https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc

Full-physics NNpHSCC simulation for gas transmission pipelines — Chen-Sutherby-Xing, BS 7910, API 579/581, Bayesian RBI.
https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc

api-571 api-579 api-581 bayesian-inference bs-7910 cathodic-protection fracture-mechanics hydrogen-embrittlement monte-carlo nnphscc pipeline-integrity python risk-based-inspection stress-corrosion-cracking

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Full-physics NNpHSCC simulation for gas transmission pipelines — Chen-Sutherby-Xing, BS 7910, API 579/581, Bayesian RBI.

Host: GitHub
URL: https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc
Owner: felipearocha
License: mit
Created: 2026-05-13T04:24:07.000Z (about 1 month ago)
Default Branch: main
Last Pushed: 2026-05-20T23:39:27.000Z (26 days ago)
Last Synced: 2026-05-21T05:52:28.894Z (26 days ago)
Topics: api-571, api-579, api-581, bayesian-inference, bs-7910, cathodic-protection, fracture-mechanics, hydrogen-embrittlement, monte-carlo, nnphscc, pipeline-integrity, python, risk-based-inspection, stress-corrosion-cracking
Language: Python
Homepage: https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc
Size: 3.38 MB
Stars: 1
Watchers: 0
Forks: 0
Open Issues: 0
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Citation: CITATION.cff

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README

          # Integrity Code Series — Week 10 — NNpHSCC Full-Physics Simulation

[![CI](https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc/actions/workflows/ci.yml/badge.svg)](https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc/actions/workflows/ci.yml)

[![Release](https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc/actions/workflows/release.yml/badge.svg)](https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc/actions/workflows/release.yml)

[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE)

[![Python 3.10+](https://img.shields.io/badge/python-3.10%2B-blue.svg)](https://www.python.org/downloads/)

[![Tests](https://img.shields.io/badge/tests-194%20passed-brightgreen.svg)](#validation)

[![Code style: ruff](https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/astral-sh/ruff/main/assets/badge/v2.json)](https://github.com/astral-sh/ruff)

[![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.20172241.svg)](https://doi.org/10.5281/zenodo.20172241)

**Author:** Felipe Rocha — Independent Researcher

## Integrity Code Series

Part of an ongoing series of physics-first integrity simulators by Felipe Rocha:

| # | Repo | Domain |

|---|---|---|

| Week 3 | [Integrity-code-series-3](https://github.com/felipearocha/Integrity-code-series-3) | F1 lap simulation (six coupled ODEs) |

| Week 6 | [Integrity-code-series-week6-smartphone-galvanic](https://github.com/felipearocha/Integrity-code-series-week6-smartphone-galvanic) | Smartphone galvanic corrosion (Laplace + Butler-Volmer) |

| Week 7 | [integrity_code_series_week7_h2_lferw](https://github.com/felipearocha/integrity_code_series_week7_h2_lferw) | LF-ERW H2 conversion (B31.12 + NACE TM0316) |

| Week 8 | [integrity-code-series-week8-creep-fatigue-heater](https://github.com/felipearocha/integrity-code-series-week8-creep-fatigue-heater) | Creep-fatigue 9Cr-1Mo (Norton/Omega + Coffin-Manson) |

| Week 9 | [integrity-code-series-week9-cui](https://github.com/felipearocha/integrity-code-series-week9-cui) | CUI thermohygro-electrochemical (3 PDEs, Strang) |

| Week 10 | [integrity-code-series-week-10_nnph_scc](https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc) | NNpHSCC full-physics (Chen-Sutherby-Xing + BS 7910) |

| Bonus | [Vibration-Accelerated-Corrosion-Coupled-Mechano-Electrochemical-Simulation](https://github.com/felipearocha/Vibration-Accelerated-Corrosion-Coupled-Mechano-Electrochemical-Simulation) | Vibration-accelerated corrosion (SDOF + Butler-Volmer + Archard) |

| Bonus | [synthetic-integrity-digital-twin-piml](https://github.com/felipearocha/synthetic-integrity-digital-twin-piml) | Physics-informed neural-network surrogate |

| Bonus | [integrity-data-foundation](https://github.com/felipearocha/integrity-data-foundation) | Engineering data validation baseline |

## Quick Start

```bash

# Clone and install

git clone https://github.com/felipearocha/integrity-code-series-week-10_nnph_scc.git

cd integrity-code-series-week-10_nnph_scc

pip install -e .[dev]

# Validate

pytest tests/ -q                          # 194 tests

python -m validation.benchmarks           # textbook constants

# Reproduce all panels + audit-chained outputs

python run_all.py

```

Browse `equations.html` in any modern browser for the full LaTeX equations reference.

## Problem Statement

Near-Neutral pH Stress Corrosion Cracking (NNpHSCC) accounts for a major fraction of

reportable incidents on gas transmission pipelines in North America. Two specific incidents

motivate this package:

- **2018 Prince George, BC rupture** — 914mm gas pipeline; NNpHSCC cause; downstream of compressor

- **2015 Unityville, PA rupture** — 609mm gas pipeline; NNpHSCC; [SOURCE: Sun et al. 2021 JIPR]

PHMSA §192.611(a)(4) (effective March 16, 2026) requires integrity assessment for class location

changes. This package provides the physics foundation for that assessment.

