Filling vessel with Nitrogen

[teokal]

Hi all...
We have completed a vessel (CS material) and we are now ready to fill it with Nitrogen before we store and transport it. Our client and we have a contradiction of how much should be the pressure of the Nitrogen. The time period that the vessel will remain sealed, is unknown. Does anyone know how much that pressure should be (we claim 0,1 barg) and if there is any part of ASME suggesting that?
Thank you all...

 

[alanw7272]

Teokal,
0.1 barg sounds a little low. In all likelyhood the nitrogen will leak slowly, especially when the vessel is transported. Thus it will need to be topped up more often once the pressure has fallen! On what basis did you arrive at 0.1 barg? ie: is this vessel rather large?

We are doing something similar and setting the initial nitrogen fill at 1 barg, to be topped up when it falls to 0.5 barg. These are for exchangers though and probably with much less volume than your vessel!

 

[MJCronin]

teokal..

ASME would not address this transportation issue.

I have had boiler/HX components shipped at 2-5 psig N2 blanket .

What is important in your decision is how long the item will be stored at the plant site and the possible danger introduced from the nitrogen.

Higher pressure simply costs more money and offers no more corrosion protection.

If .1 barg can be adequately monitored over the time of storage, I think it would be acceptable.

-MJC

 

[gr2vessels]

Nothing much to add to the above replies, perhaps that the vessel exposed to the ambient will loose eventually the N2 pressure, depending on the effectiveness of openings seal/closures. The vessel will expand and shrink a bit in the sun or in the rain;- if the N2 pressure gets low, perhaps less than 0.5 psi, you risk that during the next cycle to create a small internal vacuum and then ingrease of air and moisture, defeating the purpose of N2 blanketing. You can always attach a small bottle of N2 to one of the nozzle covers, a pressure indicator and someone to monitor every say 2 days the internal pressure, top it up if needed. 2 - 5 or even 15 psi is still low enough pressure to not be really concerned with the cost and damages.
Cheers,
gr2vessels

 

[unclesyd]

To counter some of the potential problems mentioned above I would throw in a Vapor Phase Inhibitor along with the N2.


If this vessel is large enough for human entry there needs to be very visible signage that states the fact that this vessel is fill with N2 and needs to be purged and tested prior to vessel entry. I was witness to a fatal incident in a case where the N2 wasn't purged and tested prior to a vessel entry.

 

[engrom]

approx 35kPa
suggest frequent monitoring during the storage period

 

[vesselguy]

Further on this subject, can I ask the folks here on what is the cost of providing N2 blanketing for shipment? I have spec N2 blanketing when I worked on the clad reactors from Japan and Italy but I never knew what kind of cost is involved. Just curious to know.

Also, correct me if I'm wrong but as far as I know, we would only require inert gas protection for sea shipment (or any sort of transportation) if the equipment is S.S. or alloy. If it is just c.s. then we won't need to do so since the rust coating is a natural protective coating. Am I right?

 

[MJCronin]

vesselguy...

I believe that large feedwater heaters and many other vessels are shipped with an N2 blanket by many of the major fabricators.

The N2 blanket for large expensive carbon steel "things" serves a contractural function. When the purchaser finally opens the vessel, he knows that the interior (with it's light coat of rust) is just the way it left the fabricator's facility and no degradation occured in transit.

For large expensive carbon steel "things" it is a modest additional cost.

-MJC