Inputs Required for Piping Stress Analysis

This article outlines the essential inputs required for conducting a comprehensive piping stress analysis. Each input will be briefly introduced to provide readers with a foundational understanding of its role and significance in the analysis process. By systematically presenting these elements, the article aims to offer clarity and guidance to engineers and professionals navigating the complexities of piping systems.

1. Pipe Size

Pipe size is a fundamental input when initiating piping geometry modelling within stress analysis software. It is typically specified in the line tag, either as Nominal Bore (NB) or in inches. This data is readily available through key project documents such as the line list and piping and instrumentation diagrams (P&IDs).

2. Pipe Material

Material specifications are critical for determining allowable stress values as defined by applicable codes. These values vary by material and are essential for conducting accurate stress analyses. Material properties also inform the calculation of empty pipe weight, based on material density. When standard materials are used, stress analysis software automatically retrieves the corresponding allowable stress values from its integrated code library. In cases involving non-standard materials, manual input of these values is required. However, standard materials are commonly employed in most projects, making manual entry an infrequent task. Material specifications can be sourced from the piping material specification document or the line list. The material class is typically indicated in the line tag and is traceable across P&IDs, isometric drawings, and line lists.

3. Process Parameters

Process parameters significantly influence stress analysis results, as allowable stress values may vary with pressure and temperature. Key parameters include design, operating, and hydrotest pressures and temperatures. These values are typically documented in the project line list and may also be referenced in P&IDs or isometric drawings.

4. Design Ambient / Site Installation Temperature

Site ambient temperature—often referred to as the installation temperature—serves as the baseline for calculating thermal expansion under design and operating conditions. The difference between this baseline and the system’s operating temperature provides the basis for evaluating thermal behaviour. This information is generally recorded during site surveys and may also be found in documents such as the process design basis, piping design basis, or pipe stress analysis design basis.

5. Piping Fluid Density

Fluid density is a key factor in estimating the filled weight of a piping system. The combined densities of the fluid, insulation, and pipe material determine the overall system weight, which affects the system's response to sustained and seismic loads. Fluid density is often expressed as specific gravity and is typically listed in the project’s line list. If not available, it should be formally obtained from the Process Engineering department.

6. Operating Philosophy

Understanding the operating philosophy of the piping system is essential for identifying which pipelines are active under varying operating conditions. In large interconnected systems, not all pipelines carry hot fluid concurrently. For example, only a subset of pumps may operate at any given time, while others remain in standby mode, leading to uneven temperature distribution across the network. This variation results in different stress scenarios across the system, which are addressed through dedicated load cases during analysis. The operating philosophy is generally developed by the Process Engineering department and forms a key input for stress analysts.

7. Piping Thickness / Schedule

Details regarding pipe thickness and schedule are specified in the Piping Material Specification (PMS), which is prepared by the piping material engineer.

8. Piping Isometric Drawings

Piping isometric drawings are essential for generating the piping stress analysis model. These drawings provide precise geometry needed for analysis. As preliminary documents, they may be subject to updates following recommendations from the stress engineer to meet stress qualification requirements. The stress analyst may either manually model the system in the software based on these isometrics or import the geometry directly using a .pcf file from 3D modeling software. Isometric drawings are produced by piping layout engineers and can be requested from the Piping Layout department.

9. Pipe Stress Analysis Design Basis

The Pipe Stress Analysis Design Basis is a foundational document that guides the stress engineer before commencing analysis. It outlines the scope of stress-critical lines, applicable load types, and scenario considerations. This document is typically prepared at the project’s inception by the stress engineering team or may be provided by the client for brownfield projects. Due to the breadth of topics covered, the design basis merits a dedicated article for comprehensive treatment.

10. 3D Model

A 3D model is essential for evaluating the feasibility of alternative piping configurations recommended during stress analysis. To mitigate stress levels, engineers may propose re-routing sections of piping, which must be validated against spatial constraints and support feasibility. This assessment ensures no clash with adjacent equipment or piping. 3D models are typically developed by piping layout designers and reviewed using platforms such as Navisworks.

