Many oil and gas processing facilities are located near waterways to facilitate transporting products via tankers and barges. Jetties extend far from the shore to deeper water so multiple vessels can tie up and transfer contents. While jetties don’t always get the attention of offshore platforms, they can be massive structures and are subject to many of the same problems as their deep-water counterparts, including corrosion.
Jake Davies examines this problem in the Winter 2017 Tanks & Terminals supplement to Hydrocarbon Engineering, Keeping an Eye on Corrosion. He looks at the sources of corrosion, and why terminal jetties are particularly vulnerable to problems and potential environmental disasters.
In most instances, it is not cost-effective to construct jetty pipelines from stainless or alloy steel, so carbon steel is used instead. The use of carbon steel, however, creates a risk of internal corrosion, particularly where higher sulfur content oils (such as fuel oils) are concerned, or when fuels contain potentially corrosive additives. The presence and build-up of water allows for the accumulation of bacteria that cause microbial-induced corrosion. This issue is especially likely to occur in jetty lines since they have intermittent or slow flow rates, allowing water to settle in low points.
This type of situation normally calls for a program of routine inspections, but these are easier said than done. For starters, these pipes aren’t often placed in the jetty structure with ease-of-access as the main consideration. Even when inspectors can get to them, often via boat, making a visual inspection of the outside of a pipe doesn’t tell the full story. As Jake pointed out, the most insidious corrosion comes from the inside out, so smart inspectors will use portable ultrasonic wall-thickness instruments.
Performing manual inspections for pipeline corrosion requires the services of a trained ultrasonic technician, and access by boat or scaffolding for suspended pipelines. Typical access and manpower costs are US$1000 per measurement location for suspended pipelines, and manual inspections are typically carried out every two months at a cost of US$25,000 per inspection. This results in an annual inspection cost for a jetty with 25 monitoring locations and inspections of US$150,000. Environmental clean-up costs following an oil leak can run upwards of US$250,000, depending on the size of the spill, and are likely to incur significant fines, regulatory pressure, reputation damage, and losses due to operational outages, which are often far more than clean-up costs.
The more beneficial approach is to install Permasense ultrasonic corrosion sensors at strategic points on the pipelines. Once installed, these sensors send information via WirelessHART to a historian via a gateway, where trends can be established. With continuous measurements, it is a simple matter to see if specific oil types or products are having an especially detrimental effect on the piping.
This technology makes it feasible for integrity data across multiple locations to be monitored by experts at a central location, such as at company headquarters or a technical center. Specialized data visualization and analytics software, such as data manager from Emerson, provides corrosion rate calculations and flags variations as they arise, enabling end-users to focus on issues at specific locations. Corrosion rate data can be used to forecast when lines need to be replaced with a high degree of accuracy.
All this aims at avoiding problems and leaks able to cause environmental incidents, large and small, with their resulting fines.
The cost of a leak includes ceasing jetty operations while the leak is repaired, and the cost of spill response and clean-up, as well as closer scrutiny from environmental regulators and potential reputation damage. In many jurisdictions, environmental regulations force an enhanced inspection and reporting regime in order to minimize the probability of a leak. Continuous corrosion monitoring systems provide a means to measure and report corrosion rates.
You can find more information like this, and meet with other people looking at the same kinds of situations in the Emerson Exchange365 community. It’s a place where you can communicate and exchange information with experts and peers in all sorts of industries around the world. Look for the WirelessHART and IIoT Groups and other specialty areas for suggestions and answers.
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