Svetsaren 1/2007 - Esab

Figure 4. Another example of an exotic joint. Macro of a PQR. 22mm thick CuAl (UNS C61400) connected to 20 mm duplex stainless steel, welded with semi-automatic TIG with
automatic wire feeding. The duplex material (right) is buffered with two layers of OK Autrod 19.92 (ERNi-1), two layers of OK Autrod 19.93 (ERNiCu-7) and finally with four layers
OK Autrod 19.49 (ERCuNi-7). Subsequently, the two sides are joined with OK Autrod 19.44 (ERCuAl-A2). One layer is welded with MIG, just to get the process approved.
On the duplex side, all buffering layers have been dye-penetrant tested. The first layer of OK Autrod 19.44 (ER CuNi) showed minor indications of cracking. These areas were
ground out and repaired with OK Autrod 19.49 before continuing with OK Autrod 19.44. The arrow shows the repaired area on the macro photo.
science and previous experience. Usually,
corrosion and other material problems are
associated with other system components such
as pumps and valves.
Examples of dissimilar joints
As seen in Table 1, a variety of materials is used
when building a MSF unit and, naturally, many
dissimilar joints have to be welded . Consumables
and welding procedures have to be selected to
ensure both the highest possible mechanical
properties and preservation of excellent corrosion
resistance in salt water, as well as avoiding hot
cracking problems. In addition, it is often
advantageous to have a gradual change in
compositions across a dissimilar weld to distribute
stresses and strains more evenly. Examples of
this approach are shown in procedures presented
in Figures 1, 3 and 4.
The duplex steel (UNS S31803) is lined with 4
mm thick 90/10 copper nickel sheet that is plugwelded
to the duplex material. The plug welds are
made with a very thin layer of OK Autrod 19.92
(ERNi-1), followed by an intermediate layer of OK
Autrod 19.93 (ERNiCu-7) and finally a cap layer
welded with OK Autrod 19.49 (ERCuNi).
In the fillet welds, four different alloy type consumables
are used. As with the plug welds, the
first layer is welded with an ERNi-1 type filler to
minimise the weld metal Fe-content and,
thereby, prevent hot cracking of the following
layers. An alternative approach would have been
to weld the fillet welds with OK Autrod 19.44
(ERCuAl-A2) only. However, the mechanical
properties would not have been on the same
level as with the chosen combination.
Figures 3 and 4 show PQR macros of two other
dissimilar joints and the complicated welding
solutions needed to connect materials that are
not directly compatible from a metallurgical point
of view. These joints could be described as ‘a
welding engineer’s dream’ – but, at the same
time, a nightmare.
The future of desalination in the Middle East
The future for new desalination plants in the Middle
East looks bright due to increasing
development and influx of people. Many countries
investing in tourism require green areas such as
golf links, parks and gardens, all with high daily
water consumption. The general consensus is that
future demand for fresh water can only increase.
ABOUT THE AUTHOR:
JOHAN INGEMANSSON IS PRODUCT MANAGER
CONSUMABLES AT ESAB MIDDLE EAST, DUBAI,
UAE.
26 - Svetsaren no. 1 - 2007