Maximum Allowable Pressure Drop

[ivegotgas]

I'm designing a new piping system for a client, They have an inhouse specification that indicates that the maximum allowable pressure drop in a pipe carying dry fuel gas is 11.5kPa/100m.

The majority of the piping system meets this requirement howeve there are short sections of pipe near the end of the run that exceed this spec ( 20-70kPa/100m) however for short runs of less than 3m each) The system has the excess pressure to spare, and this is a brown field installation, meaning I would like to salvage as much pipe as possible, and operating these short spans of pipe will save me in the neighbourhood of $50-80k

I am looking for any Industry standard documentation that may suggest the implications of running with a higher pressure drop, or perhaps a standard that indicates a suggested pressure drop. (Something similar to API 14e perhaps.)

Any help would be appreciated.

 

[BigInch]

I don't think you're going to find one.

Implications would be increased erosion of the pipe wall, but with relatively clean fuel gas, I wouldn't worry about it too much. Your clinet however may have other feelings.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[dcasto]

pressure drop specifications are economic based. Physical limits are velocities that would be to high and would damage the pipe via errosion. velocities under 100 ft/sec should be ok for dry gas. API RP14E should address this standard in more detail.

 

[BigInch]

Admitedly a long time since I've looked at 14E, but I find it hard to believe it would suggest a limit of 100 fps for clean fuel gas, would it?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[zdas04]

dP/length numbers are absolutely economics based. When these values were being established (in the 50's and 60's), the important consideration was that any pressure drop must be made back up with compression.

For short lengths, the dP that has to be made up is trivial (i.e. 70 kPa/100m over 2m is 1.4 kPa or .2 psi). If the velocities in the short sections are within guidelines I would ignore the dP/length spec on short segments.

By the way, the only place you will ever see a dP/length spec is in company rules/guidelines/bid packages. No government or quasi-government (like ASME or API) would ever assume the liability of telling you that if you design pipe for 11.5 kPa/100m it will never fail from dP or velocity related events.

David