Boiler Survey & Const

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Guide Book for Marine Engineers

BOILER INSPECTION:

Boiler surveys or inspections are carried out at regular intervals due to following reasons:

Boilers are inspected to maintain the class requirement.

Regular internal and external examinations during such survey constitute the preventive maintenance schedule

the boiler goes through to have a safe working condition.

Frequency of Surveys:

Water tube high-pressure boilers are surveyed at 2 yearly intervals. All other boilers including exhaust gas boilers are surveyed at 2 yearly intervals until they are 8 years old and

then surveyed annually.

Scope of Surveys:

A complete boiler survey allows us to check out if any build-up deposits has taken place and deformations or

wastage of plate-work, piping or any of the various parts which may compromise the safe working order of the

unit. The survey should include finding reasons for any abnormality found and should also ensure that any repair

carried out does not affect that safe working order of the boiler. A complete survey means full internal and external examination of all parts of the boiler and accessories such

as super-heater, air-heater and all mountings. The examination may lead the inspector to require hydraulic testing of pressure parts or thickness gauging of

plate or tubes that appear to be wasted and eventually assign a lower working pressure. The seating tools,hangers and rolling stays are also to be checked for good working condition.

The survey is not complete until the boiler has been examined under steam and the following items dealt with:

(a) Pressure gauge checked against a test gauge.

(b) Testing of water level indicators and protective devices.(c) Safety valves adjusted under steam to blow off at the required pressures.

(d) The oil fuel burning system examined.(e) Testing of remote control gear for fuel shut off valves.

For gas fired boilers, the Chief Engineer floats the safety valves at sea at the first opportunity. Survey record is not

assigned until a statement is received from the C/E conforming the pressure at which the safety valves were set.

Survey Consists of:

a. Examination of the item.

b. Statement whether a problem / defect exists.c. Determining the cause of problem.

d. Define the repair and whether temporary / permanent.

Arrangement before Survey:

Boiler must be sufficiently cleaned and dried to make a thorough examination possible.

Boilers should be manually wire-brushed to clean the internal surfaces.

In case of difficulty in manual cleaning chemical cleaning with hydrochloric acid plus an inhibitor to prevent

acid attacking the metal without affecting removal of deposits is the best procedure.

For oil contamination, alkali boil-out using tri-sodium phosphate solution (which produces a detergent action)is essential prior to acid cleaning. Thorough water flushing must be carried out after acid cleaning to avoid acid

concentrating in crevices and captive spaces. All internals, which may interfere with the inspection, has to be removed.

Wherever adequate visual examination is not possible, surveyor may have to resort to drilling, ultrasonic or

hydraulic testing. All manhole doors and other doors must be opened for a reasonable time previous to survey for ventilation.

If another boiler is under steam arrangement of locking bar and other security devices must be in position

preventing the admission of steam or hot water to the boiler under survey. The smoke trunking (separatingdevice), exhaust gas shut-off etc. must be in position and in proper working condition.

Plants staff or repairers staff should stand by the manhole in case of emergency and to take note for

defects/repairs required.

Before survey, the surveyor should acquaint himself with the boiler type in question (drawings carried on board)and during the survey it is advisable to follow a planed routine in order not to miss parts of the boiler or importantitems.

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LOW PRESSURE TANK TYPE BOILER INSPECTION:

SURVEY OF A SUNROD CPH BOILER

Poor condition in this type of boiler may stem from: Poor workmanship during construction or repair.

Deterioration due to leaks or deposits.

Local overheating.

Combined effects of mechanical stress and corrosion.Damage condition would show up in the form of (a) wastage, grooving or pitting, corrosion or, (b) distortion or, (c)

crack.

Survey Routes:

Any boiler to survey, the inspector must plan out a route for his movement. Almost always, the inspection must start at the furnace. The reason being, the furnace reveals the quality of

combustion and its effects and any distortion at the crown or the tube walls signifying the problems originating

at the waterside. In fact, a good clean furnace with no signs of distortion could assure the inspector that theboiler is in good running condition.

The next in succession should be the burner unit, the bottom header and the boiler bottom.

Mounting attachments on the upper shell will follow before entry is made through the manhole to inspect the

waterside of the steam space. Top mountings will be checked before entering the gas space through the inspection door for a look at the

Sunrod tubes. The inspector will end with a check on the dismantled mounting parts arranged in order for the purpose.

If in doubt of gas side corrosion, checks on the gas uptake could be done as a final step in the survey route.

Furnace:

Sludge deposits continue to be the prime cause of non-operation of internal controls and overheating of furnace in

vertical boilers.

Overheating distortion on the furnace crown is due mainly to a deposit of oil, scale or sludge deposits on the

heating surface or due to water shortage. The lower section of the crown causes overheating distortion due to

the sludge deposits. The furnace connecting to the shell may be welding cracks due to rapid fluctuation of thermal and mechanical

stresses, results of improper starting up/ shutting down procedures. Direct flame impingement resulting in deformation of the crown or a local bulge in wall tubes opposite the

burner opening is also possible. Dry cracks in furnace mouth, crown or the furnace tubes caused by flame impingement is possible due to scale

encrustation at the water side and forcing of the boiler. Areas suffering from poor circulation or relatively

uncooled areas are also susceptible to the above failure. Deep cracks in furnace mouth, crown or the furnace tubes caused by flame impingement is possible due to

scale encrustation at the water side and forcing to boiler. Areas suffering from poor circulation or relatively

uncooled areas are also susceptible to the above failure. Deep cracks on plating should be stopped by drilling a hole at each end, opening up and then welding.

Indifferent feed water may cause pitting of the furnace crown. A careful examination through the bottom

manhole door would require to detect the above grooving.

Brickwork protecting the foundation, if damaged, may cause distortion of the bottom plating underneath the

furnace. Damaged brickwork need be removed to inspect the bottom plating for distortion before repairs to thebrick work is carried out.

