Toolbox: Pipe Stressing

Beca AMEC has the computer resources and expertise to perform stress analysis on piping systems. The computer stress analysis package used is AutoPIPE. AutoPIPE offers a high degree of flexibility in modelling techniques and produces user friendly output data. The Importance of Stress Analysis

Stemming from the conceptual process design phase is the detail engineering phase, involving piping layouts and isometrics. It is important that all hot piping systems are assessed on thermal expansion to give an initial indication into the likely problem areas. This logical approach ensures the layout will not require reworking at a later date and provides a complete design solution.

Pipe Routing & Supporting

Harmful piping systems such as steam, condensate and natural gas which are required to be designed to a code require a complete stress analysis to gain statutory approvals. Manual calculations become difficult, time consuming and expensive.

Process lines which are non-coded with diameters >Ø150mm and with temperature differentials >60°C should also be stressed as these lines have the potential to produce high stresses and support forces.

Invariably piping systems initiate or terminate at equipment nozzles. The piping system induces loads to these nozzles, which have specified allowable loads, to which a comparison must be made.

Piping systems carrying hazardous fluids require rigorous stress analysis to ensure that the contents do not leak under specific load combinations such as a seismic event.

Model Building

All the piping components and details are inputted as node points to create a realistic piping model. Typical node points would locate piping fittings, valves, supports, etc. Piping components are chosen from a wide range of material options.

The model is displayed in 3-D with all the input data presented in a list file allowing easy checking.

Features

A complete stress analysis can be performed for the following load cases:

• Gravity
• Pressure cases (3)
• Thermal cases (3)
• Hydrotest
• Static earthquake / seismic (3 directions)
• Soil (buried pipe)
• Wind cases (8)
• Static analysis
• Modal analysis
• Anchor & support movements
• Spring Hanger selection (10 manufacturers)
• Response spectrum
• Tank settlements / nozzle flexibility
• Beam elements for modelling frames
• Gaps / frictions / yielding
• Code compliance
• Model consistency check

Piping systems can be analysed to the following codes:

• ANSI/ASME B31.1
• ANSI/ASME B31.3
• ANSI/ASME B31.4
• ANSI/ASME B31.8
• International piping codes

As mentioned earlier the stress analysis has the feature of checking the piping loads on equipment nozzles. The following pieces of rotating equipment can be checked:

• Turbines (NEMA 23)
• Pumps (API 610)
• Compressors (API 617)

The results from the analysis can be displayed in a tabular or graphical form with either screen or hard copy printouts. Output data can be displayed in Metric, Imperial, SI or other units. Typical results given are:

• Support and anchor forces
• Restraint reactions
• Global forces and moments
• General pipe stress report
• Stress intensifications to code compliance
• Displacements
• Flange check
• Model point data listing
• System result summary
• System analysis summary