**Key finding from v2:** Even the best available NNpHSCC crack growth model has COV = 61.2% on

validated full-scale test data. This package explicitly incorporates that model structural

uncertainty as a sampled variable — not a footnote.

---

## Governing Equations

### PDE 1 — Laplace (soil electrochemistry)

∇·(σ_soil·∇φ) = 0 in soil; Butler-Volmer BC at coating holiday

### PDE 2 — Oriani-Fick (H diffusion in steel wall)

∂C_L/∂t = D_eff·∂²C_L/∂r²;  D_eff = D_H(T)/(1+K_trap_eff)

### PDE 3 — Chen-Sutherby-Xing crack growth (most accurate available model)

**[SOURCE: Chen & Sutherby 2007; Xing et al. via Sun et al. 2021]**

    da/dN = A_CF × (K_max × ΔK² × f_eff^(-0.1))^n × HE_factor

    HE_factor = (C_H_bulk / C_H_ref)^n_HE        Xing HEDE multiplier

    f_eff = max(f, f_crit = 10^-3 Hz)            frequency saturation

    n = 2.0   [SOURCE: Chen & Sutherby 2007]

    n_HE = 0.88 [SOURCE: Sun et al. 2021, Xing model]

### Variable Amplitude Loading (Type I underload)

**[SOURCE: Chen 2007 — "10x enhancement under underload VA loading"]**

    da/dt = f_major × da/dN_major + f_minor × da/dN_minor × F_INT

    F_INT = 10  [SOURCE: Chen 2007 — underload-minor interaction factor]

### Crack Dormancy Criterion (Stage I → Stage II)

**[SOURCE: Zhao et al. 2017 — >95% cracks remain dormant below 1mm]**

    Dormant if: ΔK < ΔK_th_Stage2 = 2.2 MPa√m  OR  C_H < C_H_crit

### 3D Semi-Elliptical Crack (two coupled EDOs)

**[SOURCE: Newman & Raju 1981]**

    da/dt = v(K_A, ΔK_A)    (deepest point)

    dc/dt = v(K_C, ΔK_C)    (surface point)

### Crack Tip Acidification

**[SOURCE: Turnbull 1993]**

    pH_tip = pH_bulk − 0.6×log10(c/a) − 0.3×v_diss + buffering_correction

    C_H_corrected = C_H_0 × 10^(0.3 × Δ_pH)

### Residual Stress SIF

**[SOURCE: BS 7910:2019 Annex Q]**

    K_I_res = sqrt(π·a) × (σ_res_m × Y_m + σ_res_b × Y_b)

### ILI POD (Weibull)

**[SOURCE: PHMSA TVC; general EMAT performance]**

    POD(a) = 1 − exp(−(a/a_90)^k)    a_90 = 4mm, k = 2 [ASSUMED]

### Model Structural Uncertainty

**[SOURCE: Sun, Zhou & Kang 2021 JIPR — 39 full-scale CanmetMATERIALS tests]**

    da/dt_real = da/dt_model × ε_model

    ε_model ~ LogNormal(mean=1.06, COV=61.2%)

### BS 7910 Coalescence Rule

**[SOURCE: BS 7910:2019 Clause 7.3]**

    Merge if: gap between cracks s < min(a_i, a_j)

### Bayesian Posterior Update (particle filter)

**[SOURCE: Straub 2004 — inspection-based reliability]**

    p(θ | a_obs) ∝ p(a_obs | θ) × p(θ)

---

## Repository Structure

```

integrity_code_series_week10v3_nnph_scc_fullphysics/

├── run_all.py

├── requirements.txt

├── README.md

├── conftest.py

├── src/

│   ├── constants.py              All parameters with [SOURCE] tags

│   ├── hydrogen_diffusion.py     Oriani-Fick PDE + C_H_surface_from_potential

│   ├── pressure_spectrum.py      Chen-Sutherby-Xing + VA loading

│   ├── microstructure.py         HAZ vs base metal zones (incl. vintage ERW)

│   ├── crack_growth_v2.py        3D shape + residual stress + dormancy

│   ├── crack_tip_chemistry.py    Turnbull acidification

│   ├── model_uncertainty.py      Sun 2021 COV=61.2% epistemic error

│   ├── pod_ilicurve.py           ILI POD + post-inspection a0

│   ├── crack_colony_v2.py        Full-physics colony + BS 7910 coalescence

│   ├── bayesian_update.py        Particle filter posterior

│   ├── fad_assessment.py         API 579-1 Level 2 FAD

│   ├── monte_carlo_v2.py         8-param MC with all gaps closed

│   ├── surrogate_gbr.py          GBR surrogate (8 features)

│   ├── audit_chain.py            SHA-256 hash-linked audit log

│   ├── cp_optimization.py        Non-monotonic CP curve (v3)

│   ├── h2_blending.py            H2 blend K_IH degradation (v3)

│   └── inspection_optimizer.py   RBI re-inspection interval (v3)

├── validation/benchmarks.py      Analytical benchmarks

├── visualization/

│   ├── plot_all_v2.py            8 v2 panels + colony GIF generator

│   └── plot_new_v3.py            3 v3 panels (CP, H2, inspection optimizer)

├── tests/test_week10v2.py        194 tests

├── assets/figures/               11 panels (300 DPI)

├── assets/animations/            Crack colony GIF

├── assets/audit_chain.json

└── linkedin/                     Post drafts (not in GitHub)

