This document discusses water chemistry and corrosion control in HRSGs. It describes the components of HRSGs, including economizers, steam drums, evaporators, and superheaters. It outlines treatment methods for different sections of the HRSG to control corrosion and deposition, including phosphate and volatile amine treatments. It also discusses common corrosion mechanisms like pitting, crevice, and stress corrosion cracking that can occur in HRSGs and outlines best practices to minimize corrosion.

1. 1
HRSG Water Chemistry and
Corrosion control
Prepared by:
Md. Abdul Hannan
Plant Chemist, MPL.
9th July, 2018

2. 2
HRSG
HRSGHRSGs consist of four major components: the Economizer, Steams consist of four major components: the Economizer, Steam
Drum, Evaporator and Super heater.Drum, Evaporator and Super heater.
MPLMPL’s’s HRSGHRSGs are multi pressure, its triple pressure steam drumss are multi pressure, its triple pressure steam drums
consist of three sections: (i) an LP (low pressure) section, (ii) aconsist of three sections: (i) an LP (low pressure) section, (ii) a
reheat/IP (intermediate pressure) section and (iii) an HP (highreheat/IP (intermediate pressure) section and (iii) an HP (high
pressure) section.pressure) section.
Each section has a economizer, a steam drum and an evaporatorEach section has a economizer, a steam drum and an evaporator
section where water is converted to steam.section where water is converted to steam.
Steam then passes through super heaters to raise the temperatureSteam then passes through super heaters to raise the temperature
and pressure past the saturation point.and pressure past the saturation point.

3. 3
.
.
DMW TP
Compressor
Washing
CCW HT Dozing T
Condensate
make-up
CEP
Discharge
LP Econo LPD during
start up
LP Evaporator
LPSH
BFP
HP Economizer
HPD
HP Evap
IP EcoHPSH
IPDIPSH
Condenser
Water box
priming

4. 4
Meghnaghat - HRSG
IP Steam
Drum
30 Bar
HP BFW
RH Steam
SH HP Steam
HP Steam
Drum
100 Bar
HP Let-Down
HP
Evap
HP
Evap
RH
SH
2
IP
SH
RH
SH
1
HP
SH
1
HP
SH
2, 3
LP
SH
IP BFW
LP Steam
Drum
3.2 Bar
LP Steam
Cold RH Steam
IP
Evap
LP
Evap
HP
Econ
3
HP
Econ
1
HP
Econ
2
IP
Econ
LP BFW
HP BFW
IP BFW
LP Heater
Pegging Steam

5. 5
System Parameters Limit Value Measurement
CEP pH 9.7~9.9 9.80
Discharge Cond’ty, µs/cm 14~20 15.30
Dissolved O2 (ppb) 10~20 14
HP Drum pH 9.4 ~ 10.0 9.63
Cond’ty, µs/cm <40 11.50
Silica ppb <500 200
PO4 ppm 3~5 3.00
Iron ppm <0.5 0.21
IP Drum pH 9.4 ~ 10.0 9.82
Cond’ty, µs/cm <100 21.30
Silica ppb <1000 380
PO4 ppm 5~8 6.30
Iron ppm <0.5 0.20
LP Drum pH 9.5~9.7 9.60
Cond’ty, µs/cm 9~14 9.62
HP SH Steam PH
9.4~10 9.64
Cond’ty, µs/cm 5~20 9.76
Silica ppb <20 10.60

6. 6
CCW TreatmentCCW Treatment
The treatment chemicals of CCW are: (i) Nitrite based corrosionThe treatment chemicals of CCW are: (i) Nitrite based corrosion
inhibitor (Bulab-9077/9079/9316 ) and biocide to kill micro-inhibitor (Bulab-9077/9079/9316 ) and biocide to kill micro-
organism (Bulab-6057).organism (Bulab-6057).
pHpH
ConductiConducti
vityvity IronIron
TurbidTurbid
ityity NitrateNitrate NitriteNitrite
CorrosiCorrosi
onon TBCTBC RemarksRemarks
µs/cmµs/cm mg/lmg/l NTUNTU
mg/lmg/l
as NOas NO33
mg/lmg/l
as NOas NO22 mpympy
TotalTotal
volumvolum
e=e=
125m3125m3
8.5-10.58.5-10.5 <3000<3000 0 - 20 - 2 0-200-20 600-1200600-1200 <5<5 <10000<10000
9.949.94 22702270 0.500.50 0.590.59 872872 780780 0.003570.00357 <100<100

