Load Sharing of Pipeline Repair Sleeves

[PaulLange]

Hello, I have just joined this forum as I work in pipeline repair using composite sleeves. Not having a formal engineering qualification I am having to self study quite a lot of things. I have found answers before by searching the forums so thought I would join. Also I do have a question that I cannot find the answer to.

It has previously been explained to me that the load sharing between a pipe and a repair sleeve is determined by the respective stiffness of the pipe and sleeve material. Stiffness being determined by the material's Young's Modulus and wall thickness. I have performed the calculations to determine the stresses in the sleeve and pipe and the load sharing ratio and obtained I what I thought was the expected results. However, I have noticed that if I change the wall thickness of the pipe or sleeve the load sharing ratio remains the same; it seems to be determined solely by the ratio of the Young's Moduli. The values for both the respective stresses do change but the difference as a ratio does not.

Is this correct or have I missed something?

Thanks in advance for any help that can be given.

 

[Compositepro]

The stains in both layers will be the same (unless thickness is very high). Then the stresses in each material will proportional to the modulus. Load is stress times cross-sectional area (thickness).

 

[PaulLange]

Thank you Compositpro, I knew that the strains would be the same but I didn't think about how that factored in to the issue.

 

[LittleInch]

Paul,

The load share is determined by the respective YM and strain. The actual value of stress will change depending on the wall thickness, for the same pressure and diameter, but all this will do is increase the strain and the actual stress value.

If you set out your equations you should see that the ratio of load is the ratio of YM.

Why don't you post your calculations here?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[PaulLange]

Thank you LittleInch, I realise now why the load sharing remains constant, but stress changes, if the wall thickness / repair thickness changes. I used Excel for the calculations, IF you would like to have a look the Dropbox download link is here:

https://dl.dropboxusercontent.com/u/100220628/Pipe Sleeve Stress Sharing.xlsx

Nothing exiting, it just allows me to determine the stress and strains (less any conservative factors) in a prospective composite repair.