FIELD OF THE INVENTION
The present invention relates to a method to measure fireside corrosion
resistance of boiler components of ultra super critical boiler using Indian coal ash
or fly ash at simulated boiler condition.
BACKGROUND OF THE INVENTION
Stainless steels are widely employed in boiler components wherever high
temperature and corrosion are expected. Stainless steels play an important role
as corrosion resistant including oxidation resistant material. Austenitic stainless
steels have high ductility, low yield stress and relatively high ultimate tensile
strength, when compared to typical carbon steel. With austenitic stainless steel,
the high chromium and nickel content suppress the phase transformation from
austenite to a mixture of ferrite and cementite, thus keeping the material fully
austenite on cooling.
Fireside corrosion in coal-fired power plants is a leading cause for boiler tube
failures. Online monitoring of fireside corrosion can provide timely data to plant
operators for mitigation implementation. This invention presents a novel
methodology of measuring the fireside corrosion resistance. Laboratory-scale
experiments demonstrated the feasibility of design, fabrication, and operation of

the sensor for fireside corrosion resistance. Corrosion metal loss resulted in a
proportional decrease in life of the boiler material. Laboratory experiments using
a tubular furnace with a simulated boiler environment demonstrated that ultra
super critical boiler material with Indian coal ash / Fly ash and at very high
temperature. Measured corrosion rates depend on temperature, with metal
thickness and corrosive environment.
The power generation industry around the world is under tremendous pressure
to generate a sufficient amount of power which is sustainable, affordable and
reliable; and meet the industrial, transport, and domestic requirements. Fossil
fuels (coal, oil and natural gas) are still the main sources used within the power
generation industry. Further, the conventional steam turbine power plants are
still widely used across the globe as the main source of power generation. The
demand of power is increasing, and so is the requirement of increasing the
efficiency of the plants. To increase the efficiency of the plant the superheaters
and reheaters tubes are known to be made by Ultra Super Critical Boiler grade
materials.
Fireside corrosion is a major problem for boiler plants and often a complicated
process. Metal loss is a superheater can occur due to oxidation, sulfidation
erosion-corrosion, or a combination of these. Chlorine-containing deposits may
also be one of the crucial factors causing the metal loss.

The most common metal degradation mechanism encountered in combustion is
oxidation. Oxidation takes place when the oxygen in the flue gas gets in contact
with the superheater steel surface. The oxidation of the alloy surface creates a
protective iron or chromium oxide layer which prevents diffusion of oxygen.
Because of the decreased diffusion, the oxidation rate slows down, and a stable
oxide layer is formed on the steel surface. This type of oxidation is called
selective, and the mechanism is widely used for protection against corrosion.
The oxidation rate constants depend on the metal, the temperature, and the
diffusion coefficient of oxygen through the oxide layer. If the diffusion rate
through the oxide layer is high, the oxide forms no protection against further
oxidation.
Sulfur corrosion, often referred to as sulfidation, is a very common phenomenon
in coal combustion, but it can also occur with other fuels. In the combustion
process, the sulfur in fuel reacts with oxygen in the combustion air forming SO2,
and, if the residence time and O2 content are sufficient, it also forms SO3. The
initial sulfidation reaction seldom continues so as to result in internal sulfidation
of the metal.

Chlorine-induced corrosion is a common corrosion type in waste combustion.
This type of corrosion can also take place in combustion of other chlorine-
containing fuels, for example biofuels and high-chlorine coals. Chlorine corrosion
is often accelerated by alkaline components in the fuel. At low temperatures,
chlorine corrosion can take place as hydrochloric acid corrosion, but in the case
of super heater corrosion, the mechanism is initiated when the fuel contain
sufficient amounts of chlorine, and the super heater tube temperature is
sufficient for chlorides to form molten eutectics.
United States Patent 7,678,471, entitled "Surface modification to improve fireside
corrosion resistance of Fe-Cr ferritic steels", teaches an article of manufacture
and a method for providing an Fe—Cr ferritic steel article of manufacture having
a surface layer modification for corrosion resistance. According to this prior art,
Fe—Cr ferritic steels can be modified to enhance their corrosion resistance to
liquid coal ash and other chemical environments, which have chlorides or sulfates
containing active species. The steel is modified to form an aluminide /silicide
passivating layer to reduce such corrosion.
United States Patent Number 4190421 describes an improved method of
introducing fuel additives into the fireside of coal fired boiler tubes to facilitate

removal of slag and like deposits from the fireside, to lower acid smut pollution,
to control corrosion, and to improve the electrical resistivity of particulate
emission. The improvement is achieved by addition of pulverized coal to the fuel
additive.
United States Patent 4796548 entitled "Method of conditioning fireside fouling
deposits using super large particle". According to this prior art, coal is fired in a
coal fired boiler of the type having a combustion zone, a convection zone located
downstream from said combustion zone and having a plurality of heater tubes
disposed therein adapted to heat water or steam disposed therein, and in which
the convection zone combustion residues emanating from said coal have a
tendency to stick to or agglomerate upon said tubes. The invention teaches a
method of decreasing said tendency to stick or agglomerate, comprising burning
said coal in the presence of an additive consisting essentially of super large
magnesium oxide particles, a major mass fraction of which is about 150 microns
in diameter or greater.
United States Patent 5314643 describes a process for inhibition of corrosion
caused by naphthenic acid and sulfur compounds during the elevated
temperature processing of crude oil by use of a corrosion inhibitor consisting of
Tri alkyl phosphate and an alkaline earth metal phosphonate-phenate sulfide.

United States Patent Number 4917968 discloses a structure which is resistant to
corrosion at high temperatures, and comprises a ductile layer of a platinum
group metal, such as iridium, and a layer of a refractory metal having a high
strength at high temperatures, such as rhenium. A solid solution of the two
metals is present between and metallurgically bonded to the two metal layers.
Further, the structure may include a layer of ceramic such as zirconia or hafnia
on the exposed face of the platinum group layer.
United States Patent Number 4960817, discloses a coating for metallic substrates
which provides corrosion inspection and is thermally stable at high temperatures.
It comprises a binder formed from a blend of a silicone resin and a silicone alkyl
co-polymer resin, a sacrificial anodic particle pigment such as zinc dust for
providing chemical protection against corrosion, a leafing pigment such as leafing
aluminum for providing barrier protection against corrosion, and solvents.
United States Patent number 6602355 teaches method for enhancing protection
of high temperature alloys containing iron, nickel and chromium against high
temperature corrosion by carburization or metal dusting by deposition a thin
layer of a metal selected from one or more of the noble metals, precious metals,
metals from groups IVA, IVB, and group VA, VB of the Periodic Table and

mixtures thereof with a thickness in the range of from 0.01 to 10 m on the
surface to be protected, and annealing the treated surface in an inert
atmosphere at a predetermined temperature for a sufficient time to render the
treated surface resistant to carburization or metal dusting.
United States Patent number 5135709 describes a method for lowering the
corrosion potential on components formed from carbon steel, alloy steel,
stainless steel, nickel based alloys, or cobalt based alloys, and exposed to high-
temperature water comprised of oxidizing species, comprising: providing a
reducing species in the high temperature water that can combine with the
oxidizing species, and forming the component to have a catalytic layer of a
platinum group metal.
United States Patent number 4028268 discloses metal corrosion inhibiting
compositions prepared by utilizing a selective and critical multicomponent
formulation comprising in combination functionally operative proportions of A
specific quaternized cyclic nitrogen base, A specific acetylenic alcohol, A surface
active agent, and A formic acid derivative. The above formulation can be
substantially improved by adding certain functionally operative additional
surfactants. The choice of these surfactants is unobvious and it has been found
that only a few critically selective species are operable for the purposes of the
invention.

