Slide 1
STEAM BLOWING
OBJECTIVESteam blowing of MS lines, CRH,HRH,SH,RH,HP & LP
bypass pipe lines of turbine is carried out in order to remove
welding slag, loose foreign materials, iron pieces, rust etc. from
the system, generated during manufacturing, transportation &
erection.PRINCIPLE OF STEAM BLOWINGTo ensure that sufficient
cleaning forces are applied to the piping, the steam momentum
during the steam blow must be equal to or greater than the steam
momentum at normal maximum load condition. The Cleaning Force Ratio
(CFR) is typically used to evaluate if satisfactory blow conditions
are obtained.
PRECONDITIONS FOR STEAM LINE BLOWINGChemical cleaning should be
completedSH primary and secondary de-superheater piping and RHs
emergency de-superheater piping ready for operationAll permanent
piping & temporary piping insulated and supports/hangers are
released with cold settingSilencer should be connected at temporary
pipe exitSoot blowing for APH should be availableMake up for
deaerator made readyMotor Driven BFP with all controls made
ready
8) Hydraulic test of the following lines completed:Feed LinesMS,
HRH, CRH LinesMS to Aux. PRDS LineAll other auxiliary lines
identified for steam blowing 9) Sampling system made ready10) All
safety valve disc installed after removing hydro-static plug in
drum(sub-critical), superheaters and reheaters11) Adequate
communication between control room, boiler and TG area ensured.
12) Flow nozzle, control valves and NRV flaps wherever
applicable should be not erected before steam blowing and suitable
spool pieces are erected. Strainers in the path should be
removed.
13) Required number of Target Plates and holder made
available
BASIC TECHNIQUE USEDPUFFING METHOD
PURGING METHOD / CONTINEOUS BLOW METHOD
To give a thermal shock to the contour being purged, to dislodge
the scale etc.
Procedure: Raise the boiler pressure to a pre-determined value
(40-60 kg/cm2), shut off firing and at the same time open the quick
opening valve(EOTV), thus allowing the steam to escape to atm. with
high velocity carrying with it the loose debris.PUFFING METHOD
The initial procedure is same as puffing method except shutting
off the firing during blowing.
Continuous firing till the completion of steam blowing.
Maintain constant pressure during the blowCONTINEOUS BLOWING
METHOD
STAGESSteam blowing done in stagesStage-1(a)- SH, MSL, ESV,
temporary lines from ESV to EOTV, EOTV to CRH line, CRH lines upto
boiler end with temporary exhaust pipe.
stage 1a end point will be concluded by observing the indents on
the target plate.
STAGE- 1(a)
STAGE- 1(b)
SH,MSL, HP bypass inter connection, hand operated valve mounted
in place of HP bypass valve and CRH lines upto Boiler end with
temporary exhaust piping.
In this stage 6 to 8 blows will be given through HP bypass lines
to ensure cleanliness of the limb.
EOTV will be kept closed. Manually Operated Isolation Valves in
HP bypass lines will be kept opened fully.
STAGE- 1(b)
STAGE-2(a)
1a plus reheater, HRH lines , Interceptor Valve and temporary
pipe.
CRH line along with attemperator shall be welded with reheater
before start of stage 2a. LP bypass lines shall be blanked during
stage 2a. Stage 2a end point will be concluded by observing the
indents on target plates
STAGE- 2(a)
STAGE- 2(b)
2a upto IV + LP bypass lines with temporary exhaust pipe.
Stage 2b blowing will be parallel blow in the path 2a & 2b.
LP Bypass blanks shall be removed for stage 2b. 4 blows will be
given through L.P. Bypass line to ensure cleanliness of the
limbs
STAGE- 2(b)
TARGET PLATE Generally Stainless steel panel Target plate set at
the first, sixth, ninth, twelfth purging, thereafter set target for
each purging until purging results qualified . Width about 8% of
the steam vent tubes inner diameter(ID) and length equal to ID
Brinell hardness < 90 Steam velocity 258 m/sec Target plates to
be introduced just before steam blowing / light upto be removed
soon after blowing is completed.
STEAM BLOWING COMPLETION CRITERIA At least 2 continuous target
plates should not have ORIFICE GRANULARITY on the target shall be
not larger than 0.8 mm
No impacts with a diameter larger than 1 mm.
Not more than 4 impacts with a diameter larger than 0.5 mm. Not
more than 10 impacts with a diameter of 0.2 to 0.5 mm .
Final SH
Final SHESVESVMartyr V/vMartyr V/vHP BypassCRH LineCRH NRVCRH
Drain PotRH O/L HdrHRH Line
MSVLP BypassIP SV
OpenCloseMartyr Valve
Steam Blow Line
Temporary LinePre Step # 1 : MS Line Steam Blowing
Final SH
Final SHESVESVMartyr V/vMartyr V/vHP BypassMS LineCRH NRVCRH
Drain PotRH O/L HdrHRH Line
MSVMSVLP BypassIP SV
OpenCloseMartyr Valve
Steam Blow Line
Temporary LinePre Step # 1 : MS Line Steam Blowing
LPBP V/ v
Final SH
Final SHESVESVMartyr V/vMartyr V/vHP BypassMS LineCRH LineCRH
NRVCRH Drain PotRH O/L HdrHRH Line
MSVMSVLP BypassIP SV
OpenCloseMartyr Valve
Steam Blow Line
Temporary LinePre Step # 2 : HPBP / CRH Line Steam Blowing
Final SH
Final SHESVESVMartyr V/vMartyr V/vHP BypassMS LineCRH LineCRH
NRVCRH Drain PotRH O/L HdrHRH Line
MSVMSVLP BypassIP SV
OpenCloseMartyr Valve
Steam Blow Line
Temporary LineMain Step # 1 : HRH Line Steam Blowing
Final SH
Final SHESVESVMartyr V/vMartyr V/vHP BypassMS LineCRH LineCRH
NRVCRH Drain PotRH O/L HdrHRH Line
MSVMSVLP BypassIP SV
OpenCloseMartyr Valve
Steam Blow Line
Temporary LineMain Step # 2 :LPBP Line Steam Blowing
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