Wall Thickness

Module from the Piping Engineering Curriculum curriculum.

Module 4 — Wall Thickness & Schedule Selection · Learning Objectives · 1. Compute B31.3 pressure design thickness for straight pipe · 2. Apply mill tolerance and corrosion allowance to arrive at ordering thickness · 3. Select next heavier commercial schedule from the ANSI B36.10 / B36.19 chart · 4. Check wall thickness adequacy under external pressure (vacuum) per B31.3 §304.1.3 · 5. Derate piping when thinning approaches retirement thickness · Commercial Pipe Schedules (NPS 4 Example)

Schedule	Wall (in)	ID (in)	Wt (lb/ft)	Area (in²)	Rated P (psi)*	Notes
Sch 10	0.120	4.260	5.61	14.25	630	Utility low-P
Sch 40 (Std)	0.237	4.026	10.79	12.73	1,280	Most common CS
Sch 80 (XS)	0.337	3.826	14.98	11.50	1,850	Higher P
Sch 120	0.438	3.624	19.00	10.32	2,430	High P
Sch 160	0.531	3.438	22.51	9.28	2,975	Very high P
XXS	0.674	3.152	27.54	7.80	3,830	Specialty
*Rated pressure based on A106-B at 100 °F, E=1.0, Y=0.4, c=0.0625", 12.5% mill tol. For design use actual service conditions.
Corrosion Allowance by Service (typical)
Service	CA (in)	Basis	Retirement Limit	Inspection Freq	Reference	Notes
Clean hydrocarbon	0.0625	20-yr life, low CR	Tmin per B31.3	5 yr	API 570	Standard
Crude unit overhead	0.1250	NH4Cl / HCl corrosion	Tmin	1 yr	API RP 571	Inject neutralizer
Sour water	0.1875	Wet H2S + CO2	Tmin	2 yr	NACE	NH4HS velocity
Amine	0.0625	Slow, alkaline	Tmin	5 yr	API RP 945	Velocity limit
Hydrogen hot	0.0625	HTHA if above Nelson	Tmin	5 yr	API RP 941	Upgrade material
Cooling water (closed)	0.0625	Treated	Tmin	10 yr	—	—
Cooling water (open)	0.1875	O2 + biofilm	Tmin	2 yr	—	Check MIC
Acid service	0.25+	Aggressive	Upgrade material	1 yr	NACE SP0106	Consider Alloy

Source: Piping_Engineering_Curriculum_v1.xlsx · Sheet: Wall Thickness

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