49 CFR 192.105 & ASME B31.8-2022 Compliant
Gas transmission and distribution piping. Design factor based on location class.
T ≤ 250°F: T = 1.00
T > 250°F: Derating per Table 841.1.8-1
Common API 5L grades:
• Grade B: 35,000 psi
• X42: 42,000 psi
• X52: 52,000 psi
• X60: 60,000 psi
• X65: 65,000 psi
• X70: 70,000 psi
• X80: 80,000 psi
Location class based on building count within 220-yard sliding mile per 49 CFR 192.5
Understand hoop stress principles, Barlow's derivation, and code requirements
Specified Minimum Yield Strength (SMYS) for common API 5L line-pipe grades — the yield strength used in Barlow's formula and %SMYS checks. For the X-grades, the grade number is the SMYS in ksi.
| API 5L grade | SMYS (psi) | SMYS (MPa) |
|---|---|---|
| Grade B | 35,000 | 241 |
| X42 | 42,000 | 290 |
| X52 | 52,000 | 359 |
| X60 | 60,000 | 414 |
| X65 | 65,000 | 448 |
| X70 | 70,000 | 483 |
| X80 | 80,000 | 552 |
SMYS stands for Specified Minimum Yield Strength. It is the minimum stress at which a pipe material will begin to permanently deform. Common grades include Grade B (35,000 psi), X52 (52,000 psi), and X70 (70,000 psi).
Hoop stress is calculated using Barlow's Formula: S = (P × D) / (2 × t), where S is stress, P is internal pressure, D is outside diameter, and t is wall thickness.
Barlow's formula relates internal pressure to hoop stress in a thin-wall pipe: S = (P × D) / (2 × t). Rearranged for allowable pressure, P = (2 × S × t × F × E × T) / D, where F is the design factor, E the joint factor, and T the temperature derating factor. It is the basis for pipe wall-thickness and MAOP design in ASME B31.8, B31.3, B31.4, and 49 CFR 192.
The Design Factor (F) is a safety multiplier used to calculate MAOP. For gas pipelines under 49 CFR 192, factors range from 0.72 (Class 1, Rural) to 0.40 (Class 4, Urban).