Walking the pipeline

Pipeline leak detection technology is a rapidly growing field, with multiple highly sensitive technologies monitoring pipelines 24/7 gaining traction in the industry.

However, some argue that no matter how sensitive the technology is, nothing beats visual inspection. Many operators have commissioned studies into what form of leak detection technology is best, but, it seems there is no one-size-fits-all solution.

An efficient leak detection system needs to allow fast detection of the leak with a low fraction of false alarms, and allow fast remedial action.

“Leak detection systems should be carefully designed with the right measurement instrumentation, data acquisition, and analytical equipment that work together to provide an accurate picture of what is happening in the pipelines,” explains David Fisher, flow measurement & solutions advisor, Emerson Process Management Middle East and Africa.

The man on the ground
While there may be no single solution that fits all pipelines, many agree that no matter what technology is applied, there will always be a need to have either someone physically walk the length of the above ground pipeline, or in remote areas, check the pipeline by air.

“There will always be a requirement to walk or fly the line, if only for peace of mind, and 24×7 pipeline monitoring will become a standard across the world, as it already has in many parts of South America, Europe, Middle East and Africa,” states Alex Baird, regional director, MENA at pipeline sensor technology specialist OptaSense.

But, while there are thousands of kilometres of above ground pipelines, equally, there are thousands of kilometres of pipeline that are underground, are wrapped, or are insulated.

“Pipelines which are either wrapped, insulated or below ground restrict visual inspection to only those pipelines that are above ground with no wrapping to determine areas of material degradation on a pipeline surface. For the rest some form of non-intrusive inspection is required such as an Ultrasonic or Electromagnetic inspection techniques,” explains Dean Mason, manager Advanced Inspection Services, Stork Middle East.

“Ultimately all the various forms of inspection methods including a ‘man on foot’ leak detection systems and corrosion monitoring programmes should be at the disposal of a pipeline inspectors and asset management teams to assure the integrity of a pipeline and to better help prevent the possibility of pipeline leaks.”

Article continues on next page …

One of the problems with the ‘man on foot’ form of pipeline leak detection is that sending people to physically inspect pipelines can be dangerous and unreliable.

“Pipelines carry combustible hydrocarbons and this can pose huge potential risks to equipment, facilities, and personnel. Sending people to physically visit the pipelines is laborious and dangerous, and the effectiveness of manual detection is dependent on a person’s sensitivity and experience,” explains Fisher.

One of the most efficient methods of pipeline leak detection is volume/mass balancing, which is designed to compute the total mass flow of products entering and leaving a pipeline. When an imbalance occurs between what goes in and what goes out, it indicates a potential leak and the system should issue an alarm to the operators, according to Emerson.

“An advanced method of volume/mass balancing is Real Time Transient Modelling [RTTM]. RTTM uses mathematical models to compare measurements between the real-time and ideal operation of pipelines, taking into consideration indicators such as mass flow, pressure, density and temperature,” states Fisher.

Baird says that mass balance systems have been seen to be economical but suffer from a high false alarm rate, especially when used with multiphase products.

“False alarms can be worse than no alarm at all as the real events are lost in the clutter. Dynamic modelling is reliant upon the right information being fed into the programme and traditional acoustic pipeline leak detection methods are only as accurate as the number of sensors installed along the line,” explains Baird.

“Unfortunately this does not provide real time monitoring and the leak may only be detected when oil or gas comes to surface or begins to effect vegetation. At this point much of the damage has already been done,” he says.

Another method of leak detection is Pressure Point Analysis (PPA), which monitors the pressure points inside the pipeline and detects the changes created by a leak.

According to Stork, the most common and probably the most efficient non-intrusive technique would be a Pipeline Inspection Gauge (PIG) system which runs along the inside bore of a pipe.
These ‘PIGging’ systems are able to run several hundreds of kilometres either above or below ground and subsea.

“Good measurement is critical in maintaining pipeline integrity. It gives better insight into throughput and fluid properties and improves reliability and operator confidence in the chosen leak detection system. Moreover, hydrocarbon producers should apply current best practices for measurements, especially of flow, to reduce uncertainty in their measuring points,” explains Fisher.

Article continues on next page …

Until there is a wider acceptance and understanding of the newer pipeline leak detection systems then there will always be a scenario where people on the ground will initially detect a higher percentage of the leaks, according to Stork.

“The newer high tech leak detection systems without a doubt work well and are noted to be capable to detect smaller and smaller leaks under right conditions. Until there is an assurity to the owners of pipelines that there is a certain value for money and the newer systems actually work under field conditions there is some understanding that there is some reticence from pipeline owners to use this equipment.

If the newer leak detection systems consistently signal false positivity’s then owners start losing confidence in the technology. Like any new technology there is initially a wait and see approach, this helps gain some confidence in using the new system after witnessing several successful campaigns, and the leak detection systems are able to detect the leaks under different environmental conditions,” explains Mason.

