Mod 1 - Carbon & Alloy Steels

Module from the Materials and Corrosion Curriculum curriculum.

CARBON AND ALLOY STEELS · Learning Objectives · 1. Identify common carbon and low-alloy steel grades used in refining 2. Understand heat treatment (normalizing, tempering, quenching) effects on properties 3. Select Cr-Mo alloy steels for elevated temperature service 4. Specify PWHT (post-weld heat treatment) requirements per ASME · Common Refinery Carbon and Low-Alloy Steels

ASTM Grade	Common Name	Chemistry	Max Service Temp (°F)	Typical Application	PWHT Required?	Notes
A 106 Gr B	Carbon steel pipe	0.30%C, 0.29-1.06% Mn	800	Piping — ambient to 650°F service	Above 3/4" wall	Most common refinery piping material
A 516 Gr 70	CS plate	0.31%C, 0.79-1.30%Mn	800	Pressure vessel plate	If >1.5" or PWHT spec	Normalized for impact testing
A 335 P11	1¼Cr-½Mo	1.00-1.50%Cr, 0.44-0.65%Mo	1050	Pipe for hydroprocessing, reformers	Yes (all)	Resistance to creep, moderate H2 attack
A 335 P22	2¼Cr-1Mo	1.90-2.60%Cr, 0.87-1.13%Mo	1200	Heater tubes, HDS reactor piping	Yes (all)	Better H2 attack resistance than P11
A 335 P91	9Cr-1Mo-V (Grade 91)	8.00-9.50%Cr, 0.85-1.05%Mo, 0.18-0.25%V	1200	High-temp steam lines, supercritical service	Yes (all)	Modern creep-resistant, careful PWHT critical
A 387 Gr 22 Cl.2	2¼Cr-1Mo plate	Same as P22	1200	Hydroprocessing reactor shells	Yes (all)	Quenched & tempered, high toughness
A 387 Gr 11 Cl.2	1¼Cr-½Mo plate	Same as P11	1050	Small hydroprocessing reactors, exchangers	Yes (all)	Q&T for higher strength
A 312 TP304	18Cr-8Ni	18-20%Cr, 8-10.5%Ni	1500	Moderate temp stainless piping	No	Most common austenitic SS
A 106 Gr C	Higher-C CS	0.35%C	800	Heavier wall piping, special services	Above 3/4" wall	Higher strength than Gr B
A 333 Gr 6	Low-temp CS	0.30%C, +Si	-50°F (to 800°F high)	Low-temp piping, LNG, NGL service	Above 3/4" wall	Impact tested at -50°F
PWHT (Post-Weld Heat Treatment) Requirements
Material	PWHT Temperature	Hold Time (per inch)	Purpose	ASME Reference	Hardness Limit
Carbon Steel (>3/4" wall)	1100-1200°F	1 hour	Stress relief, reduce H2 cracking risk	ASME VIII UCS-56	HB 200 max after PWHT
1¼Cr-½Mo (P11)	1250-1300°F	1 hour	Stress relief, carbide redistribution	ASME VIII UCS-56	HB 220 max
2¼Cr-1Mo (P22)	1275-1325°F	1 hour	Stress relief, creep strength development	ASME VIII UCS-56	HB 235 max
9Cr-1Mo-V (P91)	1350-1400°F	1 hour (4 hr min)	Tempering of martensitic microstructure — CRITICAL	ASME VIII UCS-56, code case 2179	HB 250 max, min 180 required
309/316 SS (austenitic)	Usually not PWHT	N/A	May sensitize if heated to 800-1500°F	—	N/A (sensitization concern)
Duplex SS (2205)	Solution annealed only, no PWHT	N/A	PWHT disrupts austenite/ferrite balance	—	Avoid — can destroy duplex structure
Source: ASTM specifications, ASME Section IX, FOS Chief Files — Metallurgy folder (TEC-700-02, Material Properties BW), IPE-EP-10 series

Source: Materials_and_Corrosion_Curriculum_v1.xlsx · Sheet: Mod 1 - Carbon & Alloy Steels

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