ENGINEERING, CONSTRUCTION, & INSTALLATION
Water jet cutting an option
throughout structure’s life
Technology beats heat in many offshore applications
Technology advancements in recent years have enabled amazing things in offshore oil and gas developments. High-strength steels have been de- veloped that make structures lighter
and more effcient. In order to maximize
the performance of the steel, techniques
have been developed that make it possible
to sever steel plates with no heat affected
zone (HAZ). Heat affected zones occur with
all hot work cutting methods (oxyfuel torch,
plasma, etc.) and change the characteristics
of the material around the area where the
cutting or welding occurs. Those changes
can affect material hardness and weldability,
and can cause discoloration or distortion.
Abrasive water jet cutting technology cuts
through steel without creating a heat affected zone. This enabling technology has been
used on end-of-life operations for years, and
recently was employed on two topsides operations for a major operator.
Hot work is an effective and effcient way
to process steel structural members for offshore construction. In many applications,
the precision achieved and fnal properties of
steel members that are fabricated using hot
work methods fall within acceptable limits.
There are, however, applications where the
heat affected zone created by the high temperatures of hot work cause problems that
can limit the fnal product’s performance.
Heat-treated steel products that are cut using
hot work methods have zones where the heating causes grain growth in the material adjacent to the cutting area. This grain growth
and any other tempering effects caused by
elevated temperatures combine to reduce the
strength of the steel. In these instances, alternative cutting methods are required.
For obvious reasons, it is preferred that offshore fabrication or structural modifcations
to hydrocarbon producing structures should
be non-sparking. Performing cutting operations in a submerged environment makes the
abrasive cutting virtually spark-free.
In the 1950s, Dr. Norman Franz, a forestry
engineer searching for new ways of cutting
trees into lumber, became the frst person to
study ultra-high pressure (> 30,000 psi) water as a cutting method. He used free-falling
weights to push a column of water through
very small openings to generate highly pressurized jet streams. Though the forces used
to create the needed pressures are very different today, the nozzle arrangement is not.
Water jet technology progressed rapidly in
A diagram of a water jet cutter with a high pressure water inlet ( 1), jewel and abrasive ( 2 and 3),
mixing tube ( 4), guard ( 5), cutting water jet ( 6)
and cut material ( 7).
the 1970s, led by research and development
at Flow International Corp. With abrasives
added to the jet stream, the high-pressure water gained the needed inertia to cut through
materials that are much harder and tougher
than lumber. Water jets can cut through a
variety of metals, glass, ceramics, concrete,
rock, and other materials. Advantages of water jet cutting include a mechanically simple
system, inherent quenching and cooling of
the part being cut, and no heat affected zone.
Several iterations have been performed
in the design and development of water jet
systems, and the technology has made dramatic improvements using a variety of specialized materials to improve the wear of the
components. In the 1980s, abrasive water jet
technology was applied to decommissioning activities. A system was developed that
made it possible to cut through pin piles
below the mudline so the structures could
be toppled in place for an artifcial reef or
brought to shore for recycling and reuse.
In 2006, the Two-Axis Shape Cutter (TASC)
was developed. TASC takes water jet technology and makes it accessible in a variety of feld
applications. Straight line cuts in the x and y
directions can easily be made. By following a
template, a radius can be created with some
In 2012, multi-string conductor cutting was
introduced. The system is capable of cutting
grouted conductors ranging from 75⁄8-in. inside diameter to 36-in. diameter.
Water jet cutting technology can be the
appropriate option at any stage in a structure’s life, from onshore construction to offshore decommissioning.
Early in 2013, Kiewit Offshore Services
was completing the topsides fabrication for
an offshore platform. Because of client performance requirements, it became necessary to fnd a way to cut 72 slots measuring
5 in. in width by 9 in. in length in two capping beams for the well bay module of the
platform. Several options were considered,
and abrasive water jet cutting was selected
because of the post-cut characteristics of the
steel and concerns about the integrity of the