WRITEUP ON SAFETY VALVE & ERV

8/10/2019 WRITEUP ON SAFETY VALVE & ERV

1/28


2/28

Bharat Heavy Electricals Ltd.,

Tiruchirapalli 620 014.

Valves Engineering.

PRESSURE RELIEF VALVES(SAFETY VALVES)

Compiled by: E. Athiannavi & S. Madhulingam Page 2of 28

12.06.2010

An automatic pressure-relieving device actuated by the static pressure upstream of thevalve characterized by rapid full opening or pop action. It is used for gas or vapourservice.

b) RELIEF VALVEAn automatic pressure-relieving device actuated by static pressure upstream of the valve,which open in proportion to the increase in pressure over the opening pressure. It isprimarily for liquid service.

c) SAFETY RELIEF VALVEAn automatic pressure-relieving device, which may be used as either a safety or reliefvalve depending upon application. It is primarily a safety valve with simpler andeconomical design.Safety relief valves are usually of the closed bonnet type. To prevent escape of medium

to surroundings special Bellow design in safety Relief valves are available for use in backpressure applications.

This discharge capacity had considerable bearing on evolutions of modern high dutysafety valves. (Due to many boiler explosions in the earlier stages of development, thenational codes for boilers and pressure vessels were formed. The safety valves becomeessential provisions of National Codes). These codes pay heavy attention towards theselection, design, manufacture, testing and performance of Safety valves on boilers andpressure vessels, as the failure of this equipment may spell failure of the whole plant towhich they are adjunct.

3.0 TERMINOLOGY:Accumulat ionAccumulation is the pressure increase over the maximum allowable working pressure ofthe vessel during discharge through the pressure relief valve, expressed as a percentageof set pressure, or actual pressure units.

Back PressureBackpressure is the pressure on the discharge side of a pressure relief valve. (Also seeBuilt-Up Back Pressure and Superimposed Back Pressure, below).

BlowdownBlowdown is the difference between opening pressure and reseating pressure of a

pressure relief valve, expressed as a percentage of the set pressure, or actual pressureunits.

Built -Up Back PressureBuilt-up backpressure is pressure, which develops at the valve outlet as a result of flow,after the pressure relief valve has been opened.

ChatterChatter is the abnormal, rapid reciprocating motion of the movable parts of a valve inwhich the disc contacts the seat.


3/28



Valves Engineering.



12.06.2010

Closing PressureClosing pressure is the point at which the valve re-seats. Closing pressure on a teststand may differ from the blowdown, which is the closing pressure under actual service

conditions.

Cold Dif ferential Test Pressure (CDTP)Cold differential test pressure is the set pressure at which the valve is adjusted to openon the test stand. This pressure includes the corrections for backpressure and/ortemperature service conditions

Differential Between Operating and Set PressuresValves in process service will generally give best results if the operating pressure doesnot exceed 90% of the set pressure. However, on pump and compressor discharge lines,the differential required between the operating and set pressures may be greaterbecause of pressure pulsations coming from a reciprocating piston. It is recommended

that the valve be set as high above the operating pressure as possible.FlutterFlutter is the abnormal, rapid reciprocating motion of the movable parts of a valve inwhich the disc does not contact the seat.

LiftLift is the actual travel of the disc away from the closed position when a valve is relieving.

Maximum Allowable Working PressureMaximum allowable working pressure is the maximum gauge pressure permissible in avessel at a designated temperature. A vessel may not be operated above this pressure,or its equivalent, at any metal temperature other than that used in its design.

Consequently, for that metal temperature, it is the highest pressure at which the primarysafety relief valve is set to open.

Operating PressureThe operating pressure is the gauge pressure to which the vessel is normally subjectedin service.

OverpressureOverpressure is a pressure increase over the set pressure of the primary relievingdevice. Overpressure is similar to accumulation when the relieving device is set at themaximum allowable working pressure of the vessel. Normally, overpressure is expressedas a percentage of set pressure.

Rated CapacityRated capacity is the percentage of measured flow at an authorized percentoverpressure permitted by the applicable code. Rated capacity is generally expressed inkilograms per hour (kg/hr) for vapors; normal cubic meters per minute for gasses; andlitres per minute (L/min) for liquids.Seat Tightness PressureSeat tightness pressure is the specified inlet static pressure at which a quantitative seatleakage test is performed in accordance with a standard procedure.


4/28



Valves Engineering.



12.06.2010

Set PressureSet pressure is the gauge pressure at the valve inlet, for which the safety valve has been

adjusted to open under service conditions. In liquid service, set pressure is determined bythe inlet pressure at which the valve starts to discharge. In gas or vapor service, the setpressure is determined by the inlet pressure at which the valve pops.

SimmerSimmer is characterized by the audible passage of a gas or vapor across the seatingsurfaces just prior to pop. The difference between the start to open pressure and theset pressure is simmer, and is generally expressed as a percentage of set pressure.

Superimposed Back PressureSuperimposed backpressure is the pressure in the discharge header before the safetyrelief valve opens. This can be further defined as follows:

Constant SuperimposedThis type of backpressure remains essentially at a fixed value (constant) and exists(superimposed) continuously prior to and during opening of the valve.

Variable SuperimposedThis type of backpressure varies or changes over a range from a minimum to amaximum, or vice versa. The actual backpressure at any specific time depends onconditions in the piping system to which the outlet of the valve is connected.

Valve TrimValve trim includes the nozzle and disc.

4.0 CODES GOVERNING SAFETY VALVES:

To govern boilers and pressure vessels each nation has evolved national and industrialcodes. The codes are based on Past experience in the field and provides safety foroperation and working of boilers and pressure vessels. The manufacturers and users ofthese ranges of products must take care of the code rules for the selection, design,manufacture, testing and operation.

The important national codes and industrial standards governing safety valves are:

a) IBR

b) ASME Sec.-I, Power Boilersc) ASME Sec.-VIII, Unfired Pressure vesselsd) BS 769e) Power Test Code PTC 25.3f) API Stds, 520, 526 & 527

5.0 SELECTION & SIZING OF SAFETY VALVES


5/28



Valves Engineering.