7. 7
Risk Assessments for Silica
measurements
Reagent
Hazards Identifications (0 - 4 scale),
0=Insignificant,1=slight,2=moderate,3=high,4=extreme
Health
Rating
Flammability Reactivity
Contact
Rating
Citric Acid F 1 0 0 Irritation
Molybdate 3 3 0 1 Irritation
Amino Acid
F
2 1 0 Irritation

8. 8
Precautionary Measures & PPE
for Silica Measurements
Precautionary Measures:
Avoid contact with eyes
Do not breathe dust/fume
Wash thoroughly after handling under fume hood.
Keep away from: Oxidizers reducer’s alkalis.
Personal Protective Equipment (PPE):
Eye Protection: Safety glasses with top and side shields
Skin Protection: Disposable latex gloves, lab coat/cloth uniform
Inhalation Protection: Work under Laboratory fume hood

9. 9
Internal Treatment of Boiler
(for maintenance of high purity water conditions)
Objectives
– Control Corrosion
– Control Deposit Formation
– Hinder Scale Formation and Convert the Sticky Scale to Soft
Sludge.
– Maintain Steam Purity (parameters as per guideline)
– Maintain Steam Quality (% of moisture or H20 carry over)

10. 10
Deposit Formation
Deposition rate increases with heat flux
(Heat flux: the rate of heat energy transfer through a given
surface.)
Deposits are mainly Iron Oxides – (i)Fe2O3 (Hematite-reddish) and
(ii)Fe3O4 (Magnetite -blackish).
Start from feed water (condensate), within the boiler and
economizers.

11. Deposition Effect
Reduces Heat Transfer/Efficiency
Increases tube wall temperature
Induces corrosion and cracking through grain boundary of metal.
Ultimately - Tube failure

12. Effect of Deposition on Heat
Transfer
260 °C260 °C
WatersideWaterside
320 °C320 °C
FiresideFireside
430 °C430 °C
FiresideFireside
260 °C260 °C
WatersideWaterside
CombustionCombustion
GasesGases
Tube MetalTube Metal
InsulatingInsulating
ScaleScale
Scaled TubeScaled Tube
SurfaceSurface
Clean TubeClean Tube
SurfaceSurface

13. During High Pressure
Boilers Start-Up
Will experience
High iron in boiler water
Temperature shock
– Resulted exfoliation of magnetite layers
Excessive iron deposition in High Heat Flux Zone
- Need to increase blow down (2-3%)
High silica in boiler water & steam
- Need to blow down

14. Boiler Deposit Control
Removal of Impurities (External Treatment)
Internal Chemical Treatment control
Dissolved Oxygen level control ( By dearation)
Proper Blow down

15. ASME Boiler Feedwater Quality Guidelines for
Modern Industrial Water-tube Boilers
Drum Pressure
(psig)
0 - 300
301 - 450
451 - 600
601 - 750
751 - 900
901 - 1000
1001 - 2000
Iron
(ppm Fe)
0.10
0.05
0.03
0.025
0.02
0.02
0.01
Copper
(ppm Cu)
0.05
0.025
0.02
0.02
0.015
0.015
0.01
Hardness(ppm
CaCO3)
0.30
0.30
0.20
0.20
0.10
0.05
0.0

16. Chemical Treatment for
HP,IP & LP Boilers
For HP & IP Boilers:
-Phosphate Treatment
(Na3 PO4 or Na3PO4 +Na2HPO4)
For LP Boiler:
-All Volatile Treatment
( NH3 or Amines)

