In a nutshell:
There are over 2 million kilometers (1.55 million miles) of high-pressure transmission pipelines in operation today (reference: Global Data 2015); up to 1.5 million kilometers (960,000 miles) are still deemed “unpiggable” – but that number is decreasing as in-line inspection (ILI) technologies continue to evolve to meet the demands of these challenging pipelines. Pipelines transporting high-temperature products still seem to have a large gap in the availability of inspection solutions available in the market. The development of new solutions for these pipelines requires an extensive testing and validation process to ensure reliable and repeatable inspections are possible. This article¹ briefly introduces the development of a magnetic flux leakage (MFL) ILI solution capable of withstanding temperatures of up to 140°C for over 17 hours.
This testing and validation process was divided into four sections: 1.) A feasibility study and small-scale testing. 2.) A production and assembly phase and small-scale testing. 3.) A tool-qualification testing phase. 4.) Full-scale high-temperature testing of a complete tool setup as proof of concept.
Phase 1: The Feasibility Study – Is it Possible?
In this phase of the validation process of a new development, pipeline operators and tool developers come together to ensure a solution can be developed to meet the needed boundary conditions. Within this phase, there are again three phases, which include:
- Review: secure a full understanding of the pipeline and its operational characteristics and determine the requirements the inspection solutions need to meet.
- Assessment: conduct analyses, simulations and testing on key elements and technologies and their applications.
- Results: summarize the results in a comprehensive report including a tool design plan, test plan and inspection plan.
Though the entire feasibility study was very broad, the assessment step, specifically, had many varying elements, beginning with ensuring that the magnet circuits would be able to withstand the high temperature and that the correct magnetizer was chosen such that the high temperature would not impact the magnetization during inspection.
This test was done in the form of a finite element simulation in which a 3D model of the magnet circuit, the magnetic field strength, was simulated at a temperature of up to 190°C. This modeling would determine whether the temperature impacted the magnetization of the pipe wall and ensure that a correct magnetizer unit was utilized, i.e. one that would magnetize from 10 kA/m – 30 kA/m.
3D model of magnet circuit in finite element simulation
The next element of concern would be the temperature exchange. Within the inspection tool itself, there are components that generate heat, such as the electronics. During pipeline inspections in regular operational conditions, the medium propelling the ILI tool can act as a cooling element for these components, allowing the heat to dissipate into the medium. However, when working in high-temperature environments, the opposite is true, and the medium creates energy. Therefore, it became critical that considerations in the solution’s design would be made to keep critical components, such as circuit boards, shielded from the high temperature.
Additional testing was done on the MFL sensors themselves to determine their ability to manage the effects of the heat stresses introduced to the sensor from the medium. Each test scenario built on the results of the previous test, starting with temperatures of up to 140°C. The test setup was executed with the same set of cables and sensors that were then later used for the inspections.
The sensors passed this initial temperature test, but when it was extended to 180°C, exceeding the original technical limitations, the sensors failed. The results indicated that the coil sensors used for ID/OD discrimination contained within the sensor carrier would only perform within their standard performance specification of up to 65°C. However, neither the functionality of the sensor carrier itself nor the measurement of the magnetic flux was affected.
Ultimately, the goal of the feasibility study was to assess the limitations of currently available technologies applicable for this development and to then conduct any needed re-designs. After creating and assessing multiple tool concepts, a final concept was determined; it would consist of two segments, the first being the pull unit encapsulating all components that needed to be kept away from higher temperatures. To achieve this, an insulating concept was realized using two principles:
- An insulating board that would act as a barrier was used to keep the outside temperature of ∼140°C away from the critical components.
- A phase change medium within the tool body itself, which would consume the energy from the electronic components and the outside temperature that may have passed through the insulating board.
The second segment was equipped with the MFL magnetizer, MFL measurement sensors, and subsequent wiring and connectors that could be exposed to the high temperature.
Phase 2 and 3: Production and Assembly – from Theory to Reality
Once developers and the operator were convinced of the theory of the feasibility study, it was time to move forward with the development of the solution. In the production and assembly phase, additional testing made clear which sensors, cables and connectors could be applied to the final tool. Then it was on to Phase 3, the qualification and testing phase. Now that the ILI tool was actually built, the testing got real. A series of pull and pump tests validated the measurement capabilities of the MFL unit and confirmed passage capabilities.
The pull tests included a series of three tests, which are mandatory for every new or modified magnetic unit. The parameters included:
- Small-scale tests that would check the conformity of the tool
- Tests ensuring the quality of the specific tool
- Tests validating the behavior during measurement
After completion of all the pull tests, it was shown that the magnetization level in the pipe wall met the agreed-upon conditions.
The next section of the validation testing included a series of pump tests aimed at validating passage and determining the differential pressure required to move the solution through various pipeline features and ensure the best possible run behavior during inspection. In order to simulate actual inspection conditions, mechanical features such as bends and tees represented in the pipeline to be inspected were re-created. Although all pump tests generated positive results, developers identified options to improve tool centralization, which we implemented and subsequently successfully re-tested.
In-house testing facilities allow for new developments to undergo all necessary validations to ensure their success.
Phase 4: To the Max – Full-Scale Heat Exposure Testing
To ensure the newly developed solution would be able to perform under actual high-temperature conditions, a comprehensive test plan was constructed and executed at the ROSEN Test Facility in Newcastle. This test plan was comprised of a series of tests in which the tool would be challenged at varying degrees of temperature for varying degrees of time.
The first test took place in a bespoke purpose-built pressure chamber where data could be recorded and the temperature controlled manually. The tool passed with flying colors the first 33-hour test where the tool was exposed to 21 hours of 125°C temperatures. The next test, also in the pressure chamber, was comprised of the combination of two tests, one with 21 hours of exposure at 140°C, the second with 5 hours of exposure at 150°C. Though the tools performed without issues during the 140°C tests, issues were experienced on four sensors at higher temperatures. Two failed due to fatigue (they were used sensors from previous testing and were being tested for fatigue); one because of a damaged cable, which resulted in a modification to a cable conduit; and the third because of the overall temperature exposure. As the actual sensor heat was at 180°C due to the test setup, all the testing was deemed a resounding success. This last test trial took over 34 hours, the system controller did not exceed 73.3°C, the phase change medium performed as planned, and the battery temperature did not exceed the designed performance limitations.
Hot and Ready
Through the extensive testing and development period, the MFL ILI tool developed can withstand all needed operational conditions: 140˚C and 100 bar. This new one-of-a-kind solution has now inspected pipelines with both low- and high-temperature conditions; these successes will also be presented. As mentioned earlier, this article only presented a brief overview of the truly extensive process involved in validating a new solution.
¹ Reference: PPIM 2019, MFL high-temperature solution, Guenter Sundag, Thomas Stubbe, and Corey Richards, Rosen USA, Houston, TX, USA