United States Patent number 4917968 teaches a composite structure which is
resistant to corrosion at high temperatures comprises a ductile layer of a
platinum group metal, such as iridium, and a layer of a refractory metal having a
high strength at high temperatures, such as rhenium. A solid solution of the two
metals is present between and metallurgically bonded to the two metal layers.
Further, the structure may include a layer of ceramic such as zirconia or hafnia
on the exposed face of the platinum group metal layer.
EP 0958335 B1 describes a process for preventing high temperature corrosion.
An additive is sprayed into the combustion chambers of heating and waste
incineration plants to prevent high temperature corrosion and to reduce the fly
ash proportion in the exhaust gas. Also disclosed is a process for preventing
high temperature corrosion and for reducing the fly ash proportion in the
exhaust gas from heating and waste incineration plants. The disclosed additive
consists of acid activated bentonite and/or oxide metals, in particular glass
powder or glass dust with a melting point below 1000 deg. C, and is sprayed into
the gas chamber in areas in which the gas temperature exceeds 700 deg C.

SUMMARY OF THE INVENTION
According to the invention, there is provided a method to measure fireside
corrosion resistance of boiler components of ultra super critical boiler using
Indian coal ash or fly ash at simulated boiler condition. Initial weight as well as
the dimensions of a plurality of cut samples of base material and that of the weld
are kept over an alumina tray. A plurality of mixture prepared previously from
coal/fly ash (Indian coal ash/Indian fly ash), alkali sulfate and Sodium Chloride,
(of different composition) is kept covering all sides of the samples. A timer is set
to raise the inside temperature of resistance tubular furnace to a particular
temperature and for a known soaking hours.
The specimen is loaded under simulated boiler environment. The mixtures
consist of synthetic fly ash prepared from different combinations of Sulphate/
Chloride and actual coal ash/flyash. The temperature experienced by the
specimen is measured in the furnace by a thermo couple.
After each particular soaking hours, the sample is taken out and rinsed with
acetone is an ultrasonic cleaning machine. After that the samples are washed
with water and dried by using a dryer machine. The samples after drying out of
water and moisture, are weight weighed in a weighing machine.

Different temperature range applied to measure the corrosion rate, vary from
600°C, to 800°C. The time range for heating is varied and after every heating
cycle of a definite duration, the samples are cooled down to room temperature
and repeated the same procedure of weighing. Samples exposures were
continued with a fresh deposit mixture. The weight loss for particular
temperature range and after each heating cycle is tabulated. The dimensions of
the specimen are also measured with micrometer.
OBJECTS OF THE INVENTION
It is therefore an object of the invention a method to measure fireside corrosion
resistance of boiler components of ultra super critical boiler using Indian coal ash
or flyash at simulated boiler condition.
Another object of the invention is to propose a method to measure fireside
corrosion resistance of boiler components of ultra super critical boiler using
Indian coal ash or flyash at simulated boiler condition in which different types of
Indian coal ash/fly are used for measuring the fireside corrosion resistance.

A still another object of the invention is to propose a method to measure fireside
corrosion resistance of boiler components of ultra super critical boiler using
Indian coal ash or flyash at simulated boiler condition in which the composition
of synthetic fly ash is computed for measuring Fireside corrosion resistance.
Yet another object is to propose a method to measure fireside corrosion
resistance of boiler components of ultra super critical boiler using Indian coal ash
or flyash at simulated boiler condition in which the fireside corrosion resistance
property of the weld metal is further separately.
A still further object of the invention is to propose a a method to measure
fireside corrosion resistance of boiler components of ultra super critical boiler
using Indian coal ash or fly ash at simulated boiler condition in which free side
corrosion resistance property of different components of various types of ultra
super boiler components is measured.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a flow chart of the method for measuring fireside corrosion
resistance of boiler components according to the invention.

