Materials Selection

Chapter from the Metallurgy & Corrosion Design Guide.

MATERIALS SELECTION FOR REFINERY SERVICE

Common Materials by Service Environment

Service	Temperature Range	Key Mechanism	Recommended Material	Hardness Limit	NACE/API Standard	Notes
H2 service (high P, high T)	Above Nelson curve	HTHA (hydrogen attack)	1.25Cr-0.5Mo or 2.25Cr-1Mo	N/A for HTHA	API 941 (Nelson curves)	Check API 941 curves for P-T limits
H2 service (ambient)	Ambient	Hydrogen embrittlement	CS, max 22 HRC	22 HRC max	NACE MR0175/ISO 15156	Low-strength steels resistant
Wet H2S (<50 ppm H2S in water)	Ambient to 300°F	SSC, HIC, SOHIC	Killed CS, PWHT, max 22 HRC	22 HRC	NACE MR0175, NACE SP0472	See Wet H2S tab for details
Dry H2S (no free water)	Any	Sulfidation above 500°F	CS below 500°F, Cr-Mo above	N/A	API 939-C	Sulfidation curves by Cr content
Naphthenic acid	430-750°F	Naphthenic acid corrosion	317L SS or alloy 625	N/A	API 581 (TAN-based)	TAN >1.5 with T >430°F = risk
HCl (aqueous)	Below dew point	Acid corrosion, pitting	Alloy C-276, titanium	N/A	NACE, site-specific	Overhead system most vulnerable
Caustic (NaOH)	Above 140°F	Caustic SCC	CS + PWHT below 50% NaOH	22 HRC	NACE RP0403	Caustic SCC curve for T vs. conc
HF acid	Any	HF corrosion, SCC	CS (low residuals), Monel	22 HRC	NACE Publication 5A171	Strict CS composition limits
High-temp oxidation	>1,000°F	Oxidation, carburization	Stainless steel (304/321)	N/A	API 530, API 579	Chrome content key for oxidation
Cooling water	Ambient	MIC, pitting, erosion	CS with treatment program	N/A	NACE, site CW program	Water chemistry drives MOC
Amine service	Any	Amine SCC	CS + PWHT mandatory	22 HRC	API 945	All welds PWHT, including repairs
Sulfuric acid	Below 200°F	General corrosion	CS (conc >65%), alloy 20	N/A	NACE 5A151	Velocity critical — max 3 ft/s CS

Source: Metallurgy_Corrosion_Design_Guide_v1.xlsx · sheet “Materials Selection”

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