EROSIONAL VELOCITY CRITERIA 2

[Monagas]

Hi friends!

What erosional velocity criteria should I use to design a contract (6"x3") if my fluid is Natural Gas?. I know that gas velocity can´t be higher than erosional velocity, but I want to know if there is some criteria about a percent of the erosional velocity.

 

[zdas04]

I use Mach 0.6. Others use Mach 0.3. There are good arguments for either number.

Below those values there just isn't any way for gas alone to cause erosion. Now if your 100 ft/s gas is carrying frac sand then you have another kettle of fish., but just gas at any design velocity that you can afford (pressure drop has to be made up and that is expensive) erosion is just not the problem is is in liquid flow.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[LittleInch]

what are you designing? and BTW most people refer to these as reducers (strangely enough even when they go in flow direction from smaller to bigger), unles sof course you are referring to something else altogether.

"Natural Gas" is rather vague. I agree with zdas04, if it is clean, particle free, liquid free gas then erosion isn't your issue and how you calculate it irrelevant, though there is some debate about the API 14E method with your choice of "c". If it has any of the above in then all bets are off.

a bit more info will get you a bit more of a response.....

My motto: Learn something new every day

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

 

[zacharialamsyah]

You can refer to API RP 14E, RR115 - Erosion in elbows in hydrocarbon production, or DNV-RP-O501: Erosive Wear In Piping Systems

There are different values of erosional velocity to calculate from that references

 

[zdas04]

All of those standards are for liquid flow. None give you reasonable results for a gas that 2-3 orders of magnitude lower fluid density.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[amustha1407]

Hi,

For natural gas,i usually limit the velocity to 20 m/s at the smallest segment. But this is usually to avoid corr inhibitor ineffectiveness instead of errosion.

You may also want to check for flow induced vibration limitation (usually meassured as dynamic pressure, or Density x Velocity^2). Different operating pressure has different dynamic pressure limitation.

 

[zdas04]

Amustha1407,
Just curious what you base that 20 m/s on? Seems like an awfully round number to be physically meaningful, and is about 1/10 the number you would get with the API RP 14E equation. Don't get me wrong, it is in a reasonable range, but as an upper limit it doesn't seem quite rational.

"Corrosion inhibitor ineffectiveness?" Do you have any field data that says that corrosion inhibitor is EVER effective in a gas system? I sure can't find any and I stopped that practice in the pipe I operated in 1992 after it had been running for 2 years. All of the other operators in the field kept pumping it. 10 years later we had the lowest incidence of corrosion of any operator in the field--we replaced the corrosion inhibitor (which cannot be transported by the gas) with rigid pigging schedules (that work very well).

Changes in dynamic pressure are usually insignificant to the calculation below about 0.3 Mach (somewhere around 100 m/s).

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist