Reaming vs. Drilling Holes In Tube Sheets

[Fender]

UPS delivered some steel today, so I guess I'm committed to this project...

[Bill Shields]

I am going to stick my foot in here and suggest that all of you read what Elliott Tools has to say on this subject

I spent 10 years of my life supervising a HEX (Heat EXchanger) shop that put in 10,000 tubes a year of all sizes for everything from lube oil coolers in bulldozers to building-size heat exchangers full of all types of nasty hydrocarbons...and we used Elliott recommendations and never just DRILLED a hole.

http://www.elliott-tool.com/support-tools/

Download the BASIC PRINCIPLES OF TUBE EXPANDING

There is a section on IMPROPER PREPARATION OF TUBE HOLES and PREPARATION OF TUBE HOLES.

You might find it to be very interesting and informative reading regarding this subject.

It is amazing how the only 'non-boiler builder' here (Harold) is the one who clearly points out the obvious - warped holes around the welded areas. Andy then reinforces the point but I personally prefer to start with a round hole of a known size so that you KNOW what you are doing to the tube during the rolling process.

I know...it sounds like nit-picking but then if you are spending that much time and $$ on a boiler, why not spend a few more $$ and get reamers of the correct size?? Do you know how big a PITA it is to fix a leaky tube in a boiler?

As a workable compromise, I recommend (and practice) that AFTER the tube sheets are welded in place, you put a BRIDGE REAMER through each hole to get things to the correct size.

The holes where the tubes are inserted are typically reamed 0.005 over size so that I can get the tubes in without getting them (or the reamer for the rear tube sheet stuck in the process.

I have a reamer on a 36" extension shaft so that I can put it THROUGH the front tube sheet and ream the rear tube sheet and be sure that the holes are square.

Then calculate 8% stretch on the copper and mark the roller so that you don't over stretch the copper and cause it to crack because it work-hardens during the rolling process and CAN crack if you stretch it too far.

After all...it takes about an hour to ream all of the holes the correct size. Compared to all of the other work in building a boiler...that's peanuts!

[SteveR]

All,
How much better will it be to do all of that extra stuff compared to just drilling? How do you measure how much better it is?

OK - I've got two tubes side by side in a boiler - one reamed, one drilled. How do I test which is better? Is two enough to get a signal? How long will it take?

thanks,
SteveR

[Harold_V]

I most likely have been chastised, likely privately, for being anal about shop procedures. My suggestions are often at odds with those of others, but they are based on lessons well learned in my many years in the shop. One learns to go the extra mile, to prevent having to start the entire journey over.

Regardless of the degree of success that may be claimed by those who feel reaming isn't necessary, and that they have enjoyed success by simply drilling, I offer this. You can drive the freeway at 100 mph, and, maybe, not get a speeding ticket. Conversely, you can drive the speed limit and guarantee that you won't. And so it is with creating holes. If you hope to limit the possibility of failure, don't assume a drill will yield a functional hole. Sure---it most likely will. But if it doesn't?

You be the judge. Which bet do you hope to place? The one whereby you drill the holes on size and hope they work, or the one whereby you drill, then ream properly after welding, so the holes are not only on size, but clean and ready to accept the tubes.

It would work wonders for many of you guys to spend some time working in a shop where everything is mandated (think a shop in the defense industry), where nothing is left to chance, where you don't cut corners, because the penalty for doing so is rejected work. You learn to "do it right", and you learn to understand why it's the best approach.

Harold

[Fender]

OK, an update: a member of this forum has offered to sell me a reamer, so that's what I'll be using. Also, I'm not sure how the subject of drilling/reaming before vs. after welding came up. It was always my intention to do the final operation after the welding was completed.
In any case, thanks for the feedback.

[NP317]

Note to Harold:
It did not take me long to realize the source and extent of your Shop Experience.
I always defer to your recommendations.
Thanks for sharing your knowledge.
~RN

[Bill Shields]

measurement of success comes after a tube fails prematurely because it was not properly rolled and / or the metal fractured as a result.

multiple heating / cooling cycles and the crack propagates.

I was not in the defense industry, however was in the petrochemical industry where the price of failure was usually a tombstone. So maybe it was the self-defense industry.

I freely admit to being the shortest of the short-cutters...but never on a boiler!

Dan:

I think that you will probably need two reamers...it's a bear to get tubes through an exact-size hole into the far sheet.

I might have an over-size that you need if you can advise of the size required.

[John Landrum]

Other than conductivity and ease of rolling, what are the advantages of copper tubes? I will be re-tubing my 15" gauge engine (soon to be an 18" gauge) It is currently tubed with 19, one inch, steel tubes. Should I look at changing over to copper? Is there a difference in expansion of the tubes to the steel flue sheet and is this a problem?

[Bill Shields]

copper tubes from the standpoint of longevity clearly have an advantage.

the disadvantage is that they have a greater thermal growth which can become an issue as the size of the heat exchanger gets bigger and bigger.

copper is easier to roll and less likely to crack than steel. if you know how to properly install steel tubes then you do the same with copper. With copper you work to 8-10% wall reduction. Steel is a bit different, depending on the initial wall thickness.

Then there is the consideration that your boiler may require inspection because of its size.

If so...how does you local NB inspector feel about copper?

[Gardiner]

This article was most informative . Nelson Riedel ? Still alive? I am building a 2 1/2 in. scale model using his plans. Have figured out how to lubricate all bearing points using oil cups and grease nipples, with the exception the crosshead. Any advise on how to lubricate the crosshead would be greatly appreciated.

Thanks John G. Smith

[hoppercar]

No.matter how well you grind your drill, it will never drill a perfectly round, smooth hole. Without reaming you are running the risk of tube leaks later on. Personally, I have always had my sheets on the milling machine, and bored the tube holes...this ensures a round smooth hole

[Harold_V]

I have always had my sheets on the milling machine, and bored the tube holes...this ensures a round smooth hole

True enough, but you're ignoring the fact that those sheets will then be welded upon---with the distinct possibility of altering the holes near the welds. The holes you carefully bored.

I'm not a reamer fan. Fact is, they, too, offer the opportunity for less than straight and round holes, but the amount of deviation is miniscule when compared to a drilled hole. Reaming clearly improves the quality of a drilled hole, and provides a means of removing not only spatter, but distortion, the result of welding near the holes.

I'm not suggesting that not reaming will guarantee failure. It most likely doesn't. But it does raise the opportunity for failure. It also assures that the tubes will be installed without a battle. As much as I dislike reamers, I certainly endorse their use in this instance, just as I do for their use when installing dowel pins.

H