Pipeline Maximum Allowable Operating Pressure (Barlow)

From Barlow's hoop-stress relation with the design factors 49 CFR 192 and ASME B31.8 apply to it. Barlow, P = 2 S t / D, gives the pressure at which the pipe wall reaches its specified minimum yield; the multipliers turn that into an allowable operating pressure. The design factor is the big one and it is a property of the ROUTE, not of the pipe: 0.72 in Class 1, 0.60 in Class 2, 0.50 in Class 3 and 0.40 in Class 4. As development grows around a line its class location changes, the allowable factor drops, and a line that was compliant at 0.72 in open country is not compliant at 0.50 once a subdivision is built beside it. That recalculation is triggered by population rather than by anything happening to the steel, and it is a routine and consequential part of integrity management -- which is why the MAOP at every class location is reported here rather than only the one selected. The longitudinal joint factor catches older pipe. Pre-1970 electric-resistance-welded and furnace-welded pipe carry factors below 1.0 because their seams are less reliable, and applying 1.0 to a 1950s line overstates its MAOP directly. The temperature factor derates above roughly 250 degF. Wall loss from corrosion changes the thickness this relation multiplies, and an in-service line with measured metal loss is governed by a remaining-strength evaluation instead, which is a different calculation on the same pipe. This is a design screen on nominal wall: it does not establish MAOP of record, which depends on the pressure test history, the manufacturing and construction records, and the grandfathering provisions; it does not evaluate seam integrity, cyclic fatigue, or dents and gouges; and it does not address liquid lines, which are designed to a different factor under B31.4 and 49 CFR 195. The operator's integrity management program, the pipeline engineer of record, and the regulator govern.

Barlow at yield P = 2 S t / D, then the code multipliers: MAOP = that x design factor F x longitudinal joint factor E x temperature derating factor T; hoop stress at an operating pressure = P D / (2 t), reported as a percent of SMYS; and the wall a target pressure needs is that relation inverted.

Barlow's relation with the design factors 49 CFR 192.105 and 192.111 and ASME B31.8 apply -- F by class location at 0.72, 0.60, 0.50 and 0.40, the longitudinal joint factor E, and the temperature derating factor T. A design screen on NOMINAL wall. It does not establish the MAOP of record, which depends on pressure test history, manufacturing and construction records and the grandfathering provisions; it does not evaluate seam integrity, cyclic fatigue, dents or gouges; and it does not cover liquid lines, designed under ASME B31.4 and 49 CFR 195.

One multiplication and three factors read off a table; no code text is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: od_in, wall_in, smys_psi, class_location, joint_factor, temperature_factor, operating_pressure_psig, target_pressure_psig, barlow_yield_psi, maop_psig, maop_class_3, hoop_stress_psi, pct_smys

• Nominal wall corrosion changes the thickness this multiplies, and a line with measured metal loss is governed by a remaining-strength evaluationASME B31G
• The joint factor is entered it depends on the pipe's vintage and manufacturing process49 CFR 192.113
• Not the MAOP of record test history, records and grandfathering establish thatthe operator's integrity management program