Offshore Gas Release 1

[AreJay]

Hi guys,

Some help is required regarding a gas leak rate calculation. We had a gas release through a eqivilant hole diameter of 1mm. The release was from our export pipe which was pressured at 142bar and was being released to atmosphere. This lasted for a duration of ten minutes. I am comfertable doing this calculation and dont need any help.

What I do need help with is that when we started to depressurise the line we dropped the pressure from 142bar down to 38bar with the leak continuous. This was over a period of 1 hour. When the pressure went below 38bar the leak stopped so we think it is a passing seal. When calculating the leak rate for the hour with decreasing pressure, how is it done? Do I do the same calculation as with above and just extend the duration? Do I take the pressure drop over the time period and calcualte from there?

Thanks in advance

R

 

[MortenA]

What is the aim of the calculation? I guess that its release rate. Then:

If you have a continious pressure measurement and a temperature measurement logged then you can just calculate the density in the gas phase multiply with the trapped volume and use that to calculate the release rate for each time step in the temperature log.

In all cases you would need the gas temperature - even if you wanted to calculate the release rate based on upstream conditions and a hole size. But "my" methode seems a lot easier if you have the data.

Best regards

Morten

 

[MortenA]

and i meant "each time step in the data log" not "..temperature" log. Use an excel sheet and import the data here. I dont know the format of your data, but very frequently the control system stores a value with a time stamp - and if your lucky its the same timestamp for the two instruments.

If you know the density at time n and time n+1 then the total loss from timestep n to timestep n+1 is dRho*total vlume - and then you could assume a steady release rate for each time step - if they are not too long compared to the release rate.

Best regards

Morten

 

[AreJay]

Thanks for the help Morton. I do have the temperature of the gas and using assumptions I can work out the release mass.

R

 

[dcasto]

http://www.eng-tips.com/viewthread.cfm?qid=219324&page=4

this thread has the equation in english units