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PIPING STRESS INTERVIEW Q&A SET-2
In Caesar II, software used for pipe stress analysis, identifying stress critical
systems is crucial for ensuring the structural integrity and safety of piping
systems. Here are some criteria commonly used for this identification:
a. High Operating Temperatures and Pressures: Systems operating at high
temperatures and pressures are more prone to stress concentrations and
potential failure. These systems should be analyzed thoroughly to ensure
they can withstand the imposed loads.
b. Complex Piping Configurations: Piping systems with complex configurations, such as multiple bends, branches, or changes in diameter, can experience stress concentrations at these points. Analyzing such systems helps in identifying potential stress hotspots.
c. Critical Service: Systems carrying critical fluids or serving critical processes within a plant are usually designated as stress critical. Failure in these systems can have severe consequences, including safety hazards and production losses.
d. Special Components: Piping systems containing special components like expansion joints, flexible hoses, or bellows are prone to stress concentrations at the interface between these components and the main piping. These areas require careful analysis.
e. High Vibrations: Systems subjected to high levels of vibration, whether from external sources or internal flow-induced vibrations, need to be analyzed to ensure that vibration-induced stresses are within acceptable limits.
f. Dynamic Loads: Systems experiencing dynamic loads such as water hammer, seismic loads, or wind loads need to be analyzed for stress to ensure they can withstand transient conditions without failure.
2. Can you select a proper spring hanger if you do not make it program defined in your Caesar 2 software? What is the procedure?
Selecting a proper spring hanger without utilizing specialized software like
Caesar 2 can be done manually, although it requires knowledge of
engineering principles and calculations. Here's a general procedure to
follow:
Determine Load Requirements: Start by understanding the load
requirements of the piping system. This includes the weight of the piping
and any additional loads such as thermal expansion or seismic loads.
Identify Operating Conditions: Consider the operating conditions of the piping system, including temperature, pressure, and fluid type. These factors can influence the selection of the spring hanger material and design.
Calculate Load Range: Calculate the expected load range for the piping system. This includes the static load (weight of the piping) as well as any dynamic loads (such as thermal expansion or transient loads).
Select Spring Hanger Type: Based on the load requirements and operating conditions, select the appropriate type of spring hanger. There are various types available, including variable spring hangers, constant spring hangers, and variable effort spring hangers. Each type has its own advantages and limitations.
Calculate Spring Hanger Characteristics: Calculate the required characteristics of the selected spring hanger, such as spring rate, travel range, and load capacity. These calculations may involve considerations such as the expected deflection of the piping system and the required support stiffness.
Consider Installation and Maintenance: Factor in considerations such as ease of installation and maintenance requirements when selecting the spring hanger. This includes accessibility for adjustment and inspection, as well as any special installation requirements.
Consult Standards and Guidelines: Refer to industry standards and guidelines, such as ASME B31.1, ASME B31.3, and MSS SP-58, for guidance on spring hanger selection and design.
Verify Selection: Once a spring hanger is selected, verify that it meets the requirements of the piping system through calculations and analysis. This may involve performing stress analysis or finite element analysis to ensure that the spring hanger can adequately support the piping loads.
Document Selection: Document the selected spring hanger, including its specifications, installation details, and any calculations or analysis performed to verify its suitability for the application.
By following this procedure and considering the relevant factors, you can select a proper spring hanger for your piping system even without using specialized software like Caesar 2. However, it's important to note that using engineering software can streamline the process and provide more accurate results, especially for complex piping systems or critical applications.
3. Why Horizontal Displacement is specified in the datasheet? What will you do if the angle due to displacement is more than 4 degrees?
In piping engineering, horizontal displacement refers to the lateral movement of a pipe from its original position. This displacement is specified in datasheets for several reasons:
1. Structural Integrity: Pipes are often designed to withstand certain forces and loads. Horizontal displacement limits help ensure that the pipe remains within its design parameters to maintain structural integrity.
2. Operational Safety: Excessive horizontal displacement can lead to issues such as stress concentration, misalignment of connected equipment, and potential failure during operation. Specifying limits helps ensure safe and reliable operation.
3. Space Constraints: In many piping systems, there are spatial constraints that must be considered. Limiting horizontal displacement helps ensure that the piping system fits within its designated space without encroaching on other equipment or structures.
If the angle due to displacement exceeds 4 degrees, several actions can be taken:
1. Reevaluate Design: It may be necessary to reassess the design of the piping system to determine the cause of the excessive displacement and identify potential solutions.
2. Adjust Supports: Additional supports or repositioning of existing supports may be required to limit the displacement and bring it within acceptable limits.
3. Redesign or Reroute: In some cases, it may be necessary to redesign or reroute the piping to reduce the angle of displacement and ensure compliance with specifications.