17. Magnetite Formation
( Fe3O4 )
protective oxide film

18. 18
Corrosion
Corrosion specifically refers to any process involving theCorrosion specifically refers to any process involving the
deterioration or degradation of metal components by chemical ordeterioration or degradation of metal components by chemical or
electrochemical reaction with its environment and can take placeelectrochemical reaction with its environment and can take place
internally as well as on the surface.internally as well as on the surface.
No metal is truly insoluble, and all have a tendency to pass intoNo metal is truly insoluble, and all have a tendency to pass into
solution. The solubility depends on the attraction of valence spinsolution. The solubility depends on the attraction of valence spin
electron to the nucleus i.e. field of pure potentiality of the atom.electron to the nucleus i.e. field of pure potentiality of the atom.
The de-coference of electron depends on the availability ofThe de-coference of electron depends on the availability of
electron coordinator, acceptor or donor environment as well aselectron coordinator, acceptor or donor environment as well as
friction of the environment with the valence energy levels of thefriction of the environment with the valence energy levels of the
metal. The lower the attraction force the higher is the solubility. Itmetal. The lower the attraction force the higher is the solubility. It
also depends on the attraction of the available electronegative ionsalso depends on the attraction of the available electronegative ions
(O(O--
, Cl, Cl--
, F, F--
etc.) or radicals (OHetc.) or radicals (OH--
, SO, SO44
----
, CO, CO33
----
, HCO, HCO33-, PO-, PO4-4-
----
etc.) of theetc.) of the
environment and friction between the metal atom & waterenvironment and friction between the metal atom & water
molecules due to high water flow velocity.molecules due to high water flow velocity.

19. 19
Corrosion occur when metal ions transfer from the base metal toCorrosion occur when metal ions transfer from the base metal to
water.water.
Corrosion products that are formed in the boiler or transported to
the boiler can deposit and impede heat transfer, causing tube
metal overheating. They can also act as a concentrating
mechanism for boiler water salts, yielding metal loss by corrosion.
At high temperatures, Fe will corrode atAt high temperatures, Fe will corrode at PPH < 9 produces ferrousH < 9 produces ferrous
and ferric ions and consequently ferrous hydroxideand ferric ions and consequently ferrous hydroxideFe (OH)Fe (OH) 22
,ferric hydroxide,ferric hydroxide Fe (OH)Fe (OH) 33 and at very alkaline conditions,and at very alkaline conditions,
complex HFeOcomplex HFeO22
--
ion. The corrosion products - hematite (Feion. The corrosion products - hematite (Fe22OO33) and) and
magnetite (Femagnetite (Fe33OO44) are solid and important iron ore constituents) are solid and important iron ore constituents
and protective under thisand protective under this PPH condition.H condition.

20. 20
Types of Corrosion
– FAC/Erosion ( for high velocity fluid flow)
– Pitting (for high Dissolved Oxygen)
– Acidic
– Embrittlement( hydrogen, caustic)
– Crevice
– Intergranular
– Fatigue cracking
– Stress corrosion cracking
– Other general corrosion of iron and copper etc.

21. 21
Crevice Corrosion of StainlessCrevice Corrosion of Stainless
SteelSteel

22. 22
Stress Corrosion Cracking ofStress Corrosion Cracking of
Stainless SteelStainless Steel

23. 23
Pitting CorrosionPitting Corrosion

24. 24
Corrosion FatigueCorrosion Fatigue

25. 25
Galvanic corrosionGalvanic corrosion

26. 26
Erosion / FAC
““Flow accelerated/Assisted Corrosion (FAC)”Flow accelerated/Assisted Corrosion (FAC)” oror “Erosion-“Erosion-
Corrosion”Corrosion” is a flow-induced corrosion process that increases theis a flow-induced corrosion process that increases the
rate of thinning of pressure part components due to excessiverate of thinning of pressure part components due to excessive
water flow velocity specially where steam-water mixture phase.water flow velocity specially where steam-water mixture phase.
Turbulence or high flow velocities contribute significantly by
rapidly transporting dissolve Iron from metal surface to the bulk
water.
Two-phase FAC can occur in the LP evaporator circuits whichTwo-phase FAC can occur in the LP evaporator circuits which
typically operates around 60 – 70 psi (0.4 - 0.5 MPa) with atypically operates around 60 – 70 psi (0.4 - 0.5 MPa) with a
temperature about 150temperature about 150OO
C(300C(300OO
F).F).
Equipment vulnerable to erosion includes turbine blades, low-Equipment vulnerable to erosion includes turbine blades, low-
pressure steam piping and heat exchangers that are subjected topressure steam piping and heat exchangers that are subjected to
wet steam. Feed water and condensate piping subjected to high-wet steam. Feed water and condensate piping subjected to high-
velocity water flow are also susceptible to this type of attackvelocity water flow are also susceptible to this type of attack
Damage normally occurs where flow changes direction.Damage normally occurs where flow changes direction.

27. 27
FAC (Erosion-Corrosion)FAC (Erosion-Corrosion)
FAC damage to header.FAC damage to header.

