Aligning Front Tubesheet

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jlakes85
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Aligning Front Tubesheet

Post by jlakes85 » Sun Sep 24, 2017 10:21 am

Hi All,

I've gotten to the point in the boiler build to finally get the front tube sheet welded in place. Right now, im using 3 pieces of ground drill rod of the appropriate length to get the exact alignment. The boiler is steel with 3/4 OD k type copper rolled in. Would there be any reason not to use all 18 tubes to do the alignment instead? The front flue sheet is 1/2 thick and is already prepped for TIG root.

-jlakes85

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Bill Shields
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Re: Aligning Front Tubesheet

Post by Bill Shields » Sun Sep 24, 2017 7:15 pm

keep tubes near the weld out during welding - or you may not be able to get them out afterward if things warp / shrink.

Tack the sheet in place, pull out all the tubes then finish the weld.

Typically you should drill the holes undersize, then AFTER WELDING run a reamer through them to get them to the correct size.

in reality, 3 tubes should be enough - you are building a boiler, not a watch.

jlakes85
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Re: Aligning Front Tubesheet

Post by jlakes85 » Sun Sep 24, 2017 7:49 pm

Hi Bill,

Sounds good. I just want to make sure I don't get to tube #18 and hear a thunk when I try to push it through the rear flue sheet.

James Powell
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Re: Aligning Front Tubesheet

Post by James Powell » Sun Sep 24, 2017 9:41 pm

One suggestion I have is to think through the order of tightening tubes, because if you have a handhole on the boiler (like, say, the dome), and something goes wrong, it is far better to have worked through a logical sequence as to which tubes get rolled in what order.

Dad made one boiler where we ended up with a slightly larger than planned hole to get the bits of tube out after expanding went wrong. (this is in a 6" barrel boiler or so...a little tighter on space than a large railway engine boiler).

James

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Bill Shields
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Re: Aligning Front Tubesheet

Post by Bill Shields » Mon Sep 25, 2017 6:41 am

you should always have enough clearance to gently slide the tubes in with a little bit of wiggle.

MANY boilers are SPECIFICALL DESIGNED so that the tube are not perfectly perpendicular to the sheet.

As mentioned, one set of holes is intentionally a little bit oversize so that the tubes can SLIDE IN and be aligned before rolling.

I have 2 sets of reamers...one that is 0.001" oversize of the tube and one that is 0.005" oversize of the tube to make installation a non-frustrating experience.

usually, I put a piece of 1/4" rod through the hole and follow it by the final tube - using the tube as a guide to find the hole.

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Fred_V
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Re: Aligning Front Tubesheet

Post by Fred_V » Mon Sep 25, 2017 7:04 am

Bill, what is the purpose of having the flue sheets not square with the tube?
Fred V
Pensacola, Fl.

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Bill Shields
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Re: Aligning Front Tubesheet

Post by Bill Shields » Mon Sep 25, 2017 8:12 am

if you look at where the top of the firebox wrapper is located (vertically) with respect to the center-line of the front tube sheet, it is often desirable to spread out the tubes on the front sheet so that they cover the entire front sheet area...basically the tubes run uphill a little bit.

For example if you have a clean out in the front sheet, (and not one in the firebox area), it may be necessary to move the front position of the tube(s) around a little so that there is space for the cleanout.

Also, if you look at the width of the rear sheet (narrower by virtue of the water legs and / or flange), you have greater 'width' on the front to space tubes out...so spacing can be increased to make life easier at that end of the boiler.

on smaller locos, where things are really jammed in, tubes are also frequently moved around so that you can get in behind the blast pipe to clean them and or get the throttle / super heater in without taking the smokebox completely off the boiler. This requires more than a little amount of planning in the design stage.

Is this tube spacing juggling necessary on a larger boiler?...generally not, but embracing the concept of 'tubes do NOT HAVE TO BE SQUARE TO THE SHEET' is yet another tool in the arsenal of the boiler builder for when the time arrives where a design decision must be made.

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Builder01
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Re: Aligning Front Tubesheet

Post by Builder01 » Mon Sep 25, 2017 7:07 pm

Also, as to tubes not being square to the tube sheets, this is quite common in many of the Martin Evans designs. Often the tube sheet hole pattern is slightly higher in the smoke box compared to the fire box. This is so the tubes run slightly "up hill" to the tube sheet in the smoke box. This helps to keep the tubes from touching the top of the throat plate and yet have the hole pattern in the fire box low. The tubes are anything but square to the tube sheets.

David

jlakes85
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Re: Aligning Front Tubesheet

Post by jlakes85 » Wed Sep 27, 2017 12:03 pm

Hi Bill,

I reamed both sheets with a new 0.750 reamer. I got the tubes today and the all seem like a nice sliding fit in the sheets. Should I still go though them with a 0.755 reamer or leave as is? Also should I anneal the tube ends (allowing to cool in air, of course) before rolling?

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Bill Shields
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Re: Aligning Front Tubesheet

Post by Bill Shields » Wed Sep 27, 2017 12:07 pm

you do not need to open holes UNLESS you cannot get the tubes all the way through to the other sheet...depends on the actual size and condition of the tubes...sometimes they are a little squashed here and there and will not push through a size to size hole.

anneal...??

if copper - not really since they are going to work harden IMMEDIATELY as soon as you start to roll...

I don't bother, but I know people who DO....but in reality don't think it is necessary.

Harold_V
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Re: Aligning Front Tubesheet

Post by Harold_V » Wed Sep 27, 2017 3:20 pm

Annealing is required only if excess work hardening occurs. That can lead to alligatoring of the metal. May not be much of a problem with rolling tubes, but it is one of serious concern when rolling (for thickness) flat stock.

H
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jlakes85
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Re: Aligning Front Tubesheet

Post by jlakes85 » Tue Oct 10, 2017 9:26 am

I went ahead and opened up both the front and rear tube sheets with a 0.005 oversize reamer and now everything fits perfectly, albeit slightly loose.

This has also been a big help in allowing a bit of flexibility for the front tubesheet vis a vis the required weld root gap to the barrel.

I'm a little concerned that the 3 ground drill rods I previously used to line everything up won't be enough to ensure the front tube sheet is perpendicular to the barrel now that there is a bit more play.

Is there another or additional method I can use to line everything up perfectly?

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