Fabrication

Module from the Piping Engineering Curriculum curriculum.

Module 8 — Fabrication, Welding & Heat Treatment · Learning Objectives · 1. Apply ASME IX qualification for WPS, PQR, and welder performance (WPQ) · 2. Specify preheat and PWHT per B31.3 Table 330.1.1 and 331.1.3 · 3. Monitor hardness limits for sour service (NACE MR0175) and hydrogen service · 4. Recognize weld map and RT coverage requirements per fluid service category · 5. Control galvanic pairs, low-alloy/CS interfaces, and PMI verification · PWHT Requirements (B31.3 Table 331.1.3) — Thickness Triggers

P-No.	Material	Thickness Trigger (in)	Hold Time (hr/in)	Min Hold	Typical Temp °F
P-1	Carbon steel (< 0.25% C)	> 0.75	1 hr/in	2 hr	1100–1200
P-1	Carbon steel (> 0.25% C)	> 0.50	1 hr/in	2 hr	1100–1200
P-3	C-Mn-Si, Mn-Mo	> 0.625	1 hr/in	2 hr	1100–1200
P-4	1.25Cr-0.5Mo	> 0.50	1 hr/in	2 hr	1250–1300
P-5A	2.25Cr-1Mo	> 0.50	1 hr/in	2 hr	1275–1375
P-5B	5Cr-0.5Mo to 9Cr-1Mo	All	1 hr/in	2 hr	1300–1400
P-5B	9Cr-1Mo-V (P91)	All	1 hr/in	2 hr	1400–1450
P-8	Austenitic SS (304, 316)	None normally	—	—	Avoid unless stress relief required
Preheat Requirements (B31.3 Table 330.1.1) — Minimum Preheat
P-No.	Tensile (ksi)	Thickness (in)	Preheat °F	Interpass Max °F	Notes
P-1 CS	< 71	< 1	50 (if < 32 °F amb)	600	Standard CS
P-1 CS	< 71	≥ 1	175	600	Higher thickness
P-1 CS	≥ 71	All	175	600	Higher strength
P-3 (Mn-Mo)	—	< 1/2	175	600	—
P-3 (Mn-Mo)	—	≥ 1/2	225	600	—
P-4 (1.25Cr)	—	All	300	600	Alloy steel
P-5A (2.25Cr)	—	All	300	600	Hot oil / H2
P-5B (9Cr-V P91)	—	All	400	600	Maintain interpass

Source: Piping_Engineering_Curriculum_v1.xlsx · Sheet: Fabrication

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