There
are probably more welders employed Fabrication welding and considerably low
volume of welders are capable in Repair and Maintenance welding. The main
reason is for the same is repair and maintenance welding is difficult compared
to fabrication welding. This is the reason that most welding utility services
category has very few experienced welders and they charge very high bills for
their service.
Repair
welding and surfacing are both considered in the field of maintenance welding
and are covered together since they are both done by the same welders. Often it
is extremely difficult to separate what is considered repair welding from
maintenance welding, and surfacing can be included in both situations. The same
basic factors apply to both weld repair and surfacing.
Parts
break and wear out continually. It may be impossible to obtain another part
exactly like the one that broke or wore out. This is particularly true of older
industrial machinery, construction machinery, agricultural machinery, machine
tool parts, and even automobiles. Repaired parts may be more serviceable than
the original part, since they can be reinforced and the weaknesses of the
original part can be corrected. It is often more economical to weld repair
since the delay in obtaining the replacement part could be excessive and the cost
of the new part would normally exceed the cost of repairing the damaged part.
Weld
repair is commonly used to improve, update, and rework parts so that they equal
or exceed the usefulness of the original part. This is normally attained, with
the possible exception of weld-repaired cast iron parts that are subjected to
heating and cooling. Weld repairs on cast iron parts subjected to repetitive
heating and cooling may or may not provide adequate service life. The problem
is that cast iron parts subjected to high-temperature heating and cooling, such
as machinery brakes, furnace sections, etc., fail originally from this type of
service and due to metallurgical changes the weld may fail again without
providing adequate service life. Except for emergency situations, it is not
wise to repair cast iron parts of this type.
The
metal that the part to be repaired is made of has a great influence on the
service life of the repaired parts. Parts made of low-carbon and low-alloy
steels can be repaired without adversely affecting the service life of the
part. On the other hand, high-carbon steels may be weld repaired but must be
properly heat treated if they are to provide adequate service life.
It
is absolutely essential that we know the type, specification, or composition of
the metal that we are planning to weld. As mentioned above, it may be unwise to
weld repair certain metals. But we should not weld on any metal unless we know
its composition.
The
economics of weld repairing are usually very favorable and this applies to the
smallest or the largest weld repair job. Some weld repair jobs may take only a
few minutes and others may require weeks for proper preparation and welding.
Even so, the money involved in a repair job may be less than the cost of a new
part.
A
part made of any metal that can be welded can be repair welded or surfaced. In
fact, some of the metals that are not normally welded can be given special
surfacing coatings by one process or another. All the arc welding processes are
used for repair and maintenance work. In addition the brazing processes, the
oxy-fuel gas welding processes, soldering, thermit welding, electro slag
welding, electron beam welding, and laser beam welding are also used. The
thermal spraying processes are all widely used for surfacing applications. In
addition, the various thermal cutting processes are used for preparing parts
for repair welding.
The
selection of the appropriate preparation process and welding process depends on
the same factors that are considered in selecting a welding or cutting process
for the original manufacturing operation.
