Title of Invention

METHOD OF TESTING INTERNAL CORROSION RESISTANCE OF COMPONENTS

Abstract This invention relates to a method of testing and evaluating corrosion resistance of selected specimens of metals / alloys, under simulated wet and dry condition comprising the steps of measuring initial thickness of said specimens at various selected locations; immersing said samples in a medium containing acetic acid, chloride, nitrite, sulphate and sulphite ions maintained at a pH of 4.5 ± 02 and a temperature of atleast 85°C; measuring the thickness of said specimens at the selected locations periodically; replacing the medium periodically to maintain the pH and the temperature; and continuing the above steps till perforation appear on the selected areas or a period of 500 hours.
Full Text FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10)
TITLE OF THE INVENTION
A Method Of Testing Internal Corrosion Resistance Of Components


APPLICANTS
TATA MOTORS LIMITED, an Indian Company
having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk
Mumbai 400 001, Maharashtra, India
INVENTORS
Hariharan Venkatraman, Dhanashree Aole and Ramesh Sarnopant
all Indian Nationals of TATA MOTORS LIMITED,
an Indian Company having its registered office at
Bombay House, 24 Homi Mody Street,
Hutatma Chowk, Mumbai 400 001,
Maharashtra, India

PREAMBLE TO THE DESCIPTION
5 JUL 2008
The following specification particularly describes the nature of this invention and the manner in which it is to be performed


FIELD OF INVENTION
This invention relates to the method of testing internal corrosion resistance of components and more particularly this relates to method of testing internal corrosion resistance of a component, which is in high temperature and corrosive gas environment.
BACKGROUND OF INVENTION
In order to have better durability, it is necessary to use material with high heat and corrosion resistance in specific applications. Hence innovative test techniques are required to be devised to evaluate the internal corrosion resistance of such materials. Internal combustion produces water vapour and corrosive gases that can condense in the internal areas such as exhaust system in the automobile. This condensate includes sulphate, sulphite, nitrate, ammonium, carbonate, bicarbonate & chloride ions, which results in rusting and severe perforation of the components in the exhaust system. Conventionally, neutral salt spray method (solution consists of 5% NaCl in a salt spray chamber at 35°C and pH of 6.5-7) is used for testing the corrosion resistance of all ferrous components. This test is not suitable for a component subjected to high temperature and corrosive exhaust fumes.
Few experiments were carried out to test the corrosion resistance of the two exhaust muffler materials i.e. stainless steel AISI 409 and aluminized steel using the conventional neutral salt spray test. The results indicated superior corrosion resistance of aluminized steel compared to stainless steel AISI 409 grade, which were contradictory to the actual field failures.
2

Warranty complaints on exhaust system indicated large amount of failures due to rusting / perforation of internal muffler material where aluminized steel was used. No rusting of internal muffler was observed where SS grade AISI 409 was used.
Neutral Salt Spray carried out on muffler material (aluminized steel) revealed resistance to red rust at exposure periods greater than 1000 hrs, whereas the stainless steel material AISI 409 was observed corroding within 300 hours. (Refer Fig 1, annex
I)
The conventional method has been focused on the appearance and the external causes such as functional rust of exterior parts, but field failures of the internal areas like the muffler of an exhaust system are now drawing keen attention and needs to be addressed. This method aims to overcome the above drawback and provides a test with which corrosion resistance of the components against the internal exhaust gases condensate is qualitatively evaluated.
OBJECTS OF THIS INVENTION
The main object of this invention is to provide a method of testing internal corrosion resistance for qualitative comparison of different components through corrosion test.
• Yet another object of the invention is to simulate the near accurate composition
of the exhaust gaseous condensates in actual field conditions.
Yet another object of the invention is to test the internal corrosion resistance of the material, which shall help in selection of different materials for muffler application.
3

Yet another object of this invention is to provide a simple and cost effective test method for testing internal corrosion resistance of components subjected to high temperature and corrosive gases.
STATEMENT OF INVENTION
This invention relates to a method of testing and evaluating corrosion resistance of selected specimens of metals / alloys, under simulated wet and dry condition comprising the steps of

