Pressure Ratings of MS Seamless Pipes

In the field of engineering materials, MS typically stands for "Mild Steel." This is a type of carbon steel with a low carbon content (typically less than 0.25%), good plasticity, moderate strength, and excellent weldability.

Therefore, MS seamless pipe refers to "mild steel seamless pipe." Its pressure rating is determined in the same way as ordinary carbon steel seamless pipe, but special attention should be paid to the material standard.

What determines the pressure rating?

The pressure rating of MS seamless pipe is not a fixed value but is determined by the following four factors:

1. Material standard and allowable stress (S): This is the most critical factor. MS materials of different standards have different strength indicators (especially allowable stress S). Allowable stress decreases significantly with increasing temperature.

2. Dimensional specifications: Primarily the outside diameter (D) and wall thickness (t). Pressure is directly proportional to wall thickness and inversely proportional to outside diameter.

3. Wall Thickness Series (Schedule, Sch): For example, Sch40, Sch80, etc. This is a universal "language" for expressing wall thickness grades.
4. Design Standard: Depending on the design standard (such as ASME B31.1 or B31.3) that the pipeline complies with, the safety factor and calculation formula may differ slightly.

Other Influencing Factors:

Temperature has a significant impact: If your pipeline's operating temperature is high (e.g., over 100°C), you must recalculate the material's allowable stress (S) based on the temperature and use the formula for calculation. The values ​​in the table above will no longer apply.

Corrosive Environments: If the media being transported is corrosive, the corrosion allowance (CA) must be deducted from the wall thickness (t), which will result in a decrease in the calculated pressure capacity.

Common MS Seamless Pipe Material Standards:

To check pressure, you must first know the material and standard of the pipe. The most common MS seamless pipe standards are:

ASTM A106 GR.B High-Temperature Seamless Carbon Steel Pipe: The most commonly used and mainstream MS seamless pipe standard, particularly for medium- and high-pressure pipelines.

ASTM A53 GR.B seamless and welded steel pipe: Primarily used for low- and medium-pressure fluids and pressure-bearing piping, but its overall performance is slightly lower than A106 GR.B.
DIN 2448 St37.0: A commonly used European standard for non-alloy steel pipe.
GB/T 8163 #20 Seamless Steel Pipe for Fluid Transportation: The most commonly used low-carbon steel pipe for fluid transportation in China's national standard, equivalent to A106 GR.B.

How to determine the pressure rating for your project?

1. Identify pipe markings: Locate the inkjet print or label on the pipe and confirm the standard number (e.g., ASTM A106) and steel grade (e.g., GR.B). This is the first and essential step.

2. Measure dimensions: Accurately measure the pipe's outside diameter (D) and wall thickness (t).

3. Determine design conditions: Identify the maximum operating pressure and temperature of the piping system.

4. Check the allowable stress (S): Based on the material standard (such as A106 Gr.B) and operating temperature, consult the allowable stress table in Appendix A of the ASME B31.3 specification to find the corresponding S value.

5. Calculation Verification: Substitute D, t, and S into the above formula to calculate the maximum allowable working pressure (P) for the pipe at the operating temperature.

6. Comparison and Judgment: Ensure that the calculated P value is greater than the system's maximum operating pressure, and allow for an appropriate safety margin.

Conclusion:

For MS seamless pipe (such as A106 Gr.B): its pressure rating is a dynamic, calculated value, not a fixed label.

Sch40 is the most commonly used standard heavyweight grade, suitable for most medium and low-pressure applications.

Sch80 is a thickened grade with significantly higher pressure capabilities than Sch40 and is used for higher pressures or more severe operating conditions.

Pressure rating should never be discussed in isolation from size, material, and temperature. Simply asking, "What pressure can Sch40 pipe withstand?" is an inaccurate question; the pipe diameter and material must be specified.

Read more:  Black Carbon Steel Pipe or  MS and GI Pipe Difference

Article source: https://article-realm.com/article/Business/76784-Pressure-Ratings-of-MS-Seamless-Pipes.html