Yards Moving Forward - GL Group

Dr. Manfred Feyer is in charge
of the new testing laboratory
in Hamburg-Harburg
ter,” says Manfred Feyer. What it always boils down to is assisting
the customer from a financial point of view, because the
services provided by GLP help to prevent damage, clarify
responsibilities, and optimize designs as well as production
processes. To put it in a nutshell: cutting costs is the name of
the game.
Calling in the Specialists
“We are
something
like technical
pathologists”
Feyer has a good example from his own professional experience:
a cylinder-head bolt from the 1500 kW main engine
of a container ship. Made of tempered chrome-molybdenum
steel and with a length of 550 mm, this high-performance
component had fractured at the first turn of the thread, as was
shown by an inspection during operation. This circumstance
led to considerable time spent in the yard, and hence enormous
expense. The aim of the testing order issued to GLP was
to identify the reasons and responsibility for the damage.
Such an investigation does not necessarily start with
sophisticated techniques. Before a case of damage is given
“intensive care” in the laboratory, Manfred Feyer first collects
as much information as possible on the general conditions
under which the damage arose. “How old is the engine? Were
Make it to break it: the stress at which the samples rupture
provides clues about the material used
MODERN DAMAGE ANALYSIS
there any irregularities in shipboard operation? Has this sort
of damage ever been encountered previously? These facts
could give us valuable pointers to a systematic error,” says
Feyer. In this initial phase, GLP cooperates closely with
“Damage & Repair”, the central GL department for damage
and repair management, which is based at Head Office of GL
in Hamburg and boasts one of the largest damage databases
in the world. “These colleagues are the specialists with operational
know-how, which we at GLP as experts for laboratorybased
failure analysis simply cannot have. When handling
cases of damage from the world of ship operation technology,
we work hand in glove,” says Feyer.
No Isolated Event
Back to our cylinder-head bolt: here a check of the operational
conditions turned up no abnormalities. But now the
formidable analysis tools of GLP were brought to bear on the
problem. The macroscopic study of the break yielded the first
important finding: this was a fatigue fracture, starting from a
crack in the root of the first thread turn. In contrast to a forced
rupture, a fatigue fracture is not an isolated event that makes
the part fail suddenly. On the contrary, a fatigue fracture
develops through crack propagation over a lengthy period of
time. Eventually, there is of course a final forced rupture and
the total failure of the component. “In most cases, a fatigue
fracture can be seen with the naked eye or by means of a magnifying
glass,” Feyer explains. “The ruptured surface exhibits
the lines of rest, or clamshell marks, which are typical of
fatigue fractures.” The lines of rest of a fatigue fracture surface
provide information about the growth of the crack. Or, to be
more precise: the “times of rest” in which the crack only grows
slowly or not at all – for example, because of machine downtime
or a change in operating conditions.
The first diagnosis was therefore fatigue fracture.
However, such damage can normally be excluded if the specified
material is used, if the installation and operation was as
required, and if the necessary maintenance was carried out
properly. So what had happened?
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