Benefits of Erosion Simulation to Oil & Gas Industry

When the average person thinks of erosion they tend to imagine the vastness of the Grand Canyon or perhaps the Mississippi river.

For oil & gas or power systems engineers, however, erosion brings up images of pipes, pumps, and steam turbines. In this case, particles in the oil, or droplets in the gas, eat way at the equipment used at oil & gas extraction facilities.

Simulation of erosion hotspots in Oil & Gas Equipment.

Using CFD simulation software, like ANSYS Fluent, engineers can better predict corrosion hotspots, plan preventative maintenance schedules, and save money from reduced downtime. Additionally, simulations have also led to some tips and tricks to limit pipe erosion.

“Erosion and equipment failure as well as unscheduled downtime are costly. Despite recent sharp drop in energy prices,   investments in simulation and R&D should not stop,” said Dr. Gilles Eggenspieler, Lead Fluid Product Line Manager at ANSYS.

 He adds, “When extracting gas, or fracking oil sands, operators often get no more information than a pressure reading. There are no cameras or sensors to tell them how fast things erode. This analysis needs to be done up front to prevent breakdowns.”

Additionally, determining the erosion tolerance of some equipment may help an engineer optimize the equipment placement in a facility. After all, it would be unwise to place equipment prone to erosion where it is hard to get service.

“You can’t always avoid erosion,” said Mohan Srinivasa Principal Technology Specialist at ANSYS. “Being able to accurately schedule maintenance is much better than equipment failing without warning. ANSYS CFD helps you to do that.”

How Do I Model Oil & Gas Erosion?

In the first erosion model type, the particles are diluted in the flow. Erosion is cause by particles impinging on surfaces or walls. This dilute flow is typically seen in turbomachinery equipment and oil and gas fields.

For this dilute application, ANSYS CFD tracks each particle’s speed and location. The software then calculates the erosion effect of the particle as it impinges on a wall. The erosion rate depends upon the particles’ speed, impingement angle and other factors.

“Even these dilute flows can have trillions of particles. ANSYS CFD has a very smart model that is able to track all those particles while maintaining a fast computation. The trick is to track large groups of particles as one parcel of particles,” said Srinivasa.

In the second erosion type, the particles are more slurries than isolated particles. Therefore, the erosion is caused by the particles rubbing against the pipe as opposed to impingements. These types of flows are common in applications dealing with extracted crude and oil sands.

“In a slurry, how you handle the particles is different,” marked Srinivasa. “You need to model a complex multiphase flow made of gas, liquid and particulates slurries. ANSYS CFD can model those flows without problems. The key indicator for erosion in this case is not impingement velocity or angle. Instead, engineers look at the particulates’ shear stress on the wall to compute the erosion rate.”

How should you select an Erosion Rate Model?

Regardless which type of erosion method is considered, Srinivasa points out that engineers and experts have developed a wide range of erosion rate models. The choice of method typically comes down to particle and pipe properties: hardness, roughness, ductility, and brittleness.

ANSYS CFD gives access to a wide range of erosion models to choose from. In fact, ANSYS users can even create their own erosion model based on their own experimentation.

 “What the particle will do once it hits the wall is dependent on many factors,” said Srinivasa. “Typically the best method is chosen by empirical validations based on experimentation of the hydrocarbons and particles being extracted on site. There are many erosion models because there are many types of particles. Typically, the best erosion models are chosen after erosion rate experimentation lasting around 2 to 6 hours.”

Srinivasa explains that even after the initial experimentation to determine a model, it may not be clear if the simulation will offer, a conservative or liberal estimate of the life of the pipe. You will typically get a good estimate of where the erosion will occur but the time scale can be a gray area. To solve this estimation problem, Srinivasa suggests validation of a simplified model to lab tests. Once the model is validated it will be safer to use for more complicated models.

Mimic the Impact of Erosion by deforming the pipe wall mesh

“If you are looking to simulate the erosion of a system over a 10-20 hour period then the geometry of the inner wall will not change and the flow pattern will be unaffected by erosion,” said Srinivasa.

“However,” he adds, “engineers are dealing with Oil extraction equipment that operates for many months or years. In this case, erosion will more dramatically change the shape of the inner walls of the pipe and therefore influence the flow. Accurate prediction of the lifespan of such installation requires that this change in geometry be accounted for. To do this, you need to use ANSYS CFD’s Moving and Deforming Mesh capabilities,” suggested Srinivasa.

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How to Reduce Erosion

To reduce erosion in pipes Srinivasa has a few suggestions.

First is the initial pipe layout; the number of bends and twists should be limited. Additionally, he suggests that bends and twists should also be as gradual as possible. Since impingements happen when the flow domain changes, making a straighter pipe will limit this variance in flow.

For areas that are prone to erosion, Srinivasa also suggests some solutions. For instance, engineers can change the material of the pipe or assure a liquid film along the pipe. Since the rate of erosion is dependent on the material properties of the pipe, stronger, harder pipes will experience less erosion. The liquid film, however, acts as a shield slowing down the particle impingements. This film can be achieved along your pipe by adding corrosion and erosion inhibitors or by simulation flow optimizations.

Though not perfect, these tips and further simulations can help reduce erosion. As erosion is a nature of the industry, simulation can also help engineers plan for the future. Either way, it can be a very valuable tool to the oil and gas industry.

To learn more about ANSYS’ Oil and Gas erosion simulations, follow this link.

ANSYS has sponsored this post. They have no editorial input to this post - all opinions are mine. Shawn Wasserman