Lightning Protection on an offshore production platform

[David Loren Smith]

Many offshore platforms are "fixed" to the earth by use of pilings driven to refusal and then welded to the topside structure. We typically ground every electrical devise to structure steel. I have 42 years experience in this field mainly in the GOM. My company is being asked to provide either lightning arrays for critical areas which "eliminate" the lightning strike. Or, going to lighting protection at each critical circuit. Their are thousands of critical circuits, and their are many platforms operating that do not have either of these systems installed. What do the experts say about effective lightning protection of a structure that is "pinned to the earth" in seawater? Any help would certainly be appreciated.

 

[petersonra]

Many offshore platforms are "fixed" to the earth by use of pilings driven to refusal and then welded to the topside structure. We typically ground every electrical devise to structure steel. I have 42 years experience in this field mainly in the GOM. My company is being asked to provide either lightning arrays for critical areas which "eliminate" the lightning strike. Or, going to lighting protection at each critical circuit. Their are thousands of critical circuits, and their are many platforms operating that do not have either of these systems installed. What do the experts say about effective lightning protection of a structure that is "pinned to the earth" in seawater? Any help would certainly be appreciated.

First off, you cannot eliminate lightning nor eliminate the risk from lightning. You can reduce the risk from a strike. That is all you can do.

I would suggest that someone asking that you "eliminate" the lightning strike just does not understand the problem.

Personally, I am not convinced that the practice of bonding everything on an oil platform to the structure does all that much good, but it is a long time practice on oil rigs.

It might make sense to ask the person who is making this request for some additional information on just what it is they he really wants. He may have read a misleading article somewhere that gave him a bad idea.

 

[mgookin]

Many offshore platforms are "fixed" to the earth by use of pilings driven to refusal and then welded to the topside structure. We typically ground every electrical devise to structure steel. I have 42 years experience in this field mainly in the GOM. My company is being asked to provide either lightning arrays for critical areas which "eliminate" the lightning strike. Or, going to lighting protection at each critical circuit. Their are thousands of critical circuits, and their are many platforms operating that do not have either of these systems installed. What do the experts say about effective lightning protection of a structure that is "pinned to the earth" in seawater? Any help would certainly be appreciated.

Hi David: I'm across the Gulf from you in the lightning capital of the country - Ft Myers on the edge of the Everglades. We know lots about lighting.

There are line side strikes & there are load side strikes.

You can do an array of copper spikes.
You can do line side clamping.
You can do load side clamping.

There are some really heavy duty MOV's on the market and they're very cheap. If the majority of your critical devices are instruments & computers, your solutions could be this easy. For our 3-phase protection at our plant, we paid around $800 each for the equipment. If you give your BOM to a factory applications engineer at any of these companies, they can price out the equipment quick.

Whatever system(s) you come up with, it will need periodic maintenance. The spikes blow off and the MOV's expand and are less effective on subsequent strikes.

Assuming you're in international waters, what standards do you use? NFPA 70? Are you restricted to Listed assemblies? Seems you could wire a MOV into a circuit really easy (read that cheaply) if you can get away with it. Not sure what the EC's & Inspectors on here would say about that though.

 

[petersonra]

There are some really heavy duty MOV's on the market and they're very cheap. If the majority of your critical devices are instruments & computers, your solutions could be this easy. For our 3-phase protection at our plant, we paid around $800 each for the equipment. If you give your BOM to a factory applications engineer at any of these companies, they can price out the equipment quick.

$800 is not cheap where I come from.

Bussmann makes a very nice 3 phase SPD that is < $200. Not listed though. The listed versions are all very expensive for some reason.

 

[mgookin]

$800 is not cheap where I come from.

...

$800 is cheap if you own and operate oil platforms. That's about 1 minute of downtime.

 

[weressl]

Many offshore platforms are "fixed" to the earth by use of pilings driven to refusal and then welded to the topside structure. We typically ground every electrical devise to structure steel. I have 42 years experience in this field mainly in the GOM. My company is being asked to provide either lightning arrays for critical areas which "eliminate" the lightning strike. Or, going to lighting protection at each critical circuit. Their are thousands of critical circuits, and their are many platforms operating that do not have either of these systems installed. What do the experts say about effective lightning protection of a structure that is "pinned to the earth" in seawater? Any help would certainly be appreciated.

What is the objective? Each may require different solution.

1. Protect the equipment form being damaged?
2. Protect operational continuity from false tripping due to lighitning strikes causing false signals?