12.06.2010

The factors to be considered in Safety Valve selection and sizing for steam generators foruse in India are:

a) The valves must confirm to the Indian Boiler Regulations 1950 with all itsamendments,

b) Direct spring loaded valves are preferredc) The Safety valves used for boilers and pressure vessels are of the full lift type,

The orifice area of the safety valve = the peripheral discharge area.If 'D' is the diameter of orifice and 'L' is the lift of valve,We get xD/4 = DLHence the full lift of the valve, L = D/4

d) Minimum two safety valves are to be provided in drum.e) The drum safety valves must discharge at least 75% of the maximum evaporation of

the steam generators.

f) The Super heater safety valves must discharge at least 20% of the maximumevaporation of the steam generator. Correction factor of superheated steam is to betaken into account for capacity calculations.

g) The combined relieving capacity of both drum and superheater valves shall exceed100% maximum evaporation of the steam generator.

h) Reheater outlet safety valves shall discharge at least 20% of reheater flow andcombined reheater inlet and outlet valves must discharge at least total flow throughreheater.

i) Generally welded inlet valves are preferred for high-pressure applications.j) The final selection of safety valves is done to satisfy the capacity and pressure

restrictions and to yield the best economy.

k) A power assisted relief valve may be provided on SH outlet to take care of thepressure surges in boiler operation. This valve prevents the frequent lifting of themain spring-loaded safety valves on boiler drum and super heaters due to minorpressure variations. The discharge capacity of the power assisted relief valve is notaccounted for the combined relieving capacity of all safety valves.

6.0 RODUCT REQUIREMENTS:

The Boiler Safety Valves should be designed, manufactured and tested to meet thefollowing product characteristics. Tests are to be conducted with saturated steam foracceptance of the product.

a. The valve shall be hydraulically tested to 1.5 times the maximum rated pressureb. The discharge capacity of the valve should be proved by type test.c. The lift of the valve should be measured and proved by type test.d. The Reseating pressure (closing down pressure) should be determined experimentally

by type test.e. The computed blow down = (Opening pr. - Reseating pr.)/ Opening pr. x 100%

Should satisfy the code requirements (ASME Sec I stipulates 4% & IBR specifies 5%).


6/28



Valves Engineering.



12.06.2010

f. The operating pressure of the valve at which no leakage occurs should be tested at94% of set pressure (BHEL Valves).

7.0 CONSTRUCTIONAL FEATURES:

Typical constructional features of a modern heavy-duty safety valve are:

a) Inlet nozzle is profiled to give the maximum discharge.b) Thermo disc seat provides extremely tight closure and compensates for temperature

variation around the periphery of the seat bushing in steam service. Thermal stressesare minimized, seat distortion is prevented and permanent tightness is achieved.

c) Backpressures aided closing, which results in positive and precise closing of the valve.d) Lower adjusting ring is used to obtain a clear popping action and to cushion the closing

action of the valve.

e) Upper adjusting ring is used to obtain required blow down in addition with attain full liftat the popping pressure. Its position also determines the point at which the valvebegins to drop out of full lift and starts the closing portion of its cycle.

f) Ring pins are provided to keep the ring settings in position.g) Hydrostatic plug for hydraulic testing of the boilers where the welded valves are site

mounted. These plugs are to be replaced by disc after hydraulic test of the boilers.

8.0 OPERATION & MAINTENANCE:

Though the valves are set at factory, the valves after installation should be floated andadjusted to have clear popping action and blow down in the actual operating conditions.

The set procedures laid out by manufacturers are to be followed in adjusting the valve. Itis not necessary to remove flanged or welded valves from boiler for any maintenance.The actual maintenance required are lapping plate, lapping compounds, hightemperature lubricants and ring laps. Spindle run out, which results due to over gaggingshould be checked and corrected.

BHEL Safety Valves are manufactured as per the technology obtained from M/s DresserIndustries, Inc., U.S.A., The product range covers both safety and safety relief valves.

For the power boiler applications, the following pressure relief valve product ranges aremanufactured and meets the requirements of IBR.

1. 1700 Series Safety Valves:

This is Dresser's maxiflow design with the product specialties

a. Use of thermo discb. Two adjusting ring controlc. Backpressure aided closing for achieving shorter blow down.


7/28



Valves Engineering.



12.06.2010

This series of valves are mainly used in Boiler drum, S.H. & R.H. system.

2. 1811 Series Safety Valves

This is a low cost safety valve product line with two-ring control. The valves are designedonly up to maximum pressure of 50 kg/cmg. These valves are used as soot blower linesafety valves, continuous blow down and PRDS stations. These valves are nowavailable with improved disc for better performance in high temperature application.

3. 1900 P Series Safety Relief Valves

These valves are of the closed bonnet design. Open yoke designs are also available.Thermo discs are steam application for better leak tightness of valve seats. These valvesare selected for pipelines applications for our boiler units in PRDS Systems and CBD

tank etc.,

4. 1900 Series Safety Relief Valves

These valves are mainly used in the liquid service and compressible fluid service.Typical application in power plants are Feed water heaters, oil systems and compressedair services.

9.0 SAFETY PRECAUTIONS

Do not go near discharge side of a safety valve.

Body drain and cover plate vent must be piped to a safe area. If left open, steamwill escape and present a burn hazard to personnel near the valve.

Always gag a safety valve before making ring adjustments.

When pulling hand lever for inspection purposes, a rope should be attached to thehandle of sufficient length (minimum 6 to 10 m long) to protect the operator fromescaping steam, dust, fly ash etc.,

Exercise caution when examining a safety valve for audible leakage. SUPERHEATED STEAM IS NOT VISIBLE.

Safety valves should be mounted to provide adequate access, 360 around thevalve plus overhead, for disassembly and maintenance.

Use ear-muffs during the adjustment of valves.

Use hand gloves during adjustment of valve in the hot condition.

10.0 HANDLING, STORAGE AND PRE -INSTALLATIONSafety valves should be stored in a dry environment to protect them from the weather.They should not be removed from the skids or crates until immediately prior toinstallation. Flange protectors end covers and sealing plugs should also be installed until

just prior to installation. When Safety Valves are uncrated and the flange protectorsremoved immediately prior to installation, meticulous care should be exercised to prevent


8/28



Valves Engineering.



