Surge analysis predicts pressure transients, also called surges or water hammer, caused by sudden changes in fluid velocity, such as valve closures or pump trips. It’s used to design pipelines that can withstand these pressure spikes without cracking, leaking, or failing outright.

Surge analysis is carried out to understand and predict these transients, which pose real risks to pipelines, including water hammer, cavitation, and structural damage. This article walks through how surge analysis works and why it matters, starting with how a surge actually occurs.

Key Takeaways

• A surge happens when fluid velocity changes suddenly, from valve closures, pump trips, or pipeline blockages.
• The Method of Characteristics (MOC) is the most common technique used to solve surge analysis problems.
• MOC analysis follows five steps: define the problem, formulate the equations, solve them, run scenarios, then evaluate the results.
• Surge analysis results are used to size surge tanks and other protective measures.
• The main benefits are safety, reliability, and cost savings.

Understanding Surge Analysis: Its Impact on Pipelines

A surge occurs in pipelines when there is a sudden change in the velocity of fluid caused by valve closures, pumps starting and stopping, pipeline blockages, valve operations, etc.

Velocity change in pipelines causes a wave at super speed, and in turn, it causes a wave of pressure, which can lead to very high and low pressure and velocity transients.
The variation of the lowest and highest pressure wave transients poses significant threats to pipelines, for example:

1. Impact on pipeline structures

Pressure wave transients can damage pipeline structures, causing cavitation and cracks, which can lead to leaks or ruptures.

2. Damaged control system 

Pressure surges can also damage the control system, leading to problems controlling the pipelines.

3. Fluid Losses

It can also cause significant fluid losses, such as oil and gas, leading to decreased efficiency and flow rate.

Therefore, surge analysis is crucial for designing and maintaining pipelines that can withstand pressure surges and their negative impacts.

How Is Surge Analysis Performed?

It’s not easy to study the pressure surge in the pipelines, as much of it occurs inside the pipeline system. Therefore, a surge analysis can be carried out by combining the capabilities of computer programs and mathematical modelling.

Also, surge analysis is conducted using specialised software that simulates the behaviour of water flow in the pipeline system.

What Is the Method of Characteristics (MOC)?

One of the most prominent methods of surge analysis is the Method of Characteristic( MOC).

It is a systematic and accurate method known for being versatile. It can be used for different types of pipelines and fluids, and it is inexpensive and faster than other methods.

MOC is a mathematical surge analysis technique performed in a computer simulation. Basically, it analyzes the behaviours of fluids in pipelines by a set of equations that influence the flow, such as pressure, density, viscosity, and other physical properties of fluids.

What Are the Steps in an MOC Surge Analysis?

1. Define the Problems through Surge Analysis:

The first step of surge analysis using MOC is defining the problems that could cause a surge in pipelines, such as valve closures, pump starting and stopping, potential pipeline blockages, etc.

And then, using MOC in simulation, experts can predict fluid behaviors in response to the causes of the surge in pipelines. The relationship between the causes and the resulting surges can be used in designing preventive measures to control the potential surge and its impacts to ensure reliable and safe pipeline operation.

2. Formulate the Equation through Surge Analysis:

After defining the cause of the surge, the next step is to formulate the equations based on laws such as fluid dynamics and thermodynamics, which are used to explain the behaviours of fluids in different conditions.

These equations, used in MOC, are the continuity equation that deals with the conversation of mass in the pipeline and the momentum equation that deals with forces acting on fluids.

Now, these equations are formulated regarding fluid properties, such as velocity and pressure, and are used to predict the fluid behaviors for the pipelines in response to various causes of a surge.

Equations should be formulated carefully by experts and engineers in fluid dynamics and thermodynamics as they are necessary for the simulation, predicting the behavior of fluids, and the subsequent steps in surge analysis.

3. Solve the Equation through Surge Analysis:

In this step, the equations are solved along a curve which is a path of flow of fluid in a pipeline. The flow curve is disintegrated into points in the simulation, and the equations are solved at each point to determine the fluid’s pressure, velocity, density, and other properties.

Subsequently, the result from every point is combined to form a complete picture of fluid behaviours in the pipelines. Accurately solving the equation is crucial for predicting fluid behaviour in response to various causes of pipeline surges.

4. Study Scenario through Surge Analysis:

In this step, various scenarios that can cause a surge are stimulated. For instance, closure of the valve, stopping and starting the pump, and predicting fluid behaviors in response to these causes.

This step is crucial to prevent surges caused by various scenarios and design a system immune from these conditions.

5. Evaluate the Result through Surge Analysis:

This is the final step in surge analysis using the MOC method. Experts evaluate the simulation results and use the data to design systems to prevent surges in pipelines.

For example, assume a scenario where the valve is suddenly closed. The MOC simulation can predict how pressure in the pipeline would change and how the flow rate would be affected. And then, that data can be used to design systems and measures, such as surge tanks, to prevent surges from occurring in the pipelines.

Key Benefits of Surge Analysis in Pipelines

There are many significant advantages of surge analysis in pipelines, such as:

Safety

By evaluating and identifying the problems that could cause surges in pipelines, surge analysis can help design a piping system safe for required operations, which is imperative to prevent accidents.

Reliability

Surge analysis helps predict the abnormal behaviour of fluid under specific scenarios, which is used to design a reliable piping system for the operation. It is crucial for the constant fluid supply, reducing the risk of interruption, and increasing the efficiency of piping systems.

Cost Saving

By helping to design pipelines that can withstand the negative impacts of surges, surge analysis reduces risk and failure and saves significant maintenance costs.

FAQs:

1. What causes a surge in a pipeline?

A sudden change in fluid velocity, usually from valve closures, pumps starting or stopping, or pipeline blockages. This creates a pressure wave that can spike or drop sharply.

2. What is the Method of Characteristics used for in surge analysis?

It’s a mathematical technique that solves the equations governing fluid behavior, pressure, velocity, and density, at points along the pipeline to predict how a surge will move through the system.

3. What are the main benefits of surge analysis?

Safety, reliability, and cost savings. It helps identify surge risks before they cause damage, keeps fluid supply consistent, and reduces maintenance costs tied to surge-related failures.

4. How does surge analysis help prevent water hammer damage?

By simulating scenarios like sudden valve closures, surge analysis predicts how pressure and flow rate will change, which lets engineers design protective measures, like surge tanks, before the pipeline is built or modified.

5. What data does surge analysis use to design surge tanks?

Results from MOC simulations, including predicted pressure and flow rate changes under specific scenarios like valve closure or pump shutdown, guide the sizing and placement of surge tanks and other protective systems.

Why Surge Analysis Matters for Pipeline Design

As we can see, surge analysis for pipelines is a crucial component in efficiently evaluating and understanding the behaviour of fluid flow in pipelines to maintain and design piping systems that can withstand pressure surges.

We at Mechartes provide exceptional engineering and simulation services for surge analysis for pipelines with the best expertise.

Some of our other piping analysis services are pipe stress analysis, hydraulic analysis, life assessment studies for piping, root cause analysis, and many more.
Talk to us to know more!