Any sign ofcorrosion on plating should be chipped clean and brushed clear. It is also possible to build up the

weakened areas by means of electric welding. Pitted areas are difficult to protect from further corrosion due tothe difficulty in maintaining the protective magnetic oxide layer.

Furnace crowns, which have suffered a gradual deformation, can be jacked back or pressing back to their original

shape with or without heat. A sharper deformation may require the plating to be slotted so that the metal can

extrude into the gap during heating and jacking. The slot is butt welded on completion. A much neater repair is to

burn out the affected area and replace with a butt-welded insert section cut from a salvaged furnace. For a

severely damaged furnace with a pronounced large belly, replacement could be the only answer.

Furnace tubes must be inspected for correct alignment and the tubes together must form a circular tube wall,

anywhere the tubes are deformed, the furnace shape will show up as misaligned. Distortion to a very small extent

could be accepted, but beyond that renewal of tubes will be mandatory.

Furnace tubes, if damaged (cracked, holed or deformed) need be renewed with new tubes, only under emergency

conditions, one could be allowed to operate boiler at low load, with plugged furnace tubes, plugging could be

carried out with tapered steel plugs on each tube ends. The bottom plug will have to be inserted through the

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bottom header, difficulty in doing that may also compel cutting windows on tubes from the furnace end and

manipulating the tapered plug in position (similar to that done in membrane wall boiler panels).

Bottom Header:

This contains the furnace tubes and the down comer tubes. Number of handhole doors are provided for internal

inspection and repairs to the tubes. Inspection for deposits of sludge must be carried out during the survey.

Regular blowing down from this header will be necessary to keep it clear of sludge deposits.

Sunrod Tubes: Internal wastage due to waterside corrosion and pitting is the main reason for renewal.

The reason for corroded tubes is almost always the bad quality feed used giving rise to heavy scaling and

corrosion. It is difficult to determine the condition of tubes by visual examination. A metal rod inserted at the tube ends

and worked up or down may reveal a weak tube Thermal cracks may develop at the tube ends at the hot gas entry zone. The elements could be corroded on the outside due to the hot gas containing sodium ( Na) and vanadium (V),

referred to as high temperature corrosion. Ash containing Na and V may promote melting of oxide deposits

across the tubes and cause scoring of metal at the tube externals.

Shell : Internal examination is made forcracks, corrosion wastage ordeformation of shell plating.

Any oil trace must be removed by alkali-boil out corrosion may be expected at positions with poor circulation

and places which can harbor deposits.

Pitting corrosion in way of water level to be checked for, especially on idle boilers where liberated dissolved

gas was not removed from the boiler with the steam. Boilers left with undisturbed water level for some lengthof time can develop serious pitting.

External corrosion can be caused by persistent leakage at mounting flanges and manhole or handhole doors.

Engine room floor underneath the boiler may have occasional bilge water and possess a damp atmosphere,there may also be oil deposit and stored rags or paint drums; these are all potential hazards.

Welding may reinforce the wasted shell plating but in case of extension wastage, renewal of plating is the only

remedy.

Support and Securing Arrangements:

Attachment between boiler and foundation structure should have adequate provision for expansion. Restriction

of movement imposes loads on the connections and if the part is unable to yield or bend, cracking will occur. Welded attachments such as cradles, feet and rolling stay lugs should always be inspected carefully. Cracks

due to stress concentration at the welded connections may propagate into the shell plating.

Mountings and Fittings:

Major mounting are removed, dismantled and inspected.

Gauge glasses safety valves, feed check valves, steams stop valves, are all checked for corrosion, erosion,

strength and correct operations. Internal feed and chemical injection pipes are inspected for oxygen pitting and corrosion.

Waste steam pipes are hammer tested and all drains in the exhaust system checked.

Soot blower nozzles are vulnerable to burning and to be checked for correct sweep pattern.

The air registers are to be checked and cleaned.

Clearance at the manhole and mudhole doors to be checked and should have a spigot clearance not exceeding

1. 5mm all around. Leakage from manhole doors has been cause of serious shell wastage. Where this isexceeded, the clearance can be restored by building up the door spigot with welding and hand dressing to suit.

Wastage of manhole landing faces is difficult to rectify by welding fitting a false sealing ring could be the

recommended repair. A careful check is made for strained door studs stripped and slack nuts and distorted dogs. A badly fitted door

can cause a joint to blow out under pressure. When under steam, the inspector always checks if manhole doors have been pulled up when hot and the dogs

are correctly positioned.

Cracks can occur in valve body due to water carry-over and quenching or may originate from shrinkage

defects in the casting propagation in service. The only positive solution is to replace the manifold entirely with a similar but fabricated construction.

Repair by welding the defects in the steel castings is also possible but this presents the problem of distortion.

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MEDIUM PRESSURE DRUM TYPE BOILER INSPECTION

SURVEY OF A D-TYPE BOILER

Route for inspection

01. Inside steam drum. 06. Furnace 07. Inside water drum.02. Outside steam drum (a) Roof tubes 08. Superheater space.

03. Super heater. (b) Screen tubes 09. Economiser.

04. Rear water wall headers and casing. (c) Water wall tubes 10. Uptake.

05. Side water wall headers. (d) Refractories

(e) Burner front.

Detail of Inspection and Defects:

1. Inside Steam Drum

(a) Certain internal fittings to remove for access.(b) Boiler internal to check for erosion and corrosion.

(c) Drums and tubes checked for active corrosion. Active of dissolved gases like O2 and CO2 are mainly

responsible for "pitting of the stream space.

(d) Drum openings and doors. Spigot clearance not exceeding 1. 5 mm all around.

Door studs and nuts to be free of slackness and stretched threads.

Door dogs to check for ovality and distortion.

Drum openings of mountings to be sighted to check for any planted objects in the passage.