According to Stork, when dealing with pipelines over thousands of kilometres the percentage of pipelines that actually have hi-tech leak detection systems used is very small. If the newer hi-tech leak detection systems gain greater acceptance within the pipeline industry and their use of detection monitoring increases there is no doubt that over time this perception will begin to change.

“There is no doubt that systems should be in place including an integrity programme which deals with the early detection of pipeline material degradation in all its various forms.

This may include a Risk Based Inspection programme specific to a certain pipeline taking into consideration all the various parameters. The approach would focus on the early detection and mitigation of material damage prior to any leak occurring,” states Mason.

Pipeline leak detection technology is an area of growing innovation and there are a variety of new pipeline leak detection systems currently on offer and being used, such as acoustic emission detectors and PIG gauges, which are having some success in the early detection of pipeline system leaks.

These new systems have the possibility of performing their function either running internally through a pipe, as in the case of PIG gauges or externally.

According to Emerson, in the latest trials being performed, new external detection systems include large sensor or camera systems mounted onto helicopters which travel along the pipeline looking for the vapours associated with an oil leak. These systems are able to detect leaks that are much smaller than the current industry standard.

“There are also internally inserted ‘acoustic balls’ that travel along the pipeline listening for leaks, these systems are able to potentially detect leaks down to 0.1litres/minute and a location accuracy down to ~3.0m. These systems also have a benefit of being launched in both pigable and non-pigable lines,” states Mason.

Article continues on next page …

Acoustic emission detectors, have greatly improved in the past few years, according to Emerson.

As with any new technology time and site trials are required to be performed until they gain wider acceptance in the oil & gas industry as more and more newer leak detection systems arrive the constraints of initial costs will be reduced making them a more viable solution for the pipeline industry as a whole, according to Stork.

Other inspection tools that are currently being used outside of leak detection systems are hand-held devices that are moved along the pipe surface, digitally mapping in three dimensions the surface of pipe, including any locations of bulges or dents.

This will offer the pipeline inspector valuable information regarding areas of pipeline mechanical damage and better enable the inspector make an informed decision as to the integrity of the pipeline, this method is slow and may not able to perform an inspection to large portions of a pipeline, but may be used for monitoring purposes once the areas of external material degradation are detected.

According to Stork, Pipeline Inspection Gauges perform the pipeline inspection from the inside and are able to inspect several hundreds of kilometres in one run. Inspection tools associated with the PIG can vary from Magnetic Flux Leakage (MFL) Inspection which uses Magnetic Flux that penetrates through the internal wall of the pipeline system.

When there is a break in the Flux, for example due to a corroded or pitted location, sensors detect the magnetic leakage. The location of the corroded area is registered using a device registering global positioning coordinates, allowing further investigation to be performed.

A device, such as a multi-probe Ultrasonic Thickness Gauge, measures the remaining wall thickness of the pipeline using ultrasound, and penetrates and measures the travel time of the ultrasound as it travels inside the steel, the travel time represents a certain steel thickness.

All of these types of inspection occur as the Pipeline Inspection Gauge travels along the internals of the pipeline being propelled sometimes by the oil or gas product itself.
Implementing efficient leak detection technologies does not begin once the pipeline is built, but rather during the initial planning and fabrication stages.

This is particularly important when dealing with pipelines that run hundreds of kilometres either subsea, across deserts, or in extreme heat or cold.

“Understanding the environment in which the pipeline will be travelling through will be the first step in setting up a pipeline integrity management programme, which includes the use of leak detection instrumentation systems,” states Stork’s Mason.

The pipeline management system will consider all the wide range of environmental factors which are associated with a pipeline.

The recommendations by the leak detection system equipment supplier, as well as international standards should be used as a minimum to ensure a safe and continued operation of these pipeline systems.

This may include regular checks of external leak detection systems with a consideration made as to the time of year when these integrity inspections are made.

Continuous internal pipeline monitoring systems can be performed year round with the frequency and type of internal leak detection systems used based on the pipeline service, history and location, according to Stork.

“It needs to be also noted that as much as leak detection systems have an integral part to play in the overall pipeline system, the initial planning stages of laying a pipeline will also include choosing the correct piping material, welding and inspection procedures, coating materials coupled with strict quality controls will greatly mitigate the probability of problems years down the track. Done correctly this will dramatically decrease the probability of potential leaks,” Mason explains.

To achieve pipeline integrity, operators also have to understand what should be measured and how measurements individually contribute in detecting leaks.

“Operators should be careful in making assumptions, as false alarms can cause unnecessary efforts and costs. Most important of all, they have to select and operate an integrated leak detection system that can provide the required precision, bandwidth, stability, and analysis,” says Emerson’s Fisher.

“Our customers, for example, employ leak detection programmes as a part of multiple and interdependent control, measurement and analytical systems, such as pressure relief systems, surge pressure control systems, slam shut valves, and odorising systems for natural gas. Arriving at an ideal programme can be challenging and complex, and this process is greatly helped by using experienced consultants,” he says.