How to calculate the thickness of carbon steel pipes for the transportation of natural gas, ethane, and coalbed methane according to the NOM-007-ASEA-2016 standard.

June 13, 2025.

In the transportation sector for natural gas, ethane, and coalbed methane, pipeline integrity is essential to ensure operational safety, environmental protection, and regulatory compliance. One of the key aspects in the design and evaluation of piping systems is calculating the required minimum wall thickness. In Mexico, this calculation must be governed by the provisions established in NOM-007-ASEA-2016.

1. What is NOM-007-ASEA-2016?

The Mexican Official Standard NOM-007-ASEA-2016, issued by the Agency for Safety, Energy and Environment (ASEA), establishes the technical specifications and minimum requirements for industrial and operational safety in the design, construction, operation, and maintenance of onshore pipelines used for transportation.

2. Scope and field of application of the standard

“Section 2.2 of NOM-007-ASEA-2016 states that the pipelines cover the route from the point(s) of origin to the point(s) of destination within the system, including the transportation of natural gas associated with coalbed reservoirs, to the delivery and/or consumption points” (Agency for Safety, Energy and Environment (ASEA), 2016).

The following diagram illustrates the scope and field of application of the standard, clarifying who must apply it.

Diagram 1. Facilities of a Transportation System that fall within the scope of the NOM-007-ASEA-2016 standard.

(Agency for Safety, Energy and Environment (ASEA), 2016)

3. Why is the calculation of pipe thickness critical?

An incorrect thickness can lead to:
● Risks of leakage or rupture of the pipeline.
● Fines or regulatory sanctions for non-compliance.
● Failures that compromise the safety of personnel and the environment.
● Increased operational and maintenance costs due to premature failures.

4. Definitions

Component: The elements of a pipeline system connected to each other for the transportation of fluid gases between stations and/or plants, including pipelines, pig traps, fittings, shut-off valves, and sectional valves.
Tangential stress: Stress produced by the pressure of a fluid on the wall of a pipeline, acting circumferentially in a plane perpendicular to the longitudinal axis of the pipeline.
Maximum permissible operating pressure (PMOP): The maximum pressure at which a pipeline or segment of the transportation system can operate.
Maximum operating pressure (MOP): The actual maximum operating pressure, which is the highest pressure at which a pipeline transportation system operates during a normal operational cycle.

5. Materials used in carbon steel pipes

The steel pipes must comply with the requirements outlined in the Standard and be manufactured according to the provisions of the applicable standards. These may come from national standards, codes, or current international standards, such as those mentioned below:
●  API 5L: Specification for line pipe.
● ASTM A 106: Standard Specification for Seamless Carbón Steel Pipe for High­Temperature Service.
● ASTM A 333/A 333M: Standard Specification for Seamless and Welded Steel Pipe for Low­Temperature Service.
● ASTM A 381: Standard Specification for Metal­Arc­Welded Steel Pipe for Use With High­Pressure Transmission Systems.
● ASTM A 672: Standard Specification for Electric­Fusion­Welded Steel Pipe for High­Pressure Service at Moderate Temperatures.
● ASTM A 691: Standard Specification for Carbón and Alloy Steel Pipe, Electric­Fusion­Welded for High­Pressure Service at High Temperatures.
● ASTM A 53: Standard specification for pipe, steel, black and hot dipped, zinc coated welded and seamless.

6. Equation for the calculation of the thickness of carbon steel pipes

The calculation of the thicknesses of steel pipes transporting gas is determined in accordance with the following equation:

Note: This equation is for reference purposes only. The actual calculation must consider all specific operating conditions, including external loads related to the environment, live loads, dead loads, stresses caused by earthquakes, etc.

6.1 Parameters considered in the calculation

NOM-007-ASEA-2016 is based on the thickness formula contained in international standards such as ASME B31.4 (for liquids) and ASME B31.8 (for gases). In general, the key factors are:

P = Internal design pressure, in kPa (lb/in²).
S = Minimum yield strength, in kPa (lb/in²).
D = Specified outside diameter for the duct, in mm (in).
F = Design factor, see table 1, determined in accordance with the provisions of section 7.11 (table 2) of the NOM-007-ASEA-2016 standard.
E = Longitudinal joint efficiency factor, see table 2, determined in accordance with the provisions of section 7.12 (table 3) of the NOM-007-ASEA-2016 standard.
T = Temperature correction factor, see table 3, determined in accordance with the provisions of section 7.13 (table 4) of the NOM-007-ASEA-2016 standard.

6.2 Location classes

The location class determines certain factors used in the wall thickness calculation of pipelines based on their location. It is necessary to select the location class that corresponds to the place where the pipeline will be installed.

The location classes through which a pipeline will pass must comply with the following:

Location class 1: Areas exposed to infrequent human activity with no permanent human presence. This location class reflects areas with difficult access, such as deserts and tundra regions (Energy and Environmental Safety Agency (ASEA), 2016).
Location class 2: The unit area with ten or fewer buildings occupied by people and/or places with a population density of fewer than 50 inhabitants per square kilometer. This location class reflects areas such as wastelands, grazing lands, agricultural lands, and other sparsely populated zones (Energy and Environmental Safety Agency (ASEA), 2016).
Location class 3: The unit area with more than ten and up to forty-five buildings occupied by people and/or places with a population density of 50 to 250 people per square kilometer, including multiple residences, hotels or office buildings where no more than 50 people can regularly gather, and scattered industries. This location class reflects areas with an intermediate population density between location class 2 and location class 4, such as marginal zones located around cities and towns, ranches, and estates (Energy and Environmental Safety Agency (ASEA), 2016).
Location class 4: The unit area with forty-six or more buildings occupied by people and/or places with a population density of 250 or more people per square kilometer, except where location class 5 prevails. This location class reflects areas with urban developments, residential zones, industrial areas, and other populated areas not included in location class 5 (Energy and Environmental Safety Agency (ASEA), 2016).
Location class 5: In addition to the conditions presented in location class 4, any of the following characteristics prevail (Energy and Environmental Safety Agency (ASEA), 2016):
    ● Buildings with four or more levels, including the ground floor
   ● Communication routes with heavy or mass transit, and underground facilities of priority or strategic services for the urban area.

6.2.1 Safety factor by population density for steel pipelines (F)

 The factor to be used in Equation 1 is determined according to the indications in table 1:

Table 1. Design Factor by Population Density (F)

(Agency for Safety, Energy and Environment (ASEA), 2016)

The factor of 0.77 applies only to pipelines transporting dry natural gas and must comply with the provisions outlined in Appendix C (Normative) of the NOM-007-ASEA-2016 Standard.

For gases other than natural gas considered in the NOM-007-ASEA-2016 standard, the design factor should not exceed 0.77, as specified in table 1, design factor by population density.

6.3  Longitudinal joint efficiency factor (E) for steel pipelines

The longitudinal joint efficiency factor used in equation 1 is determined according to table 2.

Table 2. Longitudinal joint efficiency factor (E)

(Agency for Safety, Energy and Environment (ASEA), 2016)

6.4 Temperature correction factor for steel pipelines (T)

The temperature correction factor to be used in equation 1 is determined according to table 3.

Table 3. Temperature correction factor (T)

(Agency for Safety, Energy and Environment (ASEA), 2016)

(*) For intermediate gas pipelines, the temperature correction factor is determined by direct interpolation.

6.5 Maximum allowable shear stress

The maximum allowable shear stress is determined using the following equation:

Where:

ST = Maximum allowable shear stress in MPa (lb/in²).   
P = Maximum operating pressure (MOP) in MPa (lb/in²).
D = Outside diameter of the pipeline in mm (in).
t = Wall thickness in mm (in).

Generally, the maximum allowable shear stress is established as a percentage of the (RMC) according to the following:

6.6 Considering corrosion in equation 1

In this revised equation, the allowable internal corrosion (c) is added to the pipelines in order to ensure a proper wall thickness in the design.

7. Pipe thickness calculation example                     

To carry out the example, input data such as the following is required:

Material specification² = ASTM A 106 Gr B

Minimum yield strength (S or RMC)³ = 241,316 kPa (35,000 PSI)

Nominal pipe size⁴ = 150 mm (6 in) NPS

Outside diameter of pipe (D)⁵ = 168.3 mm

Fluid temperature⁶ = 20 °C

Notes:

1. This is the pressure determined based on the client’s considerations and the objective of transporting the gas.
2. The material specification is determined based on cost, availability, client preferences, etc. See section 5 of this blog.  
3. The material strength is obtained from the mechanical properties specified in the material specification.
4. This is the diameter selected based on the capacity to transport the required flow, determined through calculations or simulations. See ASME B36.10.
5. This is the outside diameter corresponding to the selected nominal pipe size, which can be found in ASME B36.10.
6. This refers to the average temperature at which the fluid will be flowing inside the pipe. This value has a significant impact when temperatures are high.

Determine the missing input data:

Determination of design factor (F):
To select the design factor (F), the first step is to determine the pipeline’s location class. You can refer to section 6.2 of this blog to choose the one that best fits your needs. In this case, location class 4 will be used.

With the location class data, we review table 1, choose the area where the pipeline will be used, and you will obtain the design factor. In this case, it is F=0.55.

Determination of longitudinal joint efficiency factor (E):

This data will be obtained depending on the type of material to be used, or alternatively, the specification used. In this case, the specification: ASTM A106 Gr B, is used. With this information, we use Table 2 of this blog to determine the joint factor, which is E=1.00.

Determination of the temperature correction factor (T):

The temperature correction factor is selected based on the temperature at which the fluid will flow inside the pipeline. In this case, the temperature is 20°C, with this data, we refer to Table 3 to select the factor. In this case, it is T=1.000.

Determination of the allowable internal corrosion (c):

The allowable internal corrosion is typically within 1.6 mm, which will be used in this case. c = 1.6 mm

Calculation of carbon steel pipe thickness

General Equation (Equation 4):

Adding the obtained data, we have:

With this data, we can determine the commercial thickness for the pipe using ASME B36.10. In this case, we obtain a 6 NPS SCH 80 pipe with a thickness of 10.97 mm (0.432 inches).

8. Conclusion

The use of precise tools for the normative calculation of pipelines not only streamlines the engineering work but also ensures compliance with key Mexican regulations, such as NOM-007-ASEA-2016. Optimize your processes and guarantee the safety of your facilities with reliable and up-to-date solutions.

9. References

Agencia de Seguridad, Energía y Ambiente (ASEA). (2016). NOM-007-ASEA-2016: Transporte de gas natural, etano y gas asociado al carbón mineral por medio de ductos. Ciudad de México.