Category: News

Electroslag strip welding – an alternative to conventional cladding

June 01.12

Besides the conventional cladding procedures, as roll cladding and explosion cladding, electroslag strip welding (ESW) is another option. Electroslag strip welding is a further development of submerged arc welding. Unlike submerged arc welding there is no arc between electrode and base material. 



The slag, which is kept liquid by the electrical resistance, melts the surface of the base material and ensures that the dipping-in electrode begins to melt. The edge of the strip is submerged by the liquid slag and the welding flux.

Advantages to submerged arc welding strip cladding:

  • Elevated deposition rate by about 60 – 80%
  • Elevated welding speed by 50 – 200%
  • Due to the much lower fusion penetration, the delution is reduced to about 10-15%. So the production of one-layer claddings can be carried out at a number of cladding materials. By strips which are produced particularly for electroslag welding, a buffer layer is not required. The chemical composition and the corrosion resistance of the welding bead correspond to the comparable cladding material.
  • By the lower delution no resp. just slight hardness peak values come into being in the transition of base material and welding material. These hardness peak values affect the ductility of the weld seams in particular during the forming of cladded heads.

Advantages and disadvantages of ESW compared to roll cladding and explosion cladding. 

Advantages:

  • Cladding of small areas is feasible
  • Cladding of thick building parts without thickness limit upwards
  • Manufacture of claddings especially for cladded heads where an optimum heat treatment for the cladding is not possible (e. g. Duplex or Hastelloy C276)
  • Extremely high bonding and shear strength between base material and cladding 
  • Short-term availability of strips in a wide material range which reduce the delivery time of claddings considerably

Disadvantages:

  • Production of weld claddings is very expensive and time-consuming
  • Manufacture of cladding of thin wall thickness feasible only clearly defined 

Practical application at KÖNIG + CO GmbH 

König + Co. uses ESW mainly for the manufacture of weld cladded heads. For roll cladded resp. explosion cladded heads which have to be welded due to the existing plate sizes, the cladding will be restored by ESW in the weld area. For this purpose electroslag strip cladding is a very effective method where the normal CrNi steel can be welded with one layer. Due to the low delution, very good ductility properties will be achieved in the transition area between the weld metal of the base material and weld metal of the cladding. These properties are basic conditions for the manufacture of cladded heads during dishing and flanging. At all other possible weld procedures it has to be worked with buffer layers in order to achieve

1.    a ductile weld metal in the transition of base material and cladding 

2.    and to produce a chemical analysis and the required corrosion resistance according to the agreed specification


ESW is also applied for heads made of crown and petal i. e. where the single parts have to be formed at first and then welded. Here you have to distinguish between two variations:

Variation 1

The head has been produced of non- resp. low-alloyed steel and made of one or of several parts. The complete inside and outside surface will be cladded by electroslag strip cladding. Depending on diameter and head shape strips of 
30 mm resp. 60 mm width will be applied. Hereby it has to be considered that the plate thickness of the base material has to be ≥ 30 mm in order to guarantee the head shape after cladding and to avoid an overheating of the base material. 

Variation 2

Heads of several parts will be produced of a cladded crown and cladded petals. Hereby the petals will be welded with the crown at the base material at first. As a next step the cladding will be restored by electroslag strip welding in the area of the weld seams.
 
For these welding works a turn-tilt equipment with the following parameters is available at König + Co.:

Max. load:                    150 tons (max. work load depending on the table position)

Min. head diameter:     2500 mm OD

Max. head diameter:    8000 mm OD

This turn-tilt equipment will not only be used for the welding of cladded heads. With the newly installed control device in combination with the control of the welding equipment many head shapes of various materials can be welded by submerged arc welding as well. 

Please contact us in case of further questions.

We are looking forward to receiving your inquiry!




Extracts of ESAB Technical Handbook ed. 11/2008