28. Sl. No.
MPL
HRSG’s
Ves s els
Code
S pecificati
on Grade Alloy Type
Main
Compos iti
on
Maximum
us eful
Temperatu
re,
o
F
1 HPEV tu be S A 178 C
C = 0.06 -
0.18%
2 HPEC tu be S A 178 C
C r,Mo
n e gl i gi bl e
3 IPS H tu be S A 178 A
C u abs e n t
an d
4 IPEV tu be S A 178 A
Ni trace
l e ve l .
5 IPEC tu be S A 178 A
6 LPS H tu be S A 178 A
7 LPEV tu be S A 178 A 850
8 LPEC tu be S A 178 A
C arbon
S te e l
9
HPEV
He ade r S A 106 C
C =0.25 -
0.35%
10
HPEC
He ade r S A 106 C C r = 0.4%
11
IPS H
He ade r S A 106 B C u = 0.4%
12
IPEV
He ade r S A 106 B Mo = 0.15%
13
IPEC
He ade r S A 106 B Ni = 0.4%
14
LPS H
He ade r S A 106 B
15
LPEV
He ade r S A 106 B
16
LPEC
He ade r S A 106 B
17
HPS H
Tu be S A 213 T-22
Low al l oy
s te e l
18
Re h e ate r
He ade r(2) S A 335 P-22
21/4C r -
1Mo -1/2S i -
1/2Mn 1075
19
HPS H 3& 4
He ade r S A 335 P-22
20
Re h e at
tu be S A 213 T - 91
21
Re h e ate r
h e ade r S A 335 P - 91
C r-Mo
al l oy s te e l
9C r - 1Mo -
1/2S i -
1/2Mn
22
HPS H 1 &
2 He ade r S A 335 P - 91
23 HP Dru m C = 0.35%
24 IP Dru m S A 515 70
C -S i -Mn
al l oy s te e l s
S i = 0.15 -
0.30%
25 LP Dru m
Mn =
0.90%
MPL HRSG's tubes, he aders & drum vesse ls Metallurgy :

29. 29
Methods for minimizing FACMethods for minimizing FAC
Replacement of carbon steal module with more resistant Cr alloyReplacement of carbon steal module with more resistant Cr alloy
metal (Only 2 % chrome can reduce material losses by a factor ofmetal (Only 2 % chrome can reduce material losses by a factor of
100 with respect to CS).100 with respect to CS).
Controlling the frequent forced outages & Lengthy start-up and
shutdown procedures
Controlling duct burner firing and temperatureControlling duct burner firing and temperature
Reduction of Flow rate/water velocitiesReduction of Flow rate/water velocities
Production and maintenance of protective oxide film.Production and maintenance of protective oxide film.
Pipe geometryPipe geometry
Maintain of high-purity water conditions.Maintain of high-purity water conditions.
-- PPH maintain in proper levelH maintain in proper level
-DO control in proper range-DO control in proper range
-PO-PO44 hide-out controlhide-out control

30. 30
Velocities / flow rate
The velocity at the top of the upstream tubes of LP evaporator is
very high. The calculated average velocities for Meghnaghat
HRSG are:
Row 1, header 1 – 65 ft/sec Row 2, header 1 – 53 ft/sec
Row 1, header 2– 43 ft/sec Row 2, header 2 – 36 ft/sec
Row 3, header 2 – 29 ft/sec Row 1, header 3 – 25 ft/sec
Row 2, header 3 – 20 ft/sec Row 3, header 3 – 17 ft/sec
25 ft/sec velocity is a safe with respect to the pressure range of
MPL’s HRSG.
The velocities will be higher at the ends of the header where the
tube sees bypass flow and absorbs more heat.

31. 31
Protective oxide filmProtective oxide film
To cover and retard the base metals from the corrosion attack,To cover and retard the base metals from the corrosion attack,
magnetite(Femagnetite(Fe33OO44) layer need to produce on the metal surface) layer need to produce on the metal surface
exposed to water or steam. The solubility of magnetite changesexposed to water or steam. The solubility of magnetite changes
withwith PPH, temperature and oxygen content of environment of theH, temperature and oxygen content of environment of the
metal.metal.
Additional films of deposits, scale and corrosion products, hinderAdditional films of deposits, scale and corrosion products, hinder
heat transfer of material surface. Considerable level of DO ( say 5heat transfer of material surface. Considerable level of DO ( say 5
– 15 ppb ) passivate and stabilize the protective oxide film on steel– 15 ppb ) passivate and stabilize the protective oxide film on steel
surface as well as protect the thinning tendency of black Fesurface as well as protect the thinning tendency of black Fe33OO44..