12.06.2010

dirt and other foreign materials from entering the inlet and outlet ports while bolting orwelding in place. Ensure the disc is available. Identify the disc and store it safely with D.Usequence required for assembly. Check for disc identification dimension before

assembly.The valve, either crated or uncrated, should always be kept with the inlet down i.e., neverlaid on its side, to prevent misalignment and damage to internals. Keep valve on cradleafter removing from crate. Uncrated valves should be moved or hoisted by wrapping achain or sling around discharge neck, then around upper yoke structure in such a mannerthat will insure the valve in vertical position during lifting i.e., not lifted in horizontalposition. Never lift the full weight of the valve by the lifting lever. Never hook to the springto lift. Crated valves should always be lifted with the inlet downwards. Safety valves,either crated or uncrated, should never be subjected to sharp impact. This would be mostlikely to occur by bumping or dropping during loading or unloading from a truck or whilemoving with a power conveyor, such as a fork lift truck. While hoisting to the installation,

care should be exercised to prevent bumping the valve against steel structures and otherobjects.

10.1 Check lis t for Storage, Erection and Commissioningi. Check for tag No.or D.U.No. as per packing slip. Non-availability or discrepancy must

be informed to the manufacturing unit. Check for test certificates for each safety valve.ii. Check whether the inlet size, orifice, material grade, set pressure etc. are as per the

boiler O&M Manual.iii. Check that the seals are intact on ring pin, spring adjuster and overlap collar. Check

for transit damages, if any.iv. Ensure that the end covers are kept in position and removed only just before erecting

in place. Meticulous care should be taken to ensure dirt or foreign particles do notenter into the inlet or outlet of the valve.

v. Ensure the valves are stored in crates on sleepers in a covered area with the inlet sidedownwards. Valves should never be laid on the side to avoid damage to internals.

Erectionvi. Ensure that the disc is available, identify and keep in a safe place for final assembly as

per D.U. sequence. Identify and hand over the Hyd.test plugs to the user after theHyd.test is completed.

a. Ensure proper preservation for exposed surfaces of valve and service tools for longstorage.

b. Ensure the valves are never subjected to impact by bumping or dropping during

loading and unloading and disassembly and assembly of valve.c. Do not lift valve with lever or spring. Sling valve as described in O&M manual.vii. Valves should be erected with spindle vertical within a tolerance of 1 from the

vertical plane.viii. Ensure proper pre-heating and post heating, stress relieving and NDT procedures are

followed when welding to the stub.ix. Ensure that the vent pipe is separately supported and does not touch the drip pan unit

and that there is sufficient allowance for expansion in horizontal and vertical directions.


9/28



Valves Engineering.



12.06.2010

x. Ensure the cover plate vent and drain are connected with pipe of adequate size to safelocations.

xi. Extend insulation of vent pipe over roof to avoid rain water collection into drip pan.

Insulate the inlet and body upto the cover plate.xii. After hydrostatic test of boiler, remove hydro test plug and ensure dice is replaced

and valve reassembled without affecting setting as per O&M.Commissioningxiii. Use calibrated pressure gauges for safety valve floating. Float the lowest set safety

valve first, gag the valve after setting is over and float the next higher set valve and soon till all valves are floated and checked for the set pressure within 1% tolerancelevel.

xiv. Try to achieve the setting within a minimum no. of pops (about 3 pops).xv. Check that blowdown is within allowable limit by IBR.xvi. Apply gag load finger tight in hot condition to avoid spindle bending.

xvii. Remove gags after floating of safety valves.xviii. Check and ensure sufficient approach and maintenance space all around the valve.xix. Proper structures for mounting the slings or pulley blocks are necessary for

maintenance purposes. Same may be checked during installation itself.xx. After the valves are set in the field, release collar should be taken up and locked with

cotter pin such that minimum gap of 3.2 mm (1/8) is retained between the collar andtop lever.

11.0. RECOMMENDED INSTALLATION PRACTICEi. The safety valve or valves shall be connected be valve or valves shall be connected to

the boiler independent of any other connection, and attached as close as possible to

the boiler, without any unnecessary intervening valve or fitting. Such intervening pipeor fitting shall not be longer than the face-to-face dimension of the corresponding teefitting of same diameter and pressure. Every safety valve shall be connected so as tostand in an upright position with spindle vertical.

ii. The opening or connection between the boiler and the safety valve shall have at leastthe area of the valve inlet. No valve of any description shall be placed between therequired safety valve and the boiler nor on the discharge pipe between the safety valveand the atmosphere. When a discharge pipe is used, the cross-sectional area shall notbe less than the full area of the valve outlet of the total of the areas of the valve outletsdischarging there into. It shall be as short and straight as possible and so arranged as

to avoid undue stresses on the valve or valves. All safety valve discharges shall be solocated or piped as to be carried clear from running boards or platforms. Ampleprovision for gravity drain shall be made in the discharge pipe or near each safetyvalve or safety relief valve, and where water or condensation may collect. Each valveshall have an open gravity drain through the casing below the level of the valve seat.For iron and steel-bodied valves exceeding 63.5 mm (2-1/2") size, the drain hole shallbe tapped not less than 9.5 mm (3/8") pipe size.


10/28



Valves Engineering.



12.06.2010

iii. If a muffler is used on a safety valve or safety relief valve, it shall have sufficient outletarea to prevent back pressure from interfering with the proper operation and dischargecapacity of the valve. The muffler plates or other devices shall be so constructed as to

avoid a possibility of restriction of the steam passages due to deposits. When a safetyvalve is exposed to outdoor elements which may affect operation of the valve, it ispermissible to shield the valve with a satisfactory cover. The shield or cover, shall beproperly vented and arranged to permit servicing and normal operation of the valve.

iv. Safety valves may be attached to drums or headers by welding provided the welding isdone in accordance with Code requirements.

