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# Max No. of bank tubes can be pluged2

## Max No. of bank tubes can be pluged

(OP)
I have water tube boiler and I need to ask about the max. number of tubes in bank tubes (boiler side) can be plugged (due to leakage which difficult to be replaced) that do not cause fail or limit in steam production.

### RE: Max No. of bank tubes can be pluged

There is no magic number or percentage. You need to do some calculations based on the design of your boiler and figure out what you can live with.

### RE: Max No. of bank tubes can be pluged

Agreed with MFJewell - there is no rule of thumb as boilers are engineered for specific design conditions, even package boilers.

### RE: Max No. of bank tubes can be pluged

And it depends on the distribution of the plugged tubes.
If they are close together then you will run into issues sooner.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

### RE: Max No. of bank tubes can be pluged

(OP)
thank you for your response, can you mention the reference for such calculations?

### RE: Max No. of bank tubes can be pluged

Most thermodynamics books would have what you need.

I would look at the impact of the loss of heat transfer area and impact of velocity through the remaining tubes.

### RE: Max No. of bank tubes can be pluged

#### Quote:

I would look at the impact of the loss of heat transfer area and impact of velocity through the remaining tubes.

Hey MF [et al], maybe you can expand my knowledge...

Is not velocity in tubes generally defined by the head between upper and lower drums, the ID of the tubes, and the triad of quantity of heat transferred / amount of steam generated / percentage phase mixture at the upper / exit ends of the tubes? And since all of the foregoing are more or less fixed for a given firing rate, will not the velocity within the tubes remain relatively unchanged?

Maybe it's just me, but it seems to me that a quite significant number of tubes [and those fairly clustered -thanks, Ed] within a bank of them would have to be plugged before a substantive rise in flue gas exit temperature would occur...

If not, please forgive my ignorance; I've been away from steam for a number of years and have only recently started getting back into it, so if I'm the one getting sharpened, it would be dumb of me to complain about it...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

### RE: Max No. of bank tubes can be pluged

IMO, it can be the engineering design question as well as the Plant Maintenance/Inspection issue. Typically in the equipment design, a certain percentage is added to the required design capacity of the Boiler. It can be verified on the data sheet, said about 10% or 15%. From the maintenance history, you may know better about the operation conditions, and then, make a prediction of the remaining life of the equipment and decide a plan of repair or replacement in the future.

### RE: Max No. of bank tubes can be pluged

SukhpalSingh
Also, ensure that there are no roll leaks.

### RE: Max No. of bank tubes can be pluged

#### Quote (crshears)

Is not velocity in tubes generally defined by the head between upper and lower drums, the ID of the tubes, and the triad of quantity of heat transferred / amount of steam generated / percentage phase mixture at the upper / exit ends of the tubes? And since all of the foregoing are more or less fixed for a given firing rate, will not the velocity within the tubes remain relatively unchanged?

If you are trying to produce the same pounds per hour through less tubes, you are forcing the same mass through less cross sectional area. Therefore the velocity would increase (or you derate the boiler to produce less steam).

### RE: Max No. of bank tubes can be pluged

This might help .....

There are also ASME Code strength issues to consider when plugging.... detailed here:

https://www.nationalboard.org/SiteDocuments/E-Publ...

In my experience,for firetube boilers, I have heard of a general rule of 5 to 7 percent maximum blocked tubes.

It is important to remember that tube plugging is a temporary fix and that the tube should be replaced at the next schedules outage.

Also it is important to note that boilers in cyclic service will tend to loosen their plugs..!!!

Shell & tube heat exchangers operate under different rules and thermal overdesign is common. As a group they are likely capable of a higher percentage of plugging

MJCronin
Sr. Process Engineer

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