Corrosion Engineering MCP Server

""" Localized Corrosion Backend - Pitting and Crevice Corrosion Implements mechanistic models for: - Pitting corrosion (PREN-based CPT correlations) - Crevice corrosion (Oldfield-Sutton IR drop model) Based on: - PREN (Pitting Resistance Equivalent Number): PREN = %Cr + 3.3×%Mo + 16×%N - CPT (Critical Pitting Temperature): CPT ≈ PREN - 10 (calibrated for austenitic SS) - Chloride threshold correlations - Crevice IR drop (Oldfield-Sutton resistance term) Per Codex guidance: - Use PREN-based CPT correlations with exposed calibration coefficients - Duplex grades can deviate by ±5°C from standard correlation - Separate pitting vs crevice outputs - Share chloride threshold logic between models - Simplified Oldfield-Sutton for crevice IR drop Performance: 1-2 seconds (Tier 2 target) Accuracy: ±5°C for CPT, ±20% for chloride threshold """ from __future__ import annotations import logging import math from dataclasses import dataclass from typing import Dict, Optional, Tuple, List # Import authoritative data (BUG-013, BUG-014, BUG-016 fixes) from data import ( get_material_data, get_cpt_from_astm, get_chloride_threshold, calculate_pren as calculate_pren_authoritative, ) logger = logging.getLogger(__name__) # --------------------------------------------------------------------------- # Physical constants # --------------------------------------------------------------------------- FARADAY = 96485.3321 # C/mol R_GAS = 8.314462618 # J/mol·K # --------------------------------------------------------------------------- # PREN calibration coefficients (exposed per Codex) # --------------------------------------------------------------------------- # Standard PREN formula: PREN = a×Cr + b×Mo + c×N PREN_COEFFS = { "standard": {"a": 1.0, "b": 3.3, "c": 16.0}, # ASTM G48 standard "duplex": {"a": 1.0, "b": 3.3, "c": 30.0}, # Higher N weighting for duplex } # CPT-PREN correlation: CPT = m×PREN + b (°C) CPT_CORRELATIONS = { "austenitic": {"m": 1.0, "b": -10.0}, # CPT ≈ PREN - 10 "duplex": {"m": 1.0, "b": -15.0}, # Duplex slightly more conservative "superaustenitic": {"m": 1.0, "b": -5.0}, # Super grades more resistant } # Chloride threshold correlations (mg/L Cl⁻ vs temperature) # Based on empirical data from ASTM G48, ISO 17945 CL_THRESHOLD_BASE = { "304": 50.0, # Low PREN ≈ 18, very susceptible "316": 200.0, # PREN ≈ 24, moderate resistance "316L": 250.0, # Lower carbon, slightly better "2205": 1000.0, # Duplex, PREN ≈ 35 "254SMO": 5000.0, # Superaustenitic, PREN ≈ 43 } # --------------------------------------------------------------------------- # Data classes # --------------------------------------------------------------------------- @dataclass class MaterialComposition: """ Material composition for PREN calculation. Attributes: Cr: Chromium content (wt%) Mo: Molybdenum content (wt%) N: Nitrogen content (wt%) Ni: Nickel content (wt%, optional) grade_type: "austenitic", "duplex", "superaustenitic" """ Cr: float Mo: float N: float Ni: float = 0.0 grade_type: str = "austenitic" def calculate_pren(self, coeffs: Optional[Dict[str, float]] = None) -> float: """ Calculate PREN (Pitting Resistance Equivalent Number). Args: coeffs: Optional custom coefficients {"a": ..., "b": ..., "c": ...