4. Utilize Flexible Joints: Flexible joints or expansion loops can be incorporated into the piping system to accommodate movement and reduce the angle of displacement.
5. Consult Standards and Codes: Consulting relevant industry standards and codes can provide guidance on acceptable limits for horizontal displacement and appropriate remedial actions.
Overall, addressing excessive horizontal displacement requires a comprehensive assessment of the piping system and may involve a combination of design modifications, adjustments to supports, and adherence to industry standards.
4. Brief on Methodology to be considered for requirement of loop study and support design consideration in pipe racks?
In piping engineering, conducting a loop study and designing supports for pipe racks are critical steps to ensure the integrity and stability of piping systems. Below is a brief methodology outlining considerations for these tasks:
1. Loop Study Methodology:
a. Identify Potential Loop Locations: Review the piping layout and identify areas where thermal expansion or contraction may occur, such as changes in direction, elevation, or temperature.
b. Calculate Thermal Expansion/Contraction: Determine the expected thermal expansion or contraction of the piping system based on temperature differentials, material properties, and pipe lengths.
c. Evaluate Loop Requirements: Assess whether expansion loops, expansion joints, or other flexible elements are necessary to accommodate thermal movement. Consider factors such as pipe material, operating conditions, and space constraints.
d. Design Loop Configurations: Determine the appropriate configuration and size of expansion loops or joints to effectively absorb thermal movement while maintaining system integrity. Consideration should be given to factors such as loop type (e.g., U-bend, elbow, or concentric), flexibility, and accessibility for maintenance.
e. Incorporate Supports and Anchors: Integrate supports and anchors into the loop design to ensure stability and prevent excessive movement. Supports should be strategically placed to distribute loads and minimize stress on the piping system.
f. Review Compliance: Ensure that the proposed loop design complies with relevant industry standards, codes, and project specifications.
2. Support Design Consideration in Pipe Racks:
a. Evaluate Load Requirements: Determine the loads acting on the piping system, including dead weight, live loads (e.g., fluid contents), wind loads, seismic loads, and thermal expansion/contraction forces.
b. Select Support Types: Choose appropriate support types based on the specific requirements of the piping system, including pipe size, material, operating conditions, and layout constraints. Common support types include clamps, hangers, shoes, and rollers.
c. Spacing and Configuration: Determine the spacing and configuration of supports along the pipe rack to adequately distribute loads and minimize deflection. Consider factors such as pipe diameter, weight, span lengths, and anticipated loads.
d. Anchoring and Bracing: Incorporate anchoring and bracing systems to provide lateral stability and prevent excessive movement of the pipe rack structure. Ensure that anchors are properly installed and capable of resisting anticipated loads and forces.
e. Consideration for Expansion and Contraction: Account for thermal expansion and contraction of the piping system when designing supports and anchors. Expansion loops, expansion joints, or flexible supports may be necessary to accommodate thermal movement and prevent stress accumulation.
f. Review Compliance: Verify that the support design complies with applicable codes, standards, and project specifications, including requirements for material selection, load capacity, and installation procedures.
By following these methodologies, piping engineers can effectively address the requirements for loop studies and support design considerations in pipe racks, ensuring the safe and reliable operation of piping systems.
5. What is slug flow? What parameters are required to calculate the slug force?
Slug flow is a type of two-phase flow commonly encountered in pipelines where both gas and liquid phases are present. In slug flow, the flow pattern alternates between a slug of liquid followed by a slug of gas. This results in periodic variations in flow velocity, pressure, and composition along the pipeline.
To calculate the slug force in piping engineering, several parameters are required:
1. Slug Length (L): The length of the slug, which is the continuous portion of liquid or gas in the pipeline. This parameter determines the magnitude of the force exerted by the slug on the piping system.
2. Slug Mass (M): The mass of the slug, which is calculated based on the density of the liquid or gas and the volume of the slug. This parameter directly influences the magnitude of the force exerted by the slug.
3. Flow Velocity (V): The velocity of the two-phase flow within the pipeline. This parameter affects the rate at which slugs travel along the pipeline and consequently impacts the force exerted by the slugs.
4. Pipe Diameter (D): The internal diameter of the pipeline. This parameter influences the cross-sectional area available for the flow of slugs and affects the pressure drop and force exerted by the slugs.
5. Fluid Properties: The properties of the liquid and gas phases, including density, viscosity, and compressibility. These properties determine the behavior of the two-phase flow and impact the magnitude of the forces experienced by the piping system.
6. Flow Regime Transitions: Understanding the transition between different flow regimes, such as slug flow, annular flow, or stratified flow, is crucial for accurately predicting slug forces. Different flow regimes have distinct characteristics and require different methodologies for analysis.