2. Out Side Steam Drum

(a) All internal (removed from drum) checked and tested.(b) Feed regulator, feed check valve, water gauge fittings, and drums safety valves examined. Attention to

securing arrangements of seats in valves covers to v/v chests, and v/v chest to drum nozzles.(c) Welded connection of drum to casing to check for any possible damage creating gas leakage.

(d) Areas of drum not protected by tubes from heat radiation are shielded refractory. Thermal cracking of therefractory material to be checked

3. Superheater

(a) Internal and external examination of heaters.

(b) Thermal crack at the headers due to high stresses set up across the thick welded section is possible.

(c) Superheater safety valve and stop valve.(d) Superheater drains and vents valves and manhole openings to check.

(e) Efficiency of the screen plates to ascertain these protect headers from direct heat of furnace.

(f) Superheater tubes are also prone to high temperature creep failures and thermal fatigue cracking. Suddenquenching can cause fatigue failure.

4. Rear and Side Wall Headers

(a) Sufficient doors or handhole plugs to remove for assessment of internal condition of headers and tubes.

(b) Check for pitting and corrosion of headers, rear wall, floor, roof and side wall tubes.(c) Check for casing defect for possible gas or air leakage. For single casing boiler a complete shut down is

possible due to damaged refractory and overheated casing.(d) Check for deposit accumulation in header.

(e) Drain valves from headers to examine.

5. Furnace

a. Screen tubes:

- Check for direction due to overheating maximum permissible deviation or sag may be 2inch in 12ft.before

renewal.

- Leakage at top expansion usually shows by white stains down the outside of tubes these may be re-expanded.

- Check gas passage through superheater banks for cleanliness.

- Examine furnace end of superheater supports visible through screen tubes.

- Gas baffle conditions above and below the superheater attached to the rear screen tubes to verify which may

cause gas short circuit giving local overheat in superheater and loss of superheat

- Screen tubes exposed to excessive heat due to flame impingement, forcing etc. Possibility of high temperaturecreep cracks or circumferential fatigue fracture due to rapid thermal cycling.

b. Water Wall Tube:

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- More possibility of overheating due to restriction in circulation.

- Roof tubes having horizontal portion show effect of overheating due to water shortage very quickly. Roof

tubes with roof fired boilers are also prone to distortion due to overheat.

- Tubes around soot blower openings have more chances of overheating due to turbulence at the bents restrictingcirculation.

c. Refractory:- Front wall with its quarls receives full radiant heat and so deteriorates more rapids and may cause, spalling of

brickwork, misshapen quarls, badly burnt registers.

- Refractory to protect front part of water drum, particularly below screen tubes may fail and expose drum to

direct heat of furnace resulting in circumferential thermal cracking.

(6) Inside Water Drum:

- Normally no defects are found.

- If pitting, corrosion or deposits are earlier discovered in steam drum or headers then lower part of tube bores to

be checked from inside the drum.

- Inspections for manhole covers are as usual.

(7) Superheater Walk-in Space:

- Supports of horizontal superheater tubes to check for burning away and leave the unit unsupported and causedrainage problem.

- Superheater support tube may also crack due to effect of bending fatigue stresses due to misalignment of tubes

in the tube holes.

- Build-up of deposit is most troublesome defect in superheater. These may result in high furnace pressure, lossof superheater, and poor combustion.

- Special attention and suspicion to be reserved for tubes through which there still exist a gas path as they operate

under excessive metal temperature.

- Oxide scaling inside or outside may cause tube failure and worst case hydrogen fire when iron burns in stem at

above 700 C in an exothermic reaction, and destroys all the boiler, economizer and air heater.

8 & 9. Economizer & uptake

-The major problem at the economiser section is the low temp corrosion and the problem from the gas sidedeposits.

- Sliding and leaky expansion joints at the casing may allow accumulation of soot with severe acid attack.

- Inspection of tube bents by opening the inspection covers needs to be carried out to check these.

- Uptake areas may show cracked expansion bellows or sign of acid corrosion.

- General cleanliness of these areas indicates the combustion performance in boiler.

Hydraulic Testing of a Boiler during Survey:

General Precautions:

Warm water should preferably be used when a boiler is subjected to a hydraulic test. If tested with cold water,

rolled and riveted connections may leak because of stresses, which are non-representative of the servicecondition.

The water temperature should be about 50 C. This temperature may be obtained by careful heating of waterin the boiler.

Care should be taken to prevent rapid increase of the test pressure. Damage may occur due to sudden pressure

increase if a powerful pump is being used.

Survey Procedure:

Hydraulic test should be carried out with a test pressure not less than the working pressure and not

exceeding 1. 25 x the working pressure.Leakage Test:

The test pressure can be considerably lower than the working pressure in presence of surveyor.

The higher of the value 0. 25 x the working pressure and 7 kp/cm2 normally be sufficient. The pressure is not to exceed the working pressure.

ECONOMISER:

The economizer is called because transferring heat from the hot waste gases to the boiler feed water effects

economy. This heat which would otherwise be lost in the gases escaping up the funnel, increases the temperature of

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the feed water, hence less heat is required from the fuel per given mass of steam generated in the boiler, resulting

in increased efficiency. The economizer consists of a bank of horizontal tubes in staggered formation sometimes

with external gills shrunk on to increase the surface area and assist transference of heat.

Boiler Repairs:

Replacement of a leaky manhole joint:

Maintain proper spigot clearance ~ l. 5 mm to position the door centrally for evenly loading the gasket.

Never use an old gasket.

Do not overstrain door studs, which may stretch.

Pull-up studs by re-tightening the nuts after steam rising or warm up.

Avoid causing damage to door by holding it by rope and gently lowering it inside or taking it out.

Mark the dogs and nuts to fit back in the same order.

Check for any wear and tear on the studs and nuts.

Check the matting / landing surfaces for corrosion & erosion on the door and boiler end carefully before

reassembling.

