Friction coefficient between pipe saddle and steel rod underneath

[prabir]

Hi Everybody,
I am doing stress analysis of a 30" size pump discharge line having pressure of 1700 psi and temperature 200 deg. F.Forces on pump nozzle is coming very high.If I use steel rod under the pipe saddles assuming coefficient of friction 0.01 then the forces at nozzle are within allowable limit.
My question is whether my assumption of 0.01 friction coefficient is correct? Thanks

 

[JohnBreen]

Hello,

This is a frequently asked question.

You should search this board for the many opinions posted in previous threads.

Another question you should ask, since your pressure is so high and your diameter to thickness ratio is so big, is how much the pressure will affect your flexibility. Also, how much will Bourdon effect cause your bends to "open up". These things will all affect nozzle loadings.

Sorry - no answers from me just more questions.

Regards, John.

 

[01101998]

Hi Prabir,

have you considered using moment restraining supports in case your moments are high.
I have heard of another phenomenon for large dia pipes where the pipe deflection in axial direction can be more at the top fibres then at the bottom supported portion. have you considered this. Any advice on this from Mr. Breen.?

 

[prabir]

Thanks John and Friend,
Sorry, I did not indicate pipe thickness.It is 1.4 inch for
30" dia pipe.Hence pressure has little effect on flexibility.Moments are also within limit specified by pump vendor.Someone told me that 0.01 mu is very low.I am not convinced.What is your opinion.Thanks

 

[DSB123]

Hi prabir,
As you say a mu of 0.01 is very low especially when you consider that polished stainless steel to PTFE is normally anywhere between 0.05 and 0.2 dependant upon pressure between. By introducing a rod into the support all this does is reduce the chances of the two surfaces "welding" themselves together due to corrosion. I would say the friction factor should be taken as between 0.2 to 0.4 dependant upon how conservative you want to be. I normally take 0.4 for steel to steel to account for degradation of the surfaces. Also a rod between the surfaces introduces another problem. Dependant upon the relative hardness of the rod and saddle the softer will deform due to the high contact stresses. This could cause higher initial friction factors.