTURE CANGUARANTEE 100% QUALITY. EVERY PRESSURE VESSEL HAS AFACTOR OF SAFETY. A FACTOR OF SAFETY ACCOUNTS FORUNCERTAINTIES IN MATERIALS, DESIGN AND FABRICATION.

FACTORY OF SAFETY [FS] = ACTUAL BREAKING STRENGTHLOAD

TO BELIEVE IN THAT A F.S.MAKES A PV[PRESSURE VESSEL] SAFEIS DANGEROUSAND UNWISE. PUTTING THIS IN ANOTHER WAY, AFACTOR OF SAFETY COMPENSATE FOR IMPERFECTIONS IN THE

PRESSURE VESSEL; THEREFORE, EVERY PRESSURE VESSELSHOULD BE TREATED AS SAME REGARDLESS OF THE FACTOR OFSAFETY.

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THERE ARE FOUR TYPES OF OVER PRESSURIZATION DEVICES:

RUPTURE DISKS

RELIEF VALVES

SAFETY RELIEF VALVES

SAFETY VALVES

THE SET PRESSURE SHOULD NEVER BE GREATER THAN THE

PRESSURE VESSELS MAWP [MAXIMUM ALLOWABLE WORKINGPRESSURE].

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HERE ARE SOME SPECIAL RULES TO THE SET PRESSURE-

RELIEF VALVES, SAFETY RELIEF VALVES, AND SAFETY VALVES

SHOULD BE SET AT OR BELOW PRESSURE VESSEL ASMENAMEPLATE MAWP.

RUPTURE DISKS SHOULD BE SET NOT HIGHER THAN THE PV[PRESSURE VESSEL] NAMEPLATE. UNDER SPECIAL

CIRCUMSTANCES THE RUPTURE DISK CAN BE SET UP TO 110% OFTHE MAWP.

IN ADDITION TO THIS SPECIAL CONDITION, WHENEVER THERE ISA POSSIBILITY OF INTERNAL FIRE IN THE PRESSURE VESSEL , THERUPTURE DISK CAN BE SET NOT HIGHER THAN 160%, BUT APRESSURE VESSEL ENGINEER WILL NEED TO BE CONSULTED.

REMEMBER THERE SHOULD NEVER BE A SHUT OFF VALVE BETWEEN

THE PVANDOVER PRESSURIZATION DEVICE

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1. ALWAYS IN AN UPRIGHT INSTALLATION.

2. INSTALL THE OVER PRESSURIZATION DEVICE A FEW PIPE

DIAMETERS AWAY FROM THE PV,BUT CONSULT THE CODE ANDMANUFACTURE FOR MAXIMUM DISTANCE

3. MAKE SURE THE EXHAUST DISCHARGES SAFELY AWAY, SO NOONE COULD BE INJURED.

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RELIEF VALVES - RELIEF VALVES OPEN AT A SETPRESSUREAND RE-CLOSE AT THE SAME PRESSURE.

THESE DEVICES ARE SUITABLE FOR LIQUIDSERVICE.

SAFETY RELIEF VALVES - THESE VALVES DIFFERFROM SAFETY VALVES IN THAT THEY ARE MEANT TOHANDLE FLUID STREAMS THAT HAVE LIQUIDS ANDVAPOR. THESE VALVES POP OPEN AT A SETPRESSURE AND RESET [BLOW DOWN] AT A LOWERPRESSURE [VERY MUCH LIKE A SAFETY VALVE].

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SAFETY VALVES - SAFETY VALVES ARE

STRICTLY FOR VAPOUR OR GAS SERVICE. THE

VAPOUR OR GAS SHOULD BE RELATIVELYCLEAN TO ENSURE CONTINUED ANDSUCCESSFUL OPERATION. A TYPICAL VAPOURIS STEAM, AN EXAMPLE FOR GAS WOULD BECOMPRESSED AIR. THESE ARE NOT MEANT FORLIQUIDS. THESE VALVES POP OPEN AT A SET

PRESSURE AND RESET AT A LOWER PRESSURECALLED BLOW DOWN.

RUPTURE DISKS- RUPTURE DISKS AREPROBABLY THE MOST VERSATILE OVER-PRESSURIZATION DEVICE. THESE CAN ONLY

BE USED ONCE. THEY ARE THE ONLY DEVICETHAT CAN BE USED IN CONJUNCTION WITHOTHER OVER-PRESSURIZATION DEVICES

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CONTENT

GENERAL REQUIREMENTS

REQUIREMENTS PERTAINING TO METHODS OF FABRICATION OFPRESSURE VESSELS

REQUIREMENTS PERTAINING TO CLASSES OF MATERIALS

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PLATE

FORGINGS

CASTINGS

PIPE AND TUBES

WELDING MATERIALS

PREFABRICATED OR PREFORMED PRESSURE PARTS

BOLTS AND STUDS

NUTS AND WASHERS

RODS AND BARS

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FOLLOWING ARE THE MAIN COMPONENTS OF PRESSURE VESSELSIN GENERAL

SHELL

HEAD

NOZZLE

SUPPORT

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IT IS THE PRIMARY COMPONENT THAT CONTAINS THEPRESSURE.