Dog

ShellCompensating ring

Joint

Max. spigot clearance 1. 5 mm each side

Door

Procedure for Plugging of a Damaged Fire Tube Boiler:

Hydrostatic testing to mark the leaky tubes.

Cut the tube on one end and clear of the tube plate. At the other end the tube is collapsed inside the tube plate.

Pull out the tube from the collapsed end.

Insert a short tube into the tube plate and weld it in place.

Lap the spare tapered plugs on both stub ends in the tube plates.

Insert the tube plugs and tack-weld.

Alternatively, the plugs can be hold in place by a long steel bar threaded and bolted at both the ends.

Hydrostatic pressure test to conform no leaks.

Flush up the boiler and re-inspect the plugs for leaks under full steam pressure.

2 3 4Take out tube Insert short tube Both ends lap with plugs

Put the plugs by welding

1 CutA A

3

Instruction for Plugging / Repair of Boiler / Economizer:

( Aalborg Marine Boilers & Engineering A/S)

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In case of tube failure, the steam pressure has to be removed from the oil burner dismantled.

If the leakage is readily visible from the fire hole, the boiler can be emptied and repairs commenced.

Otherwise, the boiler is put on pressure by means of the feed pump. The position of the leakage will then be

indicated by its water flow. This flow may not be visible from the fire hole. If it is not visible, remove the inspection door and enter the

furnace. If the tube failure is still not found, then enter the generating tube section. From here the bottom of the

membrane walls and generating tubes can be inspected for leakage. If the leakage has resulted from the membrane walls or generating tube, the inspection doors at the smoke

connection pipe must be removed, and the generating tube / membrane tube in which the failure has occurred,

is pointed out. The leakage may also result from the economizer.

By removing the inspection door at the bottom of the economizer, it can be determined which uptake has

caused the leakage. If necessary other inspection doors should be removed to point out the damaged register.

When a damaged tube or convection register has been removed, and the remaining tube stubs have been

repaired / plugged, a new tube or register should be mounted as soon as possible. Operation for a longer period with one or more registers missing involves the risk of further damage to the

boiler due to increased heat leads on the parts next to the ones removed. The generating tube at the boiler can be plugged as shown below:

Temporary Sunrod Boiler Tube Repairs:

If the sunrod tube is leaking, proceed as follows to effect a temporary repair-1. Stop the burner, allow the boiler to cool and remove the soot.

2. Allow boiler to depressurize, and open the blow-down valves to drain the boiler.3. Enter the boiler flue box and cut a hole in the side of the relevant smoke tube.

4. Clean the rim of the smoke tube with a wire brush.

5. Cut a circular plate (15mm thick) of the same diameter as the smoke tube and chamfer the top edge 30bygrinding.

6. Fit the plate into the top of the smoke tube and weld it in position as shown.7. Enter the boiler furnace and cut a similar hole in this end of the relevant smoke tube as shown

8. Repeat operations 4 to 6 for lower plate.

9. Refill boiler and check for leaks before start-up.

10. Start-up boiler and check for leaks when pressurized.

Note: Temporary repairs to sunrod tubes should receive more permanent attention as soon as conveniently

possible.

Sunrod Furnace Wall (Risers) Tube Repairs WINDOW REPAIR1. Stop the burner, allow the boiler to cool and drain the boiler.2. Swing out the burner and enter the furnace through the burner aperture.

3. Cut out a window in the relevant section of pipe as shown. Note that 120 window is the maximum allowed.4. Grind a 30 chamfer on the edges of the window.5. Using a section of tube of the same diameter and thickness cut out a window to match the window cut in the

furnace wall.

6. Grind a 30 chamfer on the edges of the new section.7. Spot-weld a piece of steel strip to the top of the window as shown (position A).8. Fit the new section over the window in the tube wall as shown and spot-weld the steel strip to the riser in

position B. Note: the piece of steel strip holds the window in place and allows the new section to fit into the

window in exactly the correct position and at the correct depth.

9. Weld around the edges of the window (Note: 60 weld angle).10. When cool, knock off the steel strip and clean off the spot weld.11. Refill the boiler and test for leaks.

12. If no leaks are found, start the boiler and check that the weld is not leaking when the boiler is pressurized.

BOILER STRESS:

Stress = ( Pressure x Diameter) / (2 x Plate thickness ).

Boiler shell is subjected to internal pressure whish sets up the stresses in the circumferential and longitudinal axes.

Longitudinal stress = ( Pressure x diameter) / (2 x thickness ).

Circumferential stress = ( Pressure x diameter) / ( 4 x thickness ).

Longitudinal stress = 2 x Circumferential stress.

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Compensation for holes cut in boiler shell:

Any material cut from the shell will weaken it by an external related to the amount cut out.

Any holes cut in the shell, with a diameter greater than 2. 5 x Plate Thickness + 70 mm must be provided withcompensation for the loss of strength.

The largest holes cut in the shell include the manholes, and where these are cut in the cylindrical portion of the

shell they must be arranged with their minor axis parallel to the longitudinal axis of the boiler. This is due tothe stress acting upon the longitudinal seam being twice that acting upon the circumferential seam. Thus theshell must not be weakened more than necessary along its longitudinal axis.

How the Smoke Tubes are fitted in the Boiler?

The hot gases leaving the combustion chamber pass through smoke tubes fitted between the tube plate and the front

tube plate, on the way to the uptakes. Two types of tubes are used: Plain and Stay tubes as 3:1

a. Plain Tubes:

- The plain or common tubes are expanded into the tube plates at both ends.

- The tubes have a diameter of about 65mm with a thickness of 5mm.

- The front end of the tube is often swelled out to allow for easier tube removal.

- The back end of the tube is bell-mouthed after expansion, or may be spot-welded.b. Stay Tubes:

- The flat tube plates must be supported, so that stay tubes are fitted by screwed and then expanded into both

tube plates.

