SASO 1441 STEAM BOILERS — PART 15 ...zb.guaihou.com/stdpool/SASO 1441-1998 Steam Boliers...The transparent part of a water gauge assembly connected directly or thorough a water column

SASO 1441

STEAM BOILERS — PART 15: REQUIREMENTS FOR THE OPERATION


ICS: 27.060.30

Date of SASO Board of Directors' Approval : 1419–03–07 (1998–07–01) Date of Publication in the Official Gazette : 1419–07–17 (1998–11–06) Date of Enforcement of this Standard : 1420–01–17 (1999–05–03)

SAUDI ARABIAN STANDARD SASO 1441/1998

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TABLE OF CONTENTS

Page

1 Scope and Field of Application …………………………………………….. 2

2 Complementary References ………………………………………………… 2

3 Definitions ………………………………………………………………….. 2

4 Requirements ……………………………………………………………….. 4

4.1 Boiler Operation ……………………………………………………………. 4

4.1.1 General ………………………………………………………………………

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4.1.2 Preparing for Operation …………………………………………………….. 5

4.1.3 Starting ……………………………………………………………………... 7

4.1.4 Connecting Boiler or Line with other Boilers ……………………………… 9

4.2 Out of Service Operation …………………………………………………… 14

4.2.1 Isolation …………………………………………………………………….. 14

4.2.2 Water Side Cleaning ………………………………………………………... 15

4.2.3 Fire Side Cleaning ………………………………………………………….. 15

4.3 Storage ……………………………………………………………………… 16

4.3.1 Wet Storage ………………………………………………………………… 16

4.3.2 Dry Storage …………………………………………………………………. 16

4.4 Starting a New Boiler ………………………………………………………. 16

4.5 Starting a New Boiler After Lay-up …………………………………………

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4.6 Hydrostatic Testing ………………………………………………………….

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5. Emergency Operation ………………………………………………………. 19

6. Failures of Boilers ………………………………………………………….. 19

Appendix (A)

Typical Emergency Procedure for Loss of Water or Low Water Condition in Boiler .

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Appendix (B)

Modes of Failure of Boilers ………………………………………………………... 22


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1. SCOPE AND FIELD OF APPLICATION

This standard is concerned with the operation of steam boilers.

2. COMPLEMENTARY REFERENCES

2.1 SASO 1338/1998 “Steam Boilers – Part 8: General Safety Requirements”.

2.2 SASO 1339/1998 “Steam Boilers – Part 9: Approval of Inspection Body”.

2.3 SASO 1340/1998 “Steam Boilers – Part 10: Approval of Operators”.

2.4 SASO 1585/1999 “Steam Boilers – Part 16: Requirements for the Maintenance”.

2.5 SASO 1584/1999 “Steam Boilers – Part 14: Requirements for the Installation”.

3. DEFINITIONS

3.1 Boiler

An arrangement of pressure vessels and interconnecting parts, wherein water is heated and steam is generated by the application of heat.

3.2 Approved inspector

A person trained and qualified in accordance with the requirements of Saudi standard, employed by the inspection body and obtained approval by the authority (SASO) to carry out inspection of boilers.

3.3 Boiler operator

A person who operates and controls a boiler or a section of the boiler with the authority of the owner. This person shall possess a boiler operator’s certificate issued by a boiler inspector/inspection body.

3.4 Hydrostatic test

A strength and tightness test of a closed pressure vessel by water pressure.

3.5 Header

The piping which connects two or more boilers together. It may be either supply or return piping.

3.6 Inspection opening

The opening in a pressure vessel of a sufficient size to permit a vessel inspection.


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3.7 Damper

A device for introducing a variable resistance for regulating the volumetric flow of gas or air.

3.8 Safety valve

An automatic pressure relieving device actuated by the static pressure upstream of the valve and characterized by full opening pop action.

3.9 Cock

A plug or ball-type valve in which a 90o turn of the handle will move the valve to full open or closed position. Such cocks are designed so that they are open when the handle is parallel with the line of flow.

3.10 Drain valve

A valve connected at the lowest point for the removal of all water.

3.11 Gauge glass

The transparent part of a water gauge assembly connected directly or thorough a water column to the boiler, below and above the water line, to indicate the water level in the boiler.

3.12 Fire tube

A tube in a boiler having water on the outside and carrying the products of combustion on the inside.

3.13 Gauge cock

A valve attached to a water column or drum for checking the water level.

3.14 Steam trap

A device installed in steam piping which is designed to prohibit the passage of steam but allow the passage of condensate and air.

3.15 Chimney

A structure designed to discharge flue gases into the atmosphere.

3.16 Drum vent

A vent valve provided on top of drum to release pressure while shutting down of boiler and removing gases specially air while starting up boiler.

3.17 Drum

A vessel storing feed water to ensure continuous supply of water to boiler, located at the top of the furnace to give a positive head to the water.


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3.18 Main steam by-pass valve

A small valve connected in parallel to boiler outlet main steam valve, which equalizes the pressure at both sides of main valve sent before main valve opening. It is used to warm up the line up to the turbine uniformity.

3.19 Dust collector

A device fitted on the boiler flue gas ducts to collect the soot or dust removed from the cyclone separators.

3.20 Economizer

Heat exchanger situated in the boiler gas pass. In economizer, feed water is heated by the flue gas.

3.21 Main stop valve

The name of the valve which isolates the steam or water going or coming from the plant.

3.22 Soot blower

Boiler equipment for removing deposits from the boiler tubes and air heater by spraying with high pressure steam..

4. REQUIREMENTS

4.1 Boiler operation

4.1.1 General

4.1.1.1 After installation of a boiler and before it is put into operation, it shall be inspected by an approved inspector.

