Svetsaren 1/2007 - Esab

Practical applications of ESAB strip
cladding technology
GABRIELE GALLAZZI, ESAB ITALY, SOLVEIG RIGDAL AND MARTIN KUBENKA, ESAB AB, GOTHENBURG SWEDEN.
Stainless steel strip cladding is a
flexible and economical way of
depositing a corrosion-resistant
protective layer on a load-bearing
mild or low-alloy steel. Strip
cladding is, therefore, frequently
used in the production of
components for the chemical,
petrochemical and nuclear
industries. This article discusses
two strip cladding methods and
describes applications at two
major Italian fabricators – SICES
and Ansaldo Camozzi.
The two most productive systems for surfacing
large components which are subjected to corrosion
or wear are submerged arc and electroslag
cladding, using a strip electrode. Both proceses are
characterised by a high deposition rate and low
dilution and they are suitable for surfacing flat and
curved objects such as heat exchanger tube sheets
and pressure vessels. Submerged arc welding
(SAW) is most frequently used but, if higher
productivity and restricted dilution rates are required,
electroslag welding (ESW) is recommended.
SAW strip cladding
The well-known SAW method has been widely
used with strip electrodes since the mid-1960s.
A strip electrode, normally measuring 60 mm x
0.5 mm or 90 mm x 0.5 mm, is used as the
(usually positive) electrode and an electric arc is
formed between the strip and the workpiece.
Flux is used to form a molten slag to protect the
weld pool from the atmosphere and helps to
form a smooth weld bead surface.
ESW strip cladding
Electroslag strip cladding, which is a further
development of submerged arc strip cladding, has
quickly established itself as a reliable high
deposition rate process. ESW strip cladding relates
to the resistance welding processes and is based
on the ohmic resistance heating in a shallow layer
of liquid electro conductive slag. The heat
generated by the molten slag pool melts the
surface of the base material and the strip electrode
end, which is dipping in the slag and the flux. The
penetration is less for ESW than for SAW since
there is no arc between the strip electrode and the
parent material.
In comparison to SAW cladding, the electrical
conductivity of the molten slag must be much higher
Figure 1. Principles of electroslag strip cladding.
to avoid arc flash, which disturbs the process. The
composition of the welding flux influences the
conductivity, the solidification range and the viscosity
of the molten slag. Fluxes for ESW strip cladding are
high basic, with a high share of fluorides. To
increase the cladding speed at corresponding high
welding currents, it is necessary to use fluxes
producing a slag of even higher electrical
conductivity and lower viscosity.
The temperature of the slag pool is about 2300°C
and, as it is not fully covered with flux, it emits
infrared radiation. The resulting thermal load makes
it necessary to water-cool the contact jaws.
Because of the higher currents to be transferred, the
welding heads for ESW are more heavily built than
welding heads for SAW-strip cladding.
ESW features
Compared to submerged arc strip cladding the
electroslag cladding process shows the following
features:
• Deposition rate increased by 60% to 80%.
• Only half of the dilution from the base material
due to less penetration (about 10-15% dilution).
• Lower arc voltage (24–26 V).
Svetsaren no. 1 - 2007 - 17