- The thickness of the stay tubes must not be less than 5 mm at the base of the thread.

- After the tube has been screwed and then expanded into the tube plates, nuts are usually fitted at the front end

but not in the combustion chamber to avoid overheating.

- Welding can be used after screwing the stay tubes into the tube plates but the tubes must be expanded before

and after welding.

Front end Expanded then Thickened Screwed thenExpanded swelled out Bell Mouthed tube ends Expanded or

Seal welded

Nut at front

65 ~ 75 mm end only 65 ~ 75 mm

Front tube plate Back tube plate Front tube plate Back tube plate

22mm thick 22mm thick 22mm thick 22mm thick

Plain Tube Stay Tube

How the Water Tubes are fitted in the Boiler?

- Tubes can be attached to drums and headers by expanding or by welding.

- In most cases the generating, screen and water wall tubes are expanded into plain seats, and the bell-mouthed.

- The tube ends must be cleaned and then carefully rolled expanded into the holes in the tube plate.

- To prevent tubes pulling out of the tube plate, they must be bell-mouthed.

- This bell-mouthed is to be l mm for every 25 mm of outside diameter + l. 5 mm .- Superheater tubes are also expanded and bell-mouthed up to steam temperatures of450 C; above this value

the tubes are attached by welding.

Expanded & Bell-Mouthed Grooved Seat Welded tube

Expanded tube attachment Welded tube attachment

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BOILER SAFETY VALVE:

Safety valves are fitted to protect the boiler from the effect of overpressure.

At least two safety valves are fitted to each boiler steam drum, but if there is any superheater another safety

valve should be fitted on it. Pressure setting of superheater safety valve should be less than the design pressure of the boiler i.e. less than

the steam drum safety valve to ensure flow of steam through the superheater under blow off conditions. Pressure setting of one steam drum safety valve should be same as the design pressure of the boiler.

Pressure setting of another safety valve should be 2 ~3 % more than the design pressure of the boiler. Classification: There are 3 types of safety valves are used in boiler.

1. Improved high lift safety valve.2. Full lift safety valve.

3. Full bore safety valve.

Improved High Lift Boiler Safety Valve: Wingless valve improves steam flow and reduces risk of seizure.

Waste steam pressure acting on piston gives increased valve lift.

Special shaped seat deflects steam towards lip on valve and increases valve lift.

The valve lid is able to lift at least l/4 of the valve bore in order to provide full steam flow. As the valve lifts, the force to compress the spring increases, so the higher the valve lifts the greater the

increase in boiler pressure. The DOT limits this accumulation of pressure to l 0 % of the max allowableworking pressure.

Waste steam pressure keeps cylinder in place while piston moves, also by having a floating cylinder seizure

risk is reduced. A lip is placed around the valve seat so that, when the valve lid lifts, escaping steam is trapped in the annular

space around the valve face; the resultant build-up of pressure acting upon the greater valve lid area causes thevalve to lift sharply. This arrangement gives another advantage to close the valve cleanly and sharply with very

little blow down effect. The improved high lift safety valve makes use of waste steam pressure to increase the valve lift; this is done by

allowing the pressure to act upon the lower spring carrier, which fits within a floating ring, so forming in effecta piston. The pressure acts upon this piston causing it to move up, helping to compress the spring, and so

increase the valve lift. Loose fitting key or pad lock is provided to ensure proper closing of valve.

Loose pin is provided to secure valve lid and allow thermal expansion.

Adjustment of the valve is carried out by means of a compression nut screwing down on to the top spring plate.

A compression ring is fitted after final adjustment to ensure no further movement takes place.

A cap is then placed over this compression nut and the top of the valve spindle, and a cotter is passed through

and padlocked to prevent tampering by unauthorized persons. Clearances between this cap, the valve spindle and the cotter are such as to prevent the valve being held down

externally. Easing gear is fitted so that in the event of an emergency the valve can be opened by hand to a full lift of

[l/4] x D to release the boiler pressure.

Valve area: As = A (1 + Ts / 555)As = Aggregate area through the seating of valve(mm2) for superheated steam.A = Aggregated area through the seating of valve(mm 2)for saturated steam.Ts = Degree of superheat in C.

As is greater than A due to sp. volume of steam increases with increase of temperature at constant pressureand more escape area is required to avoid accumulation of pressure.

The area of valve chest must be at least(1 / 2) x A. The waste steam pipe and steam passage must be at least 1. 1: x A.Boiler Safety Valve Drain :

Drainpipe must be fitted to the lowest part of the valve chest on the discharge side of the valve.

The pipe should be led clear of the boiler.

The pipe must have no valve or cock fitted through its length.

The open drain of the pipe should be regularly checked.

If the pipe become choked, there is possibility of overloading the valve due to hydraulic head, or damage due towater hammer.

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The waste steam pipe of the boiler safety valve should be well secured so that no load of the pipe is on the

safety valve, which can be a cause of additional stress on the valve.

Pressure Setting of Safety Valves:

Safety valves pressure setting can be done from high to low pressure or vice versa.

Take necessary personal safety precautions and arrange tools i.e. gagging tool and 2 master gauges.

Slowly raise the boiler pressure and blow off the safety valves manually few times for thermal expansion and to

reduce thermal stress on the valves. Then screw down all the safety valves higher than the setting pressure at which you are going to set.

Raise the boiler steam pressure 2 ~3 % more than the design pressure of the boiler, then stop firing andunscrew the first valve slowly, when it blows off at 2~3% more than the design pressure then note this opening

and closing pressure. Keep this setting of the first valve, raise the boiler pressure and recheck the opening &closing pressure of the valve and finally gag it.

Raise the boiler pressure at the design pressure of the boiler and unscrew the 2nd valve, when it blows off at

design pressure then note this opening pressure and check the closing pressure also. Recheck the setting

pressure and gag the valve. Then set the superheater safety valve lower than the design pressure of the boiler in same procedure.