11.1 Outdoor Safety Valve InstallationSafety Valves operating under the best possible conditions of favorable operating gap,relatively stable ambient temperatures, absence of dirt and in relatively still air, will

provide the maximum degree of safety, tightness and dependability. When a safety valveis installed in a location such as out doors, it is exposed to wind, rain, snow, ice, dirt andvarying temperatures.The following recommendations are made for proper protection toinsure that operational dependability can be restored to a level near that of the valveinstalled under ideal conditions. The inlet neck of the safety valve and safety valve body,upto the bottom of the cover plate. Should be insulated. The exterior surface of any suchinsulation should be weather proofed by any suitable means. In addition to maintaining amore even temperature within the valve body, during widely fluctuating ambienttemperatures, this insulation will effectively reduce thermal stresses due to hightemperature gradients through the walls of the safety valve nozzles. Even in tropicallatitudes, insulation should be applied since safety valves installed in outdoor locations in

these areas are subject to hurricane conditions. Spring covers should be used to stabilizeas nearly as possible the temperature of the spring and also to prevent the accumulationof dirt, ash, and ice between coils of the spring. Lifting gear covers should be installed toprevent ice, dirt and fly ash from accumulating in areas inside the safety valve cap.

11.2 Field SettingAll Safety valves are steam tested at the factory. Every valve is set to have a cleanpopping action and to reseat tightly. However, because the boiler used in setting thevalves has a small capacity compared to the capacities of the valve. Slight adjustmentson the actual installation are necessary to maintain proper action and blowdown. Twomethods exist for field testing of valves ;use of the 1566 or 1566-2, Hydroset Unit, and full

system pressure.As previously noted, the use of a hydroset unit will serve to establish Set pressure onlyand should not be used for establish blowdown, lift, etc., Gagging of other valve not beingset generally will not be necessary; however, for setting of high set pressure valves,depending on system pressure being used, it may be required to gag the lower setvalves. Boiler safety valve tests can be conducted with the unit either on or off the line.However, with the unit on the line at full load a sudden load drop could be dangerous asmost of the safety valves will be gagged. Therefore, it is recommended that the safety willbe tested and adjusted with unit off the line or with light load. Boiler control can then be


11/28



Valves Engineering.



12.06.2010

maintained with little or no outside influence due to load change. The valves should beset within 1% of the set pressure as per ASME Sec-1. Set pressure should not bechanged without the permission of the manufacturing unit. Lab standard or test Gauges

should be used with a minimum graduation of 0.5% of the full scale reading and accuracyof 0.25%.Gauges should be of sufficient range so that reading is in the middle third ofthe scale. Factors Which Can affect Safety valve operation are:i. Ambient temperatureii. Discharge Stack binding against drip pan elbow.iii. Vibration of the header from upstream bends, etc.iv. Operating gap.

12.0 HYDROSTATIC TESTING AND GAGGING12.1 During any hydrostatic test all safety valves on the unit must be gagged. Thisgagging procedure prevents the possibility of damage of the safety valve internals in the

event that the test procedure exceeds the safety valve set pressure. When valves aresubjected to working hydrostatic tests not exceeding the set pressure of the low setvalve, valves may be gagged rather than using hydrostatic test plugs. For higherpressures hydrostatic plugs should be used and valves should be gagged. Probably themost common source of Safety Valve trouble is over gagging.During Hydrostatic Testing and Safety Valve Setting Gags should be applied onlyhand tight. During setting, over gagging will also cause damage to the seating surfaceand the resultant leakage. In applying gags remember that the valve spring will hold thevalve closed against its set pressure. The additional gag load applied should be onlyenough to insure that the valves do not lift at the expected over-pressure.Gags should never be applied when the boiler is cold. The spindle of the safety valve

expands considerably with the temperature increase as pressure is raised. If it is not freeto expand with this temperature change it may become seriously bent. Boiler pressureshould be brought up to within 80% of the pressure of the low set valve before applyingthe gags. Tighten the gags of drum and superheater valves with only a light force appliedto the gag stem. Reheater valves require a greater force applied to the gag stem to holdthe valve closed during hydrostatic test.

Appl ication of Test Gags (All Pressures)i. Remove top lever pin (130), top lever (128) then loosen cap screw (238) remove cap

(126) and Drop lever (127) as an assembly. The release collar (131) is fixed to spindle(046) by means of a cotter pin (185). Note that the release collar (131) does not quiteengage top of spring adjuster (101). See fig for details or release collar position.

ii. Center the test gag stem on the exposed end of the spindle (046) and hook the legs ofgag under the sides of the yoke.

DO NOT APPLY THE GAG LAOD UNTIL THE BOILER HYDROSTATIC PRESSURE ISEQUAL TO 80%OF THE PRESSURE TO WHICH THE LOW SET VALVE IS

ADJUSTED.iii. Apply the gag load by turning the gag stem clockwise. Any attempt to pinch off the

leakage through the valve without first lowering the hydrostatic pressure is liable toresult in damage to the valve seats. If the gag on the valve has not been tightenedsufficiently, the valve will leak and sometimes the leakage is accompanied by Sizzling


12/28



Valves Engineering.



12.06.2010

sound. If this occurs the hydrostatic test pressure should be reduced until the valvebecomes tight and then gag should be tightened further. This procedure must befollowed exactly since it is very difficult to stop the leak by additional gagging once it

has started.iv. After the hydrostatic test is completed, the gags should be removed when the

hydrostatic pressure has been reduced to 85% to 90% of the pressure of the low setvalve.

Nomenclature List:002 Base

003 Seat Bushing


13/28



Valves Engineering.



12.06.2010

004 Inlet Neck

008 Yoke

009 Yoke rod

011 spring012 Upper Spring Washer

016 Lower Spring Washer

026 Disc

028 Disc Holder

029 Disc Collar

031 Guide

036 Upper Adj.Ring

037 Upper Ring Pin

038 Lower Adj.Pin

039 Lower Ring Pin046 Spindle

052 Lift Stop

054 Overlap Collar

056 Cover plate

057 Lower Washer Retainer

058 Lower Floating Washer

059 Lower washer Retaining Pin

061 Top Plate

062 Upper Washer retainer

063 Upper Floating Washer

064 Upper Washer Retaining Pin101 Spring Adjuster

102 spring Adjuster Lock Nut

105 Service Port Plug

126 Cap

127 Drop Lever

128 Top Lever

129 Drop Lever Pin

130 Top Lever Pin

131 Release Collar

182 Disc Collar Cotter Pin

183 Lift Stop Cotter Pin184 Overlap Collar Cotter Pin

185 Release Collar Cotter Pin

226 cover plate stud

229 cover plate nut

231 Yoke Rod Nuts

232 Lower Yoke Rod Nuts

237 Retainer screw (Top Plate)


14/28



Valves Engineering.