• measuring initial thickness of said specimens at various selected locations;
• immersing said samples in a medium containing acetic acid, chloride, nitrite, sulphate and sulphite ions maintained at a pH of 4.5 + 02 and a temperature of atleast 85°C;
• measuring the thickness of said specimens at the selected areas periodically;
• replacing the medium periodically to maintain the pH and the temperature; and continuing the above steps till perforation appear on the selected areas or a period of 500 hours.
SUMMARY OF THE INVENTION
This invention relates to a method of testing and evaluating corrosion resistance of components under simulated and wet & dry conditions of internal combustion engine comprising the steps of partially immersing selected samples of metals/alloys and the like of desired thickness at specified points, in a medium containing acetic acid, chloride, nitrite, sulphate and sulphite ions maintained at a pH of 4.5 ± 0.2 by the addition of ammonia in a closed container, maintaining the pH and the concentration of ions in said medium by periodic replacement of the medium for a period of at least
4

500 hrs, contents of said container being maintained as a temperature of at least 85°C, cleaning said samples periodically to remove deposited corroded mass therefrom, and continuing the operation till perforations appear on said samples and evaluating the rate of corrosion.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the figures wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same.
Fig no. 1: shows salt spray test results on aluminized sheet & SS 409 after 1000 hrs by
conventional method
Fig.No.2: shows corrosion test results on aluminized steel & SS 409 after 500 hrs in
accordance with this invention
Fig No. 3: shows corrosion levels of different materials at different conditions
Fig. No. 4: Graph shows difference in thickness reduction at point Al and A2
(completely in wet condition) with time
Fig No. 5: Graph shows difference in thickness reduction at point B1 and B2 (in wet
& dry condition) with time
Fig 6: Graph shows difference in thickness reduction at point Al (completely in wet
condition) & Bl (wet & dry condition) with time of aluminized steel sheet
Now referring to Figs. 2 & 3:
STEPS FOR CARRYING OUT THE INTERNAL CORROSION TEST ON THE MUFFLER MATERIAL
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same
5

The testing of the specimen is to be carried out under specified condition.
The test facilities to be required for the process consists of two 300 ml cylindrical glass flask, a glass rod for mixing the solution, pH meter and an oven with air circulating facility.
Specimen dimensions were as follows: 120mm X 40mm X 10 mm. Two locations were marked on the test specimens at 20 and 50 mm from the bottom at exactly the centre of the specimen. The locations are required to be marked to ensure thickness measurement at the same location after specified hours.
Points for thickness measurement should be selected so that one of the points shall be constantly under immersion and the other, partially. This is to simulate the actual conditions where the vehicle may be in running condition for sometime and idling when not in use.
Al represents the point 20 mm from the bottom of the Aluminized sheet and at the mid point, widthwise. This-point is continuously immersed in the test solution during test (wet condition).
Bl represents the point 50 mm from the bottom of the sheet and at the mid point, widthwise. This point is intermittently in contact with the test solution due to partial drying up of the solution during test (wet & dry condition).
A2 represents the point 20 mm from the bottom of the SS 409 sheet and at the mid point, widthwise. This point is continuously immersed in the test solution (wet condition).
6

B2 represents the point 50 mm from the bottom of the SS 409 sheet and at the mid point, widthwise. This point is continuously immersed in the test solution (wet & dry condition).
Initial thickness was measured at points Al, Bl, A2, B2. The support angle of the specimen was kept around 45°.
Initially 10 litres of solution was prepared. The test solution was prepared by dissolving following acids in water in the following sequence, based on density:
Table 1

The pH of the solution was maintained at 4.5+/- 0.2 by adding ammonia. Sodium bisulphite (NaHS03) is added just before starting the test and is added in small amount (2-3 ml) without disturbing the pH of the solution. Sodium bisuiphite is prepared by dissolving 20 gm of Sodium meta-bisulphite (Na2S2O5) in 100 ml of water & stirring it properly. After few minute, when the reaction with water is over, SO2 is evolved & sodium bisulphite is formed, which later on gets dissociated in the
7