Finally take out the gagging tools. Pressure setting should be done in presence of surveyor.

Improved High Lift Safety Valve

Cap Clearance at least D/4

Cotter Clearance at least D/ 4

__ __ ___

Easing gear

Easing gear arms

Compression screw / nutCompression ring

Top spring carrier

Neck bush

Vent

Spring

Spindle

Floating ring Valve body

Lower spring carrier acting as waste steam piston

Spindle guide

Drain

Loose pin To Waste Steam Pipe

Valve lid / disc

Drain

Valve seat

High Pressure Steam

Safety Valve Lip Clearance: E

Controls the huddling chamber(below the valve disc) to improve the performance.

Controls the pop action of the valve.

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Lower clearance makes the valve simmer before closing, which increases the valve blow down closing

pressure will be lower.

Larger clearance makes the valve simmer before opening and reduces valve blow down closing pressure

will be higher.

Safety Valve Blow Down Ring:

Controls the huddling chamber pressure of the valve.

When lowered, valve tends to simmer before opening and reduces valve blow down. When raised, increases blow down, valve might simmer before closing, and gives the valve good pop action.

Valve LidIncrease blow down, E

Decrease blow down Valve Seat

Blow Down Ring

UPTAKE FIRES:

An analysis of soot fire indicates that they are more likely to occur during manoeuvring, following staying in port.

There are 3 dominant parameters that will influence the tendency to go on fire. They are:1. Gas velocity:Velocities dropping below 10 m / s, due to poor design, fouling, reduced engine load etc. will

increase the tendency to deposit soot.

2. Soot stickiness: Soot stickiness is insufficient by the unburned residues of fuel and lub oils. More prominent is

during manoeuvring. These unburned liquids can lower the ignition temperature from 300 ~150 C.3. Low circulation rate in boiler: This reduces heat absorption from the gas, hence gas temperature remains high

with increased risk of soot ignition.

Early Indication of Uptake fire: Sparks emission from the funnel.

Increase in the flue gas temperature or fire alarm.

High steam generating rate.

Action in case of Uptake fire:

Slow down or stop main engine.

Stop the auxiliary blower, blank off T/C inlet ducting. This reduces O2 supply.

Restore or maintain forced circulation of water. This cools inside of the tubes.

Rig fire hoses. Do not use soot blowers. This cools out side of the tubes.

Remove casing, tackle fire with jet cooling not spray. Check water drainage point for overflow.

If not possible to restore forced circulation, drain and vent the boiler.

Uptake fires are avoided by: Maintain the correct exhaust pressure difference across the boiler to maintain gas velocity.

Soot blow before or after manoeuvring to keep clear tube bank.

By-pass exhaust gas during manoeuvring.

Clean tube bank, after water washing the T/C.

Maintain water circulation after shutting down for12 ~24 hours. Ensure proper engine operating condition.

Furnace Blow Back:

Furnace blowback is prevented by going through a safe start up procedure, which involves:

A furnace pre-purge before attempting ignition. This is usually 25% (100%) max. air flow through the furnace

for 3 minutes. Allowing an oil spray at the correct pressure/temperature from the atomizer to pass across the igniter for

sufficient time to achieve ignition. This time is less than the time required to cause an explosive air / fuel

mixture to form in the furnace.

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CAUSE OF FLAME FAILURE: Why Steam Pipe is insulated?

Fuel oil filter choked or FO pump failure. To protect heat radiation.

Empty of FO tank or low temperature of fuel. Safety of personnel.

Water contamination in fuel. To keep cool engine room environment.

Defective burner. To protect weak point of pipe lines from damage.

Nozzle choked. To protect fire in case of FO spray due to any leakage.

Air failure. Photo cells failure or dirty.

Electrode clearance incorrect.

Hair crack in the electrode.

Electrodes dirty.

Effect of Air Inside Boiler:

Oxygen of air or gas at 550 C will react with the tube material and cause oxidation, which is the cause of crackand tube failure.

Action in case of Boiler Low Low Water Level and Tube Red Hot:

Stop firing the boiler.

Close the main steam stop valve and take necessary action for purifier and main engine fuel oil heating. Stop feed water pump and do not fill the boiler with water.

Allow boiler to cool down to normal.

Start feed water pump and fill up the boiler at low level.

Star firing the boiler at slow rate.

Electrically Operated Water Level Alarm & Cut-out:

A float within the chamber relates to water level and moves an attached magnet up and down in response to any

changes of water level within the steam drum.

Three micro-switches with magnetically operated arms are fitted on the outside of the balance chamber. They

are arranged so that, when the internal magnet comes level with one of these external magnets, like poles are

presented, and so, repelling each other, operate the micro-switch.

The positions of the switches are set to correspond to predetermined water levels within the steam drum. One switch will correspond to a low water level condition, and when this is reached will operate an alarm.

If then no corrective action is taken, or it prove ineffective and water level continues to fall, the next switch

positioned to a predetermined low low water level will trip out the fuel oil shut-off valve, so shutting the boilerbefore damage can occur.

The other switch is positioned in a similar manner for high water levels, operating an alarm for a predetermined

high water level in the drum.

Steam inlet

WL Float

Magnetic micro switchesWater inlet

High high water level trip

High water level alarm

Low water level alarm

Control Low low water level trip

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Boiler


BoxAlarm

Drain valve

Solenoid

Fuel oil shut off valve

Water level in the boiler is critical. If it is too low, damage may result from overheating; too high and priming

can occur with resultant carryover of water and dissolved solids into superheater, steam lines etc.

Automatic feed regulators are therefore fitted to control the flow of water into the boiler and maintain the water

level at its desired value. They are fitted in the feed line, before the main feed check.

Spalling Due to flame impingement, the firebrick layer tends to break.

Slagging Due to Na deposits which will reduce the melting point of refractory material.

