In a nutshell:
Sometimes pipeline inspections can be like reading a book. When you quickly skim the pages, you don’t catch all the details, but if you slow down, you get a better understanding of what you are reading. Similarly, if an in-line inspection tool ‘flies’ through the pipeline too fast, data isn’t optimally collected, or cleaning isn’t properly carried out, and valuable details can be missed. Ideal cleaning performance and data collection are achieved when tools travel through the line at speeds of below 5 m/s, with a bit of variance depending on the robustness of the given technology and the various pipeline characteristics such as size, product, and general geometry. However, lowering the production speed of any asset also has an effect on operations and financial performance, and therefore is not the best solution. There are various elements that can be integrated into ILI proceedings to combat these high speeds and still gain high-resolution data.
Equinor (formerly Statoil), the largest operator in Norway, among the world’s largest offshore operators, requested as a Technical Service Provider for and on behalf of Gassco AS as an Operator, a pigging campaign for a 42” pipeline with high gas flows between 9.7 up to 11.7 m/s. The gas export pipeline system transports the product between the Europipe I and II receiving facilities and towards a gas terminal 47 km away. In order to establish safe operational pressure and to describe the internal geometry of the line, a cleaning, gauging and ILI campaign focusing on metal loss detection due to corrosion was conducted. As is so often the case, the project execution window was tight and regular operations could not be affected during the inspection. So, the mission was clear: provide effective and efficient pre-inspection cleaning/gauging within one run and collect high-resolution data with the following in-line inspection — all without slowing down production.
One Run Clean
Each element of the campaign had to be given the chance for optimal success, making speed reduction a primary concern. Starting off with the cleaning campaign, customized tools equipped with a unique speed reduction valve that enables them to slow down to 3–5 m/s were used. This new EcoSpeed system utilizes a mechanical valve system allowing for product bypass through the tool body and thereby achieving smooth run conditions. As the high-velocity gas passes, the forces acting on the rear of the tool are reduced significantly so that the tool is propelled forward not at the velocity of the gas, but rather significantly more slowly, thereby negating the need for altered product throughput. Based on the combination of the operator’s knowledge of their dry gas system and this optimized cleaning run, the project team trusted that the pipeline would be sufficiently clean after one run.
Figure 1: Chart showing the effects of velocity vs. differential pressure when EcoSpeed Valve is active.
Calculated Speed Control
The next item on the list was to slow down the combined axial magnetic flux leakage (MFL-A) and internal eddy current (IEC) inspection tool to follow. This, in turn, was equipped with a high-delta speed control unit. In this case, the product bypass is most efficiently controlled by an active valve system. The target tool velocity can be pre-set inside the tool electronics, thereby achieving smooth run conditions. Detailed bypass flow calculations created by 3D finite element modeling confirmed product bypass of up to 50%. This meant that the tool was able to travel slowly enough to achieve the needed performance specifications, without reducing the production speed of the pipeline. All in all, even with a reduced gas flow of 25% at the time of the inspection, the speed control mechanism, using an active bypass valve, proved to create optimal run behavior for the needed data collection and further integrity activities.
Figure 2: Calculated Bypass for Speed Control Valve.
Efficiency Through Technology
In our industry, efficiency is key; we can increase and improve our output by making the correct choices in terms of technology selection, but also through the proper application of said technology. This case ultimately shows how Equinor was able to continue operation during the required inspection work and still gain high-resolution data or insight into the state of their assets by applying the best-suited speed control systems and by combining the two ILI technologies.