CORROSION STUDY ON WELDMENTS OF AUSTENITIC STAINLESS STEEL

8/20/2019 CORROSION STUDY ON WELDMENTS OF AUSTENITIC STAINLESS STEEL

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International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882

Volume 3, Issue 5, August 2014 897

CORROSION STUDY ON WELDMENTS OF AUSTENITIC

STAINLESS STEEL

V. Gopalakrishnan1, V.BaluSamy2, S.O. Mohammed Rafi3

1Associate Professor, Department of Mechanical Engineering, Dhanalakshmi Srinivasan engineering college, Perambalur 2Associate Professor,Department of Mechanical Engineering, PSG college of Technology, Coimbatore

3Student, Department of Mechanical Engineering, Dhanalakshmi Srinivasan engineering college,

Perambalur

[email protected]

ABSTRACT 304 (Fe-Cr-Mn-Ni) stainless steel is the mostwidely used for general corrosive resistant tubing and pipe applications in boiler; it is used in chemical plants, refineries, paper mills, and food processingindustries. Stress corrosion cracking (SCC) is acommon mode of failure encountered in boiler

components especially in austenitic stainless steeltubes at high temperature and in chloride-rich waterenvironment. Welding in stainless steel forms thecorrosion due to carbide precipitation in heat affectedzone. The SCC behaviour of 304 stainless steel inwelding joint has been widely described in this work.Keywords- 304 stainless steel, Stress corrosioncracking, carbide precipitation, chloride-rich water.

I. I N T R O D U C T I O N

Stainless steels or, more precisely, corrosion-resistingsteels are a family of iron-base alloys having excellentresistance to corrosion. These steels do not rust and

strongly resist attack by a great many liquids, gases,and chemicals. Many of the stainless steels have goodlow-temperature toughness and ductility. Most of themexhibit good strength properties and resistance toscaling at high temperatures. All stainless steelscontain iron as the main element and chromium inamounts ranging from about 11% to 30%. Chromium

provides the basic corrosion resistance to stainlesssteels.

Manganese steels are not harden able by heat treatmentand are nonmagnetic in the annealed condition. Theymay become slightly magnetic when cold worked orwelded. This helps to identify this class of stainlesssteels. All of the austenitic stainless steels are weldable with most of the welding processes, with theexception of Type 303, which contains high sulphurand Type 303Se, which contains selenium to improvemuch inability.The austenitic stainless steels have about 45% higherthermal coefficient of expansion, higher electricalresistance, and lower thermal conductivity than mild-

carbon steels. High travel speed welding isrecommended, which will reduce heat input andcarbide precipitation, and minimize distortion. Themelting point of austenitic stainless steels is slightly

lower than melting point of mild-carbon steel. Becauseof lower melting temperature and lower thermalconductivity, welding current is usually lower. Thehigher thermal expansion dictates that special precautions should be taken with regard to warpingand distortion. Tack welds should be twice as often as

normal. Any of the distortion reducing techniques suchas back-step welding, skip welding, and wandering

sequence should be used. On thin materials it is verydifficult to completely avoid buckling and distortion.Stainless Steel (type 304) is one of three materialstaken for the experiment. Type 304 stainless is themost widely used analysis for general corrosiveresistant tubing and pipe applications; it is used inchemical plants, refineries, paper mills, and food processing industries. Type 304 has a maximumcarbon content of .08%. It is not recommended for use

in the temperature range between 800° F and 1650° Fdue to carbide precipitation at the grain boundarieswhich can result in inter-granular corrosion and earlyfailure under certain conditions. Stainless steel 304type has very has very low thermal conductivity in theorder of 16 w/m.k. Welding of Stainless Steel” Due tothe low thermal conductivity, the heat transfer rate isalso very low, which will results low tensile strength.Experiments are conducted to increase the strength thewelding process selected for stainless is shield metal

ARC welding and TIG welding.

Austenitic stainless steels (which contain 18% Cr – 8%

Ni) are engineering materials widely used in many branches of industry, especially in the food and

beverage manufacturing and processing sector, due totheir attractive combination of good mechanical properties, formability, and corrosion resistance. Theircorrosion resistance is afforded by a thin Cr 2O3 surface

film (typically 1 – 3 nm thick), known as passive film,which has self-healing capability in a wide variety ofenvironments. However, when austenitic stainlesssteels are exposed to the critical temperature range of

425 – 870 _C for a given period of time, chromium (Cr)carbides are formed at the grain boundaries and Cr

depletion occurs adjacent to these carbides, affectingtheir corrosion resistance.Corrosion occur mainly dueto dust inclusion, moisture present in the gas and heataffected in the weld zone.

