When to Analysis Piping System

One of the most difficult decisions plant personnel face is whether or not to analyze an existing or new piping system. It is often hard to assess the point at which a piping system should be field-routed or when a full analytic solution is required. Although there are no simple answers to these questions, below there are some conditions under which piping analysis is advisable:

Conditions for piping analysis

  • Piping is attached to load-sensitive equipment or is carrying category M fluids (hazardous chemicals, as defined by ASME B31.3 rules), and the design temperature is > 250°F
  • The pressure exceeds the maximum pressure for an ANSI Class 2500 B16.5 fitting
  • The system temperature is > 400°F
  • The system carries gas that has cooled to a liquid state
  • The product of the pipe outside diameter (in.) times the pressure (in psi) is ≥1,157
  • The system pressure is > 3,000 psi
  • The system uses Glass Reinforced Epoxy (GRE) pipe.
  • The piping connects to rotating equipment
  • The system uses one or more expansion joints
  • Most piping codes, and perhaps 90% of all pipe stress analyses, involve three principal loading types:
    1. Sustained loads, such as pressure and weight
    2. Expansion Loads (i.e., from thermal conditions) and
    3. Occasional loads, such as from wind and earthquakes.

Other types of loads include those caused by transient fluids, ice and snow, ship or platform pitch and roll, explosion loading's, pressure loads, frost heave, fault movement, fluid sloshing and through-wall thermal effects. These can all be analyzed, but are typically reserved for more experienced pipe-stress analysts.

When is pipe stress analysis required

Stress analysis is obligatory in piping engineering and design for different reasons, but mostly for justification of the piping system safety, reliability and integrity. Here are some situations and scenarios where pipe stress analysis is necessary:Here are some situations and scenarios where pipe stress analysis is necessary:

High Pressure and Temperature: When a piping system is required to operate in high pressure and high temperature conditions mechanical stress is applied. Stress analysis on the pipe ensures that the system is capable of handling these conditions without straining or tiring the pipe or causing it to fail.

Critical Service: Those piping systems that transport, high risk, toxic or flammable fluids are categorized as critical piping systems. Stress analysis in pipe systems are important so as to avoid pipe leaks or burst, or even the occurrence of safety disasters due to mechanical failure.

Complex Geometry: Piping layouts with many interconnections, multi branch systems, or geometries that are different from simple circle-shaped often need stress analysis for determine effect of these conditions for the piping system.

Vibration Analysis: Fluctuations in the fluid flow and/or motion of other connected equipment such as pumps and compressor can cause vibrations of the piping system. Pipe stress analysis assists in the determination and eradication of the stress that may be caused by vibration hence causing fatigue failure.

Thermal Expansion and Contraction: It is common knowledge that pipes expand in the event that temperature increases while they contract if the temperature decreases. These thermal effects are considered in stress analysis to avoid over stressing or addition of misalignment in the various components of the Pipe.

Support Design: Proper designs on supports should be provided in order to avoid issues such as support sag, undue load on support and improper positioning of the piping. Pipe stress analysis also helps in determining the supports, their designs and positions correctly.

Code Compliance: It is common for many industries to have set code and standards used in the design and development of the piping system. Adherence to these codes entails specifying the methods including pipe stress analysis to show that the system is safe and performs as expected.

Start-Up and Shut-Down Conditions: Pipe stress analysis looks into the stresses that are likely to happen at certain conditions like start up, shut down and or transient. It makes sure that the established operational changes do not lead to the system’s failure.

Material Selection: Pipes and components should also be based on the mechanical properties with regards to stress the equipment is likely to encounter. Through stress analysis one is able to establish that the materials to be used are fit for the purpose that they are intended for.

Expansion Joints: Expansion joints are used in piping systems as they facilitate movement due to the thermal forces of expansion and contraction, these systems need stress analysis for the effective functioning without damages.

Corrosion Assessment: Recently when corrosion or erosion has occurred to some of the pipes this method assists to evaluate the remaining strength that is left on those certain part of the components and decides whether to replace or to repair.

Re-Rating or Re-Purposing: When installing a new pipe system or if the conditions of an existing system are to be altered, pipe stress analysis must be done to see whether the piping system is capable of holding the new values without failure.

Concisely, pipe stress analysis is one of the most important branches of engineering that deals with the safety of the piping systems in different fields . It aids in discovering problems, improvement of designs and ways to reduce risks, which is correlated to mechanical forces, changes in temperature and everything that could influence the performance of a piping system.

Piping analysis

Piping analysis is the verification of stresses and strains on piping system. It is applied to declare that the piping system is secure and effective.

Piping analysis can be performed using a variety of methods, including:Piping analysis can be performed using a variety of methods, including:

  • Hand calculations: Piping systems that are relatively simple can easily be assessed manually. But this can be sometimes misleading and it takes lots of times for the completion of the task.
  • Finite element analysis: Besides, finite element analysis can be said as a more accurate means of piping analysis. It employs a computer to discretise the piping into elements which forms a mesh. In this step, stresses and strains in each element are determined with the help of the equations derived from the basic physical laws.
  • Pipe stress analysis software: A considerable amount of work has been done in presenting pipe stress analysis in the form of software packages. These packages can be useful in piping analysis for cumbersome piping structures.