4.1.1.2 The operation of the boiler shall be carried out by a competent operator who has obtained a valid boiler operator’s certificate.

4.1.1.3 The operation of a boiler shall not be initiated or continued unless the boiler has a valid report of the result of examination carried out by an authorized inspector, as specified in the Saudi standard mentioned in item 2.1

4.1.1.4 An operator shall not operate any pressure equipment system without appropriate training. The owner shall ensure that each operator receives sufficient training and retraining to maintain correct and safe operation of the pressure equipment.

4.1.1.5 Preventing explosion

In order to prevent explosions the following shall be performed:

4.1.1.5.1 Start up and shut down events shall be performed during the initial operation to prevent potentially dangerous moves during mental lapses or moments of crisis.


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4.1.1.5.2 The boiler furnace, generating bank, economizer, air heater and ducts shall be sufficiently purged before operating any source of ignition.

4.1.1.5.3 The purging shall be sufficient to provide adequate velocity to clear any dead spots in the entire unit

4.1.1.5.4 The purging shall be repeated in case of any accidental loss of ignition.

4.1.1.6 Maintaining water level

When the boiler water level control and furnace pressure control are part of the combustion control system, the following shall be carried out.

4.1.1.6.1 Check the water level of all boilers by checking the water gauge regularly.

4.1.1.6.2 Place all automatic controls (if provided) for maintaining water level on automatic operation as soon as possible.

4.1.1.7 Safety requirements for inspection before operation.

4.1.1.7.1 Before entering any boiler, isolate and tag all equipment connected to the boiler and fuel system and place a sign at the operating controls indicating that a workman is inside the boiler.

4.1.1.7.2 Before entering any boiler, make sure it is properly isolated at “All” fuel, flue gas, steam and water sources and properly cooled.

4.1.1.7.3 Make sure that the boiler is sufficiently vented by consulting the responsible person.

4.1.1.7.4 Use only low voltage lights or explosion-proof flashlights inside the boiler.

4.1.1.7.5 Notify the responsible person in charge at the site when beginning and upon completion of the inspection.

4.1.1.7.6 Make sure that another person is watching you from outside the boiler.

4.1.1.7.7 Always be aware of the nearest escape routes.

4.1.1.7.8 Before closing manholes and furnace doors, it is essential to make sure that all personnel are out of the boiler.

4.1.2 Preparing for operation

4.1.2.1 The cleaning of boiler shall be done mechanically, chemically or by both methods depending on the accessibility of the heating surface and the type of deposits if the condition of the boiler requires the above-mentioned cleaning.

4.1.2.2 Chemical cleaning shall be done under the supervision of experienced personnel thoroughly familiar with the hazards of such operations.

4.1.2.3 Before starting a boiler, the following check shall be carried out:


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4.1.2.3.1 Water side check

– The water side including drums, tubes, and headers shall be free of extraneous materials such as dirt, tools, rags, wood or trash.

– All internal fittings shall be in serviceable condition and securely installed in the correct position.

– Evidence of corrosion on pressure parts.

– Corrosion at mating surfaces, manways, handhole caps and flanges.

– Note location and type of deposits in boilers, if any.

4.1.2.3.2 Fire side check

– All combustion air and flue gas passages such as the furnace, convection bank, ductwork, and fans shall be free of extraneous material.

– Remove all combustible material that might ignite, burn and trigger the explosion of unburned fuel if ignition is lost.

– Dampers and burners shall be operated to confirm that they are free to travel from fully closed to wide open.

– Check to verify that the refractory is correctly located and properly installed. Burner orifices, overfire air nozzles, observation ports, and instrument taps must not be covered or plugged. Repairs shall be made if refractory is missing or significantly damaged. Slag should not be removed from the surface of the refractory unless it interferes with normal operation.

– Turn off the light occasionally while inside the unit and look about for daylight shining through holes that indicate air or flue gas leaks.

– Carry a note pad and pencil and make notes of conditions found.

– Look for corrosion of pressure parts:

* under deposits;

* at tube-to-tube plate joints;

* where the flue gas may have been below its dew point;

* under refractory or insulation if it has been water soaked for a period of time.

– Look for erosion

* of induced draft fan housings and wheels components handling flue gas;

* in the vicinity of soot blowers;

* at sharp turns or points where flue gas flow may concentrate;

* in areas near where any steam or water leaks have occurred


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– Look for overheating

* of tubes in the areas of high application, especially if there is evidence of deposits inside the tubes.

* at the top end of tubes in boilers that may have experienced operation at low water level.

* whenever tubes are warped or otherwise physically distorted.

* on the fire side face of headers close to stokers or burners.

* on the front row of superheater tubes.

4.1.2.3.3 External check

– Free access shall be provide to the burner fronts, observation ports, and operating valves.

– Temporary construction restraints shall be removed to permit free thermal expansion.

– Top supported power boilers shall have expansion indicators installed so that actual movement can be compared to expected movement. Piping shall be free to move from the cold to hot position.

– All instrumentation and controls shall be complete, operational, and checked for proper calibration and action.

– External indicators permanently marked or installed on damper shafts and registers are necessary for positive determination of position while the boiler is in service.

– Safety and relief valve outlets shall be piped so they cannot discharge on people or any property that may be damaged. The discharge piping shall be supported so that loads transmitted to the relief valves are minimized.

– Personnel protection from hot surfaces shall be provided by restricting access or by covering the hot surfaces with insulation.

4.1.3 Starting

The following shall be carried out before starting the boiler.

4.1.3.1 All instrumentations and protective devices that provide the required safe operation shall be checked and operable prior to starting the boiler.