7. Pipeline Geometry and Layout: Factors such as pipeline geometry, layout, bends, fittings, and obstructions can affect the occurrence and behavior of slug flow. These factors must be considered when calculating slug forces and designing piping systems to withstand them.
By considering these parameters and conducting detailed analysis, piping engineers can accurately predict slug forces and design piping systems capable of safely handling slug flow conditions. Additionally, empirical correlations and computational fluid dynamics (CFD) simulations can be used to further refine slug force calculations and optimize piping system designs.
6. What are hot sustained stresses? Why do we check it? Do we need to check expansion stresses?
Hot sustained stresses refer to the stresses experienced by a piping system while operating at elevated temperatures over an extended period, typically during steady-state conditions. These stresses are caused by factors such as thermal expansion, pressure, and weight of the piping components. It's crucial to check hot sustained stresses because they can lead to deformation, fatigue, and ultimately failure of the piping system if not adequately addressed. Here's why we check hot sustained stresses:
1. Safety and Integrity: Excessive hot sustained stresses can compromise the structural integrity of the piping system, leading to leaks, ruptures, or catastrophic failures. Checking these stresses helps ensure the safety of personnel and assets.
2. Compliance: Various industry standards, codes, and regulations mandate the evaluation of hot sustained stresses to ensure that piping systems meet specific design criteria and safety requirements.
3. Prevention of Material Degradation: Prolonged exposure to high temperatures can cause material degradation, including creep and thermal fatigue, which can accelerate the aging process and reduce the lifespan of the piping components. Checking hot sustained stresses helps identify potential areas of concern and mitigate the risk of material failure.
4. Optimization of Design: Evaluating hot sustained stresses allows engineers to optimize the design of the piping system by selecting appropriate materials, dimensions, and support configurations to minimize stress concentrations and ensure long-term reliability.
Regarding expansion stresses, yes, it's essential to check expansion stresses in piping engineering. Expansion stresses occur due to thermal expansion and contraction of the piping system as it heats up or cools down during operation. These stresses can lead to issues such as pipe movement, distortion, and increased loads on supports and connections. By evaluating expansion stresses, engineers can ensure that the piping system is adequately designed to accommodate thermal movement without exceeding allowable stress limits. Expansion stresses are typically considered in conjunction with other stress factors, including hot sustained stresses, to comprehensively assess the structural integrity of the piping system.
7. What is the minimum loop cases required to consider while performing a stress analysis of a column reboiler connected piping system?
When performing stress analysis for a column reboiler connected piping system, the minimum loop cases to consider typically include:
1. Vertical Expansion Loop: This loop case accounts for vertical expansion or contraction of the piping system due to temperature variations. It is essential to accommodate changes in elevation between the column reboiler and other connected equipment or piping.
2. Horizontal Expansion Loop: Horizontal expansion loops address lateral movement of the piping system caused by thermal expansion or contraction. This loop case is necessary to prevent excessive stresses and displacement, particularly in long horizontal runs or where changes in direction occur.
3. Combined Vertical and Horizontal Expansion Loop: In some scenarios, both vertical and horizontal expansion loops may be required to adequately absorb thermal movement in the piping system. This combined loop case ensures comprehensive stress analysis, considering both vertical and horizontal displacement.
These minimum loop cases are essential to account for thermal expansion and contraction of the piping system, which can lead to stress buildup and potential structural issues if not properly addressed. By analyzing these loop cases, engineers can ensure that the piping system is adequately designed to withstand thermal variations and maintain integrity during operation. Additional loop cases may be considered based on the specific configuration, operating conditions, and project requirements of the column reboiler connected piping system.
8. Brief on the nozzle load evaluation procedure for lines connected to pump lines? Why alignment check is required in rotating equipment?
Nozzle Load Evaluation Procedure for Lines Connected to Pump Lines: When evaluating nozzle loads for lines connected to pump lines in piping engineering, the following procedure is typically followed:
1. Identify Loads: Determine the loads acting on the pump nozzles, including forces and moments due to piping weight, pressure, thermal expansion, seismic events, and other external factors.
2. Calculate Loads: Use engineering calculations and analysis techniques to quantify the magnitude and direction of the loads on the pump nozzles. Consider factors such as pipe size, material, operating conditions, and layout configuration.
3. Evaluate Allowable Loads: Refer to pump manufacturer specifications, industry standards, and codes to determine allowable loads for the pump nozzles. Consider factors such as nozzle size, material, design, and intended operating conditions.
4. Compare Loads to Allowable Limits: Compare the calculated loads on the pump nozzles to the allowable limits specified by the pump manufacturer and relevant standards. Ensure that the loads are within acceptable ranges to prevent overstressing and potential damage to the pump equipment.
