In a Nutshell:
Imagine the following scenario: an event is just around the corner, and you finally got everything nicely planned out, schedule and all. But suddenly, the weather – an unpredictable force – turns all your expectations upside down and ruins your plans. Obviously, you were unable to calculate such a scenario in advance. Still, now you have to deal with it. In some cases, pipeline operators cannot consider the weather as a variable when building a new pipeline, and what possible impact it can have on their assets, especially the ones that lie hundreds of meters below sea level. In the case of a new construction in China, a typhoon disrupted the construction plans of a subsea pipeline, causing unforeseeable damage. Consequently, the pipeline was in need of an inspection to guarantee the integrity and safety of the asset.
KEEPING FAILURE AT BAY
A Chinese pipeline operator was in the process of installing a corrosion resistant alloy (CRA) and carbon steel (CS) pipeline in the southern sea. During the construction stage, however, a typhoon crossed the plans of the operator and brought construction to a stop. When the work resumed after the tropical cyclone, a close examination of the pipeline showed that seawater had leaked inside of the pipe because the sealing of the pipe plug was lost. This resulted in severe damage to the inside pipe wall. When the operator withdrew a spool out from the subsea environment, the findings were substantial: severe metal loss had occurred on the layer of the CRA. This posed a great threat to the pipeline’s integrity.
The operator needed to evaluate the general metal loss in the CRA via an in-line inspection. Therefore, ROSEN was contracted to carry out the inspection of the 18-inch pipeline with a length of 5.9 km. Another factor that had to be considered was that, in the future, the pipeline would transport products that contain hydrogen sulfide (H2S), a colorless hybrid gas that is highly toxic, corrosive and explosive when mixed with air. Hence, precautions were in order, and it was necessary to detect even the smallest defects in the pipeline. The operator needed to guarantee that the CRA would resist the product.
GUIDING THE WAY
The solution ROSEN offered combines the evaluation of the two different in-line inspection data sets. ROSEN’s technicians used a combination of our IEC (Internal Eddy Current) and MFL-A (Axial Magnetic Flux Leakage) technologies during this inspection. Although MFL-A has stood the test of time, and magnetization levels can be very high, especially in offshore pipelines with high wall thickness, supporting the technology with IEC guarantees the best results.
ROSEN is able to merge together different inspection technologies on one in-line inspection tool, making only one inspection necessary, which significantly reduces involved risks and efforts. Together the two technologies MFL-A and IEC detect:
- internal corrosion in heavy wall pipelines,
- general thinning and pitting corrosions, and
- closely adjacent features
ROSEN carried out the in-line inspection during the construction phase of the subsea pipeline, before it was put into production, using water to move the tool through the pipeline. In total, the on-site team ran four tools through the subsea asset – two for cleaning, one IEC and one MFL-A tool. That means that prior to the ILI, the pipeline was sufficiently cleaned with a foam pig and an 18” multi-bolt cleaning pig with guiding disc, sealing disc and gauge plate fit for short-distance lines. Cleaning the pipeline beforehand helped to avoid product contamination upon initial start-up of the asset. Two tools equipped with the IEC and MFL-A technologies were individually launched afterwards. The performance of the used tools is not influenced by the wall thickness of the pipeline, meaning they still collect high-resolution data irrespective of how thick the pipeline walls actually are.
The in-line inspection delivered a comprehensive picture of the pipeline’s status concerning all kinds of anomalies, such as internal and external corrosion or geometry defects. In this case, ROSEN technicians and data analysts found severe anomalies in the inspected pipeline. Two of the features were more than 7 mm deep, with the CRA only being 3 mm and the CS only 15 mm thick. With a total wall thickness of 18 mm, this means some features were almost half way through the pipe wall! After detecting the features, the operator is planning to replace the spool that contains severe metal loss. For the re-inspection of the line in the upcoming year, the combination of IEC and MFL-A technologies will again be applied, ensuring the pipeline will operate efficiently and, more importantly, safely.
The benefits of MFL-A and IEC as measurement technologies are lengthy, especially regarding metal loss detection.
THE BIG PICTURE
Ensuring the integrity of this subsea pipeline prior to its commissioning not only allows for optimal operation and likely an extended lifetime but also its safety. Taking a comprehensive look at this line, especially after having faced the force of nature, means not “just” sending a pig through the line but rather taking goals, operational needs and environmental circumstances into consideration. All elements of this solution – the cleaning, the metal loss and geometry inspections, and the future inspection – have their purpose, both to ensure the success of the inspection and to provide a solid foundation for this pipeline’s future lifetime.