In pipeline design, does the thickness corresponding to the pipe designation include the corrosion allowance for the pipeline?
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I would like to ask the experts: is the thickness corresponding to the pipe size calculated based on the pressure rating alone, or is it the thickness resulting from the pressure rating plus an allowance for corrosion? According to the regulations, it should be the theoretical thickness; the corrosion allowance shouldn’t be included. I’m not sure if this understanding is correct In other words, in the design process, when selecting the pipe thickness, the thickness corresponding to the pipe schedule should be used, plus an allowance for corrosion. I hope the experts can give me some advice.
The design institute has taken into account the corrosion allowance when designing the pipes, so there’s no need to worry too much
Well, the design institute must have taken corrosion allowance into consideration. The problem we’re facing now is that the piping was designed on our own, without going through the design institute, and thus we run into issues regarding the appropriate thickness for each pipe section.
The pipes need to be designed by oneself; when calculating the wall thickness of the pipes, a corrosion margin must be taken into account. The final wall thickness chosen (which can correspond to a value in a table) should include the thickness calculated based on the relevant formulas, the corrosion margin, as well as manufacturing tolerances and other factors.
Well, thank you. So what you’re saying is that the wall thickness values specified in the pipe section table provided by the design institute already take into account the corrosion allowance? The problem I’m facing is that the calculated theoretical thickness, plus a 1.5 mm corrosion allowance, is greater than the thickness indicated on the pipe specifications; whereas the thickness listed for those pipe sections lies between the theoretical thickness and the theoretical thickness plus the corrosion allowance. I’m a bit confused.
The corrosion allowance is not necessarily 1.5 mm; it could also be 1 mm. For stainless steel, it might even be 0. The calculated wall thickness should be divided by the lower limit of the manufacturing error. For example, if the allowable error is ±12.5%, then the calculated value is divided by 0.875, and the corrosion margin is added...
The wall thickness value of the pipe finally selected in the design certainly includes a corrosion margin.
Thank you all for your help. I checked the calculation formulas on page 44 of GB50316-2000, and indeed the final results (the thicknesses indicated in the pipe section table) take into account factors such as corrosion allowance, processing thinning, and tolerances. For example, for a DN15 20# steel pipe with a pressure rating of 1.0 MPa, the calculation result provided by the design institute is a wall thickness of 2 mm, which already takes into account the corrosion allowance. However, the corrosion allowance here is not 1.5 mm, because if it were 1.5 mm, the effective thickness of this pipe would be only 2 – 1.5 = 0.5 mm. I have benefited greatly from the help of all of you experts; thank you once again! ! ! !
https://bbs.hcbbs.com/thread-2038280-1-1.html Those who are interested in process design should take a look at this post
Same question: design pressure 13 MPa, temperature 129, outer diameter of the pipe 88.9. I calculated the thickness to be 3.2 mm; adding a corrosion allowance of 4 mm and a negative deviation of 0.3 mm, the wall thickness was rounded up to 8 mm. However, calculated based on the pipe specification code, Sch72 (with a value of 80 is used), the thickness as indicated in the table is 8 mm. Should I still add a corrosion allowance?
Same question: design pressure 13 MPa, temperature 129, outer diameter of the pipe 88.9. I calculated the thickness to be 3.2 mm; adding a corrosion allowance of 4 mm and a negative deviation of 0.3 mm, the wall thickness was rounded up to 8 mm. However, calculated based on the pipe specification code, Sch72 (with a value of 80 is used), the thickness as indicated in the table is 8 mm. Should I still add a corrosion allowance?