Bulging Due to overheating, deformation of tube banks.

TYPES OF TUBES IN WATER TUBE BOILER:

Generating Tubes:

These consists of number of small diameter tubes placed in the main flow of hot gases, so forming a large heat

exchange surface; the gas generation of steam takes place mainly by convection.

Screen Tubes:

These are placed adjacent to the furnace, so receiving heat from the flame together with the heat from the hot

gases leaving the furnace; therefore they need a relatively large diameter to keep the ratio of steam to water lowenough to prevent overheating.

The duty of the screen tubes is to protect the superheater tubes from the direct radiant heat of the furnace flame.

Water Wall Tubes:

These are used basically to contain the heat of furnace, thus reducing the amount of refractory material

required. In some types of boilers, water-cooled refractory walls are used. These consist of tubes with studs welded into

them, covered with refractory material, which can withstand the high temperatures without damage.

Down Comer Tubes:

These consist of large diameter, unheated tubes placed outside the gas stream which act as feeders to the waterdrum and headers.

Riser / Return Tubes:

These are used to return steam and water from the top water wall headers to the steam drum.

Superheater Tubes:

These consist of small diameter tubes placed in the main gas stream, after the screen tubes.

Their duty is to superheat the saturated steam leaving the drum to a temperature suitable for use in the main

turbines. They must be protected from direct radiant heat, as they are liable to overheating due to the much smaller

specific heat of stem compared to that of water.

Superheater Support Tubes:

These relatively large diameter tubes act basically as water-cooled supports for the superheater tubes.

Steam Drum

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Rear / Front water wall headersFlue gas

Water wall tubes Superheater

Burner front

Superheating tubes

Generating tubes

Water drum

Header

Drum Type Boiler

VERTICAL SMOKE TUBE BOILER:

The Cochran is a typical tank boiler of vertical type suitable for producing relatively small amounts of low-pressuresteam for auxiliary purposes.

ManholeSafety valve Main steam stop valve

Steam drum

Exhaust gas uptake

Gusset staysWater level

Exhaust gas inlet

Oil fired gas uptake

Refractory

Smoke tubes

Smoke box

Shell

Water

Feed water inletManhole

Handhole / Mudhole

WBurner

Ogee ring Furnace

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Boiler


Blow down

The cylindrical boiler shell with its hemispherical crown, together with the hemispherical furnace forming the

bottom of the pressure space, requires no stays. Gusset Stays: The top of combustion /heating chamber requires support, and this is provided by means of

gusset stays which transfers the stresses from the flat top of the chamber on to the boiler shell. The tube plates

are also supported by means of gusset stays.

Refractory material is fitted in the combustion chamber, on the floor and sides of the furnace. The refractoryshould be high enough to prevent direct radiant heat coming onto the ogee ring and lower parts of thehemispherical furnace crown.

Internal access to the boiler is provided by a manhole in the top of the shell, while hand holes in the lower

section of the shell provide access to the lower parts of the water apace for cleaning and inspection. Hinged smoke box doors give access to the tubes and tube plate at the front, while a removable rear panel fitted

to the combustion chamber gives access to the back tube plate.

Ogee Ring:

Connecting to the bottom of the furnace to the boiler shell plating is a seamless ogee ring.

This is pressed out of thicker plating than the furnace.

Greater thickness is necessary due to poor circulation of water in this area and deposits can accumulate between

it and boiler shell plating.

Tell tale holes drilled at equal circumferential intervals in the boiler shell enable leakage between the ogee ring

and boiler shell to be detected.Furnace

Water Space

Ogee Ring

Boiler Shell

Tell tale hole at least 3, 10mm

VERTICAL SMOKE / WATER TUBE BOILER:

[Gadelius Composite Boiler, Type: GCS] Source: MV AMBER HALO, JAPAN

Hatch cover

Main steam stop valve

Flue gas outlet

Steam space

Flue gas chamber

Water space

Manhole

Exhaust gas outletWater tube

Smoke tube

Exhaust gas inlet

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Boiler


W W

Soot drain

Manhole

Burner

Furnace

Madhole W W

Cause of Furnace Blowback / Flareback:

Improper pre-purging.

Accumulation of oil in furnace.

Gas side dirty (high back pressure).

Accumulation of unburned carbon deposits.

Flue gas exit passage (damper) blocked / closed.

Excess excess air (too much air).

Too many unsuccessful light up.

Difficulty in maintining water level:

Level controller problem.

Foaming condition.

Leakage inside boiler.

Wear and tear of feed pumps / feed line valves.

Blow down line lakage.

Steam bloked in feed pump.

Boiler load fluctuations (shrink & swell effects).

Oil contamination.

High TDS content in boiler water.

Boiler Operation:Starting up a boiler should not be speeded up and it normally takes about 4 hours to complete. Strict adherence tothe manufacturer's recommended procedures will make the boiler operation more efficient and safer.

Check that the boiler is properly closed up ( especially after repairs).

Check (physically) that all appropriate valves are shut or open for safe starting of the boiler.

Boiler filled to slightly below normal level.

Boiler treatment chemicals may now be added to the boiler water.

Check and clear the furnace of any flammable materials.

Ensure that the boiler uptake passage is clear.

Pre-purging of furnace for a specified amount of time is necessary to clear the gas-side of flammable gases, to

avoid a starting explosion.

On a cold boiler, the firing-up must not be speeded up too much in order not to overstrain the boiler material

unnecessarily by quick, uneven temperature raises. Keep the boiler vents open until a heavy steam jet is flowing out (until a boiler pressure of about 1 bar is

reached).

Before the boiler is put on load, blow-through the gauge glasses, test the safety valves using easing gear and tryout the safety cutouts.