4.1.3.2 All instruments and pressure transmitters shall be calibrated and ready for use.

4.1.3.3 Blow off valves including continuous blow down valves, water column drain valves, gauge glass drain valves, gauge cocks, feed water supply valves and feed water control valves shall be closed.


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4.1.3.4 The valves between the steam drum and water column and gauge glass shut off valves (if any) shall be locked in the open position.

4.1.3.5 Gauge glass and furnace television gear (if any), water level indicators and recorders shall be ready for use.

4.1.3.6 Pressure and temperature compensating devices for water level recorders and indicators shall be ready for operation.

4.1.3.7 The safety valves shall be inspected externally and their discharge piping and drain piping are open to atmosphere and be free to expand.

4.1.3.8 Main steam stop valve stems shall be eased up just enough to reduce thermal expansion stresses which could result as they go from cold to hot.

4.1.3.9 Fans, boiler feed pumps and chemical injection equipment shall be checked to ensure that they are ready for service.

4.1.3.10 Water level

4.1.3.10.1 High quality water according to manufacturer recommendations shall be used to minimize waterside corrosion and deposits

4.1.3.10.2 The water drum vent shall be open.

4.1.3.10.3 The drum header and economizer drains shall be closed.

4.1.3.10.4 Super heater and main steam line drains shall be open.

4.1.3.10.5 The header vents shall be open.

4.1.3.10.6 The boiler shall be filled through treated feed water lines and the water temperature shall be as close as possible to the metal temperature of the drums and headers.

4.1.3.10.7 During filling check the water level in the water gauge several times to make sure that there is no trapped water or air locks which may give a false water-level indication.

4.1.3.10.8 Water level shall be maintained at the safe observable minimum level to reduce blow down losses.

4.1.3.10.9 Forced circulating boilers shall be prepared by opening suction valves, backing off the stems of combined discharge stop-and-check valves and venting air from the pump casings of circulating pumps.

4.1.3.10.10 After the first circulating pump is put in service and before lighting off a burner the low pump differential pressure fuel trip shall be checked.

4.1.3.11 Light-off

4.1.3.11.1 The rate of firing shall be strictly in accordance with the manufacturer’s recommendations, so that the boiler can freely expand and the desired operation can be established.


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4.1.3.11.2 During the initial start up raise the pressure more slowly than normal and operate the burners which will produce the most uniform gas temperature.

4.1.3.11.3 If a superheater is fitted, then the firing rate shall be so regulated throughout the start-up period so that the superheater tubes temperature does not exceed the safe temperature limits.

4.1.3.11.4 If the refractory was new or extensively rebuilt it shall be dried out in accordance with the refractory manufacturer’s dry out procedure.

4.1.3.11.5 During refractory drying out period, the firing rate shall be sufficient to produce a light flow of vapour from the open drum vent.

4.1.3.11.6 The drum vent or vents shall be closed when the steam pressure reaches manufacturer recommendations.

4.1.3.11.7 The firing rate shall be regulated so that safe limits of gas temperature are not exceeded at the furnace exit.

4.1.3.11.8 Nondrainable superheats shall be vented to permit boiling out of condensate trapped in the elements.

4.1.3.11.9 When steam pressure is initially being raised, the boiler shall be checked carefully to see that it expands freely in the manner and direction intended in its design.

4.1.3.11.10 When the steam pressure is increased, the water level shall be carefully controlled within normal limits, and if necessary, the boiler shall be blown down to keep the water level around half glass.

4.1.3.11.11 Care shall be taken not to add too much of water during initial firing.

4.3.1.11.12 Thoroughly test all water gauges and blow down each water gauge during pressure raising.

4.1.3.11.13 The manual operation of safety valves on boilers operating below 4.2 Mpa (42 kg/cm2) shall be carried out to check its function.

4.1.3.11.14 In the case of boilers operating above 4.2 Mpa (42 kg/cm2) manual operation of safety valves may be carried out provided that adequate precautions are taken to prevent personnel injury and equipment damage.

4.1.3.11.15 The manual operation of safety valves shall be carried out only when the steam pressure in the boiler is not less than 75% of the set pressure of the lowest set safety valve.

4.1.3.11.16 After overhaul the safety valves shall be tested to see that they pop and reset at the correct pressure by floating the safety valves with the main steam stop valve closed. Also on power boilers, safety valves shall be tested for required percentage of blow down and valve seat lift.

4.1.4 Connecting boiler on line with other boilers

The following precautions shall be taken to avoid water hammer and excessive temperature gradients in the piping.


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4.1.4.1 Drain the piping sufficiently to drain away water in the line and to warm it up.

4.1.4.2 Use the bypass valves around main header valves carefully.

4.1.4.3 Operate the header drains.

4.1.4.4 The steam line from the boiler to the header shall be brought up to temperature by operating bypass and drain valves to create a backflow of steam from the header.

4.1.4.5 The steam of non-return valve shall be backed off to a position corresponding to about 25% open until the boiler begins to supply steam to the header, and then the stem shall be backed off to the wide open position.

4.1.4.6 If there is no non-return valve, the boiler stop valve shall be opened slowly when the pressures in the boiler and header are approximately equal.

4.1.4.7 When two manually operated stop valves are provided, the pressure between the two valves shall be equalized by the use of bypass valve around the stop valve near the header, and then slowly open that valve wide. When the pressures in the header and boiler are approximately equal, slowly open the stop valve near the boiler.

4.1.4.8 When a boiler is not connected to a header system, the boiler and steam line shall be warmed together by appropriate operation of the drain valves to remove condensation.

4.1.4.9 In the case of boiler having two steam outlets, each equipped with a non-return valve, after it is on line ascertain if possible by the use of listening stick whether the steam is flowing through both outlets.

