Materials Selection Guide

Material selection guidance by service: sour, amine, caustic, hydrogen, high-temperature, and cryogenic.

Alloy Properties

Common Alloy Properties

Material	UNS #	Common Name	Min Yield (ksi)	Min Tensile (ksi)	Max Design Temp (°F)	Min Design Temp (°F)	Density (lb/in³)	Key Alloying Elements	Typical Use
SA-516 Gr 70	K02700	CS plate	38	70	800	-20	0.284	C-Mn-Si	Vessels, exchangers
SA-106 Gr B	K03006	CS pipe	35	60	800	-20	0.284	C-Mn	Piping, tubing
SA-105	K03504	CS forging	36	70	800	-20	0.284	C-Mn-Si	Flanges, fittings
SA-234 WPB	K03006	CS fitting	35	60	800	-20	0.284	C-Mn	Butt-weld fittings
SA-387 Gr 11	K11789	1.25Cr-0.5Mo	35	60	1100	-20	0.284	Cr-Mo	H2, high-temp service
SA-387 Gr 22	K21590	2.25Cr-1Mo	30	60	1200	-20	0.284	Cr-Mo	Hydroprocessing reactors
SA-387 Gr 5	K41545	5Cr-0.5Mo	30	60	1200	-20	0.284	Cr-Mo	High-temp sulfidation
SA-387 Gr 9	K90941	9Cr-1Mo	30	60	1200	-20	0.284	Cr-Mo	Severe sulfidation
SA-335 P91	K90901	9Cr-1Mo-V	60	85	1200	-20	0.284	Cr-Mo-V-Nb	High-temp piping
SA-240 304	S30400	304 SS	30	75	1500	-325	0.29	18Cr-8Ni	General corrosion resistance
SA-240 304L	S30403	304L SS	25	70	1500	-325	0.29	18Cr-8Ni (low C)	Welded, avoid sensitization
SA-240 316	S31600	316 SS	30	75	1500	-325	0.29	16Cr-10Ni-2Mo	Chloride, naphthenic acid
SA-240 316L	S31603	316L SS	25	70	1500	-325	0.29	16Cr-10Ni-2Mo (low C)	Welded 316 applications
SA-240 321	S32100	321 SS	30	75	1500	-325	0.29	18Cr-10Ni-Ti	High-temp, stabilized
SA-240 347	S34700	347 SS	30	75	1500	-325	0.29	18Cr-10Ni-Nb	High-temp, stabilized
SA-240 410	S41000	410 SS	30	65	1200	0	0.276	12Cr	Mild corrosion, trays/internals
SA-240 2205	S31803	Duplex 2205	65	90	600	-60	0.278	22Cr-5Ni-3Mo-N	Chloride SCC resistance
SB-424 825	N08825	Incoloy 825	35	85	1000	-325	0.294	42Ni-21Cr-3Mo-2Cu	Wet sour, acid service
SB-443 625	N06625	Inconel 625	60	120	1200	-325	0.305	58Ni-22Cr-9Mo-3.5Nb	Severe environments
SB-575 C-276	N10276	Hastelloy C-276	41	100	1250	-325	0.321	57Ni-16Cr-16Mo-5Fe-4W	Most aggressive service

Service Guide

Material Selection by Service Environment

Service / Environment	Temperature Range	Recommended Material	Alternate Material	Key Concern	Reference
Crude distillation — atm tower	< 500°F	CS (SA-516-70)	—	Naphthenic acid if TAN > 0.5	API 571
Crude distillation — hot circuits	500-750°F	5Cr-0.5Mo / 9Cr-1Mo	316 SS clad	Sulfidation + naphthenic acid	API 571, API 939-C
Hydroprocessing reactor shell	750-850°F, >1500 psig	2.25Cr-1Mo + SS clad	2.25Cr-1Mo-V	H2 attack (Nelson curves)	API 941
Hydroprocessing reactor internals	750-850°F	321 SS / 347 SS	316 SS	Polythionic acid SCC at shutdown	API 571, NACE SP0170
High-temperature H2 service piping	> 600°F	1.25Cr-0.5Mo / 2.25Cr-1Mo	P91 (9Cr-1Mo-V)	HTHA per Nelson curves	API 941
Wet H2S service (sour water)	Ambient-250°F	CS (HIC resistant)	316L SS	SSC, HIC, SOHIC	NACE MR0175
Amine service (MEA, DEA, MDEA)	< 250°F	CS (PWHT'd)	304L SS	Amine SCC — PWHT mandatory	API 945
Caustic service (NaOH)	Ambient-200°F	CS (PWHT'd)	Nickel alloys > 200°F	Caustic SCC — PWHT mandatory	API 571
HF alkylation	< 150°F	CS (Monel trim)	Monel 400	HF corrosion	API 751
Sulfuric acid (< 96%)	< 100°F	CS (velocity < 3 fps)	Alloy 20 / Hastelloy	Concentration/velocity critical	NACE
Naphthenic acid corrosion	> 430°F, TAN > 0.5	316 SS (2.5% Mo min)	317L / Alloy 625	Mo content critical (>2.5%)	API 571
High-temp sulfidation (no H2)	> 500°F	5Cr-0.5Mo or higher	9Cr-1Mo	McConomy curves for rate	API 571
Flue gas / stack service	300-800°F	CS (< 400°F) / 409 SS	316 SS (if wet)	Dewpoint corrosion	—
Cooling water	Ambient	CS / admiralty brass	316 SS / titanium	Chloride pitting	—
Steam (high pressure)	750-1050°F	P91 (9Cr-1Mo-V)	P22 (2.25Cr-1Mo)	Creep, oxidation	ASME B31.1
Chloride-containing environments	Any	Duplex 2205 / Alloy 825	Alloy 625 / C-276	Chloride SCC above 140°F for 300-series SS	—
Polythionic acid (shutdown)	Ambient	321 SS / 347 SS (stabilized)	Low-C grades + soda ash wash	Sensitized 300-series SS cracks	NACE SP0170
Cryogenic service (< -50°F)	< -50°F	304L SS / 9% Ni steel	Aluminum alloys	Brittle fracture	ASME BPVC

