Bonding Rail cars for unloading Flammables

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We have been asked to test the resistance of bonding conductor at a railcar unloading facility. The conductor is clamped to the railcar and runs to a central driven ground rod and then runs either to an above ground storage tank or to a mobile tank, depending on what they are unloading to. The purpose is to eliminate any static charges that may develop during unloading. What would be the high allowable limit for the resistance we could see on this conductor?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Re: Bonding Rail cars for unloading Flammables

I don't think it matters much. Reducing static charge does not require low impedance. I have heard numbers on this very website that it can be in the millions of Ohms.
 

charlie

Senior Member
Location
Indianapolis
Re: Bonding Rail cars for unloading Flammables

It is not even required to dissipate the static charge, it is only required to equalize the potential between the vessel being unloaded and the vessel that is being loaded. With that said, I would imagine that the Code that covers this situation requires the static charge to be removed. :D
 

friebel

Senior Member
Location
Pennsville, N.J.
Re: Bonding Rail cars for unloading Flammables

I do not understand the comments that are being made about Static Electricity. For example, one person said it does not matter what the resistance reading in ohms is. That statement is not correct.
An example of grounding rail cars for unloading or loading to eliminate static electricity. You would want a reading to ground as low as possible.
Let me give you an example of a job that I had of grounding of rail cars to eliminate Static Electricity when unloading or loading. This was in a hazardous area, classified as 1-2-D.
I purchased a unit from the Crouse-Hinds Company that made sure that you had a good ground connection to eliminate a build-up of static electricity.
If you did not have a good ground connection, the Crouse-Hinds control device would not allow you to unload or to load the railcar. You would use the Crouse-Hinds device to interlock the pump control circuit or whatever device that you were using to load or unload.
Static Electricity is a very dangerous situation, especially in a hazardous area, and you need to have personnel knowledgeable to know how to eliminate a Static build-up.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Bonding Rail cars for unloading Flammables

friebel,
It doesn't take much in the way of a conductive path to prevent the build up of static. The IEEE Green Book says that a path of 1,000,000 ohms or less will prevent the buildup of static. Just think about the static build up as you walk across the carpet in your house. This is normally only a problem in the winter when the relative humidity is very low, when the humidity rises, the static problem goes away, because the air is now more conductive and bleeds off the charge as it is created.
Don
 

charlie

Senior Member
Location
Indianapolis
Re: Bonding Rail cars for unloading Flammables

Also notice that my statement has two parts. The first part points out what can be done but would be rather stupid from a practical standpoint. The second part points towards whatever Code covers this situation. :D
 

coulter

Senior Member
Re: Bonding Rail cars for unloading Flammables

Take a look at API RP 2003. I think the latest is 1998. They know alot about filling and unloading tank cars. But I don't know they have exactly what you want. I've got a copy at home and will take a look aat it tonight

Interestingly enough, according to the API, as far as static generated sparks during tank loading/unloading are concerned, bonding is important, grounding doesn't do much of anything. However, they are quick to point out that grounding may be necessary for electrical safety.

Try their site at api.org. I think they sell them right there.

carl
 

friebel

Senior Member
Location
Pennsville, N.J.
Re: Bonding Rail cars for unloading Flammables

To: coulter, you mention that bonding is important, but grounding is not. My question to you is, "after you bond all of your equipment,where do you take the static electricity that has built up, if you do not have a good connection going to ground".
Now, I do agree with you, that bonding is very important, but right now we are not in agreement about the grounding part.
 

charlie

Senior Member
Location
Indianapolis
Re: Bonding Rail cars for unloading Flammables

Friebel, assume you are working on 765 kV transmission lines bare handed and wearing a silver threaded suit. You are not grounded but you will install bonding jumpers from your wrists to the line so you don't get hit with a charge each time you touch the line. There is no difference here. You bond to take away the potential difference and the danger is removed. Dropping the static charge is a plus for anyone who is grounded and is around the discharge point. I am sure there are rules that actually require the earthing of the system. :D
 

coulter

Senior Member
Re: Bonding Rail cars for unloading Flammables

Originally posted by friebel:
... I do agree with you, that bonding is very important, but right now we are not in agreement about the grounding part.
friebel -

You aren't in disagreement with me, rather the American Petroleum Institute Recommended Practice 2003.