5. Adjustment and Mitigation: If the calculated loads exceed allowable limits, consider adjustments and mitigation measures to reduce the loads on the pump nozzles. This may involve redesigning the piping layout, adding supports or restraints, modifying operating conditions, or selecting alternative pump equipment.
6. Documentation and Reporting: Document the results of the nozzle load evaluation, including calculations, analysis findings, and any recommended actions or modifications. Provide clear and concise reports to stakeholders, including pump manufacturers, engineering teams, and project managers.
7. Verification and Validation: Verify the effectiveness of any adjustments or mitigation measures implemented to reduce nozzle loads. Conduct validation checks to ensure that the pump equipment operates within safe and reliable limits during operation.
By following this evaluation procedure, piping engineers can ensure that lines connected to pump lines are properly designed and configured to withstand nozzle loads and maintain the integrity and performance of the pump equipment.
Alignment Check in Rotating Equipment:
In rotating equipment such as pumps, turbines, and compressors, alignment checks are required for several reasons:
1. Operational Efficiency: Proper alignment ensures efficient operation of rotating equipment by minimizing friction, vibration, and wear on bearings, shafts, and seals. Misalignment can lead to increased energy consumption, reduced equipment lifespan, and decreased performance efficiency.
2. Prevention of Damage: Misalignment can cause excessive forces and stresses on equipment components, leading to premature wear, fatigue, and potential mechanical failures. Regular alignment checks help prevent damage and prolong the service life of rotating equipment.
3. Safety Considerations: Misaligned rotating equipment poses safety risks to personnel and assets due to the potential for unexpected failures, leaks, or spills. Alignment checks are essential to mitigate these risks and ensure safe operation in industrial environments.
4. Quality Assurance: Proper alignment is critical for maintaining product quality and consistency in manufacturing processes that rely on rotating equipment. Misalignment can result in variations in product specifications, tolerances, and quality standards.
5. Compliance Requirements: Industry standards, regulations, and best practices often mandate periodic alignment checks for rotating equipment to ensure compliance with safety, reliability, and environmental regulations.
Overall, alignment checks are essential in piping engineering to ensure the optimal performance, reliability, and safety of rotating equipment. By conducting regular alignment assessments and addressing any issues promptly, engineers can minimize downtime, maximize efficiency, and extend the operational lifespan of critical assets.
9. List down the support design consideration for lines connected to rotating equipment such as pump/compressor/turbine?
When designing supports for lines connected to rotating equipment such as pumps, compressors, or turbines, several considerations need to be taken into account to ensure the integrity and stability of the piping system. Here is a list of support design considerations for such applications:
1. Equipment Loading: Determine the loads acting on the piping system due to the weight of the equipment, including the pump, compressor, or turbine, as well as any attached components such as motors or gearboxes.
2. Dynamic Forces: Consider dynamic forces generated by the rotating equipment, including vibration, pulsation, and harmonic oscillations. Select supports capable of damping and absorbing these dynamic loads to prevent fatigue and stress concentration in the piping system.
3. Thermal Expansion: Account for thermal expansion and contraction of the piping system due to temperature variations during operation. Design supports that accommodate thermal movement without imposing excessive stress on the equipment connections or piping components.
4. Flexibility Requirements: Determine the flexibility requirements of the piping system based on factors such as pipe material, diameter, operating conditions, and layout configuration. Select supports that provide the necessary flexibility to accommodate movement while maintaining structural stability.
5. Alignment: Ensure proper alignment between the piping and the rotating equipment to minimize shaft misalignment, bearing wear, and vibration-induced fatigue. Incorporate alignment features into support designs to facilitate alignment adjustment and maintenance.
6. Base Isolation: Consider base isolation techniques to mitigate transmission of vibration and noise from the rotating equipment to the surrounding piping and support structures. Use vibration isolators, flexible mounts, or other damping devices to reduce vibration-induced stress and fatigue.
7. Accessibility: Design supports to allow for easy access to the rotating equipment for maintenance, inspection, and repair activities. Ensure adequate clearance and maneuverability for personnel and tools to perform tasks safely and efficiently.
8. Corrosion Protection: Implement corrosion protection measures for supports and associated hardware to mitigate the risk of degradation due to exposure to corrosive environments, moisture, or chemical substances.
9. Compliance with Standards: Ensure that support designs comply with relevant industry standards, codes, and regulations governing the design, installation, and operation of piping systems connected to rotating equipment.
By considering these support design considerations, piping engineers can develop robust and reliable support systems for lines connected to rotating equipment, ensuring safe and efficient operation of industrial facilities.
10. What are the methods for flange leakage checking in Caesar 2? Write the equation used for flange leakage checking in the pressure equivalent method?
