Corrosion under insulation poses
major threat to offshore asset integrity
The battle against corrosion is an ever- present issue for the offshore oil and gas industry, with structures, pipe- work, and equipment widely exposed to seawater and humid, salty air.
Corrosion under insulation (CUI) is a major
and well-understood threat, and the industry
is researching new technology to help identify
the impact earlier and more reliably. Mainly,
CUI affects steel components, which corrode
when they are in contact with water and air.
Insulation of plant and pipework can create a space where water can collect and rest
against the metal surface over extended periods of time. With outdoor equipment, even
very small gaps in insulating cladding can
let in sufficient volumes of water to cause
significant corrosion issues.
A further dilemma created by insulation is
that it can hide the effects of the corrosion
from view, so that a heavily corroded pipe can
appear normal when visually inspected. But
by the time the effects have become clearly
visible from the outside – often in the form
of particles of oxidized metal or discolored
water running off – significant damage may
already have occurred.
Removing insulation to check the condition
of pipework is a laborious process and a costly
method of assessing the condition of an asset. Maintenance specialists have developed
a suite of different solutions that can make
managing CUI across an installation more
efficient and help ensure pipes and structures
conform to HSE guidelines.
The biggest cost associated with inspecting
for corrosion is manpower, and this is exacerbated in the case of offshore facilities – mobilizing the right personnel onboard and ensuring
that they receive the correct briefing is a time-consuming process. The focus must therefore
be on minimizing the resources needed to
carry out the work. The preferred approach
is for the inspection and fabric maintenance
departments to work together, using three-man
teams comprising an inspector, insulator and
painter, all of whom are rope access-qualified.
Keeping the teams as small as possible can lead
to considerable reductions in cost.
It is better still to avoid the process of trans-
porting new people to site to perform an in-
spection by instead training team members
already on location to handle inspection work.
Advances in technology to help automate the
process have played a big part in making this
possible, increasing the efficiency and effective-
ness of inspection crews. Equipping teams with
CUI detection tools such as digital radiography
and pulsed eddy current (PEC) technology can
significantly speed up site inspection processes
and improve the likelihood of early detection.
Although radiographic and PEC imaging
are not new, the techniques used to perform
inspections have advanced rapidly. Previously
each radiographic exposure took several minutes to capture and subsequently needed to be
processed using lab equipment. These steps can
now be taken in a matter of seconds and images
can be viewed on the spot on a mobile device.
As recently as five years ago PEC readings
needed to be performed on a point-to-point basis,
making it time-consuming to capture all the
angles and positions required to scan a length
of pipework. In response, Bilfinger worked with
imaging specialist Eddyfi to develop a system
that runs continuously. This cuts the time taken
and significantly increases the number of data
points available, providing greater certainty of
results. Using mobile data processing devices,
engineers can now output easy-to-interpret con-
dition reports showing the location and extent
of any defects without any need for desktop
analysis. This means response times to priority
corrosion issues can be much faster.
Bilfinger was called in by a contractor operating a platform for a major global energy
company to renew the insulation on all exterior pipework where CUI was detected. The
existing insulation was mineral wool, enclosed
in neoprene cladding, and the cause of the CUI
in each case was failure of the elastomeric
sealant used in the joints between sections.
Where replacements were needed, the mineral wool was replaced with foam glass. This
was clad in banding tape sealed with Terostat
PC vapor-barrier mastic, a long-life sealant
proven to deliver better resistance than elas-
tomeric options. The insulation was applied
in the form of pre-fabricated shells supplied
tailor-made, allowing fast installation on site
and reducing costs.
The scale of the project, which involved
replacing hundreds of meters of insulation,
meant that the works took place over several
months. Throughout delivery, the project
team provided a monthly report with information on productivity, tool-time, costs, man
allocation hours, work pack tracker, health
safety, environment and quality CUI statistics
and linear distance re-insulated.
CUI is critical, especially where ageing
infrastructure is involved, and the current
trend for maximizing the lifespan of large
pieces of offshore infrastructure presents
increased challenges, especially at mature
fields on the UK continental shelf. Failure to
manage CUI can, at best, lead to expensive and
time-consuming maintenance operations; at
worst, it can pose a major threat to the safety
of facilities and personnel, so this is not an
area offshore operators can afford to overlook.
The financial burden involved in performing
inspections can be significant, but advances
in both inspection technology and strategies
have dramatically increased the efficiency of
the process in recent years, decreasing the
temptation to push back or skip what is an
essential safety monitoring process. •
Advances in imaging technology are providing
offshore maintenance crews with much more
data on the ‘hidden’ condition of their assets
than was available 10 years ago. (Photo courtesy