Steam Blowing BHEL

STANDARD PROCEDURE FOR STEAM BLOWING (210 MW)

PURPOSE

The purpose of steam blowing is to descale and remove foreign material from steam

pipelines leading to turbine in order to avoid damage to turbine from such material in the

course of normal operation.

PRINCIPLE

Steam blowing is carried out by puffing method.

a. Dislodge rust/scales from pipe work by thermal shocks.

b. High momentum of expanding steam in the pipe work purges out loosened

material.

It is required to create a higher momentum during steam blowing than possible during

operation of the unit including valves wide open (VWO) condition of the turbine. This is

applicable for all steam piping leading to turbine.

Disturbance factor is the measure of ratio of momentum during steam blowing to the

momentum at TMCR condition.

Disturbance Factor = MSB X VSB / MMCR X VMCR

Where:

MSB – Mass flow of steam during blowing

VSB – Specific Volume of steam during blowing

MMCR – Mass Flow of steam of MCR condition

VMCR – Specific volume of steam of MCR parameters.

In case of HP and LP bypass system blowing is carried out to avoid any damage later to

valve intervals due to foreign material.

Sharp elbows, miter bends and tees are to be avoided as these contribute to increased

pressure loss, under steam blowing conditions. Also care to be taken in piping and

contour to avoid critical velocities within the piping.

Procedure

The boiler is to be started in normal manner following start up procedure. All normal

recommendations and limitations with respect to fuel firing equipments, draft plant,

drains and vents, instrumentation, interlocks, protections etc. should be taken care of as

if the unit is started to synchronise the generator with the grid.

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The procedure is to raise the boiler pressure to 40 kg/cm2, shut of firing and same time

open temporary valve/boiler stop valve (blow off valve). The steam lines which are

blown should be warmed up prior to blowing. The opening of blow off valve allows steam

to escape to atmosphere at high velocity carrying with it loose and dislodged debris. To

prevent thermal stresses in the thick walled shell like drum and headers the saturation

temp. Change in drum is limited to 40 deg C maximum. Hence, for the purpose steam

blowing of all critical piping the blow off valve will be opened at 40 kg/cm² and closed at

19-kg/cm²-drum pressure.

The water level in the drum swings beyond visible limits at the start, during and at the

end of steam blowing. There are chances of water droplets to get carried over to the

saturated steam pipes and low temp. superheater. This can possibly be minimized by

keeping the water level in the drum at the lowest port (visible limit) before the start of

each steam blow off.

All the steam lines are purged in parallel and it is standard practice to limit number of

blows per day to 8 with an interval 1-1/2 hrs. For cooling in addition to overnight

cooling.

Stage –I SHà MS lines à ESV à Out

Stages – II A SHà MS lines à ESV à CRH à Out at Blr. End.

Stage – II B SH à MS lines à HPBP à CRH à Out at Blr. End.

Stage – III A SH à MS lines à ESV à CRH à RH à HRH à IV à Out

Stage – III B SH à MS lines à ESV à CRH à RH à HRH à LPBP à

Out at cond. End.

Preparation

Estimated quantity of DM water requirement for steam blowing is about 5000 M3. Fuel oil

requirement for the same has been estimated as 2000 MT.

Target plate assemblies are to be located in the temporary exhaust pipes, nearest

possible to the permanent pipe work. Sufficient quantity of carbon steel and stainless

steel polished target plates are to be kept ready.

Boiler should be ready in all respects including interlocks, protections, chemical dozing

system, instruments etc, as if the unit is started to synchronise the generator with grid.



Precautions

The temporary discharge piping should be well supported to withstand reaction forces

during blowing. The steam must be exhausted to atmosphere outside the turbine hall

building and so directed that personnel and equipment are not damaged or endangered.

The area should be cordoned off and notices displayed prominently.

For thermal expansion of the pipe, proper allowances must be given. First steam blow in

every stage should be given at a lower pressure, say 25 kg/cm² at boiler drum and the

pipe lines including temporary piping is surveyed for proper expansion and supports.

All the permanent and temporary piping must be insulated before the beginning of steam

blowing operations.

The furnace exist gas temperature should be limited to 540°C to safeguard superheaters

and reheaters.

Sufficient storage of DM water should be ensured and the rate of make up water to feed

tank is to be matched taking into account the capacity of feed tank.

Internal Boiler water treatment to be carried out with liquid Ammonia and Hydrazene

Hydrate only, to maintain a pH value of 10.0 in Boiler water and 5 to 25 ppm of N2H4 in

feed water. Total dissolved solids in boiler water should not exceed 10.0 ppm before

going in for steam blowing. If it is more, rinse the boiler till it comes down to less than

10 ppm.