12.06.2010

238 Cap Set Screw

13.0 Factory Setting Vs. Field Setting

Every Safely Valve is set and adjusted on steam before shipment from the factory.Blowdown adjustments are made is carefully and accurately as possible on the factorytest boiler. However it must be recognized that actual field operating conditions may varyconsiderably from factory test conditions.Conditions beyond the manufactures control that affect safety valve operation are:i. Quantity of steam being discharged through the valve, i.e. the actual installation

capacity exceeding that of the test boiler, thus permitting the valve to flow its full ratedcapacity.

ii. Quality of steam being discharged.iii. Discharge piping stresses and back pressure.iv. Ambient temperature.

v. Shipping or storage damage.vi. Improper gagging.vii. Improper bolting of flangesviii. Damage due to foreign material in the steam.xi. Damage, during disassembly and assembly in the fieldxii. Insufficient operating gapxiii. Vibrations

Final Safety Valve adjustments made on the actual installation is the best means ofensuring that the valves perform in compliance with the applicable code requirements.

13.1 Popping Point AdjustmentTo change the popping pressure of the valve remove the cap and lever assembly, loosenthe locknut and turn the spring adjuster clockwise to increase pressure. After eachadjustment of the spring adjuster the locknut should be tightened. The arm on top ofspring washer should always be free from bearing against the yoke rod. This can beaccomplished by holding a screwdriver between the arm and the rod to prevent anymovement of the top spring washer while adjusting the spring adjuster.

13.2 Ring Adjustment:Always gag the Safety Valve for protection, in case boiler pressure rises while makingring adjustments (See instructions for gagging). The positions of the upper adjusting ring

and the lower adjusting ring are locked by means of the upper adjusting ring pin and thelower ring pin respectively. These pins are threaded into the valve body and engagenotches, which are cut into the rings. To adjust either ring the corresponding ring pinmust be removed. A screwdriver can be used to turn the rings.Spare ring pins when supplied will be of excess length and have to be individually groundto match each valve. The tip of the pin should not touch the bottom of the ring notches.

Lower Ring Adjustment


15/28



Valves Engineering.



12.06.2010

Using Figure 1and Table1,a reference plane is established where the adjusting ring islevel with the bushing seat. From this setting, factory adjustments are made by adjustingone notch downward for each 42.2 kg/sq.cm (600 psi) of set pressure. Ring position

should be checked prior to testing. Slight deviations from these settings are possiblebecause of tests conducted in the plant.NOTE (THIS PROVIDES A STARTING POINT ONLY). The lower ring is used toobtain a clean popping action and to cushion the closing action of the valve.DO NOT ATTEMPT TO ADJUST BLOWDOWN WITH THE LOWER RING.

The ideal position must then be found for the set of operating conditions present. Ifsimmer is present or valve fails to lift, the lower ring should be moved upward slowly, onenotch at a time to remove the simmer. The most ideal position for the lower ring is thelowest position that does not introduce simmer or a buzzing sound. In this connection, itis imperative that extreme care be used in conditioning the seat surfaces, ensuring

correct alignment, and establishing the proper clearance, so that mechanical causes ofsimmer will be reduced to a minimum.Upper Ring Adjustment

When shipped from the factory, upper adjusting rings are set level with the bushing seatin accordance with Figure 1and Table1. This should be checked prior to field setting andshould be regarded as a starting position only. It is possible that this position is not strictlyin accordance with Figure 1and Table 1on some valves because of testing at the plant.The ring may be set lower than the seat level, but never before, until field tests areconducted. Starting position for blowdown check should place bottom surface of upperring level with bushing seat. Since the bushing seat is not visible through the service

ports. It is necessary to use a cross-reference relationship. Raise the upper ring until itsbottom surface in level with the disc holder, which is visible through the ports. Then,referring to Table1, Column B, lower the upper ring the required number of notches. Thiswill place the upper ring on a plane with the bushing seat. This is the starting point forblowdown tests. Further adjustments may be necessary depending on test results. Whenfurther adjustments are required to obtain final blowdown setting, the upper adjusting ringshould be moved 5-10 notches at a time as follows:


16/28



Valves Engineering.



12.06.2010

TABLE 1ADJUSTING RINGS FINAL FACTORY POSITIONS

(FIELD SETTING STARTING POSITIONS)

Orifice

Lower RingHolder to Seatin notches(Column A)

Upper RingHolder to Seatin notches(Column B)

1 7 10

2 8 12

3 12 16

4 12 16

5 12 166 30 45

7 30 45

Q 30 45

8 37 45

R 38 47

Guidelines for setting and locking adjusting rings


17/28



Valves Engineering.



12.06.2010

Gag the safety valve for protection while making ring adjustments. The lower and upperadjusting ring pins of any particular valve are not interchangeable. Spare ring pins when

supplied will be of excess length. These pins are to be ground at site so as to match thevalve under maintenance. The tip of pin should NOT touch the bottom of the ring notch(refer sketch enclosed) Also the pins should not bear against the rings. DO NOT attemptto adjust blow down with the lower ring. The upper adjusting ring should not be set belowthe seat level and the lower adjusting ring should not be set above the seat level. Lockboth the ring pin settings using a seal wire to avoid disturbance during system/valveoperation and line vibrations.

RECOMMENDED

NOT RECOMMENDED

NOT RECOMMENDED

BODY

ADJUSTING RING

ADJUSTING RING PIN

BODY

BODY

ADJUSTING RING PIN

ADJUSTING RING

ADJUSTING RING

ADJUSTING RING PIN


18/28



Valves Engineering.



