BEGINNER'S GUIDE TO
PIPELINE CORROSION MITIGATION
Maximize production and alleviate material failure with internal pipeline corrosion monitoring and mitigation.
Maximize production and alleviate material failure with internal pipeline corrosion monitoring and mitigation.
Corrosion is one of the biggest threats to the petroleum industry and preventing it is especially critical in systems susceptible to producing corrosive environments, such as:
When
water is present inside these systems, corrosion can occur. The amount depends
on a variety of factors, temperature, total pressure, CO2 and H2S content
of the gas, etc., but the result is devastating.
In order to mitigate this occurrence, accurate measurement and monitoring is crucial.
In this eBook, we will discuss internal corrosion monitoring equipment and methods that will help asset integrity engineers and corrosion technicians maximize production as well as alleviate material failure in pipelines and processing equipment.
Key topics include:
The insight provided in this eBook will start your operators on the path to real-time, continuous and periodic data obtained through internal corrosion monitoring and mitigation.
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This section will outline the equipment necessary to ensure a strong internal corrosion monitoring and mitigation program.
Pipelines carrying oil and gas experience internal corrosion when water is present inside the lines. This corrosion hinders asset integrity causing material failure in pipelines and processing equipment.
Maintaining asset integrity is possible with the right measurement and monitoring system. It can help ensure engineering goals, operator safety and provide ease of use even in extreme high-pressure conditions.
Getting started with your internal corrosion monitoring program starts with the proper equipment.
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Corrosion coupons are one of the simplest ways to monitor corrosion, and the most commonly used method in gathering systems, pipelines, processing plants and facilities of all kinds.
They come in three styles – flat, rod and disc – and provide accurate, quantitative estimates of corrosion rates within a system.
Flat coupons are required when analyzing for more than just the weight loss (corrosion rate) such as bacteria via pitting, erosion, paraffin or scale. However, they are susceptible to producing vibration induced failures from inaccurate orientation within the process fluids.
If you are merely looking for corrosion rates and paraffin or scale, rod coupons can be used. These are less likely to produce vibrations due to inaccurate orientation within the process fluids.
Disc coupons are used when retraction isn't an option and the pipeline is piggable. The monitoring must be done at the 6:00 o'clock position on a horizontal like where the water is more likely to exist.
Corrosion coupons deliver this through a clear visual signal of corrosion rate and type (after analysis in a laboratory) so plant operators can:
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Ultrasonic (UT) is a group of monitoring techniques that use short, high-frequency ultrasonic waves to identify flaws in a material. By measuring these waves, the thickness of the material as a result of internal corrosion can be identified.
These mechanical stress waves are emitted from sensors wrapped around a pipeline to map its thickness. The data extracted from these sensors is tracked via an external data logger. It provides both the energy for the sensors and identifies how the coupon loses metal in real time.
This technique is extremely sensitive and accurate for poor or non-continuous electrolyte environments, such as vapors, gases, soils, wet hydrocarbons and non-aqueous liquids. It scans over large surface areas to map the pipe or vessel thickness - accurately identifying internal corrosion.
Ultrasonic sensors wrapped around pipes and vessels to map the wall thicknesses, with an external data logger that energizes the transducers and logs the data.
A transducer measures the thickness of a replaceable weight loss coupon made of a similar metal or alloy as the pipe or vessel being monitored.
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Similarly to Ultrasonic methods, corrosion monitoring probes are used to continuously monitor corrosion within a system in real-time. There are two kinds of probes (extraneous to UT techniques) - electrical resistance (ER) probes and linear polarization resistance (LPR) probe.
Measures both electrochemical and mechanical corrosion and is suited to corrosive environments with either poor or non-continuous electrolytes, similarly to Ultrasonic probes.
Measures only electrochemical corrosion and can only be used in aqueous solutions, providing almost instant measurement of the corrosion rate. This can allow an operator to evaluate changes or monitor the effectiveness of a chemical program and adjust quickly based on the probe readings.
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IMPLEMENTING AN INTERNAL PIPELINE CORROSION PROGRAM
This section will outline the four best practices when implementing an internal pipeline corrosion program.
To maintain pipeline integrity, many facilities use cleaning pigs within the pipelines to flush out water and prevent corrosion.
Oil and Gas Companies often decide not to conduct additional monitoring for internal corrosion based on the false belief that running pigs through the lines clears out the water from every portion of the pipe.
Monitoring within non-piggable lines is crucial, but even piggable systems aren’t exempt from the need for internal monitoring. Regardless of the type of line, choosing where to monitor is critical to your program’s success.
“Each operator must develop and implement a monitoring and mitigation program to identify potentially corrosive constituents in the fluid being transported and mitigate the corrosive effects.”
The Pipeline & Hazardous Materials Safety Administration
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If you’re not sure if you have internal corrosion, you can perform a quick check by creating a low spot on your system with a drip pot assembly. This assembly provides a sample of all liquids in the system, as well as a corrosion coupon monitor and an optional bacteria collection device. This is also a great method for proving your chemical corrosion inhibitor program.
Drip pots incorporate a bleeder valve on the main chamber to relieve process pressure so the sample then can be drawn safely from the sample valve. An optional corrosion coupon can be attached to the bottom of the assembly with a fixed corrosion coupon holder for simultaneous corrosion analysis and sample collection.