A lot of my working career has been spent hanging out in petroleum bulk plants, marine terminals, and refineries. API Recommended Practices are a big part of the methods used to design, build, and operate.

That being said, here are my beliefs about API RPs:

1. API has a 100 years in the petroleum business. A lot of the concepts in the RPs is based on accumulated emperical data. They have a good idea of what blows up and why.

2. Advice from an old codger getting ready to retire when I was just getting started: "If you don't follow the codes, standards, and recommended practices, you better have a bullet-proof reason why not." He paused for a few seconds, then said, "Let me explain bullet-proof. You better be able to easily and clearly explain it to shoe clerks and babysitters, cause that's who will be on yuour jury."

RP 2003 might be a bit technical for the local library, but a university library should have a copy. The latest version is 1998.


carl
 

coulter

Senior Member
Re: Bonding Rail cars for unloading Flammables

Originally posted by dakota1sparks:
We have been asked to test the resistance of bonding conductor at a railcar unloading facility. ... What would be the high allowable limit for the resistance we could see on this conductor?
Dak -

I read API RP 2003, Sep 1998, Protection against Ignitions Arising Out of Static, Lightning, and Stray Currents. Boy, it's a real page turner. :)

carl
 

coulter

Senior Member
Re: Bonding Rail cars for unloading Flammables

friebel -

I want to be real clear that I am not downgrading any of the safety aspects your are talking about. I believe you are correct in thinking static electric discharges can be dangereous.

However, some of the concepts you stated do not match up with my research or experience.

Originally posted by friebel:
... Let me give you an example of a job that I had of grounding of rail cars to eliminate Static Electricity when unloading or loading. This was in a hazardous area, classified as 1-2-D.
I purchased a unit from the Crouse-Hinds Company that made sure that you had a good ground connection to eliminate a build-up of static electricity. ...
I'll bet a cup of yuppie coffee the CH unit did not check the ground connection. Rather it checked the bonding wires were attached to a low impedance (metallic) path. - two ways I've seen this done:

1. The bonding cable has two conductors, connected to the jaws of a bonding clamp. The unit checks to see if there is a low resistance between the two clamp jaws. This type works well when clamped to a piece of galvanized steel and thrown in the dirt. Administrative controls are required to ensure the ground/bond clamp is used properly.

2. The bonding cable is terminated in a proprietary plug. A matching receptacle is required on the tanker. This type still only checks that there is continuity between two of the pins - again not checking any grounding.

The units depend on the installation to provide a good ground to the clamp and administrative controls to use it instead of cheat it.


Originally posted by friebel:
... grounding rail cars for unloading or loading to eliminate static electricity. You would want a reading to ground as low as possible. ...
According to the API spec, bonding is important for protection against ignitions, but grounding does not reduce the risk. The API spec does point out there are other considerations that determine the required grounding.


Originally posted by friebel:
Static Electricity is a very dangerous situation, especially in a hazardous area, and you need to have personnel knowledgeable to know how to eliminate a Static build-up.
Okay, this one is touchy. I don't want to say it is not dangerous. Like most everything else, if one does not know what he are doing ...

APR RP 2003, para 4.2.5.6
In most cases, static-related fires within tank truck compartments have involved either the loading of an intermediate vapor pressure product or switch loading (see Section 4.1.4.2). Recently, it has been estimated that the frequency of static related tank truck loading ignitions is about one per one million loadings and have involved at least one of the two previously mentioned conditions. In most of these ignitions, the cause of the incident was attributed to the failure to follow recognized procedures and guidelines. However, in the few incidents where all safety procedures appear to have been followed, many of the risk factors were present at levels close to established safety limits.
I absolutely agree that one needs to be knowledgeable to mitigate the risks.

carl
 
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