A combination of aging plants, greater fluid corrosiveness
and tightening of health, safety, security and environment
(HSSE) requirements has made corrosion management a key
consideration for refinery operators. The prevention
of corrosion/erosion through live monitoring provides asset and
integrity managers with a real-time picture of how their
facility is coping with the high demands placed upon it by
corrosive fluids. This information can assist in risk
management and auditing. Continuous measurement presents a step
change in the level of corrosion rates that can be determined
and the accuracy of that determination.
Steel pipework and vessels are always at risk of corrosion
or erosion. Unless monitored, there is a risk of failure, which
may impact the safety of workers and the environment. The financial costs of
operational interruption, repairs and reputational damage must
also be considered.
As oil and gas operators produce and process ever more
corrosive or erosive hydrocarbon streams, the demands on plant
metallurgy steadily increase. Permanently installed sensor
systems can deliver a continuous picture of asset condition
over time, at a comparable cost to that of a single manual
inspection. This picture can be correlated with process
conditions that may be causing corrosion or erosion, and
strategies to minimize corrosion, such as inhibitor use. With
such knowledge, the asset manager can move beyond merely
knowing whether corrosion or erosion is occurring, to
understanding why and at what rate. This understanding enables
operators to make better-informed decisions.
Need for continuous monitoring.
There are various established techniques for the periodic
assessment of pipe and vessel integrity. The drivers of
corrosion and erosionprocess conditions, crude
constituents and abrasive solidsand the inhibitors to
hold corrosion rates in check are familiar.
Periodic inspections do not, however, deliver continuous
pipework condition data that can be correlated with either
corrosion drivers or inhibitor use to understand the impact of
process decisions and the inhibitor usage on plant integrity.
Manual acquisition of ultrasonic wall thickness data is also
frequently associated with repeatability limitations and
Permanently installed sensor systems, on the other hand,
deliver continuous high-quality data. The ultrasonic sensors
can be installed on pipes and vessels operating at up to
600°C (1,100°F). These sensors have also been certified
as intrinsically safe for use in most hazardous environments.
The system has been proven in operation over a number of years
in refinery environments, and more recently in upstream facilities.
Continuous monitoring installation data can validate that,
when corrosion is occurring, it is often an intermittent
process rather than a continuous event. It is in such cases
that it is particularly valuable to be able to correlate
thickness data over time with process and/or inhibitor
parameters. Moreover, the data highlights which prevention or
mitigation strategies are most effective.
At the core of the continuous monitoring system is an
ultrasonic sensor mounted on stainless steel (SS) waveguides.
The waveguides isolate the sensor electronics from extreme
temperatures and guide the ultrasonic signals to the pipe wall
and back without excessive signal degradation or distortion.
The system can monitor pipe wall thicknesses in the range of 3
mm to 40 mm (1⁄8 in. to 1½ in.) and can be applied
on a wide range of steels and other alloys. Frequent
measurement of wall thickness allows for metal loss detection
at the level of 10s of microns.
Each sensor is equipped with a radio, and communicates with
other sensors and a gateway (base station) within a 50-m
(55-yd) range. The sensors form a mesh or wireless network that
does not require previous installation of wireless nepetwork
infrastructure (Fig. 1). Each sensor radio can also act as a
relay, or repeater, enabling the network to span hundreds of
meters from the gateway.
Fig. 1. Wireless
communication of the continuous corrosion
The data is channeled via the gateway to a database on a
connected computer. If, as is the typical case, this computer
is networked, then browser-based visualization software enables
the corrosion/inspection engineers to view the data at their
desks. The data can also be exported in any of the file formats
required by the various process monitoring applications,
enabling seamless transfer and read-in to those packages and,
thus, correlation with the process data at the sensor
The principles of the system were developed by the
world-leading nondestructive testing research group at the
Imperial College London, led by Professor Peter Cawley. It was
refined and proven over several years of collaboration with BP
refineries. The experience gained in this collaboration helped
produce the robustness required for harsh refining environments. The system was
conceived from the outset to be cost-effective for large-scale
Cost-effective for large-scale deployment.
The sensors are battery powered. Thus, no cabling is
required, which minimizes the installation costs and imposes
fewer restrictions for remote areas and for large-scale
The sensor is secured on the pipe/vessel by means of two
studs that are welded onto the pipe. For pipe-wall temperatures
below 100°C, the studs can also be welded onto girth
clamps, which are themselves mounted on the pipe. Stud mounting
allows for dry coupling; no couplant is required between the
waveguide tip and the pipe wall. This, together with multi-year
battery life, eliminates the need for expensive maintenance access between
Stud-based mounting also enables geometric flexibility and
reduces installation time to just minutes. A two-person
installation team can typically install 50 sensors per day.
Robust wireless communication.
The sensor has been designed using high-grade materials to
allow for many years of continuous operation. A number of
systems have been in uninterrupted operation for three years.