PRESSURE VESSEL SHELLS IN THE FORM OF DIFFERENT PLATESARE WELDED TOGETHER TO FORM A STRUCTURE THAT HAS ACOMMON ROTATIONAL AXIS.

SHELLS ARE EITHER CYLINDRICAL, SPHERICAL OR CONICAL INSHAPE.

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HORIZONTAL DRUMS HAVE CYLINDRICAL SHELLS AND ARECONSTRUCTED IN A WIDE RANGE OF DIAMETER AND LENGTH.

SHELL SECTIONS OF A TALL TOWER MAY BE CONSTRUCTED OFDIFFERENT MATERIALS, THICKNESS AND DIAMETERS DUE TOPROCESS AND PHASE CHANGE OF PROCESS FLUID.

SHELL OF A SPHERICAL PRESSURE VESSEL IS SPHERICAL AS WELL.

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ALL THE PRESSURE VESSELS MUST BE CLOSED AT THE ENDS BYHEADS (OR ANOTHER SHELL SECTION).

HEADS ARE TYPICALLY CURVED RATHER THAN FLAT.

THE REASON IS THAT CURVED CONFIGURATIONS ARE STRONGERAND ALLOW THE HEADS TO BE THINNER, LIGHTER AND LESS

EXPENSIVE THAN FLAT HEADS.

HEADS CAN ALSO BE USED INSIDE A VESSEL AND ARE KNOWN ASINTERMEDIATE HEADS.

THESE INTERMEDIATE HEADS ARE SEPARATE SECTIONS OF THE

PRESSURE VESSELS TO PERMIT DIFFERENT DESIGN CONDITIONS.

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ELLIPTICAL, HEMISPHERICAL, AND TORISPHERICAL ARE THEMOST COMMONLY USED HEAD TYPES. NOTE THAT ALL HEAD TYPESHAVE A STRAIGHT FLANGE (SF) SECTION, WHICH SIMPLIFIESWELDING THE HEAD TO THE ADJACENT CYLINDRICAL SHELLSECTION.

THE ELLIPTICAL AND TORISPHERICAL HEADS HAVE ANINDICATED HEAD DEPTH (H), WHICH IS MEASURED FROM THESTRAIGHT FLANGE TO THE MAXIMUM POINT OF CURVATURE ONTHE INSIDE SURFACE.

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A NOZZLE IS A CYLINDRICAL COMPONENT THAT PENETRATES INTOTHE SHELL OR HEAD OF PRESSURE VESSEL.

THEY ARE USED FOR THE FOLLOWING APPLICATIONS.

ATTACH PIPING FOR FLOW INTO OR OUT OF THE VESSEL.

ATTACH INSTRUMENT CONNECTION (LEVEL GAUGES,

THERMOWELLS, PRESSURE GAUGES).

PROVIDE ACCESS TO THE VESSEL INTERIOR AT MANWAY.

PROVIDE FOR DIRECT ATTACHMENT OF OTHER EQUIPMENTITEMS (e.g. HEAT EXCHANGERS).

(ASME - American Society of Mechanical Engineers )

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SUPPORT IS USED TO BEAR ALL THE LOAD OF PRESSURE VESSEL,EARTHQUAKE AND WIND LOADS.

THERE ARE DIFFERENT TYPES OF SUPPORTS WHICH ARE USEDDEPENDING UPON THE SIZE AND ORIENTATION OF THEPRESSURE VESSEL.

IT IS CONSIDERED TO BE THE NON-PRESSURIZED PART OF THEVESSEL.

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SADDLE SUPPORT:

HORIZONTAL DRUMS ARE TYPICALLY SUPPORTED AT TWOLOCATIONS BY SADDLE SUPPORT.

IT SPREADS OVER A LARGE AREA OF THE SHELL TO PREVENT ANEXCESSIVE LOCAL STRESS IN THE SHELL AT SUPPORT POINT.

ONE SADDLE SUPPORT IS ANCHORED WHEREAS THE OTHER ISFREE TO PERMIT UNSTRAINED LONGITUDINAL THERMALEXPANSION OF THE DRUM.

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LEG SUPPORT:

SMALL VERTICAL DRUMS ARE TYPICALLY SUPPORTED ON LEGSTHAT ARE WELDED TO THE LOWER PORTION OF THE SHELL.

THE MAX. RATIO OF SUPPORT LEG LENGTH TO DRUM DIAMETER ISTYPICALLY 2 : 1

REINFORCING PADS ARE WELDED TO THE SHELL FIRST TO

PROVIDE ADDITIONAL LOCAL REINFORCEMENT AND LOADDISTRIBUTION.

THE NUMBER OF LEGS DEPENDS ON THE DRUM SIZE AND LOADSTO BE CARRIED.