Figure 2 - shows a schematic of measuring fireside corrosion resistance in a
base metal specimen under simulated boiler condition operating with Indian coal
ash/fly ash.
Figure 3 - shows a schematic of measuring fireside corrosion resistance in a
weld specimen under simulated boiler condition operating with Indian coal
ash/fly ash.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows the method steps for measuring fireside corrosion resistance in
both base/weld metal specimen in simulated boiler condition operating with
Indian coal ash/ fly ash.
a) In a tubular furnace (1) having a tray (3), a test (base metal) (2) is
taken, and exposed to synthetic flyash of different composition of Indian
fly ash/ coal ash (4). A thermocouple (5) is inbuilt within the furnace (1)
to record the temperature. The specimen is pre weighed and dimensions
and thickness of the specimen are known. The specimen is kept in the
furnace (1) through an inlet having a leak proof gasket (7). Now the

specimen is exposed to fireside corrosive environment , so that the
specimen is under high temperature and corrosion environment. The
specimen is kept for a specific duration depending on the material. The
specimen is removed from the furnace (1) through an outlet (6).
b) The same method as described in (a) above is applicable for weld metal
region (2), all weld specimen is exposed to fireside corrosive
environment, so that the specimen is under high temperature and
corrosion environment. The specimen is kept for a specific duration
depending on the weld material. The specimens prepared from the base
metal as well as the welded specimens are taken for fireside corrosion
evaluation.

WE CLAIM :
1. A method to measure fireside corrosion resistance of boiler components of
ultra super critical boiler using Indian coal ash or flyash at simulated boiler
condition, comprising the steps of:
- preparing a plurality of specimen formed of a base material corresponding
to that of the boiler components;
- preparing a plurality samples of weld corresponding to that used in said
boiler components;
- determining individually initial weight including dimension of all the base
material specimen including that of the weld samples;
- preparing a plurality of mixtures formed of coal ash/ fly ash, alkali sulfate,
and sodium chloride, each of said plurality of mixtures being formed of
different composition of said constituent materials;

- setting a timer and activating a thermocouple in the boiler simulation and
placing the specimen/samples inside the simulator, the specimen/samples
being covered with one of said plurality mixture;
- raising the temperature in stages within the simulator corresponding to
that of resistance tubular furnace and allowing soaking of the
specimen/samples for predetermined period and recording simultaneously
the temperature through the thermocouple;
- taking out the specimen/samples after completion of soaking from the
simulator and cleaning with acetone in an ultrasonic cleaning machine;
- washing with water and drying the cleaned samples/specimen by a drying
machine; and
- measuring the weight and dimension of each specimen/sample to
determine the corrosion loss.

2. The method as claimed in claim 1, wherein the step of soaking is
reiterated at varied temperature and for different soaking period, and
wherein the specimen/samples are cooled down to room temperature
after completion of each heating cycle and covered with fresh mixture
before re-exposing to fresh soaking.
3. The method as claimed in claim 1 or 2, wherein the temperature range
varies between 600°C to 800°C.


the simulator corresponding to that of resistance tubular furnace and allowing
soaking of the specimen/samples for predetermined period and recording
simultaneously the temperature through the thermocouple; taking out the
specimen/samples after completion of soaking from the simulator and
cleaning with acetone in an ultrasonic cleaning machine; washing with water
and drying the cleaned samples/specimen by a drying machine; and
measuring the weight and dimension of each specimen/sample to determine
the corrosion loss.
{ FIGURE 1}

ABSTRACT

The invention relates to A method to measure fireside corrosion resistance of
boiler components of ultra super critical boiler using Indian coal ash or flyash
at simulated boiler condition, comprising the steps of: preparing a plurality of
specimen formed of a base material corresponding to that of the boiler
components; preparing a plurality samples of weld corresponding to that
used in said boiler components; determining individually initial weight
including dimension of all the base material specimen including that of the
weld samples; preparing a plurality of mixtures formed of coal ash/ fly ash,
alkali sulfate, and sodium chloride, each of said plurality of mixtures being
formed of different composition of said constituent material, setting a timer
and activating a thermocouple in the boiler simulation and placing the
specimen/samples inside the simulator, the specimen/samples being covered
with one of said plurality mixture; raising the temperature in stages within
the simulator corresponding to that of resistance tubular furnace and allowing
soaking of the specimen/samples for predetermined period and recording
simultaneously the temperature through the thermocouple; taking out the
specimen/samples after completion of soaking from the simulator and
cleaning with acetone in an ultrasonic cleaning machine; washing with water
and drying the cleaned samples/specimen by a drying machine; and
measuring the weight and dimension of each specimen/sample to determine
the corrosion loss.