12 replies to this topic

[hades_lear]

Hi!

I am working on a document where the different allowable velocities of steam and water are fixed depending on pipe diamater and nature of the process. For instance, it is known that is possible to use higher velocities in bigger pipes than in smallers as well as it is not the same design velocity in a process where a steam is involved or other process where you have, for explame a PSV which is used for condensate water.

I would like to get some advice about which standard or books are being used by process engineers in order to make a proper design of those systems,

Thanks in advance,

[breizh]

let you try the search function in this forum and you will get answer.
Breizh

[shin29]

For liquid lines pipe sizing , what litrature should i use 

[Raj Mehta]

The materials for Velocity Guidelines are shared by Mr. Ankur & Mr. Kkala at the following forum, have a look at it.  

 

http://www.cheresour...ing/#entry42693

 

Moreover, as a process engineer, velocity is selected in such a way that it should not erode the surface of the pipe at high velocities (thus increasing the pressure drop across line) and nor the velocity should be too low. It is always optimized keeping the pressure drop in mind. 

 

Dependent  parameters:

1. fluid type

2. line size

3. Pipe MOC.

4. Viscosity.

5. Process requirement downstream. 

 

Thanks. 

Edited by Raj Mehta, 14 March 2013 - 01:08 AM.

[Ajay S. Satpute]

Hi,

 

Try this link. It might help you.

http://www.cheresour...velocity-check/

 

Regards.

 

Ajay

[shin29]

Dear Ajay and Raj thanks for your valuable support .

what i want to know is what are reason ( that could be felt ) behind all recomendation to limit flow in line 

I mean what happen if more velocity in line say errosion , how can it be theroitically realised.

Regards

[Raj Mehta]

I did not understand. Can you elaborate a please as to what you want to know ?

 

Thanks

[Ajay S. Satpute]

Hi,

 

Please refer chapter 7, 8 & 12 of the attachment. This may provide some basis for selecting a particular velocity, which shall minimize the erosion wear.

 

However, I would be more inclined to go by the company or international standards for selecting the velocity criteria.

 

 

 

Regards.

 

Ajay

 

Attached Files

•  rp-o501_2007-111.pdf   1.13MB   238 downloads

[shin29]

dear raj ,
I have been reading in standards that we should keep below 10 m/s velocity in liquid line now  i am reviewing , designer  has gone to a velocity of 20m/sec for a very small section of pipeline ( see attached file for explanation) .
I want to  know  what are the after effect with theoretical  realization i.e standards and formulas . i want to supporting work for my argument.

 

 

 

 

Regards

Sahil

Attached Files

•  line section.xlsx   10.9KB   97 downloads

[Raj Mehta]

I highly doubt shin

 

I have not come across such high velocity in a line and as far as effects are concerned of such high velocity, it will definitely erode your pipe in a very short time leading to leakage. Also the pressure drop in a line varies as square of velocity. So for such high velocity, you will have tremendous pressure drop. 

 

Hope it helps.

 

Thanks

[Steve Hall]

I believe that the pipeline velocity "rules of thumb" are based largely on experience with different materials. For non-abrasive liquids that can withstand any amount of turbulence, I think you'll find that the recommended velocity ranges are similar to each other.

 

What factors result in settling on a particular velocity range? Cost! As indirectly pointed out in this thread, velocity has an impact on the life cycle cost of the installation because velocity affects: pipe diameter, pipe weight (bigger diameter = higher weight = higher cost for foundations and supports), pressure drop (higher pressure drop = higher pumping cost), valve size, etc. Sure, there are operability factors including water hammer being greater with higher velocity, but it really comes down to the overall cost equation.

 

Since some fluids require alloy or non-metallic piping systems, the cost analysis differs from one fluid to the next and therefore the recommended velocity range may differ.

 

Similarly, if a fluid is erosive or corrosive, velocity probably plays a significant role in determining the life of the pipe. This experience is factored into the recommendations. But it still really comes down to cost.

 

So the cost factors considered include:

- capital cost for piping, components, insulation, and prime movers

- installation costs

- replacement costs and frequency

- operating costs including labor, power, and maintenance

- cost for downtime when maintenance or replacement are needed

 

Steam and gas piping velocity recommendations are similarly grounded in experience, but again the experience is shaped by life cycle cost.

 

Two important takeaways, if you agree with my argument:

1) Cost factors can change over time and in different geographies, and so do velocity recommendations. If you construct a Pie Chart with segments for the various cost factors (net present value over the project lifespan), you'll find that the relative importance of the factors changes with the labor market, cost of transportation, energy  cost, etc. Therefore, the published recommendations are only a guideline. This brings me to the second takeaway,

2) It's not at all unusual for small sections of an installation to deviate widely from the recommended values. As long as the hydraulics work, go ahead and double the velocity in that 20 ft long branch line if that's what seems to make sense.

 

Additional possible process reasons for limiting size (higher velocity):

- maintain turbulent flow regime

 

Additional possible process reasons for increasing size (lower velocity):

- maintain laminar flow regime

- decrease pressure drop

- decrease noise

- decrease erosion

- decrease corrosion

- flexibility to accommodate future capacity increase

[Raj Mehta]

Hi!

I am working on a document where the different allowable velocities of steam and water are fixed depending on pipe diamater and nature of the process. For instance, it is known that is possible to use higher velocities in bigger pipes than in smallers as well as it is not the same design velocity in a process where a steam is involved or other process where you have, for explame a PSV which is used for condensate water.

I would like to get some advice about which standard or books are being used by process engineers in order to make a proper design of those systems,

Thanks in advance,

 

 

HI can you please give the reference for your statement " it is known that is possible to use higher velocities in bigger pipes than in smallers as well as it is not the same design velocity in a process where a steam is involved " I am unable to understand this point of yours.

 

If you keep the flow constant, increasing the pipe diameter would lead to decrease in velocity and not increase. ( from the continuity equation) 

 

Thanks

[shan]

Here, we size lines per criteria set by API 14E "Recommended Practice for Design and Installation of Offshore Products Platform Piping Systems"