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1.0 INTRODUCTION

Most
of the engineering applications require both strength and corrosion resistant
materials for long term reliability and performance. Stainless steels with
excellent corrosion resistance and good mechanical properties can be used but
the material cost becomes very high due to its high alloying additions. A
possible solution for achieving the combination of both mechanical and
corrosion properties is to use a cladded combination of steel and a suitable
corrosion resistant alloy. These cladding processes have been developed rapidly
and are used in industries such as chemical plants, storage tanks, pressure
vessels and desalination equipment 1. For example, a cladded combination of
carbon steel and super duplex stainless steels has been used as a hull material
on the Japanese icebreaker ‘Shirase’1. Thus the cladded combination of
stainless steel and structural steels are being considered for a wide range of
applications involving a highly corrosive environment. This work involves
analyzing the effect of welding process on cladded combination of Austenitic
stainless steel (AISI 316) and IS 2062 structural steel. This type of welding
analysis can be very much used in cases where the repairing of cladded
assemblies is involved. 

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2.0 METAL CLADDING

The use of corrosion resistant alloys (CRAs) for the control of
corrosion in variety of application systems has a number of benefits.
Nevertheless, CRAs contain expensive alloying elements, particularly the more
highly alloyed materials required for corrosive sour production systems. Clad
steel is a product of a thin layer of highly alloyed material with that of a
low cost base material. The cladding layer which will be in contact with the
corrosive fluids is made of the corrosion resistant alloy whilst the less expensive
backing steel provides the strength and toughness required to maintain the
mechanical integrity. Because high strength backing steel can be utilized, wall
thicknesses can be reduced relative to solid CRAs thus reducing fabrication
time and costs. Clad steel plates have been utilised with great success in
processing vessels, heat exchangers, tanks and a variety of material handling
and storage facilities as well as for making longitudinally welded clad pipe.
Various forms of clad, weld overlaid and lined steel have been widely used in
the chemical, oil refining and chemical transport industries and for oil and
gas production.

In this project, explosive cladding process will be used to clad
austenitic stainless steel and structural steel material. Explosive bonding
uses the very short duration of high energy impulse of an explosion to drive
two surfaces of metal together, simultaneously cleaning away surface oxide
films and creating a metallic bond 2. The two surfaces do not collide
instantaneously but progressively over the interface area. The pressure
generated at the resulting collision front is extreme and causes plastic
deformation of the surface layers. In this way, the surface layers and any
contaminating oxides present upon them are removed in the form of a jet
projected ahead of the collision front 2. This leaves perfectly clean
surfaces under pressure to form the bond. The selection and quantity of the
explosive charge are determined by the strength and thickness of the materials,
the specific material combinations and the area which is to be bonded 2.
Explosive bonding can be used to join a wide combination of materials more
effectively in a short period of time. Explosive bonding is followed by a
rolling process to increase the bonded area and to smooth out the wavy
interface at the bonded surface.

3.0 SCOPE OF THE PROJECT

The
project will aim at validating the response of a Austenitic Stainless Steel and
structural steel cladded plate when subjected to a fusion welding process. In
this case Gas Tungsten Arc Welding (GTAW) has been chosen as it creates a
better joint than Gas Metal Arc Welding (GMAW) 3 and moreover the thickness
dealt in the project can be conveniently welded using GTAW. This project will
focus on developing a comprehensive finite element model for simulation of the
welding process and performing experiments to determine the behavior of these
weldments under tension, impact and in corrosive environment.

4.0 OBJECTIVES

The objectives
of the project are

1.   
To
clad AISI 316 and IS 2062 using explosive welding technique.

2.   
Selection
of a consumable for welding of the claded plates.

3.   
Analysis
of welding process through Finite Element Approach.

4.   
Carry
out TIG welding of clad steels and Qualifying the weldments for their

1.   
Tensile
strength

2.   
Impact
toughness (sub zero temperature and DBTT point determination)

3.   
Corrosion
properties

4.   
Establishing
relationship between microstructure and mechanical properties.

 

 

 

 

5.0 METHODOLOGY

 

 

 

 

 

 

 

 

6.0 MODELLING AND FEA

            An assembly of a cladded plate was
created with Structural Steel (IS 2062) as the base plate and Stainless Steel
(AISI 316) as the flyer plate. The assembly was then welded to another assembly
using a SS 316 filler wire. The weld joint was modeled in accordance with ISO
9692. The weld bead was modeled with reinforcement and the beads were assembled
together and then added to the main assembly to create the weld. The supporting
images for the welding are as follows:

 

Fig 1: ISO 9692 – Weld Joint
Preparation

Fig 2: Weld bead created for the
assembly

Fig 3: Weld assembly created for FEA
analysis

            The developed model was imported
into ANSYS for the FEA analysis. First a transient thermal analysis was carried
out on the assembly. The heat flow in accordance to the Goldak heat source
model was applied to each bead and by using birth and death of elements a
moving heat source was developed 4. The model was analysed for temperature
distribution and various temperature probes were place to determine the
temperature of the plate at various distances from the weld bead.

Fig 4: Heat flow applied to a bead

Fig 5: Temperature distribution

 

 

Fig 6: Temperature of the base plate
at Probe 4

            The results from the thermal
analysis were linked to the static analysis as input conditions. The weldment
was given with a fixed support and force from toggle clamps as the loading
condition and the resulting weld distortion was predicted.

Fig 7: Ansys analysis links created

Fig 8: Weld distortion predicted

 

7.0 FUTURE
WORK

            The works to be done in Phase II of
project work are as follows

            1. To finalize the welding
parameters those are to be optimized and thereby select a suitable orthogonal
array for optimization.

            2. To compare the results of FEA to
actual welding process and make suitable correction to get a comprehensive FEA
model for welding of claded plates.

            3. To procure the base plate (IS
2062) and AISI 316 sheet and explosively clad them.

            4. To carryout welding of the
material and test them for their tensile, impact and corrosion resistance
properties.

            5. To study on the microstructure of
the weldment and relate it to the mechanical behavior of the weldment.

 

 

 

 

 

 

BIBLIOGRAPHY

1
HyojinSong, HaksooShin, YongtaekShin, Heat-treatment of clad steel plate for application
of hull structure, J. Ocean Engineering 122 (2016) 278-287.      

2 L.M.
Smith, “Engineering with Clad Steel,” NiDI Technical Series No.
10,064, Nickel Development Institute, 1992

 

3 Robert N
Gunn, “Stainless Steel – Microstructure, properties and application”,
Abington Publishing Woodhead Publishing Ltd in association with The Welding
Institute.

4
http://tutorials.vaftsycae.com/m.moving_heat_source_ansys.html

 

 

 

 

 

 

 

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