SUPPORT LEGS ARE ALSO USED FOR SPHERICAL PRESSURIZED

STORAGE VESSELS.

CROSS BRACING BETWEEN THE LEGS IS USED TO ABSORB WINDOR EARTH QUAKE LOADS.

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LUG SUPPORT:

VERTICAL PRESSURE VESSELS MAYALSO BE SUPPORTED BY LUGS.

USE OF LUGS IS TYPICALLYLIMITED TO PRESSURE VESSELSOF SMALL AND MEDIUM DIAMETER

(1 TO 10 FT)

ALSO MODERATE HEIGHT TODIAMETER RATIOS IN THE RANGEOF 2:1 TO 5:1

LUGS ARE TYPICALLY BOLTED TO

HORIZONTAL STRUCTURALMEMBERS IN ORDER TO PROVIDESTABILITY AGAINSTOVERTURNING LOADS.

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SKIRT SUPPORT:

TALL VERTICAL CYLINDRICAL PRESSURE VESSELS ARE TYPICALLY

SUPPORTED BY SKIRTS.

A SUPPORT SKIRT IS A CYLINDRICAL SHELL SECTION THAT ISWELDED EITHER TO THE LOWER PORTION OF THE VESSEL SHELLOR TO THE BOTTOM HEAD (FOR CYLINDRICAL VESSELS).

THE SKIRT IS NORMALLY LONG ENOUGH TO PROVIDE ENOUGHFLEXIBILITY SO THAT RADIAL THERMAL EXPANSION OF THESHELL DOES NOT CAUSE HIGH THERMAL STRESSES AT ITSJUNCTION WITH THE SKIRT.

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TWO IMPORTANT ISSUES FOR CARBON AND LOW ALLOY

STEELS:

POST WELD HEAT TREATMENT (PWHT)

IMPACT TEST

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TEMPERATURES TO CONSIDER

MINIMUM DESIGN METAL TEMPERATURE (MDMT)

LOWEST TEMPERATURE AT WHICH COMPONENT HAS

ADEQUATE FRACTURE TOUGHNESS

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STRESS RELIEVING AT AROUND 600 CENTIGRADE

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POSTWELD HEAT TREATMENT IS MANDATORY UNDER THEFOLLOWING CONDITIONS:

a. FOR WELDED JOINTS OVER 112 in. (38 mm) NOMINALTHICKNESS;

b. FOR WELDED JOINTS OVER 114 in. (32 mm) NOMINALTHICKNESS THROUGH 112 in. (38 mm) NOMINAL THICKNESSUNLESS PREHEAT IS APPLIED AT A MINIMUM TEMPERATUREOF 200F (95C) DURING WELDING;

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THERE ARE THREE MAIN TYPES OF PRESSURE VESSELS IN

GENERAL

HORIZONTAL PRESSURE VESSELS

VERTICAL PRESSURE VESSELS

SPHERICAL PRESSURE VESSELS

HOWEVER THERE ARE SOME SPECIAL TYPES OF VESSELS LIKEREGENERATION TOWER, REACTORS BUT THESE NAMES ARE GIVENACCORDING TO THEIR USE ONLY.

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THE MAX. SHELL LENGTH TODIAMETER RATIO FOR ASMALL VERTICAL DRUM ISABOUT 5 : 1

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CONSTRUCTED IN A WIDER

RANGE OF SHELL DIAMETERAND HEIGHT.

THEY CAN BE RELATIVELYSMALL IN DIA AND VERYLARGE (e.g. 4 FT DIA AND 200FT TALL DISTILLATION

COLUMN.

THEY CAN BE VERY LARGE INDIA AND MODERATELY TALL(e.g. 3 FT DIA AND 150 FTTALL TOWER).

INTERNAL TRAYS ARE NEEDEDFOR FLOW DISTRIBUTION.

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FIGURE SHOWS A TYPICAL

REACTOR VESSEL WITH ACYLINDRICAL SHELL.

THE PROCESS FLUIDUNDERGOES A CHEMICAL

REACTION INSIDE AREACTOR.

THIS REACTION IS NORMALLYFACILITATED BY THEPRESENCE OF A CATALYST

WHICH IS HELD IN ONE ORMORE CATALYST BEDS.

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AS COMPLETE AN EXAMINATION AS CAN BE REASONABLY MADEOF THE INTERNAL AND EXTERNAL SURFACES OF A BOILER OR

PRESSURE VESSEL WHILE IT IS SHUT DOWN AND WHILEMANHOLE PLATES, HANDHOLE PLATES OR OTHER INSPECTIONOPENING CLOSURES ARE REMOVED AS REQUIRED BY THEINSPECTOR.
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ERROR IN DESIGN AND CONSTRUCTION

IMPROPER OPERATION

CORROSION

FAILURE TO INSPECT PROPERLY

LACK OF PREVENTATIVE MAINTENANCE


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RK

JAISWAL

+91 9650993009

[email protected]

NKTUTEJA

+91 9810174125

[email protected]

Thank You

08.06.2015 pressure vessels

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