12.06.2010

Ensure that the above settings are properly locked: Periodically check whether the pinsare in their appropriate place and are effective. This can be checked through the serviceport, provided in the valve body. A sketch showing acceptable ring pin positions is

enclosed. Excessive line vibrations, presence of foreign particles, discharge pipingstress, back pressure, reaction force etc., can lead to pin failure over a prolonged periodof exposure. The ring pins being the most critical spare part, it is desirable that one pinper valve (for drum and SH SVs) and one ring per four valves (for RH SVs) is stocked asessential spares by customer. Adherence to the above aspects would eliminate cases ofpremature pin failure and lead to a satisfactory valve performance.

To reduce blowdown -MOVE RING UP-TURN COUNTER CLOCKWISE.To increase blowdown -MOVE RING DOWN-TURN CLOCKWISE.It is possible to raise the upper ring too far and prohibit attainment of full lift. When thisoccurs, lower to the point where full lift is attainable and finalize the blowdown setting with

the overlap collar (See Overlap Collar Position). If valve fails to lift the lower adjusting ringrequires further adjustment. (See Lower Adjusting Ring Position)

Check the ring pins to see that the engage the ring grooves, but without touching thebottom. The pins should not bear against the rings.

GUIDELINES FOR THE STEAM TESTING OF BOILER SAFETY VALVESImplementing the following procedures will benefit your company in good valveperformance, reduced labor time and fuel savings.

Mechanical1. We highly recommend a preliminary test at reduced pressures of the boiler valves with

our 1566 hydroset prior to steam. Savings in fuel and time will easily justify this step.2. Only calibrated test gauges should be used for testing safety valves. Gauges not

calibrated can cause problems with operating pressure later or even necessitate theretesting of all the safety valves.

3. Gage for each valve should be available and in good condition.4. Discharge piping has to be inspected for binding on the valves, supports and welds on

piping. Binding of the discharge could make the valve hang up on closing. Insufficientwelds and supports could cause the discharge piping to fly off during valve activation.

5. A rope approximately 5 to 7 meters with a hook one end should be attached to thevalve lifting lever before activation. Should the valve chatter or not lift at set pressures,the rope can pulled, Eliminating chatter and stop over pressure of the vessel.

6. Have the correct tooling available. Looking for tools means lost lime. Having incorrecttools can cause damage to compression screws and other valve parts.

7. Establish a good communication system between the boiler and control room.This eliminates mistakes that could be dangerous and time consuming.

Operational1. If the unit has a power assisted relief valve Electromatic, place this valve in operation

first. Since safety valves are tested one at a time and the other valves are gagged, the


19/28



Valves Engineering.



12.06.2010

pilot actuated relief valve will increase the safety factor of the unit while testing. Pilotoperated valves can be actuated from the control room if some emergency shoulddevelop during the controlled burner firing associated when tests are being conducted.

The electromatic will help clean contamination from system.2. The Drum valve should be tested first Possibilities of valve part damage because of

girl blasting are greater on superheated valves in contrast to the drum valves. If asuper heated valve is gagged after seat damage while testing of other valvescontinues, the total valve damage will most likely be increased. Temperatures of theboiler increase during the testing cycle of the Drum Valves. Consequently highertemperature steam will be available for testing the Superheater valves and producemore accurate results.

3. Keep water level down as low as possible while testing drum valves. If drum valveslevel is high the Safety Valve may be stugged with water causing a long blowdown andpossibly damage the valves

4. Pressure should be brought up evenly and fairly rapid rate A slow raise in pressure willincrease the simmer of the valve possibly causing the valve to life erratically. Werecommended 2 to 3 kg/cm2 per minute increase in pressure during testing to beoptimum. Should a burner or other systems fail when pressure is near the set pressureof the valve, drop boiler pressure at least 10 percent below set pressure before raisingboiler pressure again.

5. Holding boiler pressure near the set pressure of the valve will induce simmer, possiblycausing the valve to lift erratically.

6. Drop pressure after a valve has lifted to a safe level before taking the gag off the nextvalve or making-valve adjustments. 20 percent of the valve set pressure will assure thenon-gagged valve will not lift prematurely.

7. If a valve has to be lifted several times, a cooling off period will be necessary. Foroutside or inside valve installation, 25-30 minutes is sufficient: If this cooling period isnot maintained, erratic operation of the valves can be expected.

8. If the valves have not been tested with the hydroset prior to the steam actuation, it isrecommended to hand lift the valves before the actual steam pop. Hand lifting thevalves will show that the valves are functional furthermore; it will help to warm up thevalve.

SafetyFor the protection of persons in testing be valves, a few simple steps can, preventaccidents and injury.

1. Have only people on the boiler absolutely necessary for the testing of the valves.2. Rope off the area where valves are going to be tested.3. When working on the valves, wear gloves4. All personnel on the boiler are to wear eye and ear protection.5. Warn people on the plant site that valve testing is being performed.

The recommendations we have made represent many years of field experience. Wehope you can implement some or all of them. Hopefully, you will have a good start up.


20/28



Valves Engineering.



12.06.2010

14.0 SITE PROBLEMS IN SAFETY VALVES:The general problems faced at various sites for the safety valves are:

I. Safety Valve Leakage:

Causes1. Seat / disc damage2. Long simmer3. Physical obstruction in seat.4. Spindle is bent5. Wrong working pressure closer than 6% of set pressure.6. Retaining nut position wrong.7. High ambient temperature8. Exhaust pipe expansion clearances not sufficient9. Impurity in steam/Foreign particles damages.

Remedy1. Change/lap the disc/seat2. Adjust the lower ring position3. Change/rectify the spindle4. Increase the set pr.5. Change the position so that a clear gap is available.6. Ambient temperature is to be reduced by identifying source.7. Change the drip pan or exhaust pipe to get ample clearances

II. Seat damages in both disc and body seats resulting in Seat passing due toforeign particles in steam

RemedyRelapping of Disc and body seats.If the damages are heavy, in body seats, due to wire drawing and seat cutting action theroto lap kit can be used for body seats for seat reconditioning. However, final seatlapping is done with ring laps. If the damages are minor hand lapping will be sufficient.

If the damages are beyond relapping level the seat is remachined using a reseatingmachine and subsequently body seat is lapped. The lapping is checked with carbonblue. Attend to safety valve leakage at the earliest otherwise the steam cutting action willdamage valve seats and trims requiring more replacement parts.

