Biphasic flow pipeline û B3!.4 or B31.8? 1

[racp12]

For designing a 16”, carbon steel pipeline, for diluted crude oil transportation, we have found that flow is approximately 50% liquid and 50% gas. We have read both the scopes for ASME B31.4 and B31.8, but we are doubtful about the applicable standard for this case.
We would appreciate very much your opinion about this case.

 

[BigInch]

Read the new version of B31.4 in context of permissible vapor pressure of the fluid mixture in question. If the vapor pressure is high, AND IT IS A TRANSMISSION LINE (AS OPPOSED TO A FLOWLINE - see scope diagrams in each code), you should use B31.8. If the vapor pressure at operating temperature is low, AND IT IS A PIPELINE (not a flowline) then use B31.8. If it is a flowline, no matter what the vapor pressure, then use B31.3

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[BigInch]

There is no limitation in the codes for vapor pressure. I was remembering a client spec as being a code provision. The code does not address the vapor pressure issue, so that would leave it up to the owner's engineer to decide if it is a case of a high vapor pressure liquid or a gas. I'd say, when in doubt, use B31.8



"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[zdas04]

You didn't say what your 50% represented. Is it volume at actual conditions, volume at standard conditions, or mass?. Just for grins let's say it was mass--you absolutely have a gas line with some liquid and it is B31.8. If it is volume at standard conditions, try again the number is meaningless. If it is volume at flowing conditions I'd still tend to go with B31.8 but it is a near thing.

I tend to draw then line at whether there is more than about 30% of the mass in the line in the gaseous state (which would work out to over 80% gas by volume depending on pressure) then I'm going to prefer a gas standard. Less than 5% gas by mass I'm going to be looking at a liquid standard. In between I'm going to be looking really hard at the kinds of equipment that are going to get installed (a mechanical separator would push me towards 31.8, a heater-treater would push me the other way)

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.