4.1.5 On line operation

4.1.5.1 Feed water treatment

4.1.5.1.1 They type of water treatment system selected shall achieve the following:

— Oxygen removal from the boiler water.

— Scale prevention for protection of heating surfaces.

— The minimization of carry-over.

4.1.5.1.2 The type and quantity of treatment of water will vary depending upon the conditions of the water to be treated and the type and duty of the boiler.

It is recommended to consult a water treatment expert.

4.1.5.1.3 To minimize deposits, scale formation and corrosion in the boiler and feedlines feed heaters, economizers, superheaters and prime movers, the chemical conditions in the boiler water shall be maintained by injecting treatment chemicals into the steam drum or by chemical dosing of the feed water before it enters the system.


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4.1.5.1.4 The following chemicals are commonly used for boiler water treatment:

Caustic soda – NaOH.

Trisodium Phosphate – Na3PO4 .

Sodium Acid Phosphate – NaH2PO4 .

Sodium Tripolyphosphate – Na5P3O10 .

Sodium Borate – Na2B4O7 .

Sodium Sulphite – Na2SO3

Sodium Nitrite – NaNO3 .

Sodium Nitrite – NaNO2 .

Sodium Alginate

Startch

Disodium Phosphate

Hydrazine

Morpholine

4.1.5.2 Oil mixing with water

4.1.5.2.1 Every effort shall be made to prevent oil from getting into the water side of the boiler.

4.1.5.2.2 Monitor the quality of condensate continuously and it shall be discarded whenever contamination with oil is detected.

4.1.5.2.3 The boiler shall be taken out of service immediately if oil gets into the boiler and the boiler shall be thoroughly cleaned.

4.1.5.3 Maintaining water level at a safe level

4.1.5.3.1 The water level shall not be allowed to go low enough to endanger the boiler through overheating, or to go high enough to interfere with correct functioning of steam and water separation devices.

4.1.5.3.2 Automatic level control devices and low and high level alarm shall be considered as operating aids and the boiler will be tripped at these levels.

4.1.5.3.3 Water level indicated by two or more devices shall be frequently compared during operation.

4.1.5.3.4 Water gauge glasses shall be well illuminated and shall be kept clean.

4.1.5.3.5 Steam or water leak from the water gauge glass, water column or its connections shall be rectified as soon as possible, while the boiler is in service.

4.1.5.3.6 Before taking over the operation of the boiler, the operating status of the boiler(s), water level controls, water level indicators and water level recorders shall be checked.


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4.1.5.3.7 Water column and gauge glass accuracies shall be checked by blowing down the water columns and water gauge glasses.

4.1.5.3.8 When water level indicator and water level recorded indicators are in agreement, blowing down the gauge glass is not necessary.

4.1.5.3.9 When the water level is below the gauge glass, fuel and air shall be shut off and the boiler shall be fed with water until the normal water level in the drum is restored.

4.1.5.3.10 The normal water level in the boiler drum shall be established by using all indicators such as feed water flow meter, steam flow meter, drum level recorder and all other instruments that properly sense the operating conditions of the boiler.

4.1.5.3.11 If the low water level is due to any damage, the boiler shall be shut off (fuel and air) and cooled down for thorough inspection.

4.1.5.3.12 When the water level is above the visible range of the gauge glass, the following shall be shut-off in sequence: (1) feed water, (2) fuel and (3) combustion air.

4.1.5.3.13 If water level does not recede into the visible rang of gauge glass, then the main emergency blow down valves shall be operated to lower the water level.

4.1.5.3.14 The water filling shall be controlled manually until the automatic control is functioning correctly and normally then the boiler shall be put on automatic control.

4.1.5.4 Boiler water blow down

4.1.5.4.1 The concentration of solids in the water shall be determined daily and the blow down shall be regulated to control the concentration within prescribed limits by adjusting the continuous blow-down frequently on the basis of water analysis.

4.1.5.4.2 If the boiler is not fitted with sampling connections, the boiler shall be blown down at least once every 24 hours or every 8 hours for boilers operating on different shifts system by operating the blow off valves.

4.1.5.4.3 During blow down an assistant shall be stationed to watch the steam drum gauge glass, and to give signal to the operator.

4.1.5.4.4 Never permit an operator at the blow off valves to leave or to perform other duty until blow down operation is completed and the valves are closed.

4.1.5.4.5 Open and close operation of blow off valves shall be done slowly.

4.1.5.4.6 Only one boiler shall be blow down at a time and shall be scheduled to blow off at reduced or moderate rates of steaming.

4.1.5.4.7 The sequence of operation of blow off valves shall be as follows:

— The valve next to the boiler is opened first and closed last.

— If a quick opening valve and a slow opening valve are in combination, the quick opening valve shall be opened first and closed last, and blowing down shall be carried out with the slow opening valve.


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4.1.5.4.8 In the case of hard-seat valve followed by a seatless valve, the hard-seat valve shall be opened last and closed first. In the case of two seatless valves where the plunger continues to move after port closure, the valve nearest to the boiler shall be opened last and closed first.

4.1.5.4.9 When a large amount of blowing down is necessary, the following operation shall be carried out:

— Open the quick opening valve first until it is half open and leave it in that position.

— Open slow opening valve until water is lowered to the desired value in the gauge glass.

— The open both valves wide until blowing down is completed.

4.1.5.5 Safety valves

4.1.5.5.1 Safety valves shall be checked for free operation without any leak.

4.1.5.5.2 Any leaks shall be repaired as soon as possible.

4.1.5.5.3 A safety valve shall not be made out of action unless the capacity of the remaining operable safety valves equals or exceeds the limits.

