hydraulic tube expanding

[roniprabowo]

Dear all,
I have heat exchanger that requires hydraulic tube expanding. My question is what the advantage of this method compare to the other ones (pneumatic and motorized system)?

Thank a lot

 

[quark]

If I didn't get it wrong, hydraulic tube expanding refers to sealing of tubes to tube sheet by using a hydraulically driven mandrel. Why hydraulics? because that is the cheaper and easiest way to do it. (pneumatics and motorized systems are not analogous in this context)

 

[rmw]

Could you use explosive expansion instead? It is often used as an "or equal" to hydraulic. Roller expanding is very slow when the tubesheets are very thick, and that generally is when hydraulic and/or explosive are utilized.

With tube rollers, you do one tube at a time, and if it is a large exchanger, you might have two or more rollers going, while with explosive, you can 'dynamite' whole rows, or combinations of rows at a time. In theory, you could do the whole Hx at once, but it is not practical. (lots of noise)

If you have a seal welded Hx, you can specify a duplex charge, so that the lead-in cordite is of a lesser charge than the actual expanding charge. For example, lets just say that the expansion requires a 40 grain/in. charge, then the leader might just be 7 grains, and attach to the expanding charge 1/2" or so behind the seal weld, so that the weld is not stressed by the setting off of the expansion charge.

rmw

 

[EdStainless]

Hydraulic expantion comes in two types. In one you seal against the tube and then fill the area between the seals with water and then pressurize to expand the tube. The other method uses a mandrel/bladder system and does not get the tubes wet.
The second method is clean and very controled. And like rmw said, on a thick tubesheet you may need to roll each tube 3 or 4 times in order to fully roll it. Hydraulic is one cycle and you are done. The mandrel can even be built to expand two areas (at the front and back, but not middle) at once.
There are some alloys that don't like exposive expantion. But for ductile materials it is great. Very good seal and good control.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[unclesyd]

Here two websites that you might be able to glean information. We used both types, but the majority of the bundles/exchangers were low pressure and having a tremendous investment in mechanical rollers, we went this route. We used explosive and hydraulic on some BFW heaters that were a bear to roll. Both systems worked well. I like the explosive as we never had a weeper. We seal welded all tubes after rolling and 3 or more groves if possible.
The people that did most of our work have since been gobbled up by different sorts.
The first reference is where Senior Engineering (explosive) went and I can find the other company that did the hydraulic expansion.

http://www.babcockpower.com/index.php?option=services&task=viewservice&coid=23&serid=61

Comparison of hydraulic versus explosive.

http://www.hpro.com/reference/ref_hp104061798.html

 

[EdStainless]

Someone else that does all types of expansion. They are very skilled at explosive.

http://www.amexservices.com/

I have seen their work and it is good.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[rmw]

Unclesyd, did you mean to say that you seal welded all tubes "after" rolling, or vice-versa.

Seal welding after rolling is only recommended for titanium tubing. With other weldable alloys, it is always recommended to seal weld first, and then roll, with the roll beginning at least 1/2" past the seal weld. That is why I extolled the virtues of the duplex explosive charge above, so as not to put a lot of explosive impact energy into the seal weld, and hence disturb, or break it, while doing the expansion of the balance of the tube.

The reason for seal welding first, is that gases build up behind the weld, and, with the tube unrolled, the gasses can escape down the path between the tube and the tubesheet, while with a rolled tube, the only place gasses can escape is out through the weld puddle, which will leave a blow out where the weld bead is finished.

With titanium, the weld process is different, and the gas pocket is not a problem.

Secondly, while I have no particular preference between explosive, hydraulic, or roller expansion, and have had more experience with explosive expansion and roller expansion than I have hydraulic, I found the second link you posted to be less than objective in its comparison of the two processes.

None the less, it was a good comparison of the two, if one realized whose dogs were in the hunt. I liked the first link, because it shows a tubesheet being set up to blow a whole row, as I referred to above.

rmw

 

[unclesyd]

rmw,
A little long and windy, I hope not to long.

We essentially built/rebuilt/repaired all the site's tube bundles from scratch from 1960 until the mid 90's. All tube bundles both CS and SS were seal welded after rolling. I am talking about hundreds of tube bundles. Most of our tube bundles were SS (304,304L,316). The average bundle was 2-3'dia x 10',12',16',20'long. We did have 4 each that were 5' x 30' and 4' x 30' . The majority were 3/4" or 1" tubes 14/16 gauge, seamless tubes. Approximately 20 of the bundles were safe ended by us. The bundles were mostly for vacuum service though about 30% were pressure rated up 1200 psig.
Again the majority of the bundles were the external floating head (lock ring), forgot the figure #.

