ALTERATION OF BLOWDOWN TANK 1

[82264]

I would like to know what things to consider before we can do alteration works to a Blowdown tank. The blowdonwn tank is ASME coded and the alteration that is going to do is to add additional 1 piece of nozzle.

Thanks

82264

 

[johnnymist2003]

Hi,

check out API 510 for guidance.

John

 

[davefitz]

You probably should confirm that the tank will not be overpressured by the additional flow.

If the tank has a design pressure of 50 psig , that is based on the assumption of all original drain lines open while the boiler is at full pressure. The "casualty flow" thru the drains to the tank is calculated, then the backpressure of the steam flowing thru the tank vent is calculated. If the new backpressure is above 50 psig ( after adding the new flow from the new nozzle), then you have a problem. The flows can be reduced by using smaller drain valves with reduced port trims. Or , you can increase the sizeof the tank vent .

 

[deanc]

This work needs to be performed by an "R" stamp firm. See NBIC Part RC. Check with the local jurisdiction and the insurance carrier.

 

[athomas236]

82264,

Is your blowdown tank an atmospheric tank discharging the steam to atmosphere or a presurised tank discharging steam to a process vessel such as a deaerator.

athomas236

 

[pablo02]

Typically the nozzles are inserted tangentially with a wear plate inside to protect the tank wall -- if you add another nozzle, follow the guidance provided by the other postings and make sure the wear plate is sufficient for the new nozzle... you may need to advise your AI and may also need an "R" stamp to affect the repairs you desire...

 

[MJCronin]

82264,

I am assuming that you are adding a nozzle to a blowdown tank in a boiler plant and that it is part of a continuous blowdown system....

If the new boiler capacity is not too large, or if you may want to add another boiler in the future, you may want to consider purchasing a larger replacement blowdown tank.....

Blowdown tanks do erode away and eventually must be replaced...sometimes the best plan for the future is an increase in capacity today. (Most managers take violent exception to this kind of thought)

My opinion only...

MJC

 

[athomas236]

The question is how do you know a blowdown is not working correctly. Well lots of visible steam from the vent, who knows that was not supposed to happen.

The other way is the water seal is broken because the pressure in the tank is too high causing steam to leave the drain when water/stem was expected. Answer just make the seal higher.

athomas236

 

[mufasa1]

Gentlemen,

I came across this thread, while I was doing a research on a similar case. In our boiler plant we would like to recover the HHS (High High Steam)condensate that is thrown out of the 3 steam traps located on HHS line at Steam Generating Plant area. HHS Steam Pressure is 84 kg/cm2 and temperature is 310 Cdeg. We assume that approximately 260 kg/h of condensate is discharged from each trap.

We consider directing the condensate to the continuous blow flush tank (operating pressure 5.5 kg/cm2) by adding a new nozzle (eg. 6") on the tank and tying the individual HHS Trap condensate lines to this nozzle.

I would like to get your opinion on this approach, especially adding a new nozzle on the tank for this purpose.

Thanks,

 

[MJCronin]

82264,

Here is some more discussion of this topic on another forum

http://www.steamforum.com/_discstm/00000fbe.htm

There are some design and safety issues to consider...IMHO

-MJC

 

[KL7P]

Check your jurisdictional requirements, NB vs API. And limitations of your authorization, if you are doing it yourself.

If you exactly duplicate an existing nozzle - size, geometry, material, joint style, etc. that should be allowed to be listed as a repair, not an alteration.

When we change anything, we have to do the change as an alteration. More hoops to jump through.

Our program allows either repairs or alterations.

 

[mufasa1]

Appreciate your feedback,

I will let you know about the outcome..Thanks for the
steam forum tip too..