The type of the method that is needed for the analysis of the piping depends on the complexity of the system and required precision.

The result of piping analysis is that one can be aware of some of the issues that may likely happen in a certain system. These problems can include:

  • Overstressed pipes: Stressed pipes can burst or leak; therefore, it requires addressing of such issues as required.
  • Undersized pipes: When the size of the pipe is less the motion of the fluid will be restricted causing problems like overheating or cavitation.
  • Improper supports: The extra supports that are fabricated inappropriately will lead to deflection of the pipes and hence stresses and strains.
  • Corrosion: The corrosion degradation affects pipes and this causes failures.

Since piping analysis can reveal possible issues of piping system, it will be useful in minimizing cases of accident and loss of lives.

By identifying potential problems in a piping system, piping analysis can help to prevent accidents and injuries.

Here are some of the benefits of piping analysis:Here are some of the benefits of piping analysis:

  • Prevents accidents and injuries: Piping analysis can make the differentiation of the problems within the piping system and reduce the risks of the accidents and injuries.
  • Improves reliability: Piping analysis is useful in ascertaining that a given piping system is safe and dependable to support listed applications.
  • Reduces costs: The pipe stress is usually a warning sign that can assist in the early detection of damage so as to avoid high costs inlays.
  • Improves efficiency: Piping analysis may thus be very useful in increasing the effectiveness of a piping system by focusing on certain segments that may be most suitable for enhanced flow.

If you are an engineer, designer or constructor involved in the design, management or maintenance of a piping system, then use of piping analysis is of benefits in attaining and maintaining a safe and reliable piping system.

Piping analysis software

There are many piping analysis software packages available, each with its own strengths and weaknesses. Some of the most popular piping analysis software packages include:

  • CAESAR IICAESAR II is a comprehensive piping analysis software package that can be used to analyze a wide variety of piping systems. It is a powerful tool that can be used to identify potential problems in a piping system and to improve the efficiency of the system.


 

CAESAR II piping analysis software

CAESAR II piping analysis software

  • AutoPIPE: AutoPIPE is another popular piping analysis software package. It is a user-friendly software that can be used to analyze simple and complex piping systems.

AutoPIPE piping analysis software

AutoPIPE piping analysis software

  • PIPESTRESS: PIPESTRESS is a specific program of piping analysis software designed for use in designs on pressure vessels. Such programs are effective utility tool for determining the stresses and strains in pressure vessels.

PIPESTRESS piping analysis software

PIPESTRESS piping analysis software

  • Patran: Patran is a finite element program which has an extensive capability in performing analysis for multitude of structures for instance, piping systems. It is a strong tool that used for analysing the multiplex piping systems.

Patran piping analysis software

Patran piping analysis software

  • ANSYS Mechanical: Another FEA software package that can be used is ANSYS Mechanical which is also a general-purpose FEA software capable of analyzing virtually any structures including piping systems. Piping stress analysis is a strong technique that can be employed in the difficulty of the piping systems.

ANSYS Mechanical piping analysis software

ANSYS Mechanical piping analysis software

There are so many piping analysis software and the user has the mandate to select the most appropriate one depending on the user’s needs. That is, if the task at hand lies in solving a difficult pipe system, it will only be correct to resort to the help of a high-end software tool such as CAESAR II or AutoPIPE. However, if you only require analyzing simple piping systems, then, you can use a comparatively less powerful software package like PIPESTRESS.

When choosing a piping analysis software package, it is important to consider the following factors:When choosing a piping analysis software package, it is important to consider the following factors:

  • The complexity of the piping system: Your piping system is that to be analyzed and the software must be capable of this kind of analysis.
  • The features and capabilities of the software: It means the software must be capable to have features and the ability to s do what is desired.
  • The ease of use of the software: It must be easy to use…
  • The cost of the software: The software should be cheap or inexpensive.
  • The recommendation of a competent engineer is also important in the selection of a piping analysis software package. An engineer will be able to inform you of the right software to get for your needs.

The recommendation of a competent engineer is also important in the selection of a piping analysis software package. An engineer will be able to inform you of the right software to get for your needs.

Piping stress analysis basics

Piping stress analysis is conducted to evaluate the effects of mechanical loads, thermal expansion and contraction, and other factors on the piping system's integrity. The primary purposes include ensuring safety, preventing failures, and optimizing the design.

Load Types:

  • Piping systems are subjected to various types of loads, including:
  • Primary Loads: These are static loads that include weight, pressure, and axial forces.
  • Secondary Loads: These are dynamic or transient loads caused by events like thermal expansion, vibration, or water hammer.
  • Occasional Loads: These are infrequent loads such as seismic events, wind, or equipment operation.

Code Compliance:

  • Piping stress analysis must adhere to industry-specific codes and standards, such as ASME B31.1 (Power Piping) or ASME B31.3 (Process Piping), which provide guidelines for design, materials, and safety.

