Suction oil in umbilical??

[Lotfalipour]

Hello dears
at a ROV after changing the Umbilical,we encounter the leakage in it,that is the normal issue.but after 2 weeks we still have this problem on and on.by now about 20 litres of oil has been sucked by umbilical.meanwhile we sealed the head of the umbilical in the oily JB.so what is the clue for this issue
Thank you.

[Rons_ROV_Links]

On the ROV the umbilical ends in a jb which is connected to a compensator.
The deeper you go the more oil from this compensator will go into the umbilical for depth compensation of this umbilical.

There can be 2 causes:

1. Normally the internal pressure (or pre-pressure) of a compensator is appr. 0.5bar higher than the outside pressure. If the pre-pressure is too high it might ‘pump’ to much oil into the umbilical causing an oily rotary jb. This happen especially in combination with point 2.

2. The umbilical is about the same length as the working depth.

[Ray Shields]

Saeed,

as Ron says, it is normal for some oil to be forced up the umbilical following a retermination. Normally you will lose oil for the first few dives until the amount of oil in the umbilical settles out. Remember that the oil inside your junction box is equal to the outside water pressure (plus the pressure of the compensator). So this oil pressure is forced inside any tiny gap (including the metal tube around the fibres if you have this type) of your umbilical until the gaps fill up and the oil stops going up the cable.

If you normally work in, say, 200 metres of water and then move to diving in 1500m of water, the oil will be forced up more of the umbilical for the first few dives until it stops.

What depth of water are you working in? 20 litres seems a lot of oil just to go up the umbilical.

Also, normally what happens is that when you go down really deep, the compensator and pressure forces the oil up the umbilical, when you come back to deck, your compensator is low. But after some time on deck some of the oil usually returns to the compensator. If the compensator is remaining flat after this time, you may actually be losing oil from a leak rather than just up the umbilical.

Are you able to use a camera to look at the compensator as you dive? If so you may be able to see if the compensator is going flat as you dive down and see if it stops losing oil once you are at depth.

[Michael Parkinson]

Hi,

Recently experienced a similar problem with a Mohican in Angola. The water depth was 700 to 800m. Oil was being ‘lost’ from the TMS main comps. Visually checked with the ROV at depth extensively but no leaks could be seen. The oil loss was up the main lift but this stabilised after about 10 dives. Subsequently discovered that the system had never been deeper than 100m previously so this was the cause i.e. ambient pressure of circa 70 to 80 Bar forcing the oil up the main umbilical.

The 20l loss seems a bit high for this type of phenomenon however, you probably have a leak somewhere.

Best of luck

[Sit Rep]

Just a thought…
Oil losses would also depend on umbilical jacket type i.e. single or double, whether both jackets penetrate JB and if there is any damage to the jacket(s) external to the JB i.e. oil forced in at JB and spewed out 20m up at a tear?

Cheers

[luckyjim37]

That is definately and excessive amount of oil to be losing up the umbilical. We have worked our system down at 3000m almost straight out of the factory and have lost nowhere near that amount up the cable. That is with the FIMT fibre system.

I would be looking for a problem there either a tear in the jacket or overpressure on the comp.

Try checking the specs of the vehicle comps against what you actually have. Is it the same type of umbilical as the old one. Possibly worth checking with the manufacturer to see if this is a common thing with the type of system you have.

[Gordon Duncan]

Saeedسلام ,

When you reterm there will be for the first two three dives oil leaking up the tether and the tether will get fully saturated with oil. The only reason on the system you are using is a hole even as small as a pin hole is causing the leak. I take it you are still diving at a depth of 850 mtrs? Slowly real off the ether from the drum and closly inspect for cuts or oil leaks, but rub your hand over the tether to check it.

Also check the main penitrator with unbilical on the JB with the neoprene gland it should also have a plastic washer make sure this has been fitted when the reterm was done, if it is not it would leak every time on every dive.

گوردون دانکن استاد راهنما ROV
😀 امیدواریم که شما تا به حال سال جدید خوب

[Adriaan Grobler]

This system has since been taken off the installation, so I don’t know if Saeed will ever see them again.
I agree with you guys, oil will be lost after the first few dives, even more at 700m. I just wish that Saeed talked to the experienced guys when this happened. FFS, we were around.

[Adriaan Grobler]

Sorry, let me correct myself.
Especially at 700m

[Scott Beveridge]

Hello dears
at a ROV after changing the Umbilical,we encounter the leakage in it,that is the normal issue.but after 2 weeks we still have this problem on and on.by now about 20 litres of oil has been sucked by umbilical.meanwhile we sealed the head of the umbilical in the oily JB.so what is the clue for this issue
Thank you.

Of course you do mean that oil has "transgressed" up the tether. Sounds like you have a leak somewhere though.

[Sit Rep]

Don’t know Scot, sucked in and spewed out may not be the correct technical expression but they add an appealing (appalling) alliterative ambience.

Well at least to this Ocker anyhow 😉

[Author]

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