} Returns: PREN value (unitless) """ if coeffs is None: coeffs = PREN_COEFFS.get(self.grade_type, PREN_COEFFS["standard"]) pren = coeffs["a"] * self.Cr + coeffs["b"] * self.Mo + coeffs["c"] * self.N return pren @dataclass class PittingResult: """ Result of pitting corrosion susceptibility calculation. Tier 1 (PREN/CPT - always available): CPT_C: Critical Pitting Temperature (°C) PREN: Pitting Resistance Equivalent Number Cl_threshold_mg_L: Chloride threshold at operating temperature (mg/L) susceptibility: "low", "moderate", "high", "critical" margin_C: Temperature margin to CPT (positive = safe, negative = unsafe) interpretation: Text summary Tier 2 (Electrochemical E_pit vs E_mix - requires DO, NRL materials only): E_pit_VSCE: Pitting initiation potential (V vs SCE), None if not calculated E_mix_VSCE: Mixed/corrosion potential (V vs SCE), None if not calculated electrochemical_margin_V: ΔE = E_mix - E_pit (V), None if not calculated electrochemical_risk: "critical", "high", "moderate", "low", None if not calculated electrochemical_interpretation: Text summary for Tier 2, None if not calculated """ # Tier 1: PREN/CPT (always present) CPT_C: float PREN: float Cl_threshold_mg_L: float susceptibility: str margin_C: float interpretation: str # Tier 2: Electrochemical (optional, requires DO and NRL material) E_pit_VSCE: Optional[float] = None E_mix_VSCE: Optional[float] = None electrochemical_margin_V: Optional[float] = None electrochemical_risk: Optional[str] = None electrochemical_interpretation: Optional[str] = None @dataclass class CreviceResult: """ Result of crevice corrosion susceptibility calculation. Attributes: CCT_C: Critical Crevice Temperature (°C) - typically CPT - 10 to 20°C IR_drop_V: IR drop in crevice (V) from Oldfield-Sutton model acidification_factor: pH drop in crevice (unitless, >1 = more acidic) susceptibility: "low", "moderate", "high", "critical" margin_C: Temperature margin to CCT interpretation: Text summary """ CCT_C: float IR_drop_V: float acidification_factor: float susceptibility: str margin_C: float interpretation: str @dataclass class LocalizedResult: """ Combined result for localized corrosion (pitting + crevice). Per Codex: Separate outputs but shared chloride threshold logic. """ pitting: PittingResult crevice: CreviceResult material: str temperature_C: float Cl_mg_L: float pH: float overall_risk: str # "low", "moderate", "high", "critical" # --------------------------------------------------------------------------- # Localized corrosion backend # --------------------------------------------------------------------------- class LocalizedBackend: """ Pitting and crevice corrosion calculator. Uses PREN-based CPT correlations and simplified Oldfield-Sutton model. """ def __init__(self): """Initialize localized corrosion backend.""" pass def calculate_pitting_susceptibility( self, material_comp: MaterialComposition, temperature_C: float, Cl_mg_L: float, pH: float = 7.0, material_name: str = "316L", custom_cpt_correlation: Optional[Dict[str, float]] = None, dissolved_oxygen_mg_L: Optional[float] = None, ) -> PittingResult: """ Calculate pitting corrosion susceptibility. FIX BUG-013: Use ASTM G48 tabulated CPT data instead of heuristic FIX BUG-014: Use ISO 18070 chloride threshold data PHASE 3 ENHANCEMENT: Dual-Tier pitting assessment - Tier 1 (always): PREN/CPT empirical (fast, all materials) - Tier 2 (optional): E_pit vs E_mix electrochemical (mechanistic, NRL materials only) Args: material_comp: Material composition (Cr, Mo, N) temperature_C: Operating temperature (°C) Cl_mg_L: Chloride concentration (mg/L) pH: Solution pH material_name: Material name for database lookup custom_cpt_correlation: Optional custom CPT correlation (for calibration) dissolved_oxygen_mg_L: Dissolved oxygen (mg/L). If provided and material is in NRL database (HY80, HY100, SS316), calculates Tier 2 electrochemical pitting potential (E_pit vs E_mix). Returns: PittingResult with Tier 1 CPT/PREN (always) and Tier 2 E_pit/E_mix (if DO provided) """ # Calculate PREN using local method (handles local MaterialComposition format) pren = material_comp.calculate_pren() # FIX BUG-013: Get CPT from ASTM G48 tabulated data cpt_data = get_cpt_from_astm(material_name) if cpt_data is not None: # Use ASTM G48 measured CPT CPT = cpt_data["CPT_C"] logger.info(f"Using ASTM G48 CPT for {material_name}: {CPT}°C (source: {cpt_data['source']})") elif custom_cpt_correlation is not None: # Use custom correlation if provided cpt_corr = custom_cpt_correlation CPT = cpt_corr["m"] * pren + cpt_corr["b"] logger.warning(f"Using custom CPT correlation for {material_name}: {CPT}°C") else: # Fallback to PREN-based estimate with warning cpt_corr = CPT_CORRELATIONS.get(material_comp.grade_type, CPT_CORRELATIONS["austenitic"]) CPT = cpt_corr["m"] * pren + cpt_corr["b"] logger.warning( f"Material {material_name} not in ASTM G48 database; " f"using PREN estimate: {CPT}°C (±20°C uncertainty)" ) # Temperature margin margin_C = CPT - temperature_C # FIX BUG-014: Get chloride threshold from ISO 18070/NORSOK authoritative data Cl_threshold = get_chloride_threshold(material_name, temperature_C, pH) logger.info(f"Using ISO 18070 Cl⁻ threshold for {material_name} at {temperature_C}°C, pH {pH}: {Cl_threshold:.0f} mg/L") # Determine susceptibility if margin_C > 20.0 and Cl_mg_L < Cl_threshold * 0.5: susceptibility = "low" elif margin_C > 10.0 and Cl_mg_L < Cl_threshold: susceptibility = "moderate" elif margin_C > 0 or Cl_mg_L < Cl_threshold * 1.5: susceptibility = "high" else: susceptibility = "critical" # Interpretation if susceptibility == "critical": interpretation = f"CRITICAL: T = {temperature_C}°C exceeds CPT = {CPT:.1f}°C by {-margin_C:.1f}°C; Cl⁻ = {Cl_mg_L:.0f} mg/L >> {Cl_threshold:.0f} mg/L threshold" elif susceptibility == "high": interpretation = f"HIGH RISK: T = {temperature_C}°C within {margin_C:.1f}°C of CPT = {CPT:.1f}°C; Cl⁻ = {Cl_mg_L:.0f} mg/L near threshold" elif susceptibility == "moderate": interpretation = f"MODERATE: T = {temperature_C}°C is {margin_C:.1f}°C below CPT = {CPT:.1f}°C; Cl⁻ = {Cl_mg_L:.0f} mg/L acceptable" else: interpretation = f"LOW RISK: T = {temperature_C}°C well below CPT = {CPT:.1f}°C (margin {margin_C:.1f}°C); Cl⁻ = {Cl_mg_L:.0f} mg/L < {Cl_threshold:.0f} mg/L" # PHASE 3: Tier 2 Electrochemical Assessment (E_pit vs E_mix) # Only if dissolved_oxygen_mg_L provided and material in NRL database E_pit_VSCE = None E_mix_VSCE = None electrochemical_margin_V = None electrochemical_risk = None electrochemical_interpretation = None if dissolved_oxygen_mg_L is not None: # Check if material is in NRL database (HY80, HY100, SS316) # Also support common aliases (316L, UNS codes) nrl_materials = ["HY80", "HY100", "SS316"] # Material alias mapping (per Codex recommendation) material_aliases = { "316L": "SS316", "316": "SS316", "UNS S31600": "SS316", "UNS S31603": "SS316", # 316L UNS "HY-80": "HY80", "HY-100": "HY100", } material_upper = material_name.upper() # Map