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STRESS CORROSION CRACKING: Stress corrosion cracking (SCC) is the growth of crackformation in a corrosive environment. It can lead tounexpected sudden failure of normally ductile metalssubjected to a tensile stress, especially at elevated

temperature in the case of metals. SCC is highlychemically specific in that certain alloys are likely toundergo SCC only when exposed to a small number ofchemical environments. The chemical environmentthat causes SCC for a given alloy is often one which isonly mildly corrosive to the metal otherwise. Hence,metal parts with severe SCC can appear bright andshiny, while being filled with microscopic cracks. Thisfactor makes it common for SCC to go undetected prior to failure. SCC often progresses rapidly, and ismore common among alloys than pure metals. Thespecific environment is of crucial importance, and only

very small concentrations of certain highly activechemicals are needed to produce catastrophic cracking,often leading to devastating and unexpected failure.

I I . M A T E R I A L A N D M E T H O D O L O G Y

MATERIAL FORMATION:

304 Austenitic stainless steel is the family of iron based alloys having excellent resistance to corrosion. Itis taken in the form plate and it is formed to thestandard dimension for testing. Without welding twospecimen are formed. With weld two specimen are

formed.

F i g . 1 S t a n d a r d d i m e n s i o n o f s p e c i m e n

Fig. 2. Dimensionof weldspecimen

F i g . 3 . A f t e r m a c h i n i n g

Fig.1 represents the dimensions of standard specimenwithout welding and the specimen which are to bewelded are as shown in fig.2, the two specimen piecesare welded to form the length of standard specimen,the welding is carried out with the help of TIG welding

with standard settings, the final view of the testspecimen after carrying out the machining as per thedimension shown in fig. 3 are as follows

F i g . 4 f i n a l v i e w o f t e s t s p e c i m e n

C O R R O S I O N A N A L Y S I S : Corrosion is the gradual destruction of materials bychemical reaction with its environment. In the mostcommon use of the word, this means electrochemicaloxidation of metals in reaction with an oxidant such asoxygen. Rusting, the formation of iron oxides, is awell-known example of electrochemical corrosion.

Corrosion can also occur in materials other than

metals, such as ceramics or polymer.

H I G H T E M P E R A T U R E C O R R O S I O N : High-temperature corrosion is chemical deteriorationof a material (typically a metal) as a result of heating.This non-galvanic form of corrosion can occur when ametal is subjected to a hot atmosphere containingoxygen, sulphur or other compounds capable ofoxidizing (or assisting the oxidation of) the materialconcerned.

C O R R O S I O N I N S T A I N L E S S S T E E L :Stainless steel can pose special Corrosion challenges,since its passivation behaviour relies on the presenceof a major alloying component (chromium, at least11.5%). Because of the elevated temperatures ofwelding and heat treatment, chromium carbide canform in the grain boundary of stainless alloys. Thischemical reaction robs the material of chromium in thezone near the grain boundary, making those areasmuch less resistant to corrosion. This creates agalvanic couple with the well-protected alloy nearby,which leads to weld decay (corrosion of the grain

boundaries in the heat affected zones) in highlycorrosive environments.

A stainless steel is said to be sensitized if chromiumcarbides are formed in the microstructure. A typical





microstructure of a normalized type-304 stainless steelshows no signs of sensitization while a heavilysensitized steel shows the presence of grain boundary precipitates. The dark lines in the sensitizedmicrostructure are networks of chromium carbides

formed along the grain boundaries.

WEIGHT LOSS METHOD: Preparation of corrosion media:1. NaCl- 3.5grams+96.5ml distilled H2O2. Oxalic acid- 5grams+95ml distilled H2O

3.Oxalic acid -10grams+90ml distilledH2O4. Nitric acid -5grams+95ml distilled H2O5.Nitric acid-10grams+90ml distilledH2O

Fig.5. Corrosion media

Stress corrosion cracking (SCC) is the growth of crack

formation in a corrosive environment. It can lead tounexpected sudden failure of normally ductile metalssubjected to a tensile stress, especially at elevated

temperature in the case of metals. SCC is highlychemically specific in that certain alloys are likely toundergo SCC only when exposed to a small number ofchemical environments. The chemical environmentthat causes SCC for a given alloy is often one which isonly mildly corrosive to the metal otherwise. Hence,metal parts with severe SCC can appear bright andshiny, while being filled with microscopic cracks. Thisfactor makes it common for SCC to go undetected prior to failure. SCC often progresses rapidly, and ismore common among alloys than pure metals.

Fig.6. NaCl - 3.5grams+96.5ml distilled water

III. RESULTS AND TABLES Five sample of base metal weight is note down andsimilarly five sample of weld metal weight is note

down. Sample is kept in corrosion medium underobservation at normal laboratory condition for 30 days.

Weight of each specimen after taken from thecorrosion medium is noted down. Finally the weight

loss of base metal and weld metal graphicallyrepresented and which as shown below.





MATERIAL/CONDITION

YIELDSTRENGTH(N/mm2)

TENSILESTRENGTH(N/mm2)

%OFELONGATION

STAINLESSSTEEL304

ithcorrosion

edia Base

351.07 617.28 54.24

STAINLESS

STEEL304ithoutcor

osionmedia base plate

361.76 624.25 55.31

T a b l e : 1 W e i g h t l o s s c o m p a r i s o n

S r . N o .

