Minimum thickness

Above is applicable for small bore piping.

Hi Sachin,

Are you referring to the transition point where the change of code from ASME B 31.3 to ASME 31.4/8 happens?

Cheers,

Ash Bandy

to compensate the increase in pressure (since pipe size is reducing)

That statement/logic is not true. The pressure in the branch-line will see a maximum pressure of what is in the main line under dead-head conditions. The pressure in the branch will decrease with increasing flowrate through it.

Please refer to Bernoulli's equation. For example - if you have a single line with flow through it and reduce the diameter of the line, the velocity must increase (to maintain conservation of mass) and according to Bernoulli's equation - the pressure decreases.

I suspect the reasoning is to ensure that the small branch lines have adequate strength for moment loads of valves, enough strength to resist abuse/impact, rough handling by operators, to ensure adequate wall thickness if the branches are threaded or to provide extra corrosion allowance due to turbulence at the connection.

I think you hit the nail on the head and you get my GA for your answer. I have many times used a Sch. 160 branch to the first valve to compensate for extra wear as well as to strengthen the branch pipe to help if the main line hammers such as in paper mills on blow line piping coming from digesters as well as on condensate pipe.

We want to know first what are the factors which the thickness of the pipe is depend on?? t=P*D/2S

1- The design pressure P in the pipe. (which will be constant in the branch as approximately) ; so it will be constant and will not affect on pipe thickness

2- The pipe diameter D (which will cause a decrease in pipe thickness as it will be smaller than main branch) as it acts in inverse proportion.

3-Allowable stress of pipe material .

So by the way we see from that "Most of the Piping Specs says that Minimum thickness of Branch coming from/to the header or equipment up to first " is right as in case of same material we will see that the P mainly will decrease in little value but will not increase and size of branch will comoing smaller so its better for more easy spec witout getting into calculations to get the same schedule of pipe