Crude Oil Offloading Rate of VLCC's? 1

[mylexicon]

Can someone confirm or corrcet the numbers that I have for Offloading rate of VLCC type ships? According to my sources which are questionable, VLCC's pump heavy crude at 9000 cubic meters/hr at 12-15 barg. Does this sound right? Do different VLCC tankers have different pumping capacities?

At this rate and pressure, we'll end up with a 48" NPS pipeline stretching 4 km at subsea & 8 km onshore before reaching the Storage Tank area.

By the way the Oil is first offloaded from the ship to a CALM Buoy unit then down through flexible hoses to the subsea pipeline.

Your input is appreciated

regards,

drno

 

[BigInch]

I'd say you're very close. Most are around 6000 to 10000 m3/hr ANSI#150 CLASS, with 2 x 16" or 18" lines on the CALM turrent? Don't forget the PLEM.

Or especially don't forget to do the transient flow analysis. I was loading a ship when a storm blew the tanker off the CALM and it was ESD button time. I saw a our pipeline terminal go from 30 to 117 barg, (17% over allowable pressure). True we were loading 500,000 bopd, not unloading. Well, just keep it in mind.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[mylexicon]

Thanks BigInch. I feel a little more at ease now, because I had based our pipe size calcs on these numbers.
Like you said, in my case we're offloading from the SPM/PLEM to the shore and I will certainly look into ESD cases downstream of the PLEM. We'll probably end up with a surge tank at the PLEM. I am really concerned about the floating hoses and submarine hoses upstream of the PLEM. I am pretty sure the VLCC tankers have some sort of relief or surge system to protect their pumps. If you have any tips on this topic, I'll certainly welcome them.
much obliged,

drno

 

[BigInch]

A surge tank at the PLEM is going to be difficult (offshore construction and all) and I don't know if ships have relief systems on their unloading system. I would think that they do, since they have pleanty of tank, all they would need is a RV and return line, but I really don't know. That's a good point to try to find the answer to. What I would do, [COLOR=yellow green]rather than considering an offshore tank, is design the 48" for a full flow shutdown surge pressure.[/color] Buying the extra pipe wall thickness would probably be cheaper than an offshore tank, and a whole lot safer. And BTW, I agree the 48" is the best diameter for your flow and lengths.

The ships I was loadingat the time (20 yrs ago) did have shut-down systems on their receiving lines. Once one activated her ESD by mistake and when I heard our pipes slamming around and noticed our pressures rising, I shut our station down too. All our piping and hoses survived, but the ship's piping did not. They broke one flange. In the morning we went out to see what went on during the night and there was oil all over the deck and running off the sides into the bay. Coinciently, our relief tank was being serviced that same day. Someone installed the vacuum breaker upside down and the top "corner" had been sucked in at one spot a week before. Construction had spent 3 days cleaning the tank to make repairs the next day and the last thing they said before they left for the day was, "Try not to use the relief tank tonight". Oops!

Going the Big Inch!

http://virtualpipeline.spaces.msn.com