```

---

## New Mechanisms vs v1

| Mechanism | v1 | v2 | Source |

|-----------|----|----|--------|

| Crack growth model | Paris law | Chen-Sutherby-Xing combined parameter | Chen & Sutherby 2007 |

| Frequency dependence | Linear f | Saturation at f_crit = 10^-3 Hz | Xing et al. |

| VA loading | Constant amplitude | Type I underload with F_INT=10 | Chen 2007 |

| Crack dormancy | None | Stage I/II criterion, 95% dormant | Zhao et al. 2017 |

| Microstructure | Uniform | HAZ vs base, K_IH and da/dt different | Beavers et al. 2001 |

| ILI POD | LogNormal a0 | Post-inspection Weibull rejection sampling | PHMSA TVC |

| Model error | None | LogNormal(1.06, COV=61.2%) per crack | Sun et al. 2021 |

| Crack tip chemistry | None | Turnbull acidification, pH_tip(c/a) | Turnbull 1993 |

| Residual stress | None | BS 7910 Annex Q K_I_res at HAZ | BS 7910:2019 |

| Bayesian update | None | Particle filter posterior from re-ILI | Straub 2004 |

| 3D crack shape | 1D (a only) | 2D (a, c coupled EDOs) | Newman-Raju 1981 |

| Coalescence | Independent cracks | BS 7910:2019 Cl.7.3 merging rule | BS 7910:2019 |

---

## Key [ASSUMED] Parameters

| Parameter | Value | Basis |

|-----------|-------|-------|

| A_CF_BASE | 2.4×10^-14 | Calibrated to CEPA field: 0.3 mm/yr at a=2mm |

| K_IH base | 25 MPa√m | CEPA RP 3rd Ed. range 15–35 |

| K_IH HAZ | 17.5 MPa√m | 70% of base [ASSUMED] |

| F_INT | 10 | Chen 2007 underload interaction |

| f_crit | 10^-3 Hz | Xing et al. frequency saturation |

| a_90 (POD) | 4 mm | Modern EMAT [ASSUMED] |

| C_H_bulk X65 | 0.02 mol/m³ | Sun et al. 2021 range calibrated |

---

## Escalation Table

| Week | Topic | Key escalation |

|------|-------|---------------|

| 8 | CO2 pipeline | Supercritical EOS |

| 9 | CUI | 3-PDEs, Strang splitting |

| 10 v1 | NNpHSCC | 4-PDEs, crack colony |

| **10 v2** | **NNpHSCC full-physics** | **+12 mechanisms, Chen-Sutherby-Xing, COV=61.2% epistemic** |

---

## Cybersecurity (STRIDE)

SHA-256 hash-chain audit for all runs. Sensor integrity checks. GBR surrogate OOD fallback.

---

## How to Cite

If this software contributes to your work, please cite both the software (this repository) and the underlying methods it implements.

**Software (archived release):**

> Rocha, F. (2026). *Integrity Code Series — Week 10 — NNpHSCC Full-Physics Simulation* (Version 1.0.1) [Computer software]. Zenodo. https://doi.org/10.5281/zenodo.20172241

**BibTeX:**

```bibtex

@software{rocha_2026_nnphscc_fullphysics,

  author       = {Rocha, Felipe},

  title        = {{Integrity Code Series --- Week 10 --- NNpHSCC

                   Full-Physics Simulation}},

  year         = 2026,

  publisher    = {Zenodo},

  version      = {v1.0.1},

  doi          = {10.5281/zenodo.20172241},

  url          = {https://doi.org/10.5281/zenodo.20172241}

}

```

The two DOIs Zenodo provides are:

| DOI                                | What it points to                                                  |

|------------------------------------|--------------------------------------------------------------------|

| [`10.5281/zenodo.20172241`](https://doi.org/10.5281/zenodo.20172241) (concept) | Always resolves to the latest version — use this for citation in papers, CV, talks. |

| [`10.5281/zenodo.20172242`](https://doi.org/10.5281/zenodo.20172242) (version) | Pinned to v1.0.1 specifically — use when reproducibility matters. |

A machine-readable citation file is also available in [`CITATION.cff`](CITATION.cff) — GitHub will display a "Cite this repository" widget at the top right of the repo page that exports BibTeX / APA / RIS automatically.

---

Research tool only. Not for FFS decisions without site-specific calibration and independent review.

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