In order for drip pots to provide safe data collection they need to be well-engineered, made from non-corrosive 316L stainless steel components and pressure rated for the application, for example, up to 6,000 psi.
As discussed earlier, lines can utilize non-intrusive monitoring methods, including:
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One way to identify monitoring locations is through process flow profiling.
Flow profiling is used to predict where water might travel and settle out of the process fluids. Water generally accumulates lower in the system and is swept upward with the process fluids. The sweeping is velocity dependent. Therefore, profiling where the velocity will change, such as pipe diameter changes and direction of flow changes, can determine where you should monitor.
Sudden changes in flow velocity has the potential to damage pipelines and its fittings when turbulence is created. Flow modelling predicts the turbulence by taking into account velocity and the pipe angle.
Gravity and shear at the gas/liquid interface are two influential forces that are critical to water accumulation. By taking these factors into account, there is a level of assumption that the pipeline is under a steady state and the gas temperature is constant.
For more information on how to calculate flow modelling visit ScienceDirect.com.
Locations prone to corrosion and require monitoring include:
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Monitoring occurs horizontally or vertically and requires varied methods of measurement and devices to execute.
When monitoring on a horizontal pipeline, the measurement element as close to, but never touching, the bottom of the pipe. Additionally, you will want to mount ER probes, UT probes and coupons from a 12:00 or 6:00 o'clock position regardless of process type. This is due to water being heavier than hydrocarbons, causing water to settle at the very bottom of the pipe.
When monitoring on a vertical line, the measurement element should be placed at the center of the flow. Due to the positive process movement being focused on the center, you will receive ideal results from this placement. There is also less chance of friction occurring from the pipe walls.
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Now that you have outlined your corrosion program, this section will outline how to select the correct corrosion mitigation method for your program.
CHOOSING THE BEST CORROSION MITIGATION METHOD
Pigging pipelines is the most commonly used method for cleaning pipelines to eliminate corrosive materials and ensure the line is running smoothly. In this process, the pigs are introduced into the line via a launcher and removed at the pig trap or receiver. The pig is pushed through the line by the process fluid or towed by another device or cable. Pigs scrape the sides of the pipeline and push debris ahead, preventing buildup.
There are multiple considerations when it comes to selecting the proper pig for a line.
As every pipeline is different, this method is less stringent on a set schedule and is driven by the quantity of debris in the pipeline.
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Many hydrocarbon gas facilities use siphons to remove corrosive liquids from pipelines and vessels preventing the development of corrosion.
In pipelines, these siphons are often required for low areas in the lines, where a pig can’t clear the liquids. A siphon needs to reach great depths and usually requires a “hot tap” – a new pipeline connection point without shutting down the pipeline – to set the access the point.
The primary equipment necessary for a hot tap application includes a drilling machine, a branch fitting and a valve. This equipment can be placed vertically, horizontally or at any angle around the pipe provided there is sufficient room. Current technology has made taps available for all types of pipelines, pressures, diameters and compositions. Limitations regarding necessary operators have improved as well with new lightweight tapping machines requiring only one operator.
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Chemical treatment is the primary solution for most internal pipeline corrosion problems. Once the corrosive agent is known, the company can assess its options for implementing a chemical mitigation program.
Prior to beginning a chemical mitigation program, the corrosive constituent must be identified and quantified. That’s because corrosion inhibitors and scavengers can be tailored to address fluid phases, operating conditions, expected flow rates and product chemical variations.
A process that involves forcing the chemical into a fine mist which, when done correctly, causes the liquid to mimic the gas process. It’s required for chemical scavengers when applied to a gas process.
A mixing probe injects dense liquids into a gas stream and injects liquids into a liquid stream. This method is proven to be a better method than a quill for complete dispersion and distribution.
These should only be used when injecting liquids into a liquid process. Results are inconsistent when injecting liquids into a gas stream with velocities < 15 feet/second.
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Natural gas is diverted through a vessel filled with a scavenging fluid such as amine or triazine. Dry bed adsorbent contractors are also an option with certain restrictions.
A pig applies chemicals, such as corrosion inhibitors and biocides, along the pipe walls.
1. Choose the Right Injection Site
In many pipelines, there’s a shortage of long, straight, obstruction-free runs of pipe. Operators should carefully consider injection sites based on the locations of pipe elbows and obstructions such as valves, regulators, and orifice plates which will separate the liquid from the gas.
2. Keep the End Goal in Sight
Proper dispersion and distribution of the injected chemical is critical for thoroughly treating the entire pipeline. In a gas process system, complete and thorough atomization is a must.
3. Injection Maintenance
It’s important to remember that injection atomizers, mixing probes and quills require regular maintenance. Retractable models ensure proper maintenance is carried out on a regular basis.
4. Automate and Monitor
Chemical injection and contact vessels should be automated and remotely monitored for optimum performance.
5. Don't Use Too Many Chemicals
Overexposing the most popular chemical scavengers to corrosive constituents creates solids, which can cause additional problems within pipelines.
6. Balance Your Methods
A balanced corrosion mitigation program includes both pigging and chemical applications, so it’s important to consider using each method where it’s most appropriate.
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Providing a safe and easy method of accessing pressurized process system for corrosion monitoring, chemical injection or sample extraction is an important operational consideration in upstream and midstream processes. Learn how our Safe-T-Vise solutions provide users to execute these processes easily and effectively.