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10 comments
Commentator

Join Date: Jun 2008
Posts: 60

Flushing of Steam Piping

02/21/2011 12:14 AM

We are planning to install a new Low pressure (LP) @ 3 bar & medium pressure (MP) @ 11 bar steam lines which would be more than 1000 meters long.To flush the lines thoroughly before taking into circuit , appreciate if some one can guide reg. the quantity of steam required if the steam lines are 300 mm dia for LP steam and 200 mm dia for medium pressure steam.The steam would be taken from the TG header and exhausted to atmosphere at the end point.Would be thankful if calculation sheet is also provided without any reservations as I expect this forum is for learning and improving the knowledge.

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Guru
Australia - Member - New Member

Join Date: Feb 2008
Location: Australia
Posts: 1316
Good Answers: 148
#1

Re: Flushing of steam piping

02/21/2011 12:40 AM

I'm not from steam world, but I suggest that you need to provide more information. To maintain "steam" will require the pipes and such to be brought up to temperature (won't it)?

You might need to provide pipe material and thickness/grade as well as outside ambient and quality of insulation/lagging on the pipes. This might help the others determine the "thermal mass" invovled to give you a better indication.

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Commentator

Join Date: Jun 2008
Posts: 60
#2
In reply to #1

Re: Flushing of steam piping

02/21/2011 5:28 AM

Thanks for prompt response.Yes I agree that we have to provide insulation after conducting hydraulic test but while flushing, the steam will be vented to atmoshere.Ambient temperature would be around 35 deg.C and the inlet steam temp. would be at saturated conditions.

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Associate

Join Date: Jul 2010
Location: Witbank South Africa
Posts: 43
Good Answers: 2
#3

Re: Flushing of Steam Piping

02/22/2011 2:50 AM

I am assuming that when you say flushing you mean you want the pipework dry before connecting to your circuit. This will be impossible if your inlet steam is at saturation point. There will be a temperature and pressure drop along the pipe hence some of it will condense. You need to determine or estimate the temperature drop so you can compernsate for it by an appropriate degree of superheat.

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Commentator

Join Date: Jun 2008
Posts: 60
#4
In reply to #3

Re: Flushing of Steam Piping

02/22/2011 3:00 AM

Agreed with your view point as the steam is to be slighly superheated to avoid condensation.I need some input regarding the quantity required for the preparation of steam availability.

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Associate

Join Date: Jul 2010
Location: Witbank South Africa
Posts: 43
Good Answers: 2
#6
In reply to #4

Re: Flushing of Steam Piping

02/22/2011 4:46 AM

The quantity should be slightly higher than the quantity you need in the process. Gut feel 5 to 10% more. Observe the outlet untill the steam comes out dry. This will then be improved with every flushing. That is record the initial conditions and the time it takes to complete the flushing each time you do it and consider changing some of the parameters in order to shorten the flushing time.

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Anonymous Poster
#7
In reply to #6

Re: Flushing of Steam Piping

02/22/2011 5:28 AM

If you put in Superheated steam then it is highly likely that you will get out dry steam at the end - ok depends on the system design and setup.

I am not sure what the OP means by flushing, I take this to mean passing a certain quantity of steam through the system in order to remove any debris etc that might some how have been trapped in the system. If the system was designed properly then steam traps (say every 20m-30m or so and at the low points) should be installed aswell as air vents - this is just part of the steam distribution system setup. Perhaps if he OP actually specified what was meant with flushing then this would assist. We perform flushing on our steam system systems after modifications and we typically look to pass around 25times the volume of the steam in the tubing through the system, this is why I suggested calculating the volume and density in an earlier post. We also blow the steam out to atmosphere during the flushing.

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Commentator

Join Date: Jun 2008
Posts: 60
#9
In reply to #7

Re: Flushing of Steam Piping

02/22/2011 7:58 AM

You are absolutely correct.How long you do normally blow the steam though it depends on the quantity of debris.

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Anonymous Poster
#10
In reply to #4

Re: Flushing of Steam Piping

02/23/2011 10:56 AM

Basically steam flushing is done to blow the construction debris and to clean internal surface of pipe. in order to meet objective high steam velocities are required may be 3 to 4 times of design velocity ( Quantity can be estimated based on this).This is a low pressure operation. The pressure at the inlet will be equivallent to pressure drop at flushing velocity as out let will be at atmospheric pressure.

You have to ensure heating of line and flush the same section by section by removing steam traps and valves at drain points generally located every 20M.

while flushing keep by passes of steam traps open to prevent condensate trapping and water hammer.

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Anonymous Poster
#5

Re: Flushing of Steam Piping

02/22/2011 3:43 AM

I assume (depending on your local practices and regulations) that afer installation the system will be hydro pressure tested and perhaps even cleaned and passivated (depending on the purpose and quality of the steam tubing).

Calculate the volume in the tubing and then the density at the pressure (3bar and 11bar). The steam velcoity will be extremely high since you will be getting a 3 bar and 11bar pressure drop over the length of the tubing - this may need to be taken into account from a noise and tube support point if view. I would recommend that you visit http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-distribution/pipes-and-pipe-sizing.asp or http://www.spiraxsarco.com/resources/calculators/pipes/checking-existing-pipes.asp or contact your nearest Spirax Agent and they will be able to assist you. If you are going to work with steam systems then I suggest that you purchase a copy of The Steam and Condensate Loop by Spirax Sarco. I have a copy of this and it is invaluable (I have no connection to Spirax Sarco). Since you are only interested, I assume, in flushing out the system then the insulation etc may not be that much of a concern for you - this would only be of concern when calculating the losses from the tubing.

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Power-User

Join Date: Oct 2008
Location: Meherrin Virginia
Posts: 307
Good Answers: 5
#8

Re: Flushing of Steam Piping

02/22/2011 7:56 AM

In the power plant end of this game on new installations we used to do a steam blow. A fairly simple process of blanking off points you didn't want to blow/flush and running a temporary pipe out of the building with a "target" on the outlet opening.

The target was no more than a piece of steel welded to the end of the pipe projecting into the opening if it didn't get knocked off by the occasional chain fall that got left in the pipe, it could be inspected for foreign object damage.

We had a lot of history to work with and the blow was pretty much orchestrated by the architectural engineer.

There are vendors out there that can perform the same operation with high pressure air. I think there is an IEEE standard for steam blows.

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