Hot tightening of flanges, studs/bolts is to be done wherever such connections have

been made.

Drain going to any vessel should be left open to atmosphere suitably outside TG Hall.

Before normalizing, the drain pots should be inspected.

It should be ensured that all permanent hangers of the various lines should be erected

as per drawing and all values set accordingly to the design figures. Also ensure that he

locking of all hangers is removed, which would have been done for hydraulic test before

steam blowing.

Remove all strainer elements before start of steam blowing.

Down stream lines of ESV, IV and LP bypass valves are to be manually cleaned.

Ensure no loose debris / extraneous materials are left inside the permanent / temporary

pipe work.

Flow nozzles, Control Valves, NRV flaps and attemperators are not to be erected before

steam blowing of lines for cleanliness.



Any loops coming in the system which is steam blown should be checked after steam

blowing. Spool pieces are to be erected in its place wherever applicable.

Steam blowing of steam lines are to be started after hydraulic test of respective lines /

pressure parts.

Steam blowing of Auxiliary steam lines.

a) These lines are to be blown by continuous blowing for about 20 to 30 minutes at

a pressure of 50% of their normal operating pressure.

b) Precaution to be taken of control valves etc; as mentioned in item 13 above.

c) Lines, which are to be made ready before boiler first light up should be blown

with external steam source.

Note: Boiler and main steam valves will be inspected for tightness during drum and

superheater safety valve floating. Tightness is to be checked by keeping MSSV closed,

raising the SH pressure to MCR conditions and opening the drain lines downstream of

MSSV. Valves will be serviced if passing is established.

Completion Criteria

Indications for the result of each blowing period is the number of pitting found on the

target plate. The highest velocity of steam is in the center of the pipe. Hence judgement

should be made for the end point of steam blowing in this area. The area for the above is

3/4th the discharge pipe diameter at the center. It is recommended to install the target

plate after completing few blows in each stage.

For evaluating the cleanliness and termination point of the steam-blowing, target plate

of stainless steel are to be used. For initial stages, target plate of carbon steel is to be

used.

The results of the blowing operations can be judged by the absolute number of pitting on

the target plate in the central zone. The piping is considered clean if there are not more

than five pitting and shall not have any deformed edges. Besides there shall be no pitting

in the rim zone.



STEAM BLOWING BOM

VALVES

1. 10 NOS-GV / Nb 400 / NP 64 / BW

2. 4 NOS-GV / Nb 50 / NP 64 / BW

3. Nb 2” – 1500 Class – 4 nos

4. Nb 2” – 800 Class – 2 NOS

5. Nb 1” – 800 Class – 2 NOS

6. Nb ½” – 800 Class – 4 NOS

7. Quick closing electrically optd. Valves – 2 Nos., Time full stroke 30 s – 1 min.

Nb 400 / NP 64 / BW

PIPES:

1. f 406.4 x 12.7 = 105 M

2. f 273 x 9.27 = 20 M

3. Nb 2” = 125 M

4. Nb 1” = 15 M

REDUCERS

1. f 406.4 x f 323.9 x 12.5 – 4 NOS

2. f 406.4 x 219.1 x 10 – 4 NOS

3. f 457.2 x f 406.4 x 12.7 – 4 NOS



BENDS:

1. LR ELBOW 90° f 406.4 x 12.5 = 10 NOS (45° = 7 NOS, 90° = 6 NOS)

2. LR ELBOW 90° f 323.4 x 9.53 = 5 NOS. (45° = 4 + 90° = 6 NOS)

3. LR ELBOW 90° f 406.4 x 12.5 = 10 NOS. (45° = 7 NOS, 90° = 6 NOS)

4. f 406 à 45° = 7 NOS

5. f 406 à 90° = 8 NOS

6. f 323 à 45° = 6 NOS

7. f 273 à 45° = 6 NOS + 4 NOS = 10 NOS.

SUPPORTING STRUCTURE:

15 MB 450 – 18 M

15 MB 400 – 24.5 M

15 MB 200 – 2.2 M

15 MB 125 – 5.8 M

15 MB 300 – 7.5 M

15 MC 150 – 6.7 M

15 MC 100 – 74.6 M

15 MB 250 – 8 M – 298.4 Kg



POSITION OF ISOLATION VALVES DURING STEAM BLOWING

Sequence of

Blowing

Isolation Valves

1&2 3&4 5&6 7&8 9&10 11&12 13&14

Main steam

line

O C C C C C C

Cold reheat

line

C O C C O C C

Hot reheat

line

C O C O C O C



O – Open

C – Close

HP bypass

line

C C O C O C C

LP bypass

line

C O C O C C O





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Steam Blowing BHEL