III. Simmering of Safety Valves

1. Check misalignment of safety valve erection to vertical plane for 1.2. Check vibration of line on which safety valve is mounted3. Check escape pipe is freely supported and do not transfer any load to safety valve4. Check minimum operating gap between set pressure and operating pressure is 6%

with 1% tolerance for set pressure of safety valve. If the operating gap is critical setsafety valves to +1% tolerance level.


21/28



Valves Engineering.



12.06.2010

5. Raise Lower adj. Ring one notch at a time from the original position as per O&M toovercome simmering of valve.

6. Check for leakage of safety valve. Leaking Valves may cause simmer and erratic

behavior of Valve. Attend to Safety valve leakage by lapping valve seats.

7. Check failure of ring pins. This will result in ring position changes leading to simmeringof safety valve. Readjust rings as per O&M. Replace broken ring pins, ensuringadequate play between adjusting rings and ring pins.

Do not replace ring pins with manufactured pieces at user works as special materials areused for ring pins.Caution:

i) While assembling the ring pins, make sure it is not tight against the adjusting rings.

Tight pins will lead to breakage.ii). Lower and upper ring pins are not interchangeable

IV. Chattering of Safety Valve:Cause:1. Long inlet pipes2. Inlet restrictions3. Too short a blow down4. Too large valve capacity

Remedy:

1. Use short stubs for safety valve installation.2. Inlet opening shall be corrected to a size equal or more than safety valve inlet. Adjust

the blow down by blow down adjusting rings. Change the valve to smaller size orrestrict the lift.

V. Fly ash entering Safety ValvesThis is noted at few sites where the fly ash coming out through the furnace roof due topoor roof sealing and positive pressures in furnaces. These accumulated ashes fall intothe trim components of Safety Valves through the cover plate clearances. This leads toscale formation at guide and disc holder and disc spindle thread joints and results in

jamming of these components. These may result in Safety valve not fully lifting due to

deposits between guide and disc holder.The valves should be protected with covers in such sites where fly ash is coming out ofthe boiler through the roof.

6. Spindle bending:

Cause:Cold gagging

Remedy:


22/28



Valves Engineering.



12.06.2010

Replace bent spindle. Always apply gag load on SV spindle when the valve is in hotcondition only.

7. Locating safety valves

Service platforms and accessibility for servicing of Safety Valves maintenance are to begiven attention at site during erection. A cross beam is required in the centerline of eachsafety valve for assembly and disassembly of valve.


23/28



Valves Engineering.



12.06.2010

ELECTROMATIC RELIEF VALVE

1. GENERAL DESCRIPTIONThe BHEL ELECTROMATIC RELIEF VALVE is an electrically actuated pressure reliefdevice. It may be operated, manually at will by closing a switch or automatically bymeans of a pressure sensitive element to relieve pressure accurately within very closelimits. The application of this valve places at the command, of the plant operator a meansof instantaneously opening and closing a relief valve on some remote header. TheELECTROMATIC RELIEF VALVE may be used to purge a superheater or a header,thereby decreasing -the possibility of damaging the spring loaded safety valve seats orturbine equipment. With the pressure element set to open the ELECTROMATIC RELIEFVALVE automatically at a pressure slightly below the lowest set spring loaded safetyvalve, it will effectively prevent the safety valves from lifting except on major over-

pressures. Figure - 1 illustrates diagrammatically the relationship of the various elementsof the ELECTROMATIC RELIEF VALVE system. The Type 1537 control station isequipped with a three-position (Manual, Off, and Automatic) switch and with threeindicating pilot, lights (red, blue and green). The type 2537 VX control station is equippedwith two indicating lamps (red and amber). The type 1539 VX controller consists of apressure sensitive element consisting of a Bourdon Tube which actuates electricalcontacts, and a heavy duty relay to switch the solenoid load. The solenoid assembly thenoperates a pilot valve. The pilot valve in, turn controls the opening and closing of themain valve. Controllers are generally furnished for 220V DC; a resistor unit is built intothe solenoid assembly for the purpose of reducing the current when the solenoid is in itsholding position. In the case of AC solenoid the resistor unit is not necessary.

2.0 SAFETY NOTICEProper service and repair is important to the safe, reliable operation of all valve products.The service procedures recommended by BHEL and described in the maintenance andservice manual are effective methods of performing the required maintenance operations.Some of these service operations require the use of tools specifically designed for thepurpose. These special tools should be used when and as recommended.It is important to note that this service manual contain various warnings and cautionswhich should be carefully read in order to minimize the risk of personal injury or thepossibility that improper service methods will be followed which may damage the valve orrender it unsafe.

It is also important to understand that these warnings and cautions are not exhaustive.BHEL could not possibly know, evaluate, and advice the customer or utility of allconceivable ways in which service might be done, or of the possible hazardousconsequences of each way. Consequently BHEL has not undertaken and such broadevaluation. Accordingly, anyone who uses a service procedure or tool which is notrecommended by BHEL must satisfy himself thoroughly that neither his or otherpersonnels safety nor valve safety and proper operation will be jeopardized by theservice method he selects. Contact BHEL if there is any question on the method.


24/28



Valves Engineering.



12.06.2010

The testing, installation and removal of valve and valve products may involve the use offluids at extremely high pressure and temperature and/or corrosive or erosive.Consequently, every precaution should be taken to prevent injury to personnel during the

performance of any test, installation or removal such as, but not limited to, ear drumprotection, eye protection, and protective clothing such as gloves, etc., in and around thetesting, installation, or removal area. Due to the various circumstances and conditions inwhich these operations may be performed on our products or the possible hazardousconsequences of each way BHEL could not possibly evaluate all conditions that couldinjure personnel or equipment, but does offer these safety precautions as an assistanceonly.

3.0 SAFETY PRECAUTIONS1. Do not stand in front of the discharge side of a pressure relief valve when testing

or operating.

2. Hearing protection should be used when testing or operating valve.3. Exercise caution when examining a pressure relief valve for visible leakage.4. Never install a pressure relief valve in a horizontal position. Pressure relief valve

internals are designed to move vertically, when installed horizontally,misalignment and galling or hang-up may prevent the valve from opening orclosing properly.

