Ensuring protection under nitrogen filled carbon steel vessels 1

[sunshine419]

Would appreciate to know why Nitrogen is used during the transport of carbon steel vessels. In addition please, I would appreciate to know some insight into what sort of provisions are to be in place to ensure the conservation of the protection under nitrogen and the coatings during the transport and handling of carbon steel vessels.

Furthermore, how can one avoid pressure loss in these vessels?

In conclusion, CO2 is instead used for the transport of Stainless steel vessels, why not nitrogen?

Would ever appreciate the resourcefulness of members of this community that have been helpful with their responses and thanks in anticipation.

 

[JEB66]

If you have liquid water with free O2, then you will have localized corrosion on carbon steel. N2 is used to displace air and the O2 that comes with it. Usually a small cylinder of N2 is connected to the vessel with a pressure regulator to maitain a slight N2 pressure.

If the vessel is completely dry, then you can avoid the N2 blanket. Of course you will need to ensure that the vessel stays dry.

I have not heard of CO2 for stainless. Usually you want an oxidized atmosphere on stainless to promote the formation of a protective chrome-oxide layer (spinel).

 

[gr2vessels]

Usually, the pressure vessels are 'sealed' before delivery in the fabrication shop. Any carbon steel vessel without internal coating is protected during short term transport with dessiccant bags put inside the vessels before closing the openings with temporary plugs, covers, etc. For pressurized vessels use bolted metallic covers and rubber gaskets during transport.
For longer delivery terms, extending over several weeks, the vessel internal surface may be sprayed with a corrosion inhibitor and again using a few bags of dessiccant material to absorb any residual moisture inside the equipment.
For maritime transport which could take many days and weeks, the problem resides in the breathing of the equipment;- expanding in the daylight and contracting during night. Since there is no 100% sealing of the vessel openings, the salt ladden, moist marine atmosphere could easily be aspirated into the vessel and the moisture condense on the internal surface. Unfortunately, the normal corrosion inhibitors cannot protect the carbon steel against the chlorides disolved in the condensate, making also more difficult the corrosion protection for the common autenitic stainless steel vessels exposed to the Chlorides Induced Corrosion Cracking.
The only effective way to keep the moisture out is to lightly pressurise the vessel (5-7 psi) with the neutral N2 (the CO2 can still disolve in the condensate generating a weak acid). The vessel openings are not air tight sealed, hence a slight loss of nitrogen has to be compensated from a small gas bottle attached to a nozzle cover via small bore tube, a 0-15 psi pressure gauge and an isolation cock valve.
I'm not aware of CO2 used for presurizing the stainless steel vessels and I would strongly recommend against it, particularly for safety reasons.
Cheers,
gr2vessels

 

[jamesl]

Typically only stainless steel vessels, stainless steel clad vessels, or carbon steel vessels with a lot stainless internals installed require nitrogen purge for ocean shipping. The main purpose is to keep chlorides out.

The alternative to nitrogen is to use dry air.

 

[unclesyd]

Neither CO2 or N2 are safe as both can kill you with N2 leading the way,it's quicker.
One has to be very careful with CS Tanks are shipped, stored, or worked on wither with or without N2 fill. A clean CS tank that sits open or is filled with moist air will very easily be oxidized to the point that all internal O2 is consumed and you have a vessel full on N2, a killer. Where there have been a lot of problems is when you receive CS and want to do a little clean up so you dust blast it and go home for the weekend and comeback Monday morning go into the tank and fall over dead. CS rail cars are especially bad about killing people. Always remind your people that if a little rust is going to bother them they are suing the wrong material of construction.

Aside from the the post above correctly stating that Carbonic Acid could and would be a problem. N2 is normally readily available in the very dry form, oil pumped dry nitrogen.

The moral of this story is to get a vessel entry permit and be very careful about monitoring the O2 levels while entry.work is going on.