Regulatory Compliance

MAOP Determination

Calculate maximum allowable operating pressure per 49 CFR 192, verify design factors by location class, and establish MAOP using ASME B31.8 formulas and pressure test requirements.

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Class 1 limit

72% SMYS

Rural locations (≤10 buildings): design factor F = 0.72, maximum stress = 72% SMYS.

Test pressure

1.25-1.50× MAOP

Class 1-2: 1.25× MAOP for 8 hours. Class 3-4: 1.50× MAOP hydrostatic test required.

Class 4 limit

40% SMYS

High-density areas (≥4-story buildings): design factor F = 0.40 for maximum safety.

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1. MAOP Definition

MAOP is the maximum pressure at which a pipeline may be operated under federal regulations. For natural gas pipelines, 49 CFR Part 192 governs MAOP determination. The operating pressure must never exceed MAOP during normal operations.

Regulatory Framework

Regulation/Standard Application
49 CFR Part 192 Natural gas transmission and distribution (federal law)
49 CFR Part 195 Hazardous liquids (oil, NGL, CO₂)
ASME B31.8 Gas transmission and distribution piping systems
ASME B31.4 Pipeline transportation of liquid hydrocarbons
API 1111 Offshore pipelines
MAOP vs. MOP: MAOP is the maximum allowable pressure based on design and testing. MOP (Maximum Operating Pressure) is the actual highest pressure expected during normal operations, which should be less than MAOP to provide margin.

2. Design Formula

The fundamental equation for MAOP is based on Barlow's formula modified with design factors:

49 CFR 192.105 / ASME B31.8: P = (2 × S × t × F × E × T) / D Where: P = Design pressure (MAOP), psig S = Specified Minimum Yield Strength (SMYS), psi t = Design wall thickness, inches (see note below) D = Nominal outside diameter, inches F = Design factor (based on location class) E = Longitudinal joint factor T = Temperature derating factor
Manufacturing tolerance (ASME B31.8 §817.1): For new pipeline design, a 12.5% under-tolerance is applied to the nominal wall thickness to account for manufacturing variations: t_design = t_nominal × 0.875. If a corrosion allowance (CA) is specified: t_design = (t_nominal − CA) × 0.875.

Rearranged Forms

Solve for wall thickness: t = (P × D) / (2 × S × F × E × T) Solve for hoop stress: S_h = (P × D) / (2 × t) Percent SMYS: %SMYS = S_h / SMYS × 100 = P × D / (2 × t × SMYS) × 100

Common SMYS Values

Grade SMYS (psi) Specification
Grade B 35,500 API 5L, ASTM A53/A106
X42 42,000 API 5L
X46 46,000 API 5L
X52 52,000 API 5L
X56 56,000 API 5L
X60 60,000 API 5L
X65 65,000 API 5L
X70 70,000 API 5L
X80 80,000 API 5L

3. Design Factors

Location Class (Design Factor F)

Location class is determined by population density within a "class location unit"—a 1-mile segment with a 220-yard corridor on each side of the pipeline.

Class F %SMYS Description
Class 1 0.72 72% ≤10 buildings; rural, undeveloped
Class 2 0.60 60% 11–46 buildings; fringe areas, farms
Class 3 0.50 50% ≥46 buildings or within 100 yards of buildings with ≥20 people
Class 4 0.40 40% ≥4-story buildings above ground
Plan view of pipeline location class determination showing 1-mile by 440-yard class location unit with Class 1 example (3 buildings) and Class 3 example (52 buildings) per 49 CFR 192
Location class: Sliding 1-mile unit evaluated continuously; building count determines design factor and wall thickness requirements.

Joint Factor (E)

Pipe Type E Factor
Seamless 1.00
ERW (Electric Resistance Welded) 1.00
Flash Welded 1.00
DSAW (Double Submerged Arc Welded) 1.00
Furnace Lap Welded 0.80
Furnace Butt Welded 0.60

Temperature Factor (T)

Temperature (°F) T Factor
≤250 1.000
300 0.967
350 0.933
400 0.900
450 0.867
Typical gas pipelines: Most operate below 250°F, so T = 1.0. Use modern pipe (E = 1.0). The design factor F is usually the controlling variable based on location class.

4. Pressure Testing

New pipelines must be pressure tested before operation. The test pressure validates the MAOP and ensures construction quality.

Test Pressure Requirements (49 CFR 192.619 Table 1)

For pipelines installed on or after July 1, 2020:

Class Test Medium Minimum Test Pressure
Class 1 Air, gas, or water 1.25 × MAOP
Class 2 Air, gas, or water 1.25 × MAOP
Class 3 Water (hydrostatic) 1.50 × MAOP
Class 4 Water (hydrostatic) 1.50 × MAOP
Historical factors: Pipelines installed before July 1, 2020 may use different factors per 192.619 Table 1 (e.g., Class 1 = 1.1×, Class 3-4 = 1.4×). Always verify the applicable column based on installation date.

Test Duration

  • Hydrostatic (water): Minimum 8 hours at test pressure
  • Pneumatic (air/gas): Minimum 24 hours (more stringent due to stored energy hazard)

⚠ Wall stress during test: Ensure test pressure does not exceed 100% SMYS in the pipe wall. Calculate: S_test = P_test × D / (2 × t). If S_test > SMYS, reduce test pressure or the pipe may yield permanently.

Example: MAOP and Test Pressure

Given: 12.75" OD, 0.375" nominal wall, X52 pipe in Class 2 location

Step 1: Apply 12.5% manufacturing tolerance (ASME B31.8 §817.1) t_design = 0.375 × 0.875 = 0.328" Step 2: Calculate MAOP MAOP = (2 × 52,000 × 0.328 × 0.60 × 1.0 × 1.0) / 12.75 MAOP = 1,606 psig Step 3: Determine test pressure (Class 2 = 1.25×) Test pressure = 1.25 × 1,606 = 2,007 psig Step 4: Check wall stress during test S = 2,007 × 12.75 / (2 × 0.328) = 39,013 psi 39,013 / 52,000 = 75% SMYS < 100% ✓ OK

5. MAOP Determination Methods

49 CFR 192.619 allows several methods to establish MAOP, depending on available records:

Method 1: Design Formula

Use the design formula (Section 2) when all parameters are known from records:

  • Pipe specification (SMYS, diameter, wall thickness)
  • Seam type (joint factor)
  • Location class

Method 2: Test Pressure

MAOP based on highest test pressure:

MAOP = Test Pressure / Test Factor Test Factor by class (post-2020 pipelines): Class 1: 1.25 Class 2: 1.25 Class 3: 1.50 Class 4: 1.50

Method 3: Highest Actual Operating Pressure

For pipelines in service before certain dates with incomplete records:

  • MAOP = highest actual operating pressure during 5 years before July 1, 1970
  • Subject to additional requirements (ILI, ECDA, etc.)

Method 4: Pipe Replacement

For replaced pipe segments, use design formula with known specifications.

MAOP Reconfirmation: PHMSA requires operators to reconfirm MAOP for pipelines with incomplete records using methods in 49 CFR 192.624 (transmission lines in HCAs and Class 3/4 locations).

References

  • 49 CFR Part 192 – Transportation of Natural and Other Gas by Pipeline
  • ASME B31.8 – Gas Transmission and Distribution Piping Systems
  • PHMSA Advisory Bulletins on MAOP Verification
  • API 1160 – Managing System Integrity for Hazardous Liquid Pipelines

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