×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

(OP)
The system:
This is at one of the oil producing offshore Well Head Towers (WHT). The electrical power to this WHT is supplied through 6.6kV submarine cable. The cable is terminated in an Ex 'e' junction box installed above the boat landing level. The system is energized about an year ago.
This is an unmanned tower. The junction box has hinged door, bolted while fully closed.

Incident:
Recently, during the visit to the WHT the junction box door was found ruptured and left hanging on the junction box (JB). However there is no charred marks inside the JB. The connections are found intact.

The 6.6kV connection is not covered with insulation boot. Now there is an argument that there could be some ionization inside the box due to the exposed 6.6kV terminal thus releasing the hydrogen. The accumulated hydrogen must have resulted in an explosion, thus rupturing the JB door.

There is another school of thought which argues that there could be some chemical reaction inside the cable insulation thus generating the hydrogen and which must have reached and accumulated in the JB cavity.

Now the question:
Does anyone has such experience of hydrogen gas generation and accumulation in the cavities in the oil producing towers?

If you can share your experience, it would be very helpful to me.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Throw this into your mystery soup:

If saltwater is electrolyzed it produces chlorine. If chlorine evolves in the dark it is highly unstable and will detonate with any introduction of light.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

(OP)
Keith,

In fact I am trying to solve the mystery. If you are familiar with the oil and gas facilities, you will appreciate the gravity of the such incidents. It has a large hidden consequences.

The WHT is unmanned. When the mechanical maintenance crew visited the site, they have noticed that the cover is hanging in one bolt. The 6.6kV live terminal is exposed to the hazardous environment.

The JB has no visible mark of burns, hence people suspect that it h=could be the explosion of trapped hydrogen gas inside the JB.

For your argument of chlorine release:
The salt would help the solution to conduct. During the electrolysis process, I understand that the Oxygen and Hydrogen will be released. Not the chlorine.

Now please throw some light.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Any chance of photos?

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Hi krisys. Not hydrogen and oxygen when electrolyzing salt water but chlorine and hydrogen. The chlorine could provide the ignition.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

How tight was the box? Smaller "Explosion proof" fittings usually have vents and drains.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

It's an Ex 'e' box - it's weatherproof, probably to IP56 / IP66. Very different to a flameproof (Ex 'd') design which is loosely equivalent to explosion-proof in the US.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

My chart just describes EX e as increased safety, it doesn't really describe the construction. is it waterproof like a NEMA 4 or not like an EX d without a gasket.

I assume some sort of explosive gas built up and was ignited by a spark to blow the lid off.
Presumably the environment outside the box is not explosive so it must have been generated internally, perhaps inside the cable, is there a gas seal at the box?

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Cant you just run a gas spectrum analysis on a swipe of the dust or the contained air in the junction box?
Maybe enclose it again for a predetermined amount of time maybe using a plastic bag to isolate the box, since you dont know the reason for the box explosion.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

From the standard:

4.9 Degrees of protection provided by enclosures
4.9.1 The degrees of protection as defined in IEC 60034-5 and IEC 60529 shall be as
prescribed in a) or b), unless otherwise specified in 4.9.2, 4.9.3, or Clause 5.
a) Enclosures containing bare conductive live parts shall provide at least the degree of
protection IP54.
b) Enclosures containing only insulated conductive live parts as in 4.5 shall provide at least
the degree of protection IP44.
4.9.2 The enclosure of an electrical apparatus may be provided with drain holes or
ventilation openings to prevent the accumulation of condensation. The requirements are
dependent upon the apparatus grouping as follows.
a) Apparatus group I – compliance with 4.9.1 is required.
b) Apparatus group II – the inclusion of the drain holes or ventilation openings may reduce
the degree of protection provided by the enclosure according to 4.9.1 , but shall not be
below IP44 in item a) of 4.9.1 or IP44 in item b) of 4.9.1.
When the presence of drain holes or ventilation openings reduces the degree of protection
below the requirements of 4.9.1, the details of the drain holes or ventilation openings,
including position and dimensions, shall be stated by the manufacturer and included in the
descriptive documents according to IEC 60079-0. The marking of apparatus with drain holes
and ventilation openings that reduce the degree of protection shall include the symbol "X" in
accordance with item i) of 29.2 of IEC 60079-0 and the reduced degree(s) of protection
provided by enclosure shall be shown on the certificate.