 

[David Loren Smith]

Thanks to all, a little more information

Thanks to all, a little more information

The platform was hit by three lightning strikes during the same storm one evening. The main problem area was two of the remote I/O panels which contain the PLC's for both the control and safety system. Several I/O modules were damaged in each system, causing rack communication problems, and of course loss of the I/O. These enclosures are 316 stainless steel bolted and threaded to structural steel. They have a bonded conductor from the enclosure to structural steel. All cleaned and threaded then coated with insulation paint. We also have a isolated instrument ground bar which receives the shields from the analog I/O and we take this to structure some distance away (+10') from the bonded conductor. The shields make up an antenna to shunt any induced voltage or noise to ground so the shields are only grounded at the instrument ground bar. To add MOV's to each I/O point is almost impossible, the panel would have to engineered for the extra space that the MOV's take on the din rail. The lightning arrays seem to be the only option I have, keep in mind each array has its own copper conductor that goes down to the top of jacket area of the platform, keeping the impedance as low as practical. I work 28 & 28 and am on my off time. I appreciate all of your time and look forward to learning more about lightning protection.

 

[weressl]

The platform was hit by three lightning strikes during the same storm one evening. The main problem area was two of the remote I/O panels which contain the PLC's for both the control and safety system. Several I/O modules were damaged in each system, causing rack communication problems, and of course loss of the I/O. These enclosures are 316 stainless steel bolted and threaded to structural steel. They have a bonded conductor from the enclosure to structural steel. All cleaned and threaded then coated with insulation paint. We also have a isolated instrument ground bar which receives the shields from the analog I/O and we take this to structure some distance away (+10') from the bonded conductor. The shields make up an antenna to shunt any induced voltage or noise to ground so the shields are only grounded at the instrument ground bar. To add MOV's to each I/O point is almost impossible, the panel would have to engineered for the extra space that the MOV's take on the din rail. The lightning arrays seem to be the only option I have, keep in mind each array has its own copper conductor that goes down to the top of jacket area of the platform, keeping the impedance as low as practical. I work 28 & 28 and am on my off time. I appreciate all of your time and look forward to learning more about lightning protection.

So contrary to the accepted and conventional wisdom of the majority of the technical community we indeed developed the Lighting Eliminators DAS System at a large installation the Gulf Coast, onshore. The installation is in place for over 7 years and the plant since has not experienced shutdown due to erroneous signals generated by lighting strikes, whereas before the frequency was1-3 per year. The Waissala strike analysis indicated the same isoceuranic index as the previous five years, actually slightly increased.

So while I totaly agree thet the science behind HOW this system works is controversial and unproven, the empirical evidence proves that it indeed prevented the formation of lighting strikes in the applied area.

We went through the loop protection alternative for over 3000 loops, and it really did not make sense since the loss of a single device is miniscule compared to the production loss. The reconfiguration of the entire control system, especially high speed compressor control packages with SIL-3 levels, to analyze rate-of-rise, or any other methods to validate the magnitude of the signal change would have been another nearly impossible task.

 

[petersonra]

So contrary to the accepted and conventional wisdom of the majority of the technical community we indeed developed the Lighting Eliminators DAS System at a large installation the Gulf Coast, onshore. The installation is in place for over 7 years and the plant since has not experienced shutdown due to erroneous signals generated by lighting strikes, whereas before the frequency was1-3 per year. The Waissala strike analysis indicated the same isoceuranic index as the previous five years, actually slightly increased.

So while I totaly agree thet the science behind HOW this system works is controversial and unproven, the empirical evidence proves that it indeed prevented the formation of lighting strikes in the applied area.

On the other hand, there are many, many thousands of installations that have not had significant issues with lightning strikes causing problems that took no special precautions. Does that prove that taking no special precautions is the answer? The problem with empirical evidence is that it is basically an uncontrolled experiment with data collected in unscientific ways.

We had a customer that experienced a bunch of unexplained PLC issues that they were convinced was some kind of power problem. After many tens of thousands of dollars worth of "better" grounds, UPS, and other solutions were implemented, the real answer was probably found when the firmware was updated on the PLCs. The FW was updated for other reasons, but coincidentally, the frequency of these issues dropped off dramatically. My guess is that most of the people involved still think the "better" grounds solved the problem.

 

[weressl]

On the other hand, there are many, many thousands of installations that have not had significant issues with lightning strikes causing problems that took no special precautions. Does that prove that taking no special precautions is the answer? The problem with empirical evidence is that it is basically an uncontrolled experiment with data collected in unscientific ways.

We did NOT take 'special' precautions during initial installation, besides equipping the entire facility with conventional 780 protection. We did not have problems with lightning destroying electronics, we had problems with lightning inducing erroneous signals and shutting down the plant even with 2o3 configuration.

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