11. Coordinate System Alignment

Aligning the coordinate system of the stress analysis model with the plant’s 3D model enhances interpretability across disciplines. Project conventions may vary — in some cases, the Y-axis represents the vertical direction, while others use the Z-axis. Ensuring alignment improves cross-functional understanding of model geometry. Coordinate system details can be extracted from the 3D model or referenced from the project’s CAD plan.

12. Applicable Piping Code

Determining the appropriate piping code is critical before conducting stress analysis, as it governs allowable stress criteria and design methodology. Commonly used codes include:
• ASME B31.3 for process plants
• ASME B31.1 for power plants
• ASME B31.5 for refrigeration systems
The selected code is typically outlined in the stress analysis design criteria.

13. Piping Insulation Material and Thickness

Insulation material type and its density contribute significantly to the overall system weight. Materials such as aerogels are lightweight, while calcium silicate offers greater density. Mineral wool is commonly used in practice. Insulation thickness varies based on operational temperature and intended purpose — whether for personnel protection or thermal conservation — influencing the resulting load on the pipe. Details regarding insulation material and its thickness are specified in the insulation specification document.

14. Refractory Material Properties

Refractory materials are applied to piping to protect against potential fire scenarios and contribute additional weight. Their density and thickness must be considered during stress analysis and are typically documented in the refractory material specification.

15. Insulation Cladding

Insulation is often covered with cladding composed of stainless steel or aluminum sheets. The density and thickness of these sheets add to the system weight and should be accounted for in stress calculations. Relevant data can be sourced from the insulation specification.

16. Inline Component Loads

Inline components such as valves, strainers, expansion joints, sight glasses, flow meters, and steam traps behave as rigid bodies and differ in flexibility compared to pipes. Their concentrated weight requires explicit input during stress analysis. This information can be found in general arrangement (GA) drawings, specifications, datasheets, or vendor catalogues.

17. Expansion Bellows

Expansion bellows offer vital flexibility where required. Their dimensions, weight, and stiffness (axial, lateral, and radial) must be incorporated into the analysis to accurately predict system behavior under varied load cases. These properties are typically detailed in vendor catalogues.

18. Allowable Nozzle Loads

Piping systems interface with equipment such as pumps, compressors, turbines, tanks, and heat exchangers. Each equipment nozzle has defined load limits, usually provided by manufacturers. Some industry standards also offer guidance on acceptable nozzle load criteria. Allowable loads should be verified using these standards or confirmed directly with vendors.

19. Nozzle Displacement Data

Equipment nozzles may experience displacement due to operating conditions, such as tank bottom expansion caused by fluid weight or thermal expansion. These displacements are either provided by equipment vendors or estimated by engineers based on design assumptions. Accurate data is essential for stress modeling.

20. Standard Pipe Support Library

Following stress analysis, the engineer must recommend suitable support types at designated locations. Standard support libraries are referenced to streamline support detailing and reduce engineering effort. Access to the support standard document is necessary during this phase.

21. Existing Piping Considerations

In some cases, stress analysis is performed on existing piping sections, particularly during retrofits or system expansions. When new piping interfaces with existing networks, details of the unchanged portion — including support locations up to the first anchor point — are required. If unavailable, boundary conditions such as allowable loads or displacement criteria at the connection point must be defined for accurate modeling.

22. Occasional Load Inputs

Manual calculations for occasional loads must be carried out to provide necessary input for stress analysis. These may include:
• Seismic load calculations
• Wind load calculations
• Snow load impact
• Pressure Safety Valve (PSV) reaction loads
Stress engineers perform these calculations and incorporate the resulting factors into the final analysis.

23. Input Documents Required For Stress Analysis

Following is the list of documents where you can find Stress analysis related Inputs. Piping design basis.

1. Piping Stress analysis design basis
2. Piping Material Specification.
3. Operating philosophy of piping system
4. Valve Material Specification and valve datasheet / catalogues.
5. Piping Isometric drawings.
6. PID Markup in which the piping system that need to be analyzed is marked.
7. Piping 3D model to check the feasibility of alternative piping arrangement if required to qualify in stress.
8. Equipment GA Drawings.
9. Insulation Specification.
10. Standard Support Library.
11. Piping Line list.
12. Site survey report.