In-Service

Module from the Pressure Vessel Engineering Curriculum curriculum.

Module 10 - In-Service Inspection and Fitness for Service · Learning Objectives · 1. Apply API 510 inspection intervals by vessel classification · 2. Compute remaining corrosion allowance and corrosion rate · 3. Conduct Level 1 or 2 FFS per API 579 for LTAs (local thin areas) · 4. Perform re-rating per UG-98 and NBIC when conditions change · 5. Document inspection per ASME B31.3 owner user responsibilities · API 510 Inspection Intervals

Class	Examples	External Interval	Internal / On-Stream	Notes	Ref
1 (High)	LPG, toxics, high-P H2	5 yr	Half RL or 10 yr	Most critical	API 510 Table 6.1
2 (Moderate)	Most HC vessels	5 yr	Half RL or 10 yr	Standard	API 510
3 (Low)	Utilities, low-P	10 yr	Half RL or 15 yr	Least	API 510
RBI-managed	Per risk matrix	Per RBI	Per RBI	Extended allowed	API 580
FFS Decision Matrix (API 579 Level 1)
LTA Finding	Measurement	Level 1 Action	Level 2 Trigger	Notes	Ref
General corrosion uniform	t_avg > tmin + CA	Continue service	If near limit	Common	579 Pt 4
LTA (local thin area)	s < 1.123sqrt(Dtmin) and Rt > 0.8	Accept	LTA with Rt 0.2-0.8	Blended profile	579 Pt 4
Pitting	PI depth < 0.5*tmin	Accept (reduced CA)	If deeper	Corrosion per API 571	579 Pt 6
Crack-like flaw	Any	Level 2 or 3 required	-	Needs fracture mech	579 Pt 9
Creep damage	T > 0.4*Tm	Level 2 or 3	-	Remaining life	579 Pt 10

Source: Pressure_Vessel_Engineering_Curriculum_v1.xlsx · Sheet: In-Service

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