solution giving out sulphite ions. The equation for the above said reaction is as
follows.
► Na2S2O5+H20 --> 2NaHS03 (sodium bisulphite)
The reagents are selected keeping in view of the corrosive fumes generated from
petrol engine.
The solution was filled in beaker such that the test specimens are partially immersed
in the beaker and the beaker was closed.
The test solution was replaced by fresh solution after every 24 hrs. So, that the pH of
the solution and the required ions in the corrosive media are retained to cause proper
effect on the said test specimens.
The test was conducted continuously during the test period preferably for 500 hrs. The
time for unavoidable interruptions was minimized by maximizing the efforts to
transfer the specimen or for inspection.
The sheet was dipped in the corrosive medium with the composition as mentioned above. The two filled beakers along with the sheet specimens were kept in an oven at 85°C.
After every 100 hours, the specimen was cleaned & removed; loss of thickness, if any, was measured at the marked locations (Al, Bl, A2 & B2). Red rust, if any, was recorded.
The test samples were dried and thickness reduction on both the plates was measured after 500.hrs.
The test was stopped when severe perforations were observed on the aluminized sheet (refer point 1 & 2 in fig. 3).
The temperature of the system is of great importance to avoid the corrosion due to corrosive condensates. If the system doesn't become hot enough then the condensates
8

remains and leads to corrosion of the system. Thus the vehicles which are run over short distance are more susceptible to exhaust gases condensates (wet corrosion), sometimes referred to as cold condensate corrosion. In some cases the deterioration is also accelerated by stress and design configuration.
For example, consider the exhaust muffler where the acidity of the condensates is high due to the presence of the nitric acid, sulfuric acid and sulphurous acid. All these acids react with water vapor to form the oxides. This results in a severe corrosion of the muffler material in the absence of sufficient temperature
In the center of the exhaust system (Main muffler, connecting pipes) resistance to both high temperature and wet corrosion are needed. Depending on running conditions, either hot conditions prevail (full throttle) or wet corrosion loading dominates (short-distance driving).
But in rear section (Post silencer) wet corrosion becomes the main factor. Inside the system, condensation of combustion gases produces sulphurous acid, sulphuric acid and low levels of hydrochloric acid, creating critical conditions. These condensates, combined with accumulation of chloride ions and deposits of electrochemically active soot particles, can result in substantial wet corrosive loading on the inner surfaces of the components. Trials were carried out by replicating the pH, concentration and the temperature of the fumes condensate inside the muffled resulted into the acceptance of the AISI 409 (ferritic stainless steel) as superior material to alminized steel for internal muffler material.
9

OBSERVATION & RESULTS
Table 2: Shows reduction in thickness with time for aluminized & SS 409 sheet

Test results
Aluminized steel SS409
Time, Hrs Thickness reduction, (microns) Thickness reduction, (microns)
Al (Wet condition) Bl(Wet&
dry condition A2 (Wet condition) B2 (Wet & dry condition)
24 0 0 0 0
168 10 10 0 0
238 20 100 0 0
328 113 150 0 0
420 160 200 0 0
500 250 660 0 0
Now referring to table 1 and figure 4, 5 & 6, it is clear that:
• Pt. Al on aluminized steel panel, which is in continuous contact with the
solution, has less thickness reduction than Pt. Bl on aluminized steel panel, which is partly exposed to air and solution, (due to wet and dry condition) inside the beaker. (as shown in fig.6)
Pt. A2 on SS 409 plate, which is in contact with the solution and pt. B2 on SS 409 plate, which is partially in contact with the solution & partly exposed to air (due to drying up of the solution) did not show any thickness reduction..
Thickness of the aluminized steel sheet reduced by 660 microns after 500 hrs, whereas the thickness of the stainless steel sheet did not show any change (as shown in figs. 4& 5)
10

* SS 409 has superior internal corrosion resistance as compared to aluminized
steel under high temperature (85°C) and corrosive gas environment.
→ the test technique devised simulates the near accurate conditions of the exhaust
gaseous condensates in actual field.
→ the test technique devised, is suited to compare the corrosion resistance of
various materials under high temperature and corrosive environment
11

WE CLAIM
1. A method of testing and evaluating corrosion resistance of selected specimens
of metals / alloys, under simulated wet and dry condition comprising the steps
of:
measuring initial thickness of said specimens at various selected locations;
immersing said samples in a medium containing acetic acid, chloride, nitrite,
sulphate and sulphite ions maintained at a pH of 4.5 02 and a temperature of
atleast 85°C;
measuring the thickness of said specimens at the selected locations
periodically;
replacing the medium periodically to maintain the pH and the temperature; and
continuing the above steps till perforation appear on the selected areas or a
period of 500 hours.
2. A method of testing as claimed in claim 1 wherein pH is maintained by adding ammonia.
3. A method of testing as claimed in claim 1 wherein said medium is replaced at a period of 24hr.
4. A method of testing as claimed in claim 1 wherein thickness of the specimen measured at the specific locations at a period of 100 hr.
5. A method of testing as claimed in claim 1 wherein one of said location is continuously immersed in the medium and the other is intermittently in contact with the medium due to partial drying up of the medium during testing.
12