4.1.5.6 Leaks

4.1.5.6.1 Regular inspections during operation shall be carried out to locate water, steam, air and flue gas leaks.

4.1.5.6.2 Leaks shall not be repaired when the boiler is under pressure.

4.1.5.6.3 Leaks in pressure parts shall be examined by an authorized inspector, and his recommendations shall be fully followed.

4.1.5.6.4 Seriously leaking boilers shall be shut-down immediately and shall not be put in service unless the repairs are carried out and inspected by an authorized inspector.

4.1.5.6.5 In the case of water tube boilers leak, shut-off boiler immediately and continue to cool it as in a normal shutdown, to inspect and to carry out repair.

4.1.5.6.6 Shut-off any steam output from the boiler.

4.1.5.6.7 Adjust the feed water flow to the boiler to the maximum, and then shut-off completely when the hazard of overheating pressure parts from fuel ceases to exist.

4.1.5.6.8 White vapour stack plumes may indicate a leak specially during cold days.

4.1.5.7 Soot Blowing

4.1.5.7.1 Cleanliness of heating surfaces and effectiveness of soot blowing shall be checked by observing changes in flue gas temperature and draft loss.


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4.1.5.7.2 Soot blowers, except in air heaters, shall be operated only when the load on the boilers is above 50% of rated output.

4.1.5.7.3 On small balanced draft boilers change to manual control and increase the furnace draft to avoid positive furnace pressures and to avoid upsetting the air flow while operating a soot blower.

4.1.5.7.4 Steam soot blower piping shall be thoroughly warmed and drained to prevent wet steam from quenching hot soot blower elements.

4.1.5.7.5 Automatic soot blowing systems shall be checked frequently to avoid repeated malfunctioning.

4.1.5.7.6 Any unusual noise or vibration of soot blower elements shall be checked promptly.

4.1.5.7.7 If a soot blower is stuck up inside, it should be retracted by hand operation.

4.1.5.7.8 Steam to the soot blowers shall be isolated when the soot blowers are not in operation.

4.1.5.7.9 Sufficient amount of cooling air flow shall be passed through the soot blowers when they are in retracted condition.

4.2 Out of Service Operation

4.2.1 Isolation

When a boiler is taken out of service, the following operations shall be carried out:

4.2.1.1 The oil firing/gas firing, fuel shut-off valves shall be tripped off and all manual valves or cocks at the burners closed immediately.

4.2.1.2 Close the main feed water isolation valve and manually regulate boiler drum water level with the bypass valve.

4.2.1.3 The boiler shall be isolated when the boiler pressure falls below the header pressure and the drum water level stabilizes with no feed water flowing.

4.2.1.4 When the steam pressure falls, open the drum vents to prevent formation of a vacuum.

4.2.1.5 The boiler shall be cooled down by controlling the rate of cooling prescribed by the manufacturer.

4.2.1.6 The draining of the boiler shall be started only after the boiler is cooled down sufficiently.

4.2.1.7 As soon as the boiler is empty, an inspection shall be made to determine if any repair work is necessary and what mechanical or chemical cleaning is necessary.

4.2.1.8 After the inspection and the boiler is empty, close and lock the blow off valves, including the continuous blow down valves.


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4.2.1.9 After the inspection it shall be decided to employ dry storage or wet storage. Wet storage is preferred if freezing can be prevented and the out of service period is short and dry storage is preferable in locations where freezing temperatures are expected during standby and the out of service for extended period.

4.2.1.10 During inspection the following procedures shall be carried out:

4.2.1.10.1 Close off and lock out all sources of steam and water.

4.2.1.10.2 Oil burner guns shall be disconnected and removed.

4.2.1.10.3 Gas burners shall be shut-off by at least two valves in series with an open valve vent between them discharging to a safe area.

4.2.1.10.4 Disconnect, close and tag electrical power to fans and flame safeguard systems.

4.2.1.10.5 All dampers and burner registers shall be left open for natural draft purging.

4.2.1.10.6 The drums of a water tube boiler or the shell of a fire tube boiler shall be well-ventilated before anyone enters the boiler.

4.2.2 Water Side Cleaning

The following shall be carried out:

4.2.2.1 Examine the boiler before cleaning with special attention to the feed water and water treatment in preventing scale formation, corrosion or excessive accumulation of sludge and the adequacy of the cleaning schedule employed.

4.2.2.2 Collect samples of scale or sludge for future analysis.

4.2.2.3 Any loose deposits shall be hosed out with high pressure water.

4.2.2.4 The tubes of horizontal - return - tubular boilers shall be washed from below and above.

4.2.2.5 Any deposits shall be removed mechanically or by chemical cleaning. Scrape the surface down to clean metal.

4.2.3 Fire Side Cleaning

The following shall be carried out:

4.2.3.1 Examine the fire side before any cleaning and evaluate the burner performance, distribution of air and flue gas flow and soot blower effectiveness.

4.2.3.2 If the boiler will be returned to service in the near future, the removal of ash and soot deposits shall be carried out. More complete cleaning shall be carried out for long term storage.

4.2.3.3 If water is used to clean off deposits, the boiler shall be returned to service as soon as possible to dry it out.


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4.2.3.4 Hose streams of water shall be used prudently to prevent dangerous generation of steam by hot flue dust.

4.2.3.5 A high rate of air flow shall be maintained through the furnace while handlancing or soot blowing is underway.

4.2.3.6 Portable lamps of 12 V or less with current supplied from batteries or with safety transformers up to 42 V shall be used for lighting.

4.2.3.7 Electrical equipment used inside the boiler or furnace shall be of a type that will prevent explosion and ignition of combustible materials.

