Piping Flexibility Screening

Use this skill for public, educational piping-flexibility screening. It estimates hoop (sustained) stress, free thermal expansion, displacement (expansion) stress range against a simplified allowable, and a flange-rating pressure check so an agent can scope a pipe-flexibility study before detailed pipe-stress analysis.

When to Use

• When a user asks whether a hot pipe run needs an expansion loop or whether a flange class is adequate.
• When an agent needs a quick hoop-stress and thermal-expansion estimate for a process line.
• When examples must run without confidential isometrics, stress-analysis models, or company piping specs.

Inputs

• outside_diameter_mm: pipe outside diameter in mm.
• wall_thickness_mm: pipe wall thickness in mm.
• design_pressure_bar: internal design pressure in bar gauge.
• design_temperature_c: design (operating) temperature in degrees Celsius.
• pipe_length_m: straight run length in m.
• install_temperature_c: installation/ambient temperature in degrees Celsius, default 20.
• anchor_to_anchor: whether the run is fully restrained anchor-to-anchor, default True.
• youngs_modulus_mpa: Young's modulus in MPa, default 200000.
• thermal_expansion_coeff_per_k: mean thermal expansion coefficient per K, default 1.2e-5.
• allowable_stress_mpa: material allowable stress in MPa, default 138.
• flange_rating_class: optional ASME B16.5 flange class (e.g. 150, 300, 600).
• flange_allowable_pressure_bar: optional flange allowable pressure at temperature in bar.

Outputs

• hoop_stress_mpa: Barlow hoop (sustained) stress.
• hoop_stress_ratio: hoop stress divided by allowable stress.
• delta_temperature_k: design minus install temperature difference.
• free_thermal_expansion_mm: unrestrained thermal growth of the run.
• displacement_stress_mpa: displacement (expansion) stress estimate.
• allowable_stress_range_mpa: simplified allowable stress range.
• displacement_stress_ratio: displacement stress divided by the allowable range.
• flange_pressure_ratio: design pressure divided by flange allowable pressure, or null.
• stress_warning: ok, watch, hoop-stress-exceeded, or expansion-stress-exceeded.
• flange_warning: ok, flange-overpressure, or no-rating.
• assumptions: public assumptions used by the placeholder model.

Engineering Method

The Python class PipingFlexibilityModel uses open piping relations only:

• hoop stress uses the thin-wall Barlow relation S_h = P D / (2 t).
• thermal strain uses epsilon = alpha |T_design - T_install|.
• free thermal expansion uses dL = epsilon * L.
• displacement stress uses the fully restrained worst case S_E = E alpha dT, with a fixed relief factor when the run is not anchor-to-anchor.
• the allowable stress range uses a simplified S_A = 1.5 * S_allow (screening of f (1.25 S_c + 0.25 S_h)).
• the flange check compares design pressure to a supplied flange allowable pressure.

This is educational and screening-only logic. It assumes thin-wall pressure stress, a single straight run, constant material properties, and a fully restrained worst-case expansion stress. It is not a replacement for validated pipe-stress/flexibility analysis or qualified piping-engineering review.

Python Usage Pattern

from piping_flexibility_screening import PipingFlexibilityModel

model = PipingFlexibilityModel()
result = model.evaluate(
    outside_diameter_mm=168.3,
    wall_thickness_mm=7.11,
    design_pressure_bar=50.0,
    design_temperature_c=180.0,
    pipe_length_m=40.0,
    flange_allowable_pressure_bar=49.6,
)

print(result.hoop_stress_mpa)
print(result.displacement_stress_mpa)
print(result.stress_warning)
print(result.flange_warning)

Related NeqSim Functionality

For validated mechanical-design calculations, redirect to NeqSim classes:

• neqsim.process.mechanicaldesign.pipeline.PipelineMechanicalDesign — pipeline wall thickness and mechanical design.
• neqsim.process.mechanicaldesign.pipeline.PipingFlexibilityCalculator — proposed pipe-stress/flexibility screening (sustained and displacement stress, flange checks); candidate NeqSim gap.
• neqsim.process.equipment.pipeline.PipeBeggsAndBrills — hydraulic and thermal pipe model for line conditions.

This skill is a public triage layer that decides when to invoke a validated pipe-stress model.

Validation Checklist

• Outside diameter and wall thickness are positive and t < D/2.
• Design pressure, length, and material properties are positive.
• Tests cover hoop stress, displacement stress, the flange check, and invalid input.
• Results are described as educational screening indicators.
• Real flexibility analysis is redirected to validated NeqSim classes and qualified review.

Common Mistakes

Limitations

• No proprietary isometrics, stress-analysis models, or company piping specs are included.
• A single straight run is modelled; bends, branches, and supports are not analysed.
• Displacement stress uses a fully restrained worst case; real flexibility depends on routing.

References

• ASME B31.3, Process Piping.
• ASME B16.5, Pipe Flanges and Flanged Fittings.
• NeqSim repository: https://github.com/equinor/neqsim