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comparision between electroslag strip cladding and sumerged arc strip cladding

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comparision of essc with sasc

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comparision between electroslag strip cladding and sumerged arc strip cladding

  2. 2. Introduction All hydro processing reactors need to be internally protected from high-temperature corrosion effects or hydrogen attack. The overlay welding in heavy-wall pressure vessels is commonly carried out using strip electrodes and the two most productive systems for surfacing large components are submerged arc strip cladding (SASC) and electro slag strip cladding (ESSC). Both SASC and ESSC are characterized by a high deposition rate and low dilution, as well as a high deposit quality. As a rule of thumb, electro slag strip surfacing decreases dilution by up to 50% in contrast with submerged arc strip surfacing for the same heat input with a significantly higher deposition rate.
  3. 3. Fig. Diagram For Submerge Arc Strip Cladding
  4. 4. Cladding Cladding is the bonding together of dissimilar metals. In many cases, corrosion resistance is required only on the surface of the material and carbon or alloy steel can be clad with a more corrosion resistant alloy. Compared to carbon and alloy steels, all corrosion resistant alloys are expensive. Cladding can save up to 80% of the cost of using solid alloy. Cladding of carbon or low alloy steel can be accomplished in several ways including roll bonding, explosive bonding, weld overlaying and wallpapering. Clad materials are widely used in the chemical process, offshore oil production, oil refining and electric power generation industries. The use of clad steel is not new. Corrosion resistant alloy clad steel has been available for over 40 years
  5. 5. Weld overlaying technique of cladding is commonly used to clad the surfaces of fabricated steel structures. The actual weld overlay process used depends on many factors including access, welding position, the alloy applied, and economics. Applications of Strip Cladding: 1) The process is usually confined to relatively large and thick components which need to be manipulated to enable welding to be carried out in the flat position. 2) The technique finds its widest application in the oil, gas and fertilizer related industries and in the nuclear power generation field. 3) Generally used for surfacing the internal surfaces of pressure vessels and large diameter pipe and in the reclamation of steel mill rolls.
  6. 6. Submerged arc Strip Cladding (SASC)  This well-known SAW method has been widely used with strip electrodes since the mid-1960s.  There is no fundamental difference between submerged arc welding and cladding.  The welding wire is merely replaced with the cladding strip. The equipment is the same, except the head must be adapted to guide the strip. The principle is the same.  The energy to melt the strip and the base metal is supplied by the electric arc struck between them. On melting, the agglomerated flux protect the liquid metal and where applicable enriches it with alloying elements.  In the SAW process the strip is feed down through the contact jaws at the same time as the flux is feed down on both sides of the strip.
  7. 7.  The strip generates an arc between itself and the base material, the arc is not uniform and static, it wanders along the width of the strip but is all time sub merged under the molten slag.  It uses a strip, normally with a thickness of 0.5 mm and the width normally varies from 30 to 120 mm, but other widths are available for special applications.
  8. 8. Electro Slag Strip Cladding (ESSC)  The electro slag welding process was patented in USA in February 1940 and is a process that can weld material thicknesses from 25 up to 300 mm. It works in the vertical or very close to vertical position.  It is in use for hull welding of ships; it is used for welding heavy wall thickness vessels of different kinds and many more applications.  In the early 70’s the electro slag concept was adjusted to fit the cladding process with a metal strip.  Technological developments have driven temperatures and pressures used in the petroleum, chemical, pulp, and paper, and environmental protection industries, and increased the likelihood of serve corrosion and wear in the process pressure vessels.
  9. 9.  The electro slag welding (ESSC) process is suitable for applying weld deposits over large surface areas using strip electrodes . Fig. Schematic diagram of the ESSC process
  10. 10. COMPARISION BETWEEN ESSC & SASC 1) The penetration achieved with ESSC is less than that with for SASC because the molten slag pool is used to melt the strip and some of the parent material. 2) ESSC uses higher welding currents than SASC so the welding heads used are more heavy duty. 3) In ESSC Increased deposition rate of 60% to 80% than SASC. 4) Only half of the dilution (10%–15%) from the base material due to less penetration in ESSC. 5) Lower arc voltage (24–26 V) in ESSC. 6) Higher amperage and current density (About 1000–1250 A with strips of 60mm width, corresponding to 33–42 A/mm²). Specially developed fluxes for high productivity purposes can be welded with amperage in excess of 2000A which corresponds to a current density about 70 A/mm2.
  11. 11. 7) Increased welding speed (50%–200%), resulting in a higher area coverage 8) Lower flux consumption (about 0.5 kg/kg strip). 9) The solidification rate of the ESSC weld metal is lower, aids de-gassing and increases resistance to porosity. Oxides can rise easier out of the molten pool to the surface; resulting in a metallurgical cleaner weld metal which is less sensitive to hot cracking and corrosion.
  12. 12. SR. NO. PARAMETER SASC ESSC 1 Strip (mm) 60x0.5 60x0.5 2 Welding current (A) 750 1250 3 Voltage (V) 26 24 4 Travel speed (cm/min) 10 18 5 Current density (A/mm²) 25 42 6 Arc yes no 7 Heat input (kJ/mm) 11.7 11.25 8 Bead height (mm) 4.5 4.5 9 Bead width (mm) 65 68 10 Dilution (%) 18 9 11 Deposition rate (kg/hr) 14 22 12 Flux composition (kg/kg strip) 0.8 0.6 13 Number of layers 2 1 Typical comparison between ESSC & SASC
  13. 13. References 1)Y. K. Oh, J. H. Devletian and S. J. Chen, Welding Journal, 69 (1990) 2)Technical handbook, ESAB 3)Consumable handbook, Vostelpine Bohler 4)B. E. Paton 1997. Electro slag Welding,2nd edition 5)YU. M. KUSOV 2001. A New Approach to Electro slag Welding-Welding journal
  14. 14. Thank You….