 # Steel Pipe Maximum Bending Moment

QUESTION
I am sorry for asking such a fundamental question. I have forgotten Strength of Material Basics that I studied in 1st Yr. I just want to know what is the formula for maximum bending moment for a steel pipe?

I am not too sure exactly about the conditions. It is a 6" subsea pipeline between Well Head Platform and Production Platform with risers installed at both ends. I would like to know bending moment for subsea pipeline as well as the riser. I don’t know in which category this would come. Is it possible to determine or some more information is necessary?

I have read in a technical document, that for initial calculation Max Bending Moment can be estimated as 0.85 times SMYS. So my question is how can i get Bending Moment if I know SMYS because SMYS is a stress with units in MPa and Bending Moment units is in Kilo Newton Metre.

I am doing wall thickness calculation based on DNV-OS-F-101. In the spreadsheet, for load interaction, I need to put the value of ME (Maximum Bending Moment due to Environmental load). I know I can get the exact value once I do Dynamic Pipeline Analysis, but initially I must assume certain value to put in the spreadsheet, as based on that spreadhsheet, will give the result whether the assumed thickness is ok or not. From yielding stress, how can I get limiting moment capacity (even though it may not be too useful). In the reference document that I am mentioning, they have arrived at the value of Max Bending bending of arnd 50kNm for 6" pipeline (Grade X-52;SMYS=359Mpa) by taking it 0.85 X Yield Stress.

REPLIES

patswfc
Moment capacity of pipe = yield stress x elastic section modulus of pipe.

elastic section modulus of pipe = I/y

I = pi(d4 - (d - 2t)4) / 64 , the two 4’s are to the power of 4

y = d/2

SOURCE