6. The method as claimed in claim 1 wherein sulphite ions are generated in the medium in situ by adding sodium bisulphite prior to introduction of the selected specimen in the medium.
7. A method of testing internal corrosion resistance of components substantially as herein described with particular reference to the accompanying drawings.
Date this 5th day of August 2008
TATA MOTORS LIMITED
By their Agent and Attorney

(KARUNA GOLERIA)
of DePENNING & DePENNING
13

Documents:

1663-MUM-2008-ABSTRACT(COMPLETE)-(5-8-2008).pdf

1663-MUM-2008-ABSTRACT(GRANTED)-(2-4-2012).pdf

1663-mum-2008-abstract.doc

1663-mum-2008-abstract.pdf

1663-MUM-2008-CANCELLED PAGES(27-12-2011).pdf

1663-MUM-2008-CLAIMS(AMENDED)-(27-12-201).pdf

1663-MUM-2008-CLAIMS(COMPLETE)-(5-8-2008).pdf

1663-MUM-2008-CLAIMS(GRANTED)-(2-4-2012).pdf

1663-MUM-2008-CLAIMS(MARKED COPY)-(27-12-201).pdf

1663-mum-2008-claims.doc

1663-mum-2008-claims.pdf

1663-mum-2008-correspondence(17-9-2008).pdf

1663-MUM-2008-CORRESPONDENCE(IPO)-(2-4-2012).pdf

1663-mum-2008-correspondence.pdf

1663-MUM-2008-DESCRIPTION(COMPLETE)-(5-8-2008).pdf

1663-mum-2008-description(complete).doc

1663-mum-2008-description(complete).pdf

1663-MUM-2008-DESCRIPTION(GRANTED)-(2-4-2012).pdf

1663-MUM-2008-DRAWING(COMPLETE)-(5-8-2008).pdf

1663-MUM-2008-DRAWING(GRANTED)-(2-4-2012).pdf

1663-mum-2008-drawing.pdf

1663-mum-2008-form 1.pdf

1663-mum-2008-form 18(17-9-2008).pdf

1663-MUM-2008-FORM 2(COMPLETE)-(5-8-2008).pdf

1663-MUM-2008-FORM 2(GRANTED)-(2-4-2012).pdf

1663-mum-2008-form 2(title page)-(5-7-2008).pdf

1663-MUM-2008-FORM 2(TITLE PAGE)-(COMPLETE)-(5-8-2008).pdf

1663-MUM-2008-FORM 2(TITLE PAGE)-(GRANTED)-(2-4-2012).pdf

1663-mum-2008-form 2(tittle page).pdf

1663-mum-2008-form 2.doc

1663-mum-2008-form 2.pdf

1663-mum-2008-form 3.pdf

1663-MUM-2008-FORM 8(17-9-2008).pdf

1663-mum-2008-form 9(17-9-2008).pdf

1663-mum-2008-general power of attorney.pdf

1663-MUM-2008-REPLY TO EXAMINATION REPORT(27-12-201).pdf

abstract1.jpg

FORM9.TIF


Patent Number 251779
Indian Patent Application Number 1663/MUM/2008
PG Journal Number 14/2012
Publication Date 06-Apr-2012
Grant Date 02-Apr-2012
Date of Filing 05-Aug-2008
Name of Patentee TATA MOTORS LIMITED
Applicant Address BOMBAY HOUSE, 24 HOMI MODY STRET, HUTATMA CHOWK, MUMBAI-400001,
Inventors:
# Inventor's Name Inventor's Address
1 HARIHARAN VENKATRAMAN BOMBAY HOUSE, 24 HOMI MODY STRET, HUTATMA CHOWK, MUMBAI-400001,
2 DHANASHREE AOLE BOMBAY HOUSE, 24 HOMI MODY STRET, HUTATMA CHOWK, MUMBAI-400001,
3 RAMESH SARNOPANT BOMBAY HOUSE, 24 HOMI MODY STRET, HUTATMA CHOWK, MUMBAI-400001,
PCT International Classification Number C23C8/80
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA