Pipe leak detection systems
Does anyone like a water leak? Doubt it. I remember back home during the rainy season, many people worried about leaks, especially apartment dwellers. A leak in an apartment could make life unpleasant for the neighbours too! Finding the cause and a solution can cost a lot of time and money.
Now imagine a leak in a pipe that transports petroleum. Any loss here could cost a lot more than a water leak! Such a leak could lead to serious environmental and human health issues as well.
Regardless of the product in the pipe, we must avoid leaks as much as possible. Pipe leak detection systems (LDS) come in handy here.
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Types of pipe leak detection systems (LDS)
Pipe leak detection systems generally fall into two categories: continuous and non-continuous. And the continuous fall into two subcategories, external and internal systems.
There are three main methods of non-continuous pipe leak detection systems: inspection by helicopter, smart pigging, and tracking dogs.
Inspection by helicopter
Inspection by helicopter consists of bringing a device along in a helicopter ride to detect leakage in a pipeline. While you fly over the pipeline, you can use lasers, infrared cameras, or leak sniffers to detect the leak. This method costs more than the others, but who turns down a helicopter ride, right?
This method doesn’t involve the animal, as you might have wondered. The “pig” device cleans pipelines and performs various maintenance operations – basically the industrial version of a pipe-cleaning brush. As the pig travels through the pipe, it can collect data along the way and alert you to corrosion, cracks, wall thinning, and leaks.
This method does involve animals! You’ve seen these dogs in movies or airports. Special handlers teach the dogs to recognize certain smells, in this case, special compounds used in the pipes specifically to warn of leaks. The dogs walk along the pipeline and alert their handlers if they smell those compounds.
Continuous external methods
For continuous external pipe leak detection systems, you have four main options: fiber optic cables, acoustic sensors, video monitoring, and sensor hoses.
Fiber optic cables
This method uses fiber optics throughout the pipeline that rely on physical changes at the leak site, in this case temperature.
With the cables along the pipeline, a laser emits pulses, and molecules in the cables reflect those pulses. These signals can create a temperature profile along the pipe, and the sensors can detect leakage as a warming or cooling in an area.
Acoustic systems also rely on local changes to detect leaks. If you’ve ever used a pressure cooker or tea kettle, you know that escaping gas causes noise. So installing acoustic sensors throughout the pipeline creates a noise profile, and deviations in this profile indicate leaks.
Here you can have CCTV cameras to visually inspect the interior of pipelines. You can also use cameras which can detect certain infrared wavelengths. Certain hydrocarbons absorb infrared radiation, making it possible to detect an image of smoke on your video display.
Infrared cameras can also detect liquid leaks, as thermal conductivity differs between wet and dry ground. This difference can create temperature changes where leaks occur.
This method consists of installing semi-permeable hoses along the pipeline. If there is a leak somewhere, the product will penetrate the hose. From time to time, operators will inject test gases into the hose at the start of the pipeline. At the other end, an analyzing unit checks for hydrocarbons.
Also the operators record the time that it takes the test gas to go from one end to the other. A variation in this time could mean a leak.
Continuous internal methods
These methods use instrumentation and control systems to detect leaks. If you have a fully automated plant, you might like these methods since you can add them to your existing system.
By monitoring pressure and flow patterns along the pipeline and analyzing any changes, your control system can detect leaks for you.
Pressure point analysis
As the name suggests, this method relies on changes in the product pressure throughout the pipeline to find leakage. Any material flowing through a pipe will generate a certain pressure, so when a leak occurs, the change in the hydraulics of your system will change your pressure profile.
To measure and monitor the change of this profile over time, you need to install pressure transmitters at multiple points in your pipeline. Once you establish the pressure profile, you can then set thresholds for the pressure. That way if your profile breaches either threshold, then the system triggers an alarm.
Mass balance method
You probably heard this term while studying physics or thermodynamics, as this system operates on Lavoisier’s conservation of mass principle.
If you don’t remember this principle, don’t worry. We’ll give you a quick refresher. Lavoisier stated that the mass in a closed system remains constant, unchanged by processes inside the system. That means that if you consider your pipe as a closed system and measure the mass flow at the inlet and outlet, the difference should equal zero.
If you find any result different from zero, it means that mass is escaping the system. If that happens, then you have a leak somewhere in your pipeline.
Unfortunately, this method has a problem. Certain dynamic shifts in the contents of the pipeline, such as gas expansion or condensation, could lead to inaccurate readings and false alarms.
Statistical pipe leak detection systems uses data from other LDSs. Therefore you might use it in conjunction with one of the other systems here. When you gather data from either your mass balance system or pressure point analysis, you can create statistical hypotheses based on an alarm limit.
In this method you’ll have two main hypotheses:
- Hypothesis H0: No leak – single measurement <= alarm limit
- Hypothesis H1: Leak – single measurement > alarm limit
Real-time transient model (RTTM) systems
I mentioned that the mass balance system could give you false alarms due to dynamic changes in your process, right? Well, real-time transient time model (RTTM) systems can compensate for these changes.
To do so, these systems use basic physical laws from fluid dynamics regarding the conservation of mass, momentum, and energy. These laws describe both stationary and transient behavior of flow inside the pipe.
To create a hydraulic profile and predict performance, you must calculate the flow, pressure, temperature, and density of the product. You must also integrate them in real time for each point along the pipeline.
By measuring pressure and temperature at the inlet and outlet and knowing the properties of your process, the LDS can detect changes in the pipe contents. It can then subtract this calculation from the difference between the calculated flow values at the inlet and outlet.
Comparing these values to the flow actually measured by meters at the inlet and outlet will tell you what you need to know. If you have no difference between the measured and calculated values, then you have no leaks. If that difference doesn’t equal zero, however, then you need to find that leak!
Extended-RTTM (E-RTTM) systems
Extended RTTM (E-RTTM) systems function exactly the same as RTTM systems but with additional aid to avoid false alarms, called leak pattern recognition.
With this function, the E-RTTM LDS takes into account not only the immediate difference between measured and calculated flow but also a database of leak signatures. After this leak signature analysis, the system concludes whether an anomaly in the system is a leak or just a false alarm.
Just like choosing an instrument, choosing the right pipe leak detection system for your application will depend on a number of factors, such pipeline size, installation restrictions, product, and budget.
This article tackles the problem of detecting leaks in your process. However, once you find out you have a leak, you still need to locate and repair it. For more information on that, you can read our article about methods to repair your pipeline.
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