I have a question regarding the wall thickness of pressure pipes
Thread Content
There is a liquid propylene pipeline with a DN100 diameter. The operating temperature is 20 degrees Celsius, the operating pressure is 1.6 MPa, while the design pressure specified is 1.92 MPa; the hydrostatic test pressure is 2.88 MPa. PN40 grade 20# seamless steel pipes were chosen for this application, but I specified a wall thickness of 4 mm. After checking the chemical process design manual, it turns out that the required wall thickness at this pressure level is 4.5 mm. I would like to ask the experienced professionals here: is a wall thickness of 4 mm sufficient? The client has already purchased the materials. . .
Due to the numerous pipeline standards in use domestically, various pipeline wall thickness series as well as calculation and selection methods are widely employed, often leading to confusion in the actual design process. In actual engineering design, there is often the mistaken belief that thicker pipes are better, leading to arbitrary increases in the wall thickness of pipes. This not only raises the cost of project construction but also introduces safety risks for the pipes. This paper discusses the calculation of pipe wall thickness as well as the relationship between pipe wall thickness and pipe stress, through practical examples and real engineering cases.
1. Determine the corrosion allowance for the medium; this value can be 1.5 or 3.0 mm. 2. Different design institutes have their own tables specifying pipe grades; here, the grade table from a certain first-class petrochemical industry design institute in China is cited. For the given conditions of medium, pressure, and temperature, grade 2.5A2 is appropriate. For pipes of DN100 in this grade, the wall thickness is SCH40, which corresponds to 6.0 mm. 3. Therefore, from a stress-bearing perspective, 4.5 mm is acceptable; however, considering corrosion, this value seems insufficient. The service life will be shortened, and this needs to be explained to the user.
The 4.0mm I specified – is it feasible from a stress-bearing perspective? I calculated using the formula from national standard 50316; even with a 3mm corrosion margin, it seems sufficient
Φ114 should be used; Φ108 is definitely too small, as the wall thickness of pipes has decreased these days.
Use the formula provided in GB50316 to calculate the wall thickness; whatever value is obtained will be the appropriate thickness, and this thickness will definitely be sufficient to withstand the required pressure. In fact, if you use the wall thickness of 4 mm that you ultimately choose and calculate the pressure-bearing capacity based on that, it would be around 3–4 MPa. As for the process manual, there’s no need to worry too much about it.
The wall thickness of each pipeline needs to be calculated; consulting manuals only allows for the selection of wall thicknesses corresponding to the same pressure and corrosion margin
Don’t you know what the minimum wall thickness you’ve calculated is? . . The value taken from the manual should be greater than this minimum value, right?
Based on the conditions provided by the original poster, the wall thickness calculated using 50316 is 2.86; adding the corrosion allowance of 1.5 and the negative deviation of 12 gives the final value. 5%, which is 4.99. Rounded to 5.0 mm. It’s quite appropriate.
Why is your calculation so high? I obtained a allowable stress of 130 MPa, a joint coefficient of 0.8, and a Y value of 0.4; the outer diameter is 108, and the pressure is set at 2.88. The calculated value is only 1.4 millimeters – how did you arrive at such a high figure? Could it be that I made a mistake in my calculation?
I made a mistake; I reversed the welding coefficient and the Y value