COMMISSIONING OF BOILER PART III-HT PROCEDURE- THERMAL POWER PLANT

The first activity commissioning engineer will associate is Hydraulic Test of the Boiler.

Though the Hydraulic Test is erection activity and to be conducted by them only.

I will discuss the procedure of Hydraulic test of a Supercritical/subcritical unit .

Calculate the water  volume  of different section :-

a) Economiser b) Furnace  c) Super heater  d) Separator  and collector  d) Re heater

e) Start up system.

In  660MW unit the volume worked out is around 710 cu. metre. This is required to

calculate the chemical requirement for the test.( Ammonia and Hydrazine Hydrate)

The Unit shall be hydraulically tested for conformation to IBR code requirements.

                                                                                                                                     

It is preferable to do the hydraulic test of the complete Boiler (except Re-heater section)

in one stroke at the stipulated Hydraulic test pressure. If it is not possible to accomplish this,

the hydraulic test may be conducted in two sub stages.

Stage IA - Hydraulic Test of the drainable portion only may be conducted at a pressure

1.5 times the design pressure. Suitable dummies shall be provided at SH platen inlet link

pipes. After completing the hydrostatic test for drainable portion, the system will be

drained and vented for drying and released for subsequent work.

Stage IB – Later Hydraulic test for the entire system comprising both drainable and

non-drainable portions up to Boiler Stop valves is conducted at a pressure 1.5 times

the design pressure.

Stage II - This covers the total Reheat circuit comprising CRH lines starting from

CRH NRV, tap off lines emanating from CRH lines up to first isolation valve, HPBP

valve downstream line, Re heater hot reheat lines up to IV, LPBP lines up to LPBP valves .

                                                                                                                                                                                                                                                                                                    

                                                                                                                                                 

Air tightness test shall be performed before filling water in the Boiler (for carrying

out the hydrostatic test ). This is done to detect leakages due to valves left in open

position, forgotten gamma plugs, any cuts not observed by visual inspection etc.

For doing this station compressor should be ready to deliver air .

During testing at least two properly calibrated standard test pressure gauges of

suitable range calibrated from a NABL accredited laboratory are to be used. One of

the gauges is mounted at drum floor/near and the other near pressure raising pump.

The least count of the gauge should preferably be 1Kg/cm².

 

DM water of quality specified below containing 200 PPM of hydrazine and

having pH between 9.5 and 10.0 by addition of adequate quantity of ammonia

shall be used for Hydraulic test.

 pH at 25 ⁰C                                                   :  7 + 0.2

 Conductivity                                               :   < 0.2 m mho/cm

Total hardness                                             :  Nil

Total Silica                                         :            < 0.02 ppm

Chloride                                             :            Nil

Sodium                                             : 0.003 ppm

During testing the temperature of water should be above 21⁰C but should not exceed 49 ⁰C.

Availability of reciprocating type pressurizing pump (H and Q of the pumps):

(a) 600 Kg/cm^2, 30 LPM  and (b) 600 Kg/cm²,  50 LPM.

Availability of  reciprocating type  chemical injecting pump of 600 Kg/cm² & 12 LPM.

Alternatively, hydro test pump can be utilized as chemical dozing pump.

Availability of Boiler fill pump.

Availability of power supply to the motors of these pumps.

Availability of Temporary tanks, Temporary fill pumps and dosing pumps.

Availability of flood lights and 24V hand lamps.

Availability of reliable communications system such as walkie-talkie sets, telephones etc.

Availability of Fire Tender and Ambulance near the test area.

Readiness of stair-cases, platforms, hand rails, approaches etc.,

Delivery line of pressurizing  pump should be high pressure seamless pipe to withstand

the required test pressure.

While raising the pressure for the first time no individual should be allowed to enter

the Boiler house when the pressure in the Boiler is above 25 Kg/cm².

Medical assistance should be readily available.

Erection of the Boiler pressure parts is complete as per drawing. All necessary

welding jobs are complete, stress relieved and x-rayed. All gamma plugs are seal

welded. All Quality checks as per approved Erection FQP are also complete.

No welding including attachment welding  or welding on tube will be allowed subsequently.

Filled & signed copies of FQPs and Erection Protocols with exceptions highlighted

are handed over to the commissioning group.

Effective communication facility is available between Drum floor, pressurizing pump

area and other operating areas.

Sky climbers / Scaffolding arrangements are provided inside the Boiler. 

 A cross functional team to be formed to identify leaks at different portion of the boiler.

  

Boiler drain is suitably connected to storm water drain / DM plant neutralizing pit.

All  debris shall be removed manually from all pressure parts, buckstays etc.

All manhole closure plates  and header handhole caps are closed  and  bolted  or welded tight.

Check that hydrostatic test plugs are installed where necessary and gags are fitted correctly.

Verify that locking arrangements for spring supports are provided when required for stress compensation.

Before filling the boiler with water, an air tightness test is to be performed to detect

leakages due to valve left in open condition, X-ray plug forgotten, any cuts etc. not

observed by visual inspection. This will reduce the DM water consumption and time as well.

The  air should be filtered and free from oil and dust prior to entering the unit. 

Boiler is  to be pressurized with air  up to 2 Kg/cm² (G).

Before admitting air, close manholes, isolating valves in drain lines, branching lines

and vent lines including the vent valves in SH link, economizer link and separator link,

drain and test valves in official pressure gauge etc.

Boiler is inspected. The pressure is raised up to 25 Kg/cm² and a thorough inspection of the

Boiler is done. For Stages IA & IB the pressure is raised in steps and held for 10 minutes at

100 & 200 Kg/cm². The rate of rise of pressure should not be more than 10 Kg/cm² per minute

up to approximately 80% of the test pressure and should be 1 to 2 Kg/cm² per minute beyond

that value. The required test pressure shall never be exceeded by more than 6%.

Hand tighten safety valve gags at 80% of pressure of lowest safety valve set pressure.

After reaching the test pressure the pressurizing pump is stopped immediately and power

supply to the pump is cut off.

Pr gauge showing the Hydro test Pressure 106 kg/cm2 ( Re  heater)

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