Steam drum gen bank tube penetration
Steam drum gen bank tube penetration
(OP)
While working on a 1960's vintage B&W boiler, we noticed that the generating bank tubes only penetrate the steam drum about one inch, or one half its thickness. The steam drum is 36 inches ID and is 2.25 inches thick. We're used to seeing the tubes penetrate fully plus 3/16 plus or minus and flared inside the drum.
If someone else has seen this and understands why it would be done this way I'm curious to know.
Thanks,
Brian
If someone else has seen this and understands why it would be done this way I'm curious to know.
Thanks,
Brian





RE: Steam drum gen bank tube penetration
NOT GOOD!!!!!!
Is there any indication that something mechanically has pulled these tubes from their proper position (which would be as you describe; inserted somewhat into the drum with a flare rolled into the tube end) down into the tube hole?
Something very strange here.
rmw
RE: Steam drum gen bank tube penetration
Today, these type connections were replaced by the grooved wall tube connections that have more force and bending capacities at the connection and safer against the leak.
Some heat exchanger standards are calling for the pull test for the tube/tubesheet connections to make sure the connection is adequate.
Regards,
Ibrahim Demir
RE: Steam drum gen bank tube penetration
Thanks,
Brian
RE: Steam drum gen bank tube penetration
I'm still scratching my head over what you describe. It would seem that any tube rolled as such with less contact area would have to have grooves, not be without them.
If anyone has any documentation please scan it and upload it.
rmw
RE: Steam drum gen bank tube penetration
check the outside, they may be welded tubes and you can not see it from the inside. the technique is used in heavy wall/high pressure boilers.
genb
RE: Steam drum gen bank tube penetration
Harvey's "Theory and Design of Pressure Vessels" Fig 5.25 gives some kind of comparison of plain, one groove and two grooves expanded joint holding forces depending on the seat lengths. I guess this can give you a good idea about most commonly used lengths for expansion.
A year ago I designed drums for a boiler application and used 3 and 4 grooves with 12 mm distances between grooves with another 12 mm distance to the inner face. Even with those grooves due to the lack of proper expansion a couple of tubes left their location during the hydraulic test. Luckily it did cost only taking some line of the tubes away to be able to reach them to repair. Unfortunately the company I was working for did reject my earlier suggestion for the test at the connections and hardness limitation on the tube by relying on their previous drum applications with low pressure.
I recommend that the connection design should consider pressure trust (in case the tube change direction), and the other structural loads (the lower drum might be supported by the upper drum) in addition to sealing. Some tubes may not be contributing the load transfer and some might be overloaded due to the arrangement and distribution on the drums.
Ibrahim Demir