Starting of a Water Tube Boiler fitted with an integral Superheater

Integral superheaters fitted to boilers are prone to overheating as they are normally situated in a high temperature

path. Superheaters depend on adequate steam-flow through them to keep their tube metal temperatures withinlimits. Overheating of superheater tube element results in sagging and failure of tubes and may even trigger a

hydrogen fire in the boiler. To protect the superheater from overheating during boiler start-ups, the superheater isdrained of any accumulated condensate and a vent provided on its outlet header is left partially open until the boiler

is put on load.

Points to note while the boiler is on load:

Operate the boiler at a load where its efficiency is the highest.

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Boiler


Maintain correct air /fuel ratio; under perfect conditions a brownish hazy colour of exhaust smoke is noticed

from uptake.

CO, CO2, O2 contents as monitored in the exhaust gas will indicate the combustion condition inside the boiler.

Every morning mud is blown from the boiler through the bottom blow-off valves and float chambers. (Bottomblow is not recommended for drum type of water tube boilers while the boiler is onload).

Ensure that all safety cut-outs are perational.

Maintain the fed water quality as observed from the funnel should be brownish hazy.

Boiler care while running onload / Monitoring of perfect combustion

Flame should fill the furnace without any impingement.

Colour of flame should be moderately bright orange.

Colour of smoke as observed from the funnel should be brownish hazy.

Flue gas analysis sould give the following readings:

1. Oxygen:

3 ~ 4% by volume (for fire tube boiles)

0.5 ~ 1.5% by volume (for water tube boilers with high efficiency burners)

2. Carbon Dioxide:

12 to 14% by volume. Higher the reading,the better is the combustion efficiency. It must beremembered that the CO2 reading changes with the fuel type/quality and the level of excess air

supplied to the burners.

3. Carbon Monoxide:

A reading range of100 ~ 200 ppm indicares good combustion efficiency. This reading is very reliable

unlike in the case of CO2 reading of flue gases.

Black colour indicates improper combustion (due to insufficient air, poor atomisation etc). Whereas whitecolour of smoke indicates too much air (or profusive leakages of steam or water from the damaged boiler parts)

BOILER LAY-UP

a) Wet storag:Used for short lay-up of less than a month and the boiler is maintained in a stand-by condition.

Not suitable for boilers exposed to freezing conditions. The boiler is completely filled with hot distilled de-aerated alkaline water. The water should overflow through the vent during filling-up. Daily checks are

necessary to ensure fullness and alkalinity are maintained.

b) Dry storage: Used for longer lay-up of more than a month. The boiler is completely dried out using heaters oron light fire or passing hot air throuh the boiler parts. When dry cimpletely all the boiler outlets are sealed tightafter placing dehydrant (such as silica gel at the rate of2.7 kg /cu.metre) inside the boiler.

Treatment for Gross Oil Contamination of Boiler Feed Water

Boiler taken off load /Shutdown.

Subsequrntly to be overflown through top manhole opening.

Boiling out or chemical cleaning.

Alkaline soak/degreasing using Sodium hydroxide or phosphate, NaOH, Na3 PO4.

Wash out

Acid clean to remove mill scale (Fe3O4:Magnetite layer) 30% Concentrations of HCl with inhibitor to neutralise

Acid.

Wash out and neutralise. Passivate with Hydrazine or Alkaline chemicls.

Don't drain boiler through bottom blow down valve (to ovoid contamination).

Treatment for Small Oil Contamination

1. (non-availability of special chemical onboard):

Reduce the boiler load

Surface blow

Maintain Alkalinity by adding Alkaline chemicals

Add Anti-foam compound (if available)

2. If oil combating chemicals like "Epsom Salt" is available onboard:

Add 350 gms of Epsom salt with the boiler off load and 100 gms of Epsom salt if the boiler is on reduced load.

Maintain Alkalinity by dosing chemicals an hour after the dosing of epsom salt.

Add Anti-foam.

Give flash blow 5 to 20 secs periodically, to remove the precipitated sludges

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Prevention of Boiler Accidents

Never by-pass safety alarms and cut-outs.

A weekly routinr testing of alarms and cut-outs is essential.

Strict quality control of feed warer quality and chemical trearment.

Regular blowdown of a boiler is must irrespective of boiler water test results.

A safety check list should be maintained for all normal and emergency operational procedures for the boilerplant.

When the boiler is operated with any faulty safety cut-outs by-passed, manual watch should be kept on theboiler plant.

Safety valves should checked at least once every three months to ensure their operational readiness in the event

of overpressure in the boiler.

Safety Valve Gagging:

When testing boilers and pressure vessels, at pressure exceeding the set pressure of the safety valve, it isnecessary to mount a gag to prevent the valve from opening.

Gags are usually of the clamp type and are fitted to the valve after removal of the cap and lifting lever.

Gags must only be fitted hand tightto prevent damage to the spindle and seat surface.

Safety Valve Exhaust Pipe:

It is recommended to provide the individual safety valve with a separate exhaust pipe.

This must have a sufficient inside diameter determined by the full exhaust quantity of the valve and must be at

least one number larger than the outlet flange.

The pressure loss in the exhaust pipe of the safety valve including of the exhaust loss most amount to 10% of

the valve's set pressure at the most.

The vertical pipe must run as straight as possible and be throughly anchored to and supported by the structure

of the vessel to be able to withstand the reaction during blowing out.

It is necessary to mount an expansion between the outlet bending and the exhaust pipe or in other ways tosecure that forces from the latter are not transferred to the safety valve house with subsequent tensions and

dislocation of the house, which may result in leakages or, at the worst, destruction of the valve.

The exhaust pipe is normally expanded about 2. 5mmper meter pipe from the valve to the fixing point.

The long exhaust pipe or many bendings may necessitate that a pipe with a bigger inside diameter is chosen inorder to secure that the backpressure will not be too high.

The dimension "A" in figure must be as short as possible. A greater horzontal length increases the risk oftensions in the valve house during blowing.

Md. Abdul

Hamid

18

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