5. The body drain must be piped to a safe area. If left plugged, condensate willaccumulate inside the valve body. If left open, hot and/or corrosive media willescape and present a hazard to personnel near the valve.

6. Pressure relief valves should be mounted to provide adequate access, 360Oaround the valve plus overhead to permit removal for testing and maintenance.

7. When removing the pressure relief valve during disassembly, stand clear and/orwear protective clothing to prevent exposure to splatter of any corrosive processmedium which may have been trapped inside. Ensure valve is isolated fromsystem pressure before valve is removed.

4.0 STORAGE AND HANDLINGi. The valve, either crated or uncrated, should always be kept with the inlet flange

down, i.e. never laid on its side, to prevent damage to internals of main valve andpilot valve.

ii. Electromatic Relief Valves should be stored in the original shipping crates in a dryenvironment to protect them from the weather. They should not be removed from

the crates until immediately prior to installation.iii. End covers and sealing plugs i.e. both inlet and outlet should not be removed until

the valve is ready to be installed on the system.iv. Electromatic Relief Valves, either crated or uncrated, should never be subjected to

sharp impact. This would be most likely to occur by bumping or dropping duringloading or unloading from a truck or while moving with a power conveyor, such as afork lift truck. While hoisting to the installation care should be exercised to, preventbumping the valve against steel structures and other objects.

v. Uncrated valves shall be moved only by lifting or hoisting using eye bolts, which are


25/28



Valves Engineering.



12.06.2010

located on the valve body near the discharge collarvi. When Electromatic Relief Valves are uncrated and the end covers removed

immediately prior to installation, meticulous care should be exercised to prevent dirt

and other foreign materials from entering the inlet and outlet ports while installing inplace.

Figure 1


26/28



Valves Engineering.



12.06.2010

5.0 DOS AND DONTS DOSi. Check the valves for damage.ii. Weld the valve assembly vertically within 1 .iii. Mount the controller rigidly and away from location of vibrations as indicated in

the section CONTROLLER INSTALLATION.iv. Slope down the impulse line towards the controller and provide a syphon.V. Check the power supply for correctness with respect to solenoid requirements.vi. Check the cut off switch in the solenoid for proper function.vii. Check the pressure switch of controller for correct range.viii. Check the connection and availability of M.O.V. in the controller.ix. Set or check the reseating pressure at the controller using a hydraulic hand pump

and ensure the pilot light function before setting the valve.x. Check the smooth action of the solenoid by pressing the solenoid.

DONTSi. Do not exceed the voltage drop at the solenoid (not at source) by more than that

indicated in section 8 ELECTRICAL SUPPLY.ii. Do not operate the Electromatic Relief Valve with the pilot valve spindle pressed

down by operating lever.iii. Do not operate the Electromatic Relief Valve with the cutout switch not connected


27/28



Valves Engineering.



12.06.2010

in the circuit for solenoid with DC power supply.iv. Do not subject the solenoid controller to over heating.V. Do not connect the impulse line without blowing the line clean.

vi. Do not attempt to set the blow down to 1% without checking the blow downsetting limits.

6.0 PRE STARTUP CHECKSA. FOR VALVES WITH 1537 VX CONTROL STATION AND 1539 VX CONTROLLER

i. Close the Isolating gate valve which is below the Electromatic Relief Valve.ii. Hold the pressure below the popping point and turn the control switch to

Automatic. Now the green light must go on, this indicates that the electricalsystem is alive

iii. Turn switch to manual and observe that the solenoid plunger goes to bottom of

stroke and depresses the pilot stem by 2.4 min (3/32") to 3.2 mm (1/8") max.The Red and Blue lights should now be on. The blue light indicates that the relay isenergized.

7.0 FACTORY SETTING VS FIELD SETTINGEvery BHEL Safety Valve is set and adjusted on steam before shipment from the factory.Blowdown adjustments are made as carefully and accurately as possible on the factorytest boiler. However, it must be recognized that actual field operating conditions may varyconsiderably from factory test condition. Final safety valve adjustments made on theactual installation is the best means of ensuring that the valve performs in conformanceto IBR, ASME and other applicable code requirements.

8.0 SITE PROBLEMS IN ELECTROMATIC RELIEF VALVES:

The general problems faced at various sites for the safety valves are:I. ERV-Dismantling of main Valve seat bushing:1) Use persuader wrench, with 3 feet long pipe. Apply torque in the anti clock wise

direction; at the same time hit the opposite end of the wrench with the sledgehammer,so that the seal contact is broken. Apply penetrating oil.

2) If there is a drag or siering and bushing is difficult to turn, do not force the bushing.Apply more penetrating oil.

II. ERV: Pilot Valve Leakage:Causes:1) Pilot valve seat damage2) Pilot valve retaining spring broken or became solid3) Pilot valve seat gasket damaged.

Remedy:1. Seat to be lapped/changed2. Change the parts.


28/28



Valves Engineering.


III. Solenoid not working/burnt out

Causes:1. Incorrect voltage2. Correct voltage but varying beyond tolerable 10% at the solenoid connection.3. Too high an ambient temperature4. Ash or debris collections on solenoid

Remedy:

1. Change the voltage or install new solenoid corresponding to available voltage2. Rectify the variation.3. Identify the source and reduce the ambient temperature or replace the solenoid with

new. Insulate if the same is sufficient.4. Clean and service the parts.

Spares and Service tools:

The recommended spare parts and service tools relapping kits, Reseating machine are tobe procured and stocked at every site for reconditioning of Safety valves. In the absenceof spare parts and service tools at site the servicing of Safety valves becomes difficult.Inch spanner sets are required for Safety valves. Use Master lapping plate forreconditioning ring laps used for Safety Valves.

Service tools and spares for ERV:

The persuader wrench, the lapping tools for main and pilot valves, and the recommendedspare parts are to be stocked at site for servicing of ERV.Dismantle Safety Valves without affecting the settings, Lap seats as per O&M, Measuresettings if component wise dismantling is required at site.

1) Spring setting2) Lift setting3) Upper Adj.Ring setting4) Lower Adj.Ring setting

5) Over lap setting

WRITEUP ON SAFETY VALVE & ERV

Documents

Transcript of WRITEUP ON SAFETY VALVE & ERV