C o r r o s i o nm e d i a

I n i t i a lw e i g h t( g m s . )

F i n a lw e i g h t( g m s . )

1 N a C l 29.81 28.79

2 O x a l i c a c i d5%

28.50 27.47

3 O x a l i c a c i d10%

32.32 31.40

4 N i t r i c a c i d

5%

29.82 28.21

5 N i t r i c a c i d10%

35.47 34.43

T E N S I L E T E S T : The specimen is machined to Indian standard fortransverse tensile in universal testing machines. Thespecimen is tested and the ultimate tensile strength is

observed. The values of UTS are listed in the table.• Material Specification: SS 304• Welding Process: TIG Welding• Description: Butt Joint

T a b l e : 2 T e n s i l e v a l u e o f b a s e m e t a l

T a b l e : 3 T e n s i l e v a l u e o f w e l d m e t a l

MATERIA

L/CONDITION

YIELD

STRENGTH(N/mm2)

TENSILE

STRENGTH(N/mm2)

%

OFELONGATION

STAINLESSSTEEL30

341.07 583.52 51.

STAINLESSSTEEL30Withoutc

orrosionm

361.76 598.58 54.

3

H A R D N E S S T E S T : Hardness is a measure of how resistant solid matter isto various kinds of permanent shape change when aforce is applied. Macroscopic hardness is generallycharacterized by strong intermolecular bonds, but the behaviour of solid materials under force is complex;therefore, there are different measurements ofhardness: scratch hardness, indentation hardness, andrebound hardness.

Hardness is dependent on ductility, elastic, stiffness, plasticity, strain, strength, toughness, viscoelasticityand viscosity.

T a b l e : 4 H a r d n e s s t e s t

S r . n o . m a t e r i a l A v e r a g ev a l u e

o f H R B

1 B a s e m e t a l 90.3

2 W e l d m e t a l 87.7

O P T I C A L M I C R O S C O P E T E S T : E m b e d d i n g , materials – after embedding in resin, thespecimen is usually ground and polished to a mirror-like finish using ultra-fine abrasives. The polishing process must be performed carefully to minimize

scratches and other polishing artefacts that reduceimage quality.Sectioning – produces thin slices of specimen, semi-

transparent to electrons. These can be cut on diamondknife to produce ultra-thin slices about 60 – 90 nm





thick. Disposable glass knives are also used becausethey can be made in the lab and are much cheaper.Staining – uses heavy metals such as lead, uranium ortungsten to scatter imaging electrons and thus givecontrast between different structures, since many

(especially biological) materials are nearly"transparent" to electrons.

OPTICAL MICROSCOPE RESULT:

Fig.7. Before etching

Fig.8. After etching

IV. PROBLEM IDENTIFICATION: After testing we are identified some problems in weldmetal compare to the base metal. Problems areCorrosion is occur in both metal because of chlorine

rich environment and high temperature. Oncomparison weld metal having little bit corrosion thanthe base metal. Compare to the base metal the weightof weld metal, strength and hardness also getdecreases.Stress corrosion cracking is occurred in theheat affected zone in weld metal.

V. CONCLUSION In boiler manufacturing industries high capacity boiler800 mw and 1000 mw are under design and in the boiler the pressure and temperature is more so that

water to steam and steam to water through the pipe forthis purpose , In austenite stainless steel pipe which iswelded. Because of welding stress corrosion crackingis occur which results reduce in material property like

strength, hardness, ductility and other physical properties.

ACKNOWLEDGEMENT We give all the glory and thanks to our ALMIGHTY

GOD for showering upon, the necessary wisdom andgrace for accomplishing this work.We express our gratitude and thank our PARENTS

first for giving health and sound mind for completingthis work. We extend our gratitude to all our friendsand family member who have helped physically and

morally for the development of this work.

REFERENCES [1] .N.B.Mostafa, M.N.Khajavi, “O ptimization of

welding parameters for weld penetration in FCAW”

Journal of achievements in materials and

manufacturing Engineering , Volume16 , issue 1-2MAY-june 2006.

[2] The effect of annealing on properties of AISI 316L

base and weld metals Stjepan Kožuh1, Mirko Gojić1,

Ladislav Kosec2, RMZ – Materials and

Geoenvironment, Vol. 54, No. 3, pp. 331-344, 2007.

[3] Emerging Markets and Trends in the use of

Stainless Steels, Nickel-Based Alloys, and Titanium

presented at the Stainless Steel world 2007 conference

in Maastricht, The Netherlands , November7, 2007.www.stainless-steel- world.net.

[4] Leif karisson, ESAB AB, Gothenburg, Stainless

steels past present and future,Svetsaren no.1.2004.47.

[5] “Welding of Stainless Steel” Technical and Trade

information-CIGWELD.

http://www.stainless-steel-/




CORROSION STUDY ON WELDMENTS OF AUSTENITIC STAINLESS STEEL

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