The need for weld repair and surfacing
There are probably more welders employed doing maintenance and repair welding than
there are in any other industry grouping. The work done in the primary metal industry
is primarily maintenance and repair. This is true also of the utility services category
and by combining these with repair services you find that approximately 18% of the
welders are engaged in this type of work.
In addition, it has prime importance to welding since the earliest use of welding
was for repair work. The most famous incident happened at the outbreak of World War I
when German ships were interned in New York harbor. Their crews, hoping to make the
ships inoperable, sabotaged the engines and machinery. However, by means of welding,
repairs were quickly made and the ships were placed in transatlantic service to deliver
material from the U.S. to Europe.
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 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.
In the case of repair welding, there are usually limitations, such as the availability
of equipment for a one-time job and the necessity of obtaining equipment quickly for
emergency repair work. This limits the selection and it is for this reason that the
shielded metal arc welding process, the gas metal arc welding process, the gas tungsten
arc welding process, and oxyacetylene welding and torch brazing are most commonly
However, for many routine and continuous types of repair work some of the other
welding processes may be the most economical. For example, submerged arc welding is
widely used for building up the surface of worn parts. The electro slag process has
been used to repair and resurface parts for hammer mills, for construction equipment,
and for rebuilding rolls for steel mills. Thus there is a difference in the selection
of the welding process for the routine, continuing types of repair and surfacing work
versus the one-of-a-type or breakdown emergency repair job.
Analyze and develop rework procedure
The success of a repair or surfacing job depends on the thought and preparation prior
to doing any actual work on the project. Many factors must be considered in making a
thorough analysis. A thorough analysis as outlined may not be required in many
situations. This is due to experience gained by welders and others in analyzing jobs,
making repairs, and then checking on the service life of the repaired part. As
experience is gained many short cuts can be taken, but it is the intent to provide a
detailed method of analyzing jobs so that the repair will be as successful as
One of the reasons for such an investigation is to establish the cause of the failure
in the case of a broken part or the cause of wear or erosion in the case of a part to
be surfaced. The four points outlined are:
- Make a detailed study of the actual parts that failed.
- Learn the background information concerning the specifications and design.
- Make an investigation of the materials used.
- Make a listing of all of the facts so that at the conclusion the reason of failure
will be as accurate as possible.
There are certain situations and certain types of equipment for which repair welding
may not be done or may be done only with prior approvals.
Certain types of containers and transportation equipment must not be weld repaired or
may be welded only with special permission and approval. These include railroad
locomotive and car wheels, high-alloy high-strength truck frames, and compressed gas
cylinders. Most pieces of power-generating machinery, including turbines, generators,
and large engines, are covered by casualty insurance. Weld repair on such machinery
can be done only with the prior approval of the welding procedure by the insurance
underwriters. In some cases, approval may not be granted. An example of this can be
cast iron crankshafts in large stationary diesel engines. Certain weld repairs may be
made but it is necessary to develop a written procedure which must be approved in
writing by the underwriting company’s representative.
Repairs by welding to boilers and pressure vessels require special attention. Pressure
vessels that carry an ASME stamp or are under the jurisdiction of any state or province
or government agency must be repaired in accordance with the National regulations
issued by responsible authorities.
Repairs by welding are limited to steels having known weldable quality. It provides a
maximum carbon content of 0.35% for carbon steels and a carbon content of 0.25% for
For welding high-alloy materials and nonferrous materials the work must be done in
accordance with the ASME code. Welders making such repairs must be qualified based
on the thickness of the material and the type of material being welded. Full-penetration
welds are required with welding recommended from both sides. Permissible welded repairs
are defined as cracks, corroded surfaces, and seal welding, patches, and the replacement
A repair is the work necessary to return a boiler or pressure vessel to a safe and
satisfactory operating condition. Alterations are also permitted and this is a change
in a boiler or pressure vessel that substantially alters the original design and in
this case work can be done only by a manufacturer possessing a valid certificate
authorization from ASME. All alterations must comply with the section of code to
which the original boiler or pressure vessel was constructed.
A written repair procedure is required for doing either repair work or alterations.
In the case of an alteration a record must be made and all alteration work must be
approved. These records must be filed with the inspection agency or the jurisdictional
agency, the National Board of Boiler and Pressure Vessel Inspectors, and all work must
Alterations on bridges, large steel frame buildings, and ships may be done only
with special authorization. The alteration work must be designed and approved. The
welders must be qualified according to the code used and the work must be inspected.
Written welding procedures are required.
Once the decision has been made to make a weld repair it is then necessary to
establish why the part failed or wore out. This relates to the type of repair job since
it also determines whether reinforcing may be required. Reasons for the part to fail
or wear out can be among the following:
If the part failed because of an accident or an overload, it may be returned to service
with the weld repair made to bring it back to its original strength. The same
consideration applies if the part has been abused or misapplied. It may be necessary
to reinforce the part so that it will stand temporary overloads, misapplication, or
abuse. This decision should be made prior to the weld repair.
In the case of poor workmanship, poor design, or incorrect material the weld repair
should eliminate the poor workmanship that was responsible for the failure. In this
case, the part would be returned to its original design. If failure is due to poor
design, design changes may be required and reinforcement may be added. In a case of
wrong material it will be assumed that the material was of a lower strength level
which contributed to the failure. In this case reinforcing would be required. If the
repair or alteration job is to modify the part, it is necessary that the modification
be designed by competent designers who have the knowledge of the design conditions of
the original part. This may require reinforcing to make sure the modification or
alteration is satisfactory.
Another important factor that must be considered is what results are expected of the
repaired or reworked part. Should it be reinforced or should it be redesigned and
altered to provide necessary service life? Finally, in the case of surfacing, what
better surface could be provided to withstand the service that caused the premature
wear or failure?
A written repair procedure is required for all but the most simple jobs. It is
absolutely necessary that the type of material being welded is known. This can be found
in several ways. If possible, refer to the drawing of the part and the specifications
that are shown for the part or parts to be welded.
If this is not possible, particularly in the field or at the maintenance shop, look
for clues as to the type of metal involved. Analyze the application of the metal, for
clues. For example, an automobile engine block is normally cast iron except for some
which might be cast aluminum. Aluminum and iron are easily distinguishable. The spring
of an automobile or truck would normally be high-carbon steel. The body structure of a
car or truck would be mild steel. The appearance often helps provide clues.
As a final resort it may be necessary to obtain a laboratory analysis of the metal.
Filings or a piece of the metal must be sent to a laboratory capable of making such
The normal method of selecting the welding process will be followed once the material
to be welded has been identified. This involves the type of metal, the thickness of
the metal, the position of welding, etc. This also leads into the question of filler
metal to be used. After this, the normal method of filler metal selection is followed.
This involves matching base metal composition, matching the base metal properties,
particularly strength, and providing weld metal that will withstand the service
In surfacing, the surface characteristics desired for the finished job depend entirely
on the service to which the surface will be exposed. This is based on knowledge and
experience and on the fact that the surface has deteriorated to the point that it needs
to be reworked or resurfaced. When wear is involved, surfaces can be rebuilt many times
without reducing the strength of the part and the service life will be greatly
The repair procedure should be very similar to a procedure developed for welding a
critical part. It should include the process and filler metal and the technique to be
used in making welds.