QF RDI efforts ramp up fight against ‘silent killer’ of oil & gas pipelines

Corrosion is a phenomenon often referred to as a ‘silent killer’ of metals. It weakens the material from within, while the framework or the skeleton of the material remains seemingly intact. It eats away at the material, little by little, causing the structure to lose its integrity and making it more prone to breakdown and failure.

Corrosion is the natural degradation of materials caused by an electrochemical reaction with its environment and is the most common cause of failure in oil and gas pipelines. Corrosion-related failures have wide-ranging consequences including those on human health and the environment, as well as disruption of asset operations resulting in significant economic impact.

“Among the different types of corrosion, the one that pipelines suffer from most is internal corrosion, which is normally associated with the characteristics of the fluids they carry. The gas reserves in Qatar contain acid gas – natural gas containing significant amounts of both Carbon Dioxide (CO2) and Hydrogen Sulfide (H2S), both of which increase the risk of internal corrosion in pipelines,” said Dr. Abitha Ramesh, Corrosion Researcher at the Qatar Shell Research and Technology Centre (QSRTC), an anchor partner company of Qatar Science & Technology Park, part of Qatar Foundation Research, Development, and Innovation (QF RDI).

Monitoring the corrosion rate of pipelines is critical for the safe operation and management of pipelines. One of the most common ways to do this is by placing a ‘corrosion coupon’ in the pipeline.

A corrosion coupon is a small piece of metal, made of the same material type and grade as the pipeline. These coupons are retrieved from the pipeline at specific time intervals, cleaned and weighed. The difference in weight is used to calculate the average corrosion rate which in turn can be used to determine the integrity of the pipeline.

Unfortunately, a conventional coupon cannot help in the complex scenario where under-deposit corrosion (UDC) occurs. In an effort to tackle one of the most prominent corrosion challenges in the oil and gas industry, a team of academic and industrial experts from QSRTC, Qatar University, Imperial College London teamed up to develop an innovative corrosion monitoring device through the financial support of QF’s Qatar National Research Fund.

Dr. Ramesh explained when H2S in sour gas reacts with the walls of a steel pipeline, it produces a thin scale of iron sulfides. These iron sulfide scales along with silicon dioxide (sand) may chip off from their primary location and deposit to other locations within the pipeline. When these deposits accumulate, it subsequently leads to aggressive local chemistry underneath them. A rapid form of corrosion can occur these deposits eventually leading to significant wall loss and pitting known as UDC, which is not captured in currently used corrosion monitoring techniques.

“We have revamped the traditional corrosion coupon and created a smart version that tells us more than just the corrosion rate. The newly developed coupon incorporates three of the most commonly found deposits in sour gas pipelines, and can also include an embedded sensor to monitor conditions beneath those deposits.”

The purpose of having these deposits on the newly developed coupon is to measure the local chemistry (chloride ions, potential drop and pH) under these deposits and to pick up early warning signs that UDC may be occurring. The role of the sensor is to identify potential problems even earlier by detecting local changes in chemistry that are a precursor to corrosion.

“These coupons are retracted every two months for detailed analysis, thereby allowing us to very closely follow changes associated with UDC and its most dangerous manifestation called pitting – a rapid and localized form of corrosion in which cavities or "holes" are produced in the material,” said Dr. Ramesh.

The smart-coupons developed in this project are expected to make an immense contribution towards the early detection of UDC and pitting. In addition, the sensor in the coupon will be able to relay information in real-time as it detects changes in the local chemistry. For example, drop in the local pH or electrochemical potential or chloride ion concentration changes indicate that the environment is becoming more conducive to pitting.

Having an online sensor that can communicate this crucial information in real-time will contribute significantly towards maintaining safe operations. “Such early detection of pitting is very beneficial because when pitting starts the rate of pit propagation can be very fast and can have significant impact on the pipeline.”

“The smart-coupons are currently being tested in the field. We deployed the coupons at Pearl GTL - a joint development by Qatar Petroleum and Shell in January this year; if things go as per plan, there is a real potential for these modified corrosion coupons to replace conventional coupons in the near future”, said Dr. Ramesh.

These new corrosion coupons are manufactured in Qatar. The cost of manufacturing the first unit was equivalent to that of conventionally used coupons from the US. However, the cost is expected to go down considerably if they are mass-produced in Qatar.

Dr. Ramesh said: “Internal corrosion in pipelines, if not detected early, can affect the economics of production and processing, threaten lives and cause long-lasting environmental damage in case of failure. We can say with certainty that this novel UDC online sensor will play a significant role in ensuring the structural integrity of oil and gas pipelines not just in Qatar but also worldwide in locations with sour service pipelines.”