4.3 Storage

4.3.1 Wet storage

The following shall be carried out for wet storage:

4.3.1.1 The empty boiler shall be closed and fitted with deaerated water.

4.3.1.2 Water pressure greater than atmospheric shall be maintained during the storage period.

4.3.1.3 Short storage period boilers below 7 MPa (70 kg/cm2), condensate or feed water containing about 200 ppm of sodium sulfite, with pH 10 shall be used for filling the boiler.

4.3.1.4 If the super heater is of the drainable type, the same treated water from boiler shall be used for filling the super heater.

4.3.1.5 In the case of super heaters of non-drainable type, it shall be filled with demineralized water containing a minimum of dissolved solids not more than 1 ppm.

4.3.1.6 On boilers above 7 MPa (70 kg/cm2), hydrazine and volatile alkali shall be used to prevent any solids deposition in the boiler after storage.

4.3.1.7 Oxygen scavenger shall be added to remove remaining oxygen and oxygen introduced by air leak.

4.3.2 Dry Storage

The following shall be carried out for dry storage:

4.3.2.1 The boiler shall be thoroughly dried.

4.3.2.2 After drying, to prevent any entry of moisture, moisture absorbing materials such as quick lime, or silica gel at the rate of 3.6 kg for 2.8 m3 of boiler volume shall be placed on trays inside the boiler drums.

4.3.2.3 Seal the boiler openings completely.

4.4 Starting a new boiler

4.4.1 Prior to starting a new boiler, an inspection shall be carried out by a competent person to insure that no foreign matter such as tools, equipment, rags, etc. is left inside the boiler.


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4.4.2 Checks before filling

Before putting water into a new boiler, make sure that the firing equipment is in operating condition.

4.4.3 Operation to clean the system

Fill the boiler to the proper water line and operate the boiler with steam in the entire system for a few days to bring the oil and dirt back from the system to the boiler.

4.4.4 Boiling out

The oils and greases which accumulate in a new boiler shall be washed out by operating the boiler as follows:

4.4.4.1 Fill the boiler to the normal waterline.

4.4.4.2 Remove plug from tapping on highest point on the boiler.

4.4.4.3 If no other opening is available, the safety valve may be removed, in which case the valve must be handled with extreme care to avoid damaging it.

4.4.4.4 Provide a boil-out compound of caustic soda and trisodium phosphate in the proportions of 0.453 kg of each chemical per 190 L of water.

4.4.4.5 Mix the chemicals with water and pour into the boiler through the prepared opening/dosing system.

4.4.4.6 Replace the plug, or the safety valves.

4.4.4.7 Start the firing equipment and check operating, limit, and safety controls. Review manufacturer’s recommendations for boiler and burner start-up.

4.4.4.8 Boil the water for at least 5 hr.

4.4.4.9 Stop the firing equipment.

4.4.4.10 Drain the boiler in a manner and to a location that hot water can be discharged with safety.

4.4.4.11 Wash the boiler thoroughly, using a high pressure water stream.

4.4.4.12 Fill the boiler to the normal waterline.

4.4.4.13 Add boiler water treatment compound as needed.

4.4.4.14 Boil the water promptly.

4.4.4.15 The boiler is now ready to be put into service or on standby.

4.5 Starting a boiler after lay-up

When starting a boiler after lay up proceed as follows:

4.5.1 Review manufacturer’s recommendations for start up of burner and boiler.

4.5.2 Set all boiler controls on manual.

4.5.3 Make sure fresh air to boiler room is unobstructed.


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4.5.4 Check availability of fuel.

4.5.5 Check water level in gauge glass. Make sure gauge glass valves are open.

4.5.6 Use try cocks, if provided, to double-check water level.

4.5.7 Vent combustion chamber to remove unburned gases.

4.5.8 Clean glass on fire scanner, if provided.

4.5.9 Set main steam shut off valve in open position.

4.5.10 Open cold water supply valve to water feeder if provided. Open suction and discharge valves on vacuum or condensate pumps and set electrical switches for desired operation. Vent boiler to remove air when necessary.

4.5.11 Check operating pressure setting of boiler.

4.5.12 Check manual reset, if provided, on low-water fuel cutoff and high-limit pressure control to determine if they are properly set.

4.5.13 Set manual fuel oil supply or manual gas valve in open position.

4.5.14 Place circuit breaker or fused disconnect switch on the “On” position.

4.5.15 Place all boiler emergency switches on the “On” position.

4.5.16 Place boiler control starting switch on the “On” or “Start” position. Do not stand in front of boiler access or cleanout doors. This is a precautionary measure should a combustion explosion occur.

4.5.17 Bring pressure and temperature up slowly. Stand by boiler until it reaches the established cut-out point to make sure the operating control shuts off the burner.

4.5.18 During the pressure build up period, walk around the boiler frequently to observe that all associated equipment and piping are functioning properly. Check for proper operation and flow of flue gas.

4.5.19 Immediately after burner shuts off, inspect water column and open each dry cock (if provided) individually to determine true water level.

4.5.20 Enter in log book

4.5.20.1 date and time of start up.

4.5.20.2 any irregularities observed and corrective action taken.

4.5.20.3 time when controls shut off burner at established pressure, tests performed, etc.

4.5.20.4 signature of operator.

4.5.21 Check safety valve for evidence of simmering.

4.6 Hydrostatic Testing

4.6.1 New power boilers or boilers that have been out of service for an extended period of time shall be subjected to a hydrostatic test of 1.5 times the design pressure.


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4.6.2 A hydrostatic test at normal operating pressure may be adequate for existing units after an outage if no major pressure part repairs were made during the outage.