32. 32
pH maintain
LowLow PPH and very highH and very high PPH increase wear.H increase wear.
LowLow PPH or insufficient alkalinity can result in corrosive acidicH or insufficient alkalinity can result in corrosive acidic
attack.attack.
HighHigh PPH or excess alkalinity can result in caustic gouging/crackingH or excess alkalinity can result in caustic gouging/cracking
and foaming with resultant carryover.and foaming with resultant carryover.
To minimize the fluctuation and keep in most optimum stableTo minimize the fluctuation and keep in most optimum stable
range of therange of the PPH values of LP evaporator circuits need toH values of LP evaporator circuits need to
standardize the feed rate of Ammonia. The NHstandardize the feed rate of Ammonia. The NH33 feeding accordingfeeding according
to the specific conductivity rather thanto the specific conductivity rather than PPH values led to goodH values led to good
maintenance and elevation ofmaintenance and elevation of PPH in the LP system.H in the LP system.

33. 33
NHNH33
** NH** NH33 has less electrical conductivity, boiling point ( - 33has less electrical conductivity, boiling point ( - 33oo
C) &C) &
solubility (31% at 25solubility (31% at 25oo
C and 28% at 50C and 28% at 50oo
C). For high volatility &C). For high volatility &
alkalinity of NHalkalinity of NH33, it evaporate from the feed water and, it evaporate from the feed water and
preferentially distribute to the gaseous state and lowers the LPpreferentially distribute to the gaseous state and lowers the LP
evaporator’sevaporator’s PPH compared to the condensate extraction sample,H compared to the condensate extraction sample,
header area’s sample and LPSH sample. So, for the high volatilityheader area’s sample and LPSH sample. So, for the high volatility
&& PPH of NHH of NH33 , we can say:, we can say:
PPH of LP evaporator(say 9.50) < CEP (9.70) < Header’s area (9.8) < LPSH (10.00)H of LP evaporator(say 9.50) < CEP (9.70) < Header’s area (9.8) < LPSH (10.00)
( liquid state ) (liquid state) (liquid & gaseous state) (gaseous( liquid state ) (liquid state) (liquid & gaseous state) (gaseous
state)state)

34. 34
Relation between Ammonia,
Specific Conductivity and P
H
Sl. No. Specific
Conductivity,
μS/cm
Resultant PH from
Ammonia
NH3, ppm
1 1 8.6 0.07
2 2 8.8 0.18
3 3 9 0.3
4 5 9.2 0.65
5 6 9.3 0.8
6 7 9.4 1.1
7 9 9.5 1.7
8 11 9.6 2.5
9 14 9.7 3.7
10 15 9.75 4.6

35. 35
Effects of DOEffects of DO
Absent or very low dissolved oxygen levels increase risk of wear.Absent or very low dissolved oxygen levels increase risk of wear.
Always should maintain low level ( 5 – 15 ppb ) of oxygen toAlways should maintain low level ( 5 – 15 ppb ) of oxygen to
produce and maintain protective oxide film.produce and maintain protective oxide film.
High concentration of DO in the stream decrease the stability andHigh concentration of DO in the stream decrease the stability and
increase the solubility of the magnetic oxide layer.increase the solubility of the magnetic oxide layer.
Since Oxygen is a depolarizer, high level of DO leads to theSince Oxygen is a depolarizer, high level of DO leads to the
formation of pits i.e. pitting corrosion.formation of pits i.e. pitting corrosion.
High level causes the huge formation of non –protective porousHigh level causes the huge formation of non –protective porous
oxides such as hematite deposits.oxides such as hematite deposits.
Electrolytes in the water accelerate corrosion processes inElectrolytes in the water accelerate corrosion processes in
presence of oxygen.presence of oxygen.

36. 36
Outage Corrosion
When a Boiler is laid up for banking purposes, the boiler pressure
drops gradually and then a rarefaction (Vacuum) develops in the
drum that cause air infiltration and enrichment of boiler water
with oxygen then occur oxygen corrosion.
Even when water completely removed from the boiler system, its
internal surface remain wet and then from air oxygen contributes
to the development of electrochemical corrosion.