Corrosion Mechanisms

Common Refinery Damage Mechanisms

Damage Mechanism	API 571 DM #	Affected Materials	Temperature Range	Key Factors	Prevention / Mitigation
High-Temperature Hydrogen Attack (HTHA)	DM#36	CS, C-0.5Mo	> 400°F with H2	Temp, H2 partial pressure, time	Use Cr-Mo alloys per API 941 Nelson curves
Sulfidation (H2S corrosion)	DM#61	CS, low alloys	> 500°F	Temperature, H2S concentration	Upgrade to 5Cr/9Cr/SS per McConomy curves
Naphthenic Acid Corrosion	DM#41	CS, low-Cr alloys	430-750°F	TAN, velocity, sulfur content	316 SS with >2.5% Mo, 317L, or Alloy 625
Wet H2S Cracking (SSC/HIC/SOHIC)	DM#62	CS, low alloys	Ambient-300°F	pH, H2S, hardness, stress	HIC-resistant steel, PWHT, max HB 200
Chloride Stress Corrosion Cracking	DM#10	300-series SS	> 140°F	Cl- concentration, temperature, stress	Duplex SS, Ni alloys, or non-SS materials
Polythionic Acid SCC	DM#50	Sensitized 300-series SS	Ambient (at shutdown)	Sensitization, moisture, sulfur oxide	Stabilized grades (321/347), soda ash wash before opening
Amine Cracking	DM#2	CS (non-PWHT'd)	Ambient-300°F	Amine type, concentration, stress	PWHT all CS in amine service
Caustic Cracking (Caustic SCC)	DM#8	CS (non-PWHT'd)	> 140°F NaOH	NaOH concentration, temperature	PWHT all CS, Ni alloys above 200°F
CO2 Corrosion	DM#16	CS	Any with wet CO2	CO2 partial pressure, water	CRA or inhibition, de Waard-Milliams model
Creep / Stress Rupture	DM#17	All	CS >800°F, SS >1000°F	Temperature, stress, time	Design to creep-rupture allowable, inspection
Temper Embrittlement	DM#55	2.25Cr-1Mo, Cr-Mo-V	650-1070°F (embrittles)	Tramp elements (P, Sn, As, Sb)	Control J-factor, step cooling test, avoid 650-1070°F
885°F Embrittlement	DM#1	Ferritic SS (400-series)	700-1000°F	Time at temperature	Avoid long-term service in range
Sigma Phase Embrittlement	DM#53	300-series SS, Duplex	1100-1700°F	Cr content, time at temp	Avoid prolonged exposure, solution anneal to restore
Erosion-Corrosion	DM#20	CS, Cu alloys	Any	Velocity, solids, turbulence	Resistant alloys, velocity limits, design changes
Microbiologically Influenced Corrosion	DM#38	CS, SS, Cu alloys	< 200°F (stagnant water)	Stagnant water, bacteria	Biocides, drainage, velocity maintenance

PWHT Guide

Post-Weld Heat Treatment (PWHT) Requirements

Material	P-Number	PWHT Temp Range (°F)	Min Hold Time	Heating/Cooling Rate	Notes
Carbon Steel (SA-516)	P1	1100-1200	1 hr/in (1 hr min)	≤ 400°F/hr above 800°F	Required > 1.25" or per service (amine, caustic, wet H2S)
C-0.5Mo (SA-204)	P3	1100-1200	1 hr/in (1 hr min)	≤ 400°F/hr above 800°F	Largely discontinued — HTHA risk
1.25Cr-0.5Mo (SA-387 Gr 11)	P4	1250-1325	1 hr/in (2 hr min)	≤ 400°F/hr above 800°F	Always PWHT
2.25Cr-1Mo (SA-387 Gr 22)	P5A	1300-1375	1 hr/in (2 hr min)	≤ 100°F/hr above 800°F	Always PWHT, control max hardness
5Cr-0.5Mo (SA-387 Gr 5)	P5B	1325-1375	1 hr/in (2 hr min)	≤ 100°F/hr above 800°F	Always PWHT
9Cr-1Mo (SA-387 Gr 9)	P5B	1350-1400	1 hr/in (2 hr min)	≤ 100°F/hr above 800°F	Always PWHT, temper above minimum
9Cr-1Mo-V (P91)	P15E	1365-1435	2 hr/in (2 hr min)	≤ 100°F/hr above 800°F	Critical — must not exceed Ac1, mandatory for all thicknesses
304/304L SS	P8	Not required*	—	—	*May be needed per NACE or service (e.g., polythionic acid risk)
316/316L SS	P8	Not required*	—	—	*Solution anneal at 1900-2050°F if sensitized
321/347 SS (stabilized)	P8	Not required*	—	—	Stabilization anneal 1600-1650°F may be specified
410 SS	P6	1350-1400	1 hr/in (1 hr min)	≤ 400°F/hr above 800°F	Always PWHT — air hardens
Duplex 2205	P10H	Not recommended	—	—	PWHT generally avoided — risk of sigma phase
Alloy 825 / 625	P43/P45	Not required	—	—	Solution anneal if needed

Source: Materials_Selection_Guide_v1.xlsx

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