Most Ex 'e' enclosures exceed the minimum IP54 requirement, as I noted earlier. They generally don't look much different to a good-quality outdoor-grade enclosure.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Are there any bulges in the sides or back?
Is the core of the cable filled>
If the door is big enough you don't need much pressure to blow it off. Water in the cable and a high load ( for what ever reason) could generate enough "steam" pressure to push a door off.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Steam - good point. Was there a significant change in load prior to this event?

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

(OP)
I thank for the overwhelming responses.

The JB is IP66, manufactured as per IEC. The installation is in the tropical region offshore where the relative humidity is almost 99%.

I have attached a typical photo for the understanding.

There is not a considerable bulges on the sides and back.
There is a breather for the JB.

It is stainless steel with corrosion-proof paining.

David,
The cable size is 3 core 240 sq mm and the load current is about 20A. So there is no question of the termination/connection heating up in this case. The cable connection is still intact and no charred mark. Only the door got ruptured.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Is the drain in good shape?
I've boiled away several thousand gallons of salt water doing loading to ensure that the piston rings were well seated in new diesel generators.
Never got a whiff of chlorine, but lots of steam.
It is almost impossible to keep an electrical junction box dry in outside, humid conditions without a drain.
If the drain was plugged you may have had a steam pressure event.
Depending on several factors it is a possibility.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Where are the other end of the cables terminated? Is there any possibility of gas propagation down the cable? Should one of the remote ends be fitted with a barrier gland?

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Keith Cress
kcress - http://www.flaminsystems.com

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

(OP)
Other end of the cable is connected to another similar WHT from where the feeder is coming to this WHT.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

That box is EX e, you can't be serious

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

roydm,

Why?

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

I would bet on gas evolution or propagation through the cable.
I doubt that there was a real explosion (with combustibles) but rather 'just' over pressure event.
There is obviously no vent on this, or not a functional one.
Venting these is very problematic. Every day as the box heats the air expands and vents. At night it cools and sucks in humid, salty air which then condenses inside the box. The next day the process repeats. I have seen the insides of 'sealed' boxes heavily corroded by this process.
And then with corrosion more heat is generated, and steam, and then all sorts of things go wrong.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Cable insulation breaking down into an explosive level of any volatile gas would be a problem so huge that it would have stymied the development of the entire oil and gas industry. Yes, under the right circumstances the plastics in the insulation can be broken down during a Partial Discharge (PD) event, but generally that occurs more easily in gas /air filled electrical environments. Cable insulation is designed at 50-100 times the dielectric of even the worst gasses, making PD in cables require an extremely higher voltage before it occurs. So, what could cause that here, lightning? But how could that take place without leaving visible evidence, like charring? In my opinion, that’s highly unlikely.

Much MORE likely to me is a moisture intrusion into the cable installation, resulting in a relatively minor discharge somewhere along a large section of the cable that instantly produced steam pressure that blew out your doors. I’ve seen that with underground utility cables, where over time, moisture seeps in through micro cracks in the outer insulation. Right in front of my house, it blew up and ruptured about a 20ft section of my sidewalk, from 4ft under ground. I watched the utility crew dig it all up and the only place that showed any carbon indication of the fault was a 1/4 inch hole where the initial failure took place. But the jacket was split open for 10 ft in either direction, and the steam pressure release was like a bomb going off under ground, breaking raising the section of 6” thick sidewalk concrete about 10” above grade.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Jraef, Yes, I wasn't talking about breakdown of the insulation, but rather out-gassing (either from mfg chemicals or moisture) or simply allowing gas to pass through the cable.
I have seen both H2S and water in the junction box for a submersible pump, that had traveled up 12,000' of cable from the bottom of the well. Needless to say with H2S we actually just found pieces of the box......