alias to canonical NRL name material_nrl = material_aliases.get(material_upper, material_upper) if material_nrl in nrl_materials: try: # Import Tier 2 modules from utils.pitting_assessment import ( calculate_pitting_potential, assess_pitting_risk_electrochemical, ) from utils.redox_state import do_to_eh from utils.nrl_constants import C # Calculate E_pit using NRL Butler-Volmer pitting kinetics E_pit_VSCE, pit_details = calculate_pitting_potential( material_name=material_nrl, # Use canonical NRL name temperature_C=temperature_C, chloride_mg_L=Cl_mg_L, pH=pH, i_threshold_A_cm2=1e-6, # 1 µA/cm² threshold ) # Calculate E_mix from DO using RedoxState Eh_VSHE, redox_warnings = do_to_eh( dissolved_oxygen_mg_L=dissolved_oxygen_mg_L, pH=pH, temperature_C=temperature_C, ) # Convert SHE to SCE: E_SCE = E_SHE - 0.241 V E_mix_VSCE = Eh_VSHE - C.E_SHE_to_SCE # Assess electrochemical pitting risk electrochemical_risk, electrochemical_interpretation, electrochemical_margin_V = ( assess_pitting_risk_electrochemical(E_mix_VSCE, E_pit_VSCE) ) # Append RedoxState warnings to interpretation (per Codex recommendation) if redox_warnings: electrochemical_interpretation += f" [RedoxState: {redox_warnings[0]}]" logger.info( f"Tier 2 electrochemical pitting assessment for {material_name}: " f"E_pit = {E_pit_VSCE:.3f} V_SCE, E_mix = {E_mix_VSCE:.3f} V_SCE, " f"dE = {electrochemical_margin_V*1000:.0f} mV, Risk = {electrochemical_risk.upper()}" ) except ValueError as e: # Activation energy out of range (e.g., HY80 at seawater) logger.warning( f"Tier 2 electrochemical assessment failed for {material_name}: {str(e)}\n" f"Falling back to Tier 1 PREN/CPT only." ) # Per Codex: Add explanation to electrochemical_interpretation electrochemical_interpretation = ( f"Tier 2 unavailable: NRL coefficients out of valid range at " f"(Cl={Cl_mg_L:.0f} mg/L, T={temperature_C:.0f}°C, pH={pH:.1f}). " f"Use Tier 1 PREN/CPT assessment only." ) except Exception as e: logger.error( f"Unexpected error in Tier 2 electrochemical assessment for {material_name}: {str(e)}\n" f"Falling back to Tier 1 PREN/CPT only." ) # Per Codex: Add explanation to electrochemical_interpretation electrochemical_interpretation = ( f"Tier 2 unavailable: Unexpected error during calculation. " f"Use Tier 1 PREN/CPT assessment only." ) else: # Per Codex: Add explanation when material not in NRL database logger.info( f"Material '{material_name}' not in NRL database (HY80, HY100, SS316). " f"Tier 2 electrochemical assessment not available. Using Tier 1 PREN/CPT only." ) electrochemical_interpretation = ( f"Tier 2 unavailable: Material '{material_name}' not in NRL database " f"(supported: HY80, HY100, SS316, and aliases 316/316L/UNS S31600). " f"Use Tier 1 PREN/CPT assessment only." ) return PittingResult( # Tier 1: PREN/CPT (always present) CPT_C=CPT, PREN=pren, Cl_threshold_mg_L=Cl_threshold, susceptibility=susceptibility, margin_C=margin_C, interpretation=interpretation, # Tier 2: Electrochemical (optional) E_pit_VSCE=E_pit_VSCE, E_mix_VSCE=E_mix_VSCE, electrochemical_margin_V=electrochemical_margin_V, electrochemical_risk=electrochemical_risk, electrochemical_interpretation=electrochemical_interpretation, ) def calculate_crevice_susceptibility( self, material_comp: MaterialComposition, temperature_C: float, Cl_mg_L: float, pH: float = 7.0, crevice_gap_mm: float = 0.1, current_density_A_per_m2: float = 1e-4, material_name: str = "316L", # BUG-017 fix: Add material name for ASTM G48 lookup ) -> CreviceResult: """ Calculate crevice corrosion susceptibility. Uses simplified Oldfield-Sutton IR drop model. Args: material_comp: Material composition temperature_C: Operating temperature (°C) Cl_mg_L: Chloride concentration (mg/L) pH: Bulk solution pH crevice_gap_mm: Crevice gap width (mm) current_density_A_per_m2: Corrosion current density (A/m²) material_name: Material name for ASTM G48 CCT lookup Returns: CreviceResult with CCT, IR drop, acidification factor Per Codex: Simplified Oldfield-Sutton for IR drop iteration """ # BUG-017 fix: Get CCT from ASTM G48 tabulated data cpt_data = get_cpt_from_astm(material_name) if cpt_data is not None and "CCT_C" in cpt_data: CCT = cpt_data["CCT_C"] # ASTM G48-11 measured CCT CPT = cpt_data["CPT_C"] # Also get CPT for reference logger.info(f"Using ASTM G48 CCT: {CCT}°C (source: {cpt_data['source']})") else: # Fallback: CCT is typically CPT - 10 to 20°C (more aggressive than pitting) pren = material_comp.calculate_pren() cpt_corr = CPT_CORRELATIONS.get(material_comp.grade_type, CPT_CORRELATIONS["austenitic"]) CPT = cpt_corr["m"] * pren + cpt_corr["b"] CCT = CPT - 15.0 # Conservative estimate logger.warning(f"Material {material_name} not in ASTM G48; using CCT = CPT - 15°C heuristic") # IR drop in crevice (Oldfield-Sutton simplified) # ΔE = i × R × L # where: # i = current density (A/m²) # R = solution resistivity (Ω·m) # L = crevice depth (m) # Estimate solution resistivity from chloride concentration # R ≈ 1 / (κ × (Cl⁻ concentration)) # For seawater (19000 mg/L Cl⁻): κ ≈ 5 S/m, R ≈ 0.2 Ω·m # Scale linearly with Cl⁻ Cl_seawater = 19000.0 # mg/L R_seawater = 0.2 # Ω·m R_solution = R_seawater * (Cl_seawater / max(Cl_mg_L, 100.0)) # Assume crevice depth = 10 × gap (aspect ratio) crevice_depth_m = (crevice_gap_mm / 1000.0) * 10.0 # IR drop IR_drop = current_density_A_per_m2 * R_solution * crevice_depth_m # Acidification factor (pH drop in crevice) # Metal dissolution produces H⁺: M → M²⁺ + 2e⁻ # Hydrolysis: M²⁺ + H₂O → MOH⁺ + H⁺ # Simplified: ΔpH ≈ log10(1 + k × i × t / buffer_capacity) # Assume acidification_factor = (pH_bulk / pH_crevice) # Typically pH drops by 2-4 units in active crevice delta_pH = 2.0 + (IR_drop / 0.1) * 2.0 # 2-4 pH drop depending on IR delta_pH = min(delta_pH, pH - 2.0) # Can't drop below pH 2 pH_crevice = pH - delta_pH acidification_factor = 10.0 ** delta_pH # Factor by which [H⁺] increases # Temperature margin margin_C = CCT - temperature_C # Susceptibility (crevice is more aggressive than pitting) if margin_C > 15.0 and acidification_factor < 10: susceptibility = "low" elif margin_C > 5.0 and acidification_factor < 100: susceptibility = "moderate" elif margin_C > -5.0: susceptibility = "high" else: susceptibility = "critical" # Interpretation if susceptibility == "critical": interpretation = f"CRITICAL: T = {temperature_C}°C >> CCT = {CCT:.1f}°C; IR drop = {IR_drop*1000:.1f} mV; pH drops to {pH_crevice:.1f} in crevice" elif susceptibility == "high": interpretation = f"HIGH RISK: T = {temperature_C}°C near CCT = {CCT:.1f}°C; Crevice acidification factor = {acidification_factor:.1f}" elif susceptibility == "moderate": interpretation = f"MODERATE: T = {temperature_C}°C below CCT = {CCT:.1f}°C (margin {margin_C:.1f}°C); Monitor for crevice formation" else: interpretation = f"LOW RISK: T = {temperature_C}°C well below CCT = {CCT:.1f}°C (margin {margin_C:.1f}°C)" return CreviceResult( CCT_C=CCT, IR_drop_V=IR_drop, acidification_factor=acidification_factor, susceptibility=susceptibility, margin_C=margin_C, interpretation=interpretation, ) def calculate_localized_corrosion( self, material: str, temperature_C: float, Cl_mg_L: float, pH: float = 7.0, crevice_gap_mm: float = 0.1, dissolved_oxygen_mg_L: Optional[float] = None, ) -> LocalizedResult: """ Calculate combined pitting and crevice susceptibility. Args: material: Material name (e.g., "316L", "2205", "254SMO") temperature_C: Operating temperature (°C) Cl_mg_L: Chloride concentration (mg/L) pH: Solution pH crevice_gap_mm: Crevice gap width (mm) dissolved_oxygen_mg_L: Dissolved oxygen (mg/L). If provided, enables Tier 2 electrochemical pitting assessment for NRL materials. Returns: LocalizedResult with separate pitting and crevice results Per Codex: Separate pitting vs crevice outputs, shared Cl⁻ threshold logic Phase 3: Dual-Tier pitting (Tier 1 PREN/CPT + optional Tier 2 E_pit/E_mix) """ # Get material composition from database material_comp = self._get_material_composition(material) # Calculate pitting susceptibility (Tier 1 + optional Tier 2) pitting_result = self.calculate_pitting_susceptibility( material_comp, temperature_C, Cl_mg_L, pH, material_name=material, dissolved_oxygen_mg_L=dissolved_oxygen_mg_L, ) # Calculate crevice susceptibility crevice_result = self.calculate_crevice_susceptibility( material_comp, temperature_C, Cl_mg_L, pH, crevice_gap_mm, material_name=material ) # Overall risk (worst of pitting or crevice) risk_levels = {"low": 0, "moderate": 1, "high": 2, "critical": 3} pitting_level = risk_levels[pitting_result.susceptibility] crevice_level = risk_levels[crevice_result.susceptibility] overall_level = max(pitting_level, crevice_level) overall_risk = [k for k, v in risk_levels.items() if v == overall_level][0] return LocalizedResult( pitting=pitting_result, crevice=crevice_result, material=material, temperature_C=temperature_C, Cl_mg_L=Cl_mg_L, pH=pH, overall_risk=overall_risk, ) def _get_base_chloride_threshold(self, pren: float) -> float: """ Get base chloride threshold from PREN. Uses empirical correlation: Cl_threshold ≈ 10^(PREN/10) mg/L (rough approximation from ASTM G48 data) """ # Exponential correlation Cl_threshold = 10.0 ** ((pren - 10.0) / 10.0) return max(Cl_threshold, 10.0) # Minimum 10 mg/L def _get_material_composition(self, material: str) -> MaterialComposition: """ Get material composition from authoritative UNS database. FIX BUG-016: Use authoritative materials database instead of 5-material dict """ # Get from authoritative database mat_data = get_material_data(material) if mat_data is not None: # Convert to local MaterialComposition format return MaterialComposition( Cr=mat_data.Cr_wt_pct, Mo=mat_data.Mo_wt_pct, N=mat_data.N_wt_pct, Ni=mat_data.Ni_wt_pct, grade_type=mat_data.grade_type, ) else: # Fallback with warning logger.warning( f"Material '{material}' not in authoritative UNS database; " f"defaulting to conservative 316L" ) # Return 316L as conservative fallback mat_316L = get_material_data("316L") if mat_316L: return MaterialComposition( Cr=mat_316L.Cr_wt_pct, Mo=mat_316L.Mo_wt_pct, N=mat_316L.N_wt_pct, Ni=mat_316L.Ni_wt_pct, grade_type=mat_316L.grade_type, ) else: # Absolute fallback return MaterialComposition( Cr=16.5, Mo=2.0, N=0.10, Ni=10.0, grade_type="austenitic" )