JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013 - 41

repair

Using composites to repair steel vessels

Composite patching has proved its effectiveness
and cost benefits in the aerospace industry for
several years now. However, there are several
fundamental differences between aerospace
and steel vessel applications, which dictate
a separate approach and investigation of the
problem.

By
Elena Rodriguez
Adhesives and Plastics Welding Coordinator
Joining Technologies Plant - AIMEN Technology Centre

Another disadvantage of traditional repair methods is that the
hot sparks associated with welding in highly explosive environments such as ship holds (e.g. in a hydrocarbon tanker or
a hazardous products cargo ship) and fuel tanks necessitate a
very careful and complicated preparation and require stringent
safety precautions. This in turn can have a substantial impact on
the cost of the repair, since the ship may stay out of operation
for a relatively long period. Finally, the design and application
of a bolted or welded doubler plate is not a very straightforward
procedure, since all steps must be taken very carefully in order
to avoid the introduction of new stress raisers.
All the disadvantages associated with traditional repair and
reinforcement methods highlight the need to investigate and
assess the effectiveness of new solutions that will help overcome
currently existing problems. Composite material patching is a
very promising method for repairing and/or reinforcing steel
structures. Composite patches prevent crack growth and extend
the lifetime of the repaired structure. A composite patch works
as a crack arrestor by reducing the stress in the area of the crack
tip in the case of cracked structures. Part of the applied load is
transferred from the base plate to the composite patch through
an adhesive layer, thus reducing the stress levels in the substrate
(Figure 1).

any of the major problems faced by steel vessels during
their operational life are common, with fatigue playing
a predominant role. Repeated loading is a very common
loading condition for these structures, leading to the initiation
and growth of fatigue cracks in areas of stress concentration.
If not detected and repaired properly and timely, these cracks
can grow to critical lengths and result in catastrophic structural
failures. The traditional ways to deal with such problems are
well known. Fatigue cracks in welds or panels usually require
renewing part of the weld, welding in the cracks in a panel or
replacing the whole parent panel itself. However, there are
circumstances when these repair or reinforcement approaches
are either time-consuming and costly, or simply impossible to
implement. A typical example is the condition where the whole
structure is under significant loading due to its own weight
(especially tension), prohibiting any welding. Cutting off and
replacing a structural member is also out of the question or
necessitates a very costly solution to support the structure.

Fig. 1: Composite concept for crack repairs

Composite patching has proved its effectiveness and cost benefits in the aerospace industry for several years now, since several
thousands of composite patches are already in use in various
aluminium aircraft structural parts. However, there are several
fundamental differences between aerospace applications and
marine steel applications, which dictate a separate approach and
investigation of the problem. These differences include the different stiffness of the base metal (stiffer steel versus flexible aluminium which is more similar to composites), the completely
different geometries involved (significantly thicker plating and
larger beams are used in steel structures), the different loading
cases and the different operating and environmental conditions.

No78 January - February 2013 /

jec composites magazine 41

JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013