To ensure that the system performs in the event of a blockage
of an individual pathway or the loss of a sensor, there are
multiple pathways for data transmission through the mesh back
to the gateway (Fig. 1), which guarantees data retrieval.
The gateway channels data transmitted from all the sensors
located in the network. Typically, wall thickness measurements
are sent every 12 hours. This interval can be changed at any
time for any sensor, to as little as a few minutes if
necessary, depending on the monitoring or metal loss
determination requirement at that location.
Data is stored in the computer database to guarantee
security. This also allows the user to view a full history of
data readings, and build a clearer picture of corrosion and
The system has a wide range of applications in the
hydrocarbon processing industry. At
present, nearly 20 refineries now use this corrosion monitoring
system and it is in use on virtually all crude unit lines, air
coolers, furnaces, heat exchangers, pumps, amine units, cokers
and cracking units. Pipe materials include carbon, chrome and
stainless steel. Typical locations for sensor installation are
on elbows, which are known as thin spots, and areas of
particular turbulence. Older units, particularly those
operating outside of design specifications, are worthy of
The system allows facility operators to monitor locations
continuously without the repeated cost of access. By
correlating metal loss data with process data (composition,
hold-up, temperature), a true understanding can be gained of
what changes in parameters are driving corrosion and erosion
This understanding is enabling operators to make
better-informed decisions about changes according to these
parameters to minimize the impact of corrosion on their plant.
Furthermore, users are now optimizing their inhibitor and
biocide use, by level and location, based on insights gained
from the data.
Continuous monitoring on near-end-of-life lines enables
turnarounds to be scheduled with much greater confidence. In a
recent example, a system installed on a line with an expected
remaining life of 12 months enabled line replacement to be
postponed by a very valuable six months. Plus, the used sensors
were recovered for re-installation elsewhere.
In plants with aggressive rates of corrosion, particularly
where corrosion is intermittent and the remaining life is
uncertain, frequent manual inspection is common. Where
operating temperatures are sufficiently high and a shutdown is
necessary for safety reasons to enable manual inspection, the
lost production can come at a high cost.
Some locations in a facility can be hard to reach; thus,
technicians incur safety risks in gaining access. Where high
pipework and vessel temperatures are involved, ensuring
technician safety during manual inspection becomes even more
Permanently installed systems reduce the safety risks
associated with collecting plant condition data. In several
chemical production facilities, corrosion monitoring
system users have also been able to eliminate the periodic
shutdowns that they had previously required to enable operator
access. The installed systems are also now delivering data
where inspector availability is limited or where access is
difficult for environmental reasons, such as in Arctic
Corrosion monitoring was conducted on cast carbon steel
U-bends with a wall thickness of approximately 25 mm (1 in.),
operating at 380°C (720°F) in the Gelsenkirchen refinery operated by BP to ensure
continued safe operation (Fig. 2). Since the high temperature
prevented accurate manual ultrasonic wall-thickness
measurement, and would have exposed inspectors to significant
hazard, the continuous monitoring system was installed, as
shown in Fig. 3. This secured operation with confidence until a
turnaround. The system has been delivering reliable measurement
data for three years.
Fig. 2. Measured wall
thickness for sensors installed on
one carbon-cast steel U-bend in the
Fig. 3. Monitoring data
of the carbon steel U-bend at
New monitoring method.
Operating companies using the continuous corrosion
monitoring solution have a more accurate and timely
understanding of the corrosion and erosion rates occurring in
their facilities. Where inhibitors are in
use, the system is giving a greater understanding of their
effectiveness. The real-time data allows potential corrosion
hotspots to be remotely monitored, at time intervals of the
operators choosing. This insight allows asset managers to
make more informed decisions, to the benefit of plant
integrity, safety and operating costs.
The system has been tried and tested in some of the most
inhospitable environments, and it operates at
pipework temperatures from 30°C to 600°C
(20°F to 1,100°F). It allows operators the
freedom to choose monitoring locations irrespective of how
inaccessible they are, thanks to the use of ultrasonic sensors
and wireless networks for data retrieval. Having already been
installed for a number of years in BP refineries across the
world, the system has now been adopted by other super-major and
privately held refinery operators in the US,
Germany and Canada. This technology is making a real
difference in an industry facing new challenges every day.
Peter Collins is the CEO of Permasense. Dr. Collins joined the
Permasense board in 2010, and he is responsible for the
overall development of the company. Already an
experienced entrepreneur, he has held board-level
technical and operational roles in public and private
companies with $100 million+ revenues. His
previous roles include operations director at Sondex
plc, which specializes in the engineering and
manufacture of directional drilling and formation
evaluation systems and wireline tools for the
production of oil and gas. He was earlier technical
director at PII Ltd. and a manager at management
consultancy Arthur D. Little Ltd. Dr. Collins holds a
PhD in computational fluid dynamics from Imperial
College London, a BE degree in mechanical engineering
from the University College Dublin, and an MBA from