Question

In the design of pipeline the usual practice is to assume that due to aging of pipelines:

1. The effective roughness increases linearly with time.

2. The friction factor increases linearly with time

3. The flow through the pipe becomes linearly lesser with time.

Which of the above statements is/are correct?
1. 1, 2 and 3 
2. 3 only
3. 2 only 
4. 1 only 

Answer 1

Correct Answer - Option 4 : 1 only 

As the time progress, pipe surface becomes more and more rough as more and more sediments in pipe are getting deposited, due to this following happens:

1. Roughness increases with time. It is assumed to be linearly.

During pipeline design, the effective roughness (k) is the linear function of time which is given by:

K = k₀ + αt ;

Where K₀ is initial effective roughness i.e. pipe roughness during beginning of flow in pipe and

α is constant.

2. Cross-sectional areas of flow reduce which proportionally increase the velocity of flow in such a way that discharge remains constant.

3. Friction factor is non-linear function of time for rough pipe.

For rough pipe, the relation between f, k, D of pipe is based on Nikursade’s experiment and it is given by:

\(\frac{1}{{\sqrt f }} = 2{\log _{10}}\left( {\frac{D}{{2K}}} \right) + 1.74\)

Now, if we substitute, K = k₀ + αt ; in above equation, we get non-linear function of time.