4.6.3 Before the test, the boiler pressure parts shall be closed using new gaskets at any access points that were open during the shutdown. Feedwater, steam, blowdown, gauge glass, drain, and vent valves shall be operational so the boiler can be filled, vented, and drained.

4.6.4 Testing shall be carried out in accordance with the relevant Saudi standards and the testing fluid, water temperature shall be not more than 60oC.

4.6.5 At the end of a successful hydrostatic test the safety and relief valves shall be returned to normal operating conditions.

5. EMERGENCY OPERATION

In an emergency situation the following procedures shall be observed:

5.1 The alarm and shut down systems shall be operated.

5.2 The emergency procedures recommended by the boiler manufacturer shall be followed.

5.3 A typical emergency procedure for loss of water or low water conditions are shown in appendix (A).

6. FAILURES OF BOILERS

Serious damage and possible injury to personnel and loss of money may follow as a result of pressure part failures. To prevent this the following shall be observed:

6.1 Correct operating procedures shall be adhered to including the reporting of unusual operating incidents.

6.2 Any ancillary equipment malfunction, leakage or other signs of defective equipment shall be reported to the responsible person immediately.

6.3 Typical modes of failures of boilers are indicated in appendix (B).

7. For boilers with capacity more than 3 tons or special purpose boilers shall follow the manufacturers recommendations in addition to the requirements mentioned above.

8. MANUALS, HANDBOOKS AND TECHNICAL PUBLICATIONS

Manuals, handbooks and technical publication for boiler operation shall be prepared and provided to the purchaser of each boiler by the boiler manufacturer.


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APPENDIX (A)

TYPICAL EMERGENCY PROCEDURE FOR LOSS OF WATER OR LOW WATER CONDITION IN A BOILER

A.1 GENERAL

The correct procedure to adopt when a possible dangerous situation arises is to shut down the plant, and notify the owner responsible person. Where damage is determined the authorized inspector shall be notified.

A.2 LOW-WATER CONDITION

Check whether there is water in the water gauge glass. If there is water showing, the low water may be only of a minor nature and shutting down the combustion system and the steam outlet is all that is required. However, after cooling, the boiler should be inspected for damage and the low-water sensing device checked by a competent maintenance person. The boiler may then be returned to service.

If there is no water showing in the water gauge glass then the condition should be treated as dangerous and the following procedure shall be initiated immediately:

A.2.1 Extinguish the fire by shutting off the fuel supply and, in the case of a grate-type boiler, smother the fire with ash or draw it and shut off the draught or run the fire into the ash pit. In oil-fired, gas-fired or solid fuel in suspension fired boilers, the draught should be allowed to continue so as to purge the furnace.

In fluidized bed boilers, the fluidizing air supply shall be shut off.

A.2.2 Shut the feed check valve thus preventing the introduction of relatively cold water onto surfaces which may be overheated. This could cause ‘shocking’ of the metal, resulting in an explosion.

A.2.3 Momentarily close the steam cocks on the water gauge glasses. If water returns into each glass, then the water in the boiler will be above the water connection of the gauge glass. The boiler may now be put into service after bringing the water level back to a half glass and rectifying the reason for low water.

A.2.4 If no water rises in the gauge glass then the water is below the water connection and there is danger of the vital parts having been overheated.

A.2.5 On single boiler installations the main stop valve shall be left open to reduce the pressure in the boiler by using the steam in the plant. If two or more boilers feed into a common main, it will be necessary to shut the main stop valve and release the boiler pressure by lifting the safety valve by means of the easing gear.


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A.2.6 Allow the boiler to cool and when the pressure has been reduced to zero break the vacuum in the boiler by opening the vent or the drain cock on the gauge glass.

A.2.7 If the water level can not be positively established by utilizing the boiler accessories or appurtenances then the top manhole should be opened, in accordance with a safe procedure, and the water level ascertained. If the water level is above vital parts it is unlikely that overheating would have occurred and the manhole door may be replaced and the boiler put back into service.

In the case of water tube boilers check the water level by whatever means are appropriate.

A.2.8 If the vital parts have been exposed, then some heat damage may have occurred. In this case, no further action should be taken until it has been inspected by an authorized inspector.

A.3 VITAL PARTS

Those parts most likely to suffer damage on loss of water are referred to as the vital parts. The location of these vulnerable areas varies with each different boiler design. Typical areas are:

A.3.1 For economic or centre-fired boilers; the top or crown of the furnace and, to a small degree, the first tubeplate swept by the products of combustion.

Note: Furnace bulging or similar metal failures may also occur without a low-water condition having occurred.

A.3.2 For underfired multi-tubular boilers, horizontal return tube boilers or Colonial boilers; the section of the shell exposed to flame.

Note: Shell distortions may also be caused by heavy scale or sediment levels in the boiler.

A.3.3 For watertube boilers, a low-water condition may cause leakage at the tube-to-drum connection or the failure of tubes exposed to furnace radiation.


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APPENDIX (B)

MODES OF FAILURE OF BOILERS

B.1 SHORTAGE OF WATER

Loss of water in a boiler almost always leads to overheating of the heating surface metal. A number of factors may have contributed to this as follows:

B.1.1 Incorrect operation or lack of maintenance of the level control system is the major cause.

B.1.2 Accumulation of scale or internal deposits owing to an incorrect feedwater treatment or blowdown procedure.

B.1.3 Loss of adequate circulation.

When overheating occurs, the results may be:

(i) deformation in areas of high heat flux (such as the furnace of an internally fired boiler or the shell plate of an underfired multitubular boiler) or waterwall failure. This can result in rupture of the plate or tubes in the location of the deformation area or tearing at the endplate connections;

(ii) collapse or deformation of the reversal chamber in a wet back boiler;

(iii) hogging or sagging of tubes;

(iv) leakage from tube-to-drum or tubeplate connections;

(v) cracking of welds and of tube ends;

(vi) bulging of tubeplates;

(vii) ligament cracks.