All High pressure bundles were “ice house type” and 10,000 psig coolers were open drip coolers we also made and repaired these.

We used serrated (3) tube holes and polished (Hex-T polisher) the tube ends prior to insertion and rolling. For years the seal welding was manual TIG.

We built our first Ti tube bundle (1" x 10'tubes} in 1962 and it's still inservice only 2 tubes plugged due collision with a inlet baffle plate. The tubes were rolled and then welded.

We never experienced any problems with leaks on testing or operation. For years the failure were from the process side with and occasional Cl/SCC. Then the bugs came.

The argument of welding before are after has went on for years but we stuck with the original procedure established in shop. Our biggest mechanical problems were purchased equipment on several projects. I agree on the comparison link being lopsided and the Babcock site is the old Senior Engineering about 3 times removed.


Anecdotal for today:
I got a call this morning on how much to reroll (first time) 2" CS tubes in the vapor drum of a 12mm btu "D" type heating fluid vaporizer. There was a contractor whom I believe had never rolled a tube before sent to do the job. It ended up I went out to the plant and had to show him how to set up and how to reroll the tubes. I had to get everyone concerned into the drum and show how to reroll the tubes. My gage was to roll until the normal tight scale cracked. After checking around the tubes didn't even need rolling as they quenched the vaporizer on shut down and had four weepers. But at 52 years old I don't think it will hurt. This was my favorite vaporizer as the manway is 20" and has a 14" nozzle neck, rough on an old man as there is a demister just inside the nozzle that hadn't been removed. They were also surprised when I went to the tool crib and showed them the tools to do the job were onsite.

 

[rmw]

Unclesyd,

I read your post very carefully, as I do all your posts. I have a great deal of respect for your experience, the quality of your posts, and the specific successes you mention here.

However, since this forum is a learning place for all the readers, I am going to present a contrarian point of view, and the readers can then take what is presented, and make up their own minds as to which way they might want to go.

I, too, like you, over the last 35 years, have participated many times in the (roll first, then weld, or weld first, then roll) argument, and have heard it presented both ways quite elequently by very knowledgable people at that.

Then, only a few years ago, while in the shop of a major heat exchanger and condenser manufacturer, inspecting a titanium tube/tubesheet condenser for a client, upon noticing that they were welding after rolling, I asked the quality control manager why, as I knew for a fact that they used the opposite procedure for their high pressure Hx's.

He gave me the explaination regarding the blowout of the gas pocket that I mentioned above. Manufacturers are always concerned with shop production rates, and cannot afford to take the time to have to go back and rework tube end seal welds in a HP Hx containing literally several thousand welded tube ends. So, they were using the method that they knew would get it right the first time.

These were Hx's that can exceed 6 ft. in dia., and have tubesheets as thick as 27 in., and can be over 40 ft in length, and weigh enough that they have to be shipped on specialty equipment.

Moreover, since reading your post, I have also pulled a couple of my clients HP FWH specs. These are major Electric Utilities, where the specs basically originated with AE's like Stone and Webster, and/or Sargent and Lundy, to mention a couple, and find that these specs all call for welding first, then (1) visually inspecting, followed by (2) an air test (35 psig was the requirement on one), followed by (3) a dye penetrant test.

If all that passed OK, then, and only then, the tubes were to be expanded, and the tube seal welds were dye penetrate tested again after the expansion step. Once the shell was pulled on and welded, then the tube/tubesheet welds were to be tested yet once again, with nitrogen or air.

My experiences with several of the major FWH manufacturers, some of whom are now gone, has basically been the same. They all weld first, and then roll, except, of course, with Titanium. Senior Engineering, one you mention, now called Thermal Engineering Inc., TEI is but one of them.

In your case, you may have had excellent welders, or welding procedures that anticipated the gas pocket blow out problem, and accomodated it, or compensated for it in some way.

Or, it could just be that the expansion roll itself provided enough sealing that any flaw in the tube end seal welds was not detected. After all, many more Hx's are built 'rolled only' than are built welded and rolled (or vice versa as in your case). Whatever, it worked for your plant. And, additionally, explosive expansion normally expands most of the full length of the tube in the tubesheet, as opposed to the 2-1/2 in. manual roll that was done years ago, which helps with the sealing of the tube.

Another argument often heard is whether the weld is for sealing only, or is to contribute to the strength of the joint to resist tube pull out.

I have an anecdote regarding that. A major FWH retubing outfit once went into a plant to retube a huge HP FWH on a supercritical boiler which could not be removed from its location on the mezzanine level due to a lack of crane capacity in that area of the plant. They found one complete row of tubes that had been seal welded, but had never been expanded. (and they were having beau coup trouble with removing the tubes that had been expanded into the 27" thick TS). This row of tubes