Module 2 - Radiant Section

Module from the Fired Heater Training Curriculum curriculum.

MODULE 2: RADIANT SECTION DESIGN · Radiant Flux Fundamentals · Average Radiant Flux = Total Radiant Duty / Total Radiant Tube Area Typical Values: • General process heaters: 8,000-12,000 BTU/hr·ft² • Vacuum heaters (coking service): 6,000-8,000 BTU/hr·ft² • Reformer furnaces: 15,000-25,000 BTU/hr·ft² (alloy tubes) • Reboiler heaters: 8,000-10,000 BTU/hr·ft² Maximum Local Flux: • Peak flux occurs at the point closest to the flame • Peak/average ratio: 1.5-2.0 depending on geometry • Maximum local flux must stay below the design limit to prevent: - Tube wall overheating (creep, oxidation) - Internal coking (film temperature exceedance) - Tube failure (rupture) Flux Adjustment Levers: • Firing rate: lower firing = lower flux (proportional) • Flame shape: longer flame = more distributed flux • Tube spacing: wider spacing = lower peak flux • Number of burners: more burners = more uniform flux · Tube Metallurgy Selection

Material	Max Tube Metal Temp	Common Application	ASME Designation	Creep Life Basis	Cost Relative	Notes
Carbon Steel	750°F	Low-temperature services	SA-106 Gr B	Limited life above 700°F	1.0×	Cheapest, most common low-T
1.25Cr-0.5Mo	900°F	Moderate temperature, H2 service	SA-213 T11	Good creep to 900°F	1.3×	Standard upgrade from CS
2.25Cr-1Mo	1,050°F	High-temperature H2 service	SA-213 T22	Good creep to 1,050°F	1.5×	Hydroprocessing heaters
5Cr-0.5Mo	1,100°F	High sulfidation service	SA-213 T5	Sulfidation resistant	1.7×	High-sulfur crude service
9Cr-1Mo (P91)	1,100°F	High-temperature, high-strength	SA-213 T91	Excellent creep strength	2.0×	Reduced wall thickness
304 SS	1,500°F	Reformer catalyst tubes	SA-213 TP304	Oxidation limit, not creep	3.0×	Reformer radiant tubes
Alloy 800H/HT	1,800°F	Severe high-temperature service	SB-407 N08810	Creep + oxidation	5.0×+	Ethylene cracker tubes

Source: Fired_Heater_Training_Curriculum_v1.xlsx · Sheet: Module 2 - Radiant Section

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