37. 37
Guidelines of DO
Some industry guidelines of feed water DO are given bellow:
Industry DO (ppb)
TETRA Engineering 2
Electric Power Research Institute
(EPRI)
5
American society of mechanical
engineering (ASME)
<7
Technical Association of the pulp and
paper industry (TAPPI)
7
Humane Resources in Science and
Technology (HRST)
5 - 15

38. 38
Used Guidelines of DO &Used Guidelines of DO & PPHH
in MPLin MPL
(* means for single phase and ** means for two phase circuits in the(* means for single phase and ** means for two phase circuits in the
below table)below table)
ExpertsExperts PPHH DODO
GE-BetzeGE-Betze •*9.0 – 10.0*9.0 – 10.0
•** 8.5 – 9.5** 8.5 – 9.5
NilNil
TETRA Eng.TETRA Eng. •*9.0, >9.2*9.0, >9.2
•** 8.8** 8.8
*2.0*2.0
**0.1**0.1
HRSTHRST •*9.0 – 10.0*9.0 – 10.0
•** 9.3 – 9.7** 9.3 – 9.7
7.0, 5 -15, 10 - 207.0, 5 -15, 10 - 20
MPL’s existing practiceMPL’s existing practice •*9.4 – 10.0*9.4 – 10.0
•** 9.5 – 9.9** 9.5 – 9.9
5 - 155 - 15

39. 39
Electrochemical reactions for
Corrosion
2Fe2Fe  2Fe2Fe2+2+
+ 4e+ 4e--
Oxidation reaction (at the anode)Oxidation reaction (at the anode)
OO22 + 2H+ 2H22O + 4e-O + 4e-  4 OH4 OH--
Reduction reactions (at the cathode)Reduction reactions (at the cathode)
2Fe+O2Fe+O22+2H+2H22OO  2Fe2Fe2+2+
+ 4OH+ 4OH--
2Fe (OH)2Fe (OH)22 ( overall )( overall )
COCO22 + H+ H22O + HO + H22OO  HH22COCO33  H+ + HCOH+ + HCO33--
Fe + 2HFe + 2H++
FeFe2+2+
+ H+ H22
Fe + OFe + O22 + 2H+ 2H++
-- FeFe2+2+
+ H+ H22OO
FeFe2+2+
-- FeFe3+3+
+ e+ e--
Oxidation reactionOxidation reaction

40. 40
Electrochemical reactions for
deposit & film Formation
4Fe (OH)4Fe (OH) 22 + O+ O22 + 2H+ 2H22OO  4 Fe (OH)4 Fe (OH) 33
Fe (OH)Fe (OH) 22  FeO + HFeO + H22OO
2Fe (OH)2Fe (OH) 33  FeFe22OO33 + 3H+ 3H22O.Fe (OH)O.Fe (OH) 33  FeOOH + HFeOOH + H22OO
FeO + FeFeO + Fe22OO33  FeFe33OO44 (magnetite, ferrosoferic oxide of iron)(magnetite, ferrosoferic oxide of iron)
4Fe4Fe33OO44 + O+ O22  6Fe6Fe22OO33 + 4e+ 4e--
4Fe0
+ H2O + 3O2 ----------> 2Fe2O3 + H2O
higher temp.

41. 41
SiO2
Silica is real soluble in steam above a pressure of 20 bar.
The solubility of silica in steam is dependent upon the
concentration of silica in the drum water, alkalinity, the
temperature and the pressure.
Molybdate reactive Silica (H4SiO4 or H2SiO3), Hydrated, non-
ionized species (SiO2xH2O)
The colloidal silica are polymerized (dimmer or higher forms) and
is not react with molybdate but under boiler condition reverts to
the basic silicate monomer, which is reactive with molybdate.
Silica can causes the formation sticky silicate scales.

42. 42
Blow Down
Intermittent or Periodic or Manual blow down:
- Through a quick opening shut-off valve located in the lowest
part of the lowest boiler drum where more concentrated
suspended solids and sludge are present.
Continuous blow down :
- Through take –off line located in several inches below the low
water level ( or close to the bottom of the steam drum ) which
discharge most concentrated dissolved solid.

43. 43
Chemical cleaning of condenser
Usually perform by mineral acids (HF,HCl,HNO3,H2SO4 etc.)
HF is very effective but react with titanium.
HCl is very cheap but have chance of Cl-
attack.
HNO3 is safe with titanium but not with brass.
At first need to flash with water.
Filling and circulation, the acid solution.
Then neutralize the acid and finally flushing with water.

