Corrosion Engineering MCP Server

""" Electrochemical Pitting Assessment - E_pit Calculator Calculates pitting initiation potential (E_pit) from NRL Butler-Volmer pitting kinetics. Phase 3 enhancement: - Integrates NRL pitting coefficients with RedoxState DO-aware E_mix calculation - Provides ΔE = E_mix - E_pit driving force assessment - Complements existing PREN/CPT Tier 1 heuristics with Tier 2 mechanistic model Theory: ------- Pitting initiates when the corrosion potential E_mix exceeds the pitting potential E_pit. E_pit is defined as the potential where anodic pitting current reaches a threshold (typically 1 µA/cm²). Butler-Volmer Pitting Current (Anodic Only): i_pit = i0_anodic * exp((alpha * z * F * eta) / (R * T)) where: eta = E_applied - E_N (overpotential) i0_anodic = z * F * lambda_0 * exp(-dG_anodic / (R * T)) lambda_0 = (k_B * T) / h (Eyring rate constant) Solving for E_pit at threshold current i_threshold: E_pit = E_N + (R * T / (alpha * z * F)) * ln(i_threshold / i0_anodic) Integrated with RedoxState: E_mix = do_to_eh(DO_mg_L, pH, T) # From RedoxState module ΔE = E_mix - E_pit # Driving force for pitting Risk Assessment: ΔE > +0.05 V: CRITICAL (E_mix >> E_pit, pitting highly likely) ΔE > 0 V: HIGH (E_mix > E_pit, pitting thermodynamically favorable) -0.1 V < ΔE < 0 V: MODERATE (small margin, monitor) ΔE < -0.1 V: LOW (large margin, pitting unlikely) Supported Materials (NRL database): - HY80 (z=2, Fe oxidation) - HY100 (z=2, Fe oxidation) - SS316 (z=3, Cr oxidation) Author: Codex AI + Claude Code Date: 2025-10-19 """ import numpy as np from typing import Tuple, Optional from utils.nrl_constants import C from utils.nrl_materials import HY80, HY100, SS316 def calculate_pitting_potential( material_name: str, temperature_C: float, chloride_mg_L: float, pH: float, i_threshold_A_cm2: float = 1e-6, ) -> Tuple[float, dict]: """ Calculate pitting initiation potential E_pit using NRL Butler-Volmer kinetics. Args: material_name: Material name ("HY80", "HY100", "SS316") temperature_C: Temperature (°C) chloride_mg_L: Chloride concentration (mg/L) pH: Solution pH (1-13) i_threshold_A_cm2: Pitting current threshold (A/cm²), default 1 µA/cm² Returns: E_pit_VSCE: Pitting initiation potential (V vs SCE) details: Dictionary with { "i0_anodic_A_cm2": Exchange current density, "dG_anodic_J_mol": Activation energy for pitting, "E_N_VSCE": Nernst potential, "alpha": Transfer coefficient, "z": Oxidation level } Raises: ValueError: If material not supported or parameters out of range Example: >>> E_pit, details = calculate_pitting_potential( ... "SS316", temperature_C=25.0, chloride_mg_L=1000.0, pH=7.0 ... ) >>> print(f"E_pit = {E_pit:.3f} V_SCE") E_pit = 0.450 V_SCE # Example value """ # Validate inputs if temperature_C < 0 or temperature_C > 150: raise ValueError(f"Temperature {temperature_C}°C out of valid range (0-150°C)") if pH < 1 or pH > 13: raise ValueError(f"pH {pH} out of valid range (1-13)") if chloride_mg_L < 0: raise ValueError(f"Chloride concentration cannot be negative: {chloride_mg_L}") # Convert chloride mg/L to M (molar) # Cl⁻ molar mass = 35.453 g/mol chloride_M = (chloride_mg_L / 1000.0) / 35.453 # Initialize material instance if material_name.upper() == "HY80": metal = HY80("HY80", chloride_M, temperature_C, pH) elif material_name.upper() == "HY100": metal = HY100("HY100", chloride_M, temperature_C, pH) elif material_name.upper() == "SS316": metal = SS316("SS316", chloride_M, temperature_C, pH) else: raise ValueError( f"Material '{material_name}' not supported for pitting assessment. " f"Supported: HY80, HY100, SS316" ) # Get pitting activation energies from material dG_cathodic, dG_anodic = metal.delta_g_metal_pitting alpha = metal.beta_metal_pitting z = metal.oxidation_level_z # Calculate temperature in Kelvin T_K = temperature_C + C.convertCtoK # Eyring rate constant lambda_0 = (C.kb * T_K) / C.planck_h # Exchange current density for pitting (anodic) RT = C.R * T_K pF = z * C.F * lambda_0 i0_anodic = pF * np.exp(-dG_anodic / RT) # Nernst potential for pitting reaction # For HY80/HY100: Fe → Fe²⁺ + 2e⁻ # For SS316: Cr → Cr³⁺ + 3e⁻ if material_name.upper() in ["HY80", "HY100"]: # Fe oxidation c_reactants = 1.0 # Pure metal (activity = 1) c_products = 1e-6 # Typical Fe²⁺ concentration at surface (M) c_g_cm3 = c_products * C.M_Fe / 1000.0 EN_log = np.log(c_reactants / c_g_cm3) E_N_SHE = C.e0_Fe_ox + (RT / (z * C.F)) * EN_log elif material_name.upper() == "SS316": # Cr oxidation c_reactants = 1.0 c_products = 1e-6 # Typical Cr³⁺ concentration c_g_cm3 = c_products * C.M_Cr / 1000.0 EN_log = np.log(c_reactants / c_g_cm3) E_N_SHE = C.e0_Cr_ox + (RT / (z * C.F)) * EN_log else: raise ValueError(f"Unknown material: {material_name}") # Convert to SCE reference E_N_VSCE = E_N_SHE - C.E_SHE_to_SCE # Calculate E_pit where i_pit = i_threshold # From Butler-Volmer: i_pit = i0_anodic * exp((alpha * z * F * eta) / RT) # Solving for eta: eta = (RT / (alpha * z * F)) * ln(i_pit / i0_anodic) # E_pit = E_N + eta eta_pit = (RT / (alpha * z * C.F)) * np.log(i_threshold_A_cm2 / i0_anodic) E_pit_VSCE = E_N_VSCE + eta_pit # Assemble details details = { "i0_anodic_A_cm2": float(i0_anodic), "dG_anodic_J_mol": float(dG_anodic), "E_N_VSCE": float(E_N_VSCE), "alpha": float(alpha), "z": int(z), "material": material_name, "temperature_C": temperature_C, "chloride_mg_L": chloride_mg_L, "pH": pH, "i_threshold_A_cm2": i_threshold_A_cm2, } return float(E_pit_VSCE), details def assess_pitting_risk_electrochemical( E_mix_VSCE: float, E_pit_VSCE: float, ) -> Tuple[str, str, float]: """ Assess pitting risk from electrochemical driving force ΔE = E_mix - E_pit. Args: E_mix_VSCE: Mixed/corrosion potential (V vs SCE) E_pit_VSCE: Pitting initiation potential (V vs SCE) Returns: risk_level: "critical", "high", "moderate", "low" interpretation: Text summary margin_V: ΔE = E_mix - E_pit (V) Risk Criteria: ΔE > +0.05 V: CRITICAL (pitting highly likely) ΔE > 0 V: HIGH (pitting thermodynamically favorable) -0.1 V < ΔE < 0 V: MODERATE (small margin) ΔE < -0.1 V: LOW (large margin) Example: >>> risk, interp, dE = assess_pitting_risk_electrochemical( ... E_mix_VSCE=0.5, E_pit_VSCE=0.4 ... ) >>> print(risk) 'critical' """ margin_V = E_mix_VSCE - E_pit_VSCE if margin_V > 0.05: risk_level = "critical" interpretation = ( f"CRITICAL: E_mix ({E_mix_VSCE:.3f} V) >> E_pit ({E_pit_VSCE:.3f} V) by " f"{margin_V*1000:.0f} mV. Pitting is thermodynamically highly favorable and " f"likely to initiate. Immediate action required: upgrade material, reduce Cl⁻, " f"or apply cathodic protection." ) elif margin_V > 0: risk_level = "high" interpretation = ( f"HIGH RISK: E_mix ({E_mix_VSCE:.3f} V) > E_pit ({E_pit_VSCE:.3f} V) by " f"{margin_V*1000:.0f} mV. Pitting is thermodynamically favorable. " f"Recommend: monitor for pitting initiation, consider material upgrade or " f"chloride reduction." ) elif margin_V > -0.1: risk_level = "moderate" interpretation = ( f"MODERATE: E_mix ({E_mix_VSCE:.3f} V) is {abs(margin_V)*1000:.0f} mV below " f"E_pit ({E_pit_VSCE:.3f} V). Small safety margin. Pitting unlikely under " f"steady-state conditions, but transients (DO spikes, temperature rise) could " f"trigger initiation. Monitor for environmental changes." ) else: risk_level = "low" interpretation = ( f"LOW RISK: E_mix ({E_mix_VSCE:.3f} V) is {abs(margin_V)*1000:.0f} mV below " f"E_pit ({E_pit_VSCE:.3f} V). Large safety margin. Pitting is thermodynamically " f"unfavorable under current conditions. Material selection is appropriate." ) return risk_level, interpretation, margin_V if __name__ == "__main__": # Test E_pit calculation print("="*70) print("Pitting Potential Calculation Test") print("="*70) # Test case: SS316 in seawater conditions E_pit, details = calculate_pitting_potential( material_name="SS316", temperature_C=25.0, chloride_mg_L=19000.0, # Seawater pH=8.1, i_threshold_A_cm2=1e-6, # 1 µA/cm² ) print(f"\nMaterial: {details['material']}") print(f"Conditions: T={details['temperature_C']}C, Cl-={details['chloride_mg_L']} mg/L, pH={details['pH']}") print(f"\nElectrochemical Properties:") print(f" E_N (Nernst potential): {details['E_N_VSCE']:.3f} V_SCE") print(f" i0_anodic: {details['i0_anodic_A_cm2']:.3e} A/cm2") print(f" dG_anodic: {details['dG_anodic_J_mol']:.2e} J/mol") print(f" alpha (transfer coeff): {details['alpha']:.4f}") print(f" z (oxidation level): {details['z']}") print(f"\nPitting Potential:") print(f" E_pit = {E_pit:.3f} V_SCE (at i_threshold = {details['i_threshold_A_cm2']:.1e} A/cm2)") # Test risk assessment print(f"\n{'='*70}") print("Risk Assessment Test") print("="*70) # Scenario: Aerated seawater (E_mix ≈ 0.5 V_SCE) E_mix_seawater = 0.5 # V_SCE (typical for aerated seawater) risk, interpretation, dE = assess_pitting_risk_electrochemical(E_mix_seawater, E_pit) print(f"\nScenario: Aerated seawater") print(f" E_mix = {E_mix_seawater:.3f} V_SCE") print(f" E_pit = {E_pit:.3f} V_SCE") print(f" dE = {dE:.3f} V ({dE*1000:.0f} mV)") print(f"\nRisk Level: {risk.upper()}") print(f"\n{interpretation}")