Analysis Methods:

  • There are two primary methods for conducting piping stress analysis:
  • Static Analysis: Evaluates stresses and displacements under steady-state conditions, including pressure, weight, and thermal loads.
  • Dynamic Analysis: Considers transient conditions, such as rapid temperature changes, water hammer, or seismic events, which can lead to dynamic stresses.

Modeling and Software:

  • Piping stress analysts use specialized software to create a 3D model of the piping system, incorporating pipe dimensions, materials, supports, and loads. The software calculates stresses and displacements based on the applied loads.

Supports and Restraints:

  • Proper support design is crucial. Supports must be strategically placed to prevent sagging, excessive movement, or overloading. Restraints are used to restrict movement in specific directions.

Thermal Expansion:

  • When there is a fluctuation in the temperatures, pipes tend to get enlarged or shrink. Piping stress analysis are effects of thermal and also if the system is capable of handling these changes without stressing or getting out of line.

Flexibility Analysis:

  • Dynamic assessment considers the effects of flexibility, which is, the piping system’s capacity to accommodate thermal expansion and contraction forces without exerting too much pressure on other equipment or developing flexibility-related problems.

Stress Allowable Limits:

  • Piping codes specify allowable stress limits for different materials and conditions. Stress analysis ensures that stresses in the piping components remain within these limits to maintain structural integrity.

Fatigue Analysis:

  • For cyclic loading like in equipment start-ups and shut-downs, fatigue assessment is conducted to examine the likelihood of fatigue cracks as time goes on.

Documentation and Reporting:

  • Reports, including stress analysis, support design and evaluation, necessary recommendations for stress correction, and confirmation of code compliance, are written as records of the piping stress analysis.

Review and Approval:

  • Piping stress analysis also generates reports which are critically assessed by competent engineers and may need the certification of the regulatory bodies or other relevant departments.

Iterative Process:

  • It should be noted that quite often piping stress analysis is performed sequentially. Any modifications of the design or its parameters and conditions may be needed in order to reassess compliance of the structure with the safety requirements.

Piping stress analysis is an imperative phase in the style and build of piping systems, mostly in the industries where safety, reliability, and performance are crucial to them like; oil and gas, petrochemical, and power generation plants. Correct assessment avoids issues, minimizes expenses, and increases the durability of the piping systems.

Dynamic analysis of piping system

  • Dynamic analysis is performed to assess the response of a piping system to transient events, such as:Dynamic analysis is performed to assess the response of a piping system to transient events, such as:
    • Rapid temperature changes (thermal transients)
    • Water hammer or fluid transient events
    • Seismic activity (earthquakes)
    • Equipment start-up and shut-down
    • Vibrations from rotating machinery
    • Wind or external forces

Types of Dynamic Analysis:

  • There are several types of dynamic analysis, including:There are several types of dynamic analysis, including:
    • Modal Analysis: Checks for natural frequencies and mode shapes of the piping system and its likelihood to resonate with the external forces.
    • Response Spectrum Analysis: Checks the system response to seismic or other dynamic load to some predetermined response spectra.
    • Transient Analysis: Relates the behavior of the system during certain transient conditions, for instance water hammer, or starting of equipment among others.
    • Time History Analysis: Models the system’s response as a function of time, taking into account both temporal, as well as spatial, load and boundary condition variations.

Load Considerations:

  • Dynamic analysis accounts for time-dependent loads, including forces, accelerations, and displacements. These loads are often irregular and can vary significantly during transient events.

Modeling and Software:

  • The engineers then incorporate a specialized 3D modeling tool that enables them to apply dynamic loads on the piping system. It is a tool that enables one to determine displacements at certain points, stresses, and accelerations of the system.

Damping and Energy Dissipation:

  • Damping mechanisms are introduced in the analysis to represent the energy dissipation within the system. Damping is crucial for accurately simulating the system's response to dynamic loads.

Support and Restraint Analysis:

  • Dynamic analysis assesses the performance of pipe supports, restraints, and hangers under transient conditions. Supports must allow for controlled movement and flexibility during dynamic events.

Response Evaluation:

  • Consequently, the outcomes of dynamic analysis can either be approved to meet the allowable levels of stress, displacement, and acceleration or be redesigned. It benefits in finding more problems like resonance, excessive vibration, or essential areas for fatigue.

Mitigation Measures:

  • Based on the analysis results, engineers may recommend mitigation measures, such as adding additional supports, modifying support designs, or implementing surge control devices to reduce the impact of water hammer.

Safety and Code Compliance:

  • Unlike static analysis, dynamic analysis guarantees that the piping system is safe and adheres to the code and standards of various industries. The evaluation of seismic design criteria is very important in the seismically active regions.

Documentation and Reporting:

  • Dynamic analysis reports are always in writing form and enclosed vital information such as analysis techniques, assumptions, results, and suggested changes to the design.

The dynamic analysis is very important in the piping system industries that experience changes in operating parameters of the system or industries where dynamic events may lead to major safety concerns which include the oil and gas, chemical and nuclear power industries. They help in avoiding surge related failures and the reliability of piping system especially when expose to some conditions.