44. 44
Boiler preservation
There are many methods of preservation for preventingThere are many methods of preservation for preventing
corrosion when boilers are taken out of service.corrosion when boilers are taken out of service.
Dry preservation:Dry preservation: The shutdown boiler unit is allowed to coolThe shutdown boiler unit is allowed to cool
down,down, , all mains and pipelines are cut off by means of stoppers,
water drained when temperature will be around 100water drained when temperature will be around 10000
C so that noC so that no
water drops on inner surface of tube and closed all valves.water drops on inner surface of tube and closed all valves.
Preservation with Nitrogen: Filling the boiler system withPreservation with Nitrogen: Filling the boiler system with
Nitrogen gas and box up.Nitrogen gas and box up.
Wet Preservation:Wet Preservation: Filling the boiler system with alkaline waterFilling the boiler system with alkaline water
and holding it under excess pressure. Initial pH should beand holding it under excess pressure. Initial pH should be
maintained 10 – 10.5.maintained 10 – 10.5.
Hydrazine solution preservation: Filling the boiler system withHydrazine solution preservation: Filling the boiler system with
Hydrazine rich water and box up. Depends upon the duration ofHydrazine rich water and box up. Depends upon the duration of
shut down, concentration may vary, for a week 50 ppm Hydrazineshut down, concentration may vary, for a week 50 ppm Hydrazine

45. High or Low Boiler Water pH
Corrodes Boiler Steel
1 2 3 4 5 6 7 8 9 10 11 12 13 14
RELATIVE
CORROSIVE
ATTACK
pH
8.5 pH 12.7 pH
SAFE RANGE

46. Caustic Corrosion
Results from the concentration of caustic soda beneath scale
deposits or as a result of steam blanketing.
– Steam blanketing is a condition which permits stratified flow of
steam and water when a steam layer form between the boiler
water and the tube wall, usually occurring in a low heat input
zone such as a horizontal or included roof tube. Under this
condition insufficient water reaches on the surface for efficient
heat transfer.
Dissolves the protective magnetite layer.
Form irregular longitudinal patterns or caustic gouging.

47. Caustic Concentrate
Mechanism
Magnetite
NaOH
Steam Out
NaOH
Boiler Water in
Fe3O4 Porous
Deposit
NaOH
NaOH
NaOH
NaOH

48. Phosphate Hideout
Due to the solubility of phosphate decreases with the boiler’sDue to the solubility of phosphate decreases with the boiler’s
pressure & temperature increases,pressure & temperature increases, Phosphate hideout occur asPhosphate hideout occur as
-an increase of PO-an increase of PO44 concentration and a decrease of pH duringconcentration and a decrease of pH during
load reductionload reduction
-an increase of pH and decrease of PO-an increase of pH and decrease of PO44 concentration during theconcentration during the
load increases.load increases.
-Phosphate react with boiler iron & calcium scale and form a-Phosphate react with boiler iron & calcium scale and form a
solid soft phasesolid soft phase or precipitate to form a solid phase on the hot
boiler tube surfaces and elsewhere.
3Fe +2 NaOH3Fe +2 NaOH  NaNa22FeOFeO22
FeFe33OO44 + 4 NaOH+ 4 NaOH  NaNa22FeOFeO22 + 2NaFeO+ 2NaFeO22
CaCOCaCO33 + Na+ Na33POPO44 ---- CaCa33(PO(PO44))22 + Na+ Na22COCO33
Ca(HCOCa(HCO33))22 + Na+ Na33POPO44 ---- CaCa33(PO(PO44))22 + NaOH + CO+ NaOH + CO22