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Water in the interior of a power cable is rare but it happens. Unless the cable is cut and water runs out like it was a garden hose you may never know.
At least two cable manufactures and two utilities have procedures for removing water. They all involve purging the cable with dry air or nitrogen and monitoring the humidity of the outflow.
When water is discovered the search for why and where the water got in the cable starts. I have had to send samples of the water in the cable and the local domestic water to independent labs where is analyzed and compared to water at the cable manufactures etc.
By then it's in the hands of lawyers and people above my pay grade.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Has anyone else in the utility business come across the 'green goo'? Sounds like something similar.

AC magnetic fields in moist environments is what us in the utility world blame this on. Sounds like adding saltwater to the mix isn't going to help.

So if the box is completely weather proof, does that mean it's humidity controlled? If the box is completely sealed and air-tight you wouldn't need ignition to blow the door open, just accumulation.

My money would be on some kind of chemical reaction off gassing in the box due to the environment.

How do you ground the box, or do you ground the box?

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Hi Krisys,

I know of at least two other instances similar to yours on offshore facilities that were attributed to hydrogen. In one of them gas detection was installed post event & confirmed development of flammable gas in the JB. Some attempts were made to confirm which gas but I think inconclusive (It could be argued that that in itself suggests hydrogen, which escapes on the way to the lab).

Hydrogen from corrosion of conductor or (particularly) galvanized armour is a recognised problem for subsea cables and umbilicals (also fibre optics where it darkens the fibre). Permeation of hydrogen dissolved in the seawater is also discussed - I had thought only applicable to deep water but have seen recent references for shallow. Hydrogen-producing bacteria sometimes occur subsea. Hydrogen is very small (especially if dissociated to ions) as those who keep H2 inside generator stators, or specify pressure instruments exposed to process hydrogen, will confirm.

http://www.oedigital.com/subsea/item/269-umbilical...
http://ripr.org/post/case-closed-hydrogen-gas-comb...
http://www.jdrcables.com/case-studies/van-gogh-pro...

marks: green goo is degraded plasticiser. It is not explosive.

John.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Will an alternating electric current flowing through water or moisture produce "Brown's Gas"?
Brown's Gas: (A mixture of oxygen and hydrogen gases in the same proportion as in water?)

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

(OP)
I thank all for your active participation.

Hi aussiejohn2,
Your case appears to be more similar to this case. Can you please throw some more light on this?
I was not able to download the JRD Cables case study. Is it possible to attach the case study?

I remember in my previous assignments, we used to specify and use the lead sheathed cables in the oil and gas facilities. This is specifically important, when the cables are buried where the soil could be contaminated with the petroleum product.
The XLPE and PVC are vulnerable to the chemical attack of petroleum product when installed in the oil and gas facilities.

Please click the Link for more details.

RE: Rupturing of 6.6kV Power Junction Box installed at an offshore oil production Well Head Tower

Hi Krisys,
I could swear I had some notes from a presentation that mentioned one of the incidents, but have looked through my notebooks and not turned anything up. My memory is that it was a small unmanned platform, perhaps similar to yours. But my mental image of the photo of JB was it was small - too small to be tied to an umbilical. I've reached out to some old colleagues and will let you know if anything comes back.
The JRD reference was just to this sentence from the web page: "All electrical cable quads included special low permeation outer jackets to mitigate the impact of hydrogen gas." The issue is well recognised in small corners of the oil and gas industry; i think if you contact any of the umbilical makers they will be able to give you some details (Interestingly the offshore wind industry seems unaware, and i have not heard of any incidents even as they move into deeper water).

Nowadays there is a recognised alternative to lead sheath for oil resistance - plastic sheaths with hdpe for inorganics followed by polyamide for oils. Often there is a metalic water barrier. Lighter and without the environmental (and installer) questions around lead.

Regards
John.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close