|
ACFM
Shipping
Applications
| |
Introduction
Merchant
ships are generally constructed from large steel plates welded
together either manually or on submerged arc lines. This offers
many opportunities for ACFM inspection. The ability of ACFM
to inspect through paint, even underwater, means that ship
hulls can be inspected without having to enter dry-dock.
Using
ACFM in conjunction with a rope-access technician or diver
also avoids the need for scaffolding or overside staging.
|
Overview
As
well as inspecting ships hulls, ACFM has been used to inspect storage
and ballast tank welds on chemical and gas tanker ships, LPG spheres
and propeller blades and thrusters. In most cases large areas require
inspection, a process that can be shortened through the use of an
ACFM array probe which can be marinised if required.
Propeller blades are usually inspected underwater by a diver with
an underwater instrument. However this is one example where costs
can be reduced through the use of a topside AMIGO instrument and
a marinised probe with 50m cable in place of a subsea instrument.
Although
most of a ship is made from ferritic steel, some components (such
as the propeller) may be made from more exotic non-ferrous alloys,
for example phosphor bronze or aluminium bronze. ACFM probes can
be used to inspect virtually any type of metal, with a simple change
in set-up.
Projects
and Applications
Voith
Schneider Propulsor Blades
 |
Project |
Equipment |
|
Propulsor blade inspection
|
U19
AMIGO system
Underwater 40mm
flat array probe 5KHz
50m underwater probe
extension
Standard underwater weld probe 5KHz
|
| |
In
collaboration with a leading underwater maintenance company
in the UK, TSC Inspection Systems developed an ACFM system
and underwater array probe to provide accurate and reliable
detection of defects in aluminium bronze Voith Schneider propulsor
blades and phosphor bronze ships propellers.
The
array probe is capable of inspecting a width of 40mm at once
and detecting defects in all orientations in one pass. It
is also capable of differentiating between cracks and cavitational
pitting, a common problem on all propulsor and propellor blades.
Early
detection of defects allows instant decisions to be made on
whether components need to be replaced, or condition monitoring
carried out.
The
ability of ACFM to save all scan data allows direct comparison
of defects and assessment of any propagation over time. |
High
Strength Steel (HSS) Welds on Submarines
 |
Project |
Equipment |
| Submarine
high strength steel (HSS) weld inspection
|
U19
AMIGO system
Standard weld probe
5KHz |
| |
A
recent trial for certifying underwater welds in high
strength steel, in collaboration with one of the UK's
leading underwater ship inspection companies realised
a major breakthrough in the assurance that an underwater
welding capability, that allows warships, in particular
submarines, could be supported afloat.
This
avoids, at least, part of the cost of similar work currently
undertaken in dock on de-commissioned submarine ‘hulks'.
During 2007, tests were carried out using a nickel-based
electrode to provide fillet welds for high strength
steels. At the time, the austenitic properties of the
electrode restricted the NDT of the fillet welds to
visual inspection only. The recent trial of ACFM technology
removed that limitation.
ACFM technology was developed to allow crack sizing
underwater without the need for any electrical contact
and is already being used successfully by numerous underwater
contractors involved in defence applications, to find
and size cracks and discontinuities in warship and submarine
propeller blades.
After
a review of the available technologies, TSC's client
concluded that ACFM may also be suitable for testing
these fillet welds.
The ACFM trial was carried out at the client's UK
based offices utilising their own test tank. Divers were
used to pass an ACFM probe over fillet welds, into which
surface and sub-surface cracks had been induced.
|
|
Cargo
and Chemical Tankers
 |
Project |
Equipment |
| Tanker
cargo tank inspection
|
U19
AMIGO system
Standard weld probe
5KHz
Straight mini pencil
probe KHz
Right angled mini
pencil probe 5KHz |
| |
ACFM
inspection techniques have been used on a major international
shipping company's chemical transport tankers; for the investigation
of possible defects, located in cargo tank floors and top
and bottom sloping wall welds, as well as leak detection between
cargo and ballast tanks in chemical tankers.
In
one case, inspection was carried out during the time the vessel
was in transit between offload and load ports, thus no costly
downtime or docking was required. |
Thruster
Inspection
 |
Project |
Equipment |
| FPSO
thruster blade maintenance
|
U19
AMIGO system
Underwater
array probe
Micropencil
probe
Mini
pencil probe
50m
array umbilical
Custom
build stop hole probe |

|
ACFM
inspection was carried out on forward and aft stern
thruster blades on an FPSO located in the North Sea.
The blades on both stern azimuth thrusters had serious
cavitation erosion damage. Due to the extent of the
erosion the leading edges had become perforated, with
a subsequent loss of blade area. Such a situation could
accelerate a fatigue failure resulting in a greater
loss of blade area, rendering the unit inoperable.
The
leading edges were trimmed back to remove the edge damage
and blended into the tip without changing the diameter.
All five associated lifting padeyes on each thruster
were also inspected.
Diving
operations were carried out from a 12m Rigid Inflatable
Boat (RIB), launched from the RIB Mother Vessel (RMV).
All
areas inspected were located subsea, using diver intervention
from the RIB. Alternating Current Field Measurement
(ACFM) was used to determine the presence or absence
of surface breaking defects in all the specified areas
of the propeller blades.
|
|
Crack
Detection / Applications
/ Shipping 1 2
3 4
5 6
7 8
9 10
Next
|