49. 49
High dozes of PO4High dozes of PO4
High dozes of PO4 increases the caustic concentration as well asHigh dozes of PO4 increases the caustic concentration as well as
increase the localized areas i.e. deposition on boiler tubes & pipes.increase the localized areas i.e. deposition on boiler tubes & pipes.
Caustic can concentrate in localized areas, when porous depositsCaustic can concentrate in localized areas, when porous deposits
are present on boiler surfaces. Water & NaOH can diffuse into theare present on boiler surfaces. Water & NaOH can diffuse into the
porous deposit and trapped. Water boils and produces relativelyporous deposit and trapped. Water boils and produces relatively
pure steam and diffuses out of the deposit, leaving a concentratedpure steam and diffuses out of the deposit, leaving a concentrated
NaOH residue behind. This concentrated residue causes severeNaOH residue behind. This concentrated residue causes severe
caustic “gouging” and dissolved the protective magnetite (Fecaustic “gouging” and dissolved the protective magnetite (Fe33OO44 ))
NaNa33POPO44 + H+ H22OO  NaNa22HPOHPO44 + NaOH+ NaOH
NaNa22HPOHPO44 + H+ H22OO  NaHNaH22POPO44 + NaOH+ NaOH
NaOH + HNaOH + H22O(Water)O(Water)  NaOH (concentrate)↓ + HNaOH (concentrate)↓ + H22O(Steam)↑O(Steam)↑
FeFe33OO44 + 4 NaOH (concentrated)+ 4 NaOH (concentrated)  NaNa22FeOFeO22 + 2NaFeO+ 2NaFeO22

50. Steam Purity Guidelines
Normal Operation
Parameter ABB G E Westinghouse Mitsubishi
Na, ppb < 10 <20 < 10 < 10
SiO2, ppb < 20 < 20 < 20 < 15
Total Fe, ppb < 20 < 20 < 5
Cu, ppb < 3 < 2
Cl, ppb < 15 < 2
Cationic
Cond. us/cm <0.2 < 0.2 < 0.3 < 0.2

51. Steam Purity Guidelines
Abnormal Operation (Westinghouse)
* Time refers to continuous time in the range and also to total time in a 12-month period in
the range
Parameter 2-week * 24-Hour * Immediate
Shut Down
Cation Cond.
us/cm
0.3 - 0.5 0.5 - 1.0 > 1.0
Na, ppb 10 - 20 20 - 35 > 35
SiO2, ppb 20 - 40 40 - 80 > 80
Cl, ppb 15 -30 30 - 50 > 50
SO4, ppb 15 -30 30 - 50 > 50

52. Carryover
Mechanical Causes
Steam separation equipment
Steam drum level
Steam load
Over Firing

53. Carryover
Chemical causes
Foaming
– TDS
– Alkalinity
– Organics/ Polymer Overfeeding
– Antifoam
Selective Vaporous Carryover :
(by drum pH, pressure and temperature)
– Silica
– Others - Cl, SO4

54. 54
InspectionInspection
Need to develop a FAC inspection program to plan every year toNeed to develop a FAC inspection program to plan every year to
establish initial “benchmark” readings & to determine theestablish initial “benchmark” readings & to determine the
“baseline” thickness from adjacent sections of the same pressure“baseline” thickness from adjacent sections of the same pressure
part. From these two sets of readings, determine detectablepart. From these two sets of readings, determine detectable
material loss rate.material loss rate.
Some areas will be easier to inspect using RVI ( Remote visualSome areas will be easier to inspect using RVI ( Remote visual
inspection ) by cutting pressure parts or entering viainspection ) by cutting pressure parts or entering via
drums/flanges/valves while other areas lend themselves to UTTdrums/flanges/valves while other areas lend themselves to UTT
(Ultrasonic Thickness Testing) measurement. UTT surveys can(Ultrasonic Thickness Testing) measurement. UTT surveys can
show a reduction in thickness at the chosen survey locationsshow a reduction in thickness at the chosen survey locations
without cutting.without cutting.
Some corrosion measurement techniques can be used on-line while
others provide off-line measurement. Corrosion monitoring is the
practice of measuring the corrosivity of process stream conditions
by the use of “probes” which are inserted into the process stream

55. 55
Corrosion measurement
techniques:
Non Destructive Testing(Direct,Off-line) Analytical Chemistry(Indirect,Off-line)
• Ultrasonic testing • pH measurement
• Radiography • Dissolved gas (O2, CO2, H2S)
• Thermography • Metal ion count (Fe2+, Fe3+)
• Eddy current/magnetic flux • Microbiological analysis
• Intelligent pigs
Operational Data (Indirect, On-line) Fluid Electrochemistry
• pH • Potential measurement
• Flow rate (velocity) • Potentiostatic measurements
• Pressure • Potentiodynamic measurements
• Temperature • A.C. impedance
Corrosion Monitoring (Direct, On-line)
• Weight loss coupons
• Electrical resistance

56. 56
Thanks.