4 replies to this topic

[ayan_dg]

What is steam Out of tanks ? when we use it

[Art Montemayor]

All process vessels and tanks have a requirement to be thoroughly cleaned out - sooner or later. Think about it. They are just like dinner dishes. When you get through with them and you plan to use them again and again, you have to clean them. When you want to inspect them to see if they are cracked, you clean them. Otherwise, you wouldn't see the cracks or defects.

The same thing applies to process vessels and tanks - but on an even more important scale because in their case, hazards and personnel safety comes into play. Sooner or later you have to physically go into a tank or vessel that has previously been in chemical or hydrocarbon service - either to inspect it, repair it, or calibrate any internals that may be present inside. What is even a worse situation in my opinion is that it often is your decision to send SOMEONE ELSE into the vessel. This is probably one of the hardest and most sensitive decisions an engineer has to make. Many workers are carelessly killed or maimed for life due to accidents that occur in confined spaces such as vessels, tanks, or towers.

Prior to human entrance, thorough and detailed clean-out of the vessel or tank is very important from a safety and practical aspect. Steam is frequently used to clean out the residual sludge, oils, chemicals, and other contaminants that may remain in a purged and drained tank, vessel, or tower. Steam is convenient and efficient because its heat helps to break down viscous chemicals and its condensed water helps to flush and rinse the contents out. It also is inert and, as such, presents no combustible oxident.

HOWEVER, together with all the benefits you get from the steam-out you also have a trade off. Since the steam is a condensable, it will condense inside the vessel after it has displaced all the prior atmospheric air. When it does, it could create a partial vacuum and if the vessel is not fabricated to withstand that vacuum, it could easily collapse - causing a grave and dangerous situation. Steam should always be introduced into a vessel with an appropriately-designed vent that is sized to allow excess steam to exit and any atmospheric air necessary to break a potential vacuum to enter into the vessel immediately to avoid a partial vacuum. I always do this with vessels that are not designed to withstand vacuum as well as those that are.

I hope this serves to fully explain what the phrase "Steam-out" means to an engineer.

[Qalander (Chem)]

Dear Art Hello/Good afternoon.

Splendid explanation indeed!

Best regards
Qalander

[ayan_dg]

Thanks Art for your excellent response

[Fr3dd]

Hello Friends,

i have a little question about this specific matter:
Are "steam out" and "Steam purging" different types of operation or they are the same?

I've been doing some research and i haven't found any information to clarify this little question, and i need to know if i have to take the same design considerations for both procedures.

Also, I would like to know in which cases steam out has to be considered. Is there any criteria to specify a requirement of this kind of procedure (such as specific gravity of the handled fluid or any other property related to the service)?

Thanks in advance.

Edited by Fr3dd, 21 August 2009 - 06:22 AM.