B.2 FURNACE DISTORTION

Furnace, waterwall or tube distortion or bulging can be caused by overheating of the metal due to scale formation or steam blanketing on the water side of the furnace. The metal temperature increases and the yield strength of the metal decreases until distortion commences. This type of failure is most likely to occur when the following factors are present:

B.2.1 Scale formation on water side through inadequate water treatment.

B.2.2 Water tube blockage, leading to inadequate circulation.


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B.2.3 An excessive heat flux in the radiant zone due to over-firing.

B.2.4 A high pressure (positive or negative) occurs in the furnace particularly if higher than normal furnace or waterwall metal temperatures are present.

B.3 INCOMPLETE COMBUSTION

Incomplete combustion may cause the following:

B.3.1 High metal temperature at the entrance to the first tube pass or convection tube bank, due to incomplete combustion, can cause overheating and cracking of tubes or ligaments or cracking of welds at tubeplate attachments and distortion of superheater tubes.

B.3.2 Accumulation of unburnt fuel in air heaters, duct work, precipitators, and other spaces, which could lead to fires or explosions at those locations.

B.3.3 High temperature zones resulting in chemical attack of aggressive clinker, slag or dust deposits.

B.4 GAS-SIDE CORROSION

B.4.1 Low temperature gas-side corrosion

Low temperature gas-side corrosion can be due to:

B.4.1.1 the formation of acidic deposits, usually from sulfur, if care is not taken to keep the metal temperature above the acid dew point of the flue gas; and

B.4.1.2 the concentration of boiler water salts forming highly alkaline deposits adjacent to weeping boiler tube expansions.

B.4.2 High temperature gas-side corrosion

High temperature gas-side corrosion can be due to :

B.4.2.1 the formation of relatively low temperature eutectics with superheater tube metal and some chemicals in the fuel ash such as sodium and vanadium in fuel oil; and

B.4.2.2 the creation of a reducing zone adjacent to furnace tubes which has been known to occur under some conditions of two-stage combustion associated with low oxides of nitrogen (Nox).

B.5 CRACKING OF TUBE ENDS AND TUBEPLATES IN FIRE TUBE BOILERS

Fire tube boilers can be subject to cracking of the tube ends and tubeplates where the following conditions occur:

B.5.1 A high temperature difference between flow and return water. This could be due to lack of circulation or inadequate control of the return flow water temperature.


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B.5.2 Excessive thermal cycling as a result of rapid load changes or poor system design.

B.5.3 Over-expansion of tube ends.

B.5.4 Excessive protrusion of tube ends.

B.6 CORROSION FATIGUE

Fatigue caused primarily by severe thermal stress cycling and accelerated by corrosion can occur in internally fired fire tube boilers or similar boilers. It is usually located on the water side of the lower part of the furnace at the toe of the fillet weld to the rear tubeplate, but has been observed at the top of the furnace and at the front tubeplate. It is sometimes termed ‘stress grooving’ because of the groove which is usually present above the crack.

The factors associated with this cracking are poor weld profile, high metal temperatures and an uneven stress distribution around the furnace; it may also be associated with excessively high alkalinity of the feedwater.

B.7 EXTERNAL CORROSION

Severe wastage of the external surfaces of pressure parts may occur under insulation and refractory in localized areas where rain-water or water from leaking gaskets, valves or connections collects during idle periods.

B.8 EROSION

Wastage of areas of the heat transfer surface may occur where there has been:

B.8.1 flame impingement, causing scaling;

B.8.2 flue gas erosion owing to excessive gas velocity, together with a high dust burden in the products of combustion;

B.8.3 steam or water impingement such as may be caused by incorrect alignment of or failure to drain a soot blower prior to use; or

B.8.4 rubbing of parts owing to, for example, inadequate spacing.

B.9 FLUE GAS EXPLOSION

Flue gas explosions can be the result of a malfunction of the fuel supply and shut-off due to poor maintenance or the maladjustment of the combustion equipment and may lead to damage of the boiler water walls, casing and surroundings. Injury to personnel may also occur.

Most flue gas explosions occur during start-up, therefore the start-up procedures recommended by the manufacturer should be strictly adhered to.


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The preliminary draft of this standard has been developed by the work team composed of:

Name Agency

1. Abdul-Hamid Ibrahim Jomaa College of Engineering – King Saudi Univ.

2. Abdul-Aziz M. Al Goblon Al-Saghyir Steam Boilers Factor

The draft standard was studied and the comments received thereon from concerned bodies discussed. It has been adopted, in its present from, by the following members of Technical Committee No. (2) “Pressure Vessels and Steam Boilers”.

Name Agency

1. Abdullah Abdul Rahman Al-Azzaz Saline Water Conversion Corporation

2. Abdul-Hamid Ibrahim Jomaa College of Engineering – King Saudi Univ.

3. Ali Abdul-Aziz Al-Azizi Saudi Consulting House

4. Ibrahim Hassan Al-Hamam Saudi Aramco

5. Abdul-Aziz M. Al Goblon Al-Saghyir Steam Boilers Factor

6. Farid Ahmed Younis Saudi Arabian Standards Organization

7. Mohamed Maha Thevan Saudi Arabian Standards Organization

SASO 1441 STEAM BOILERS — PART 15 ...zb.guaihou.com/stdpool/SASO 1441-1998 Steam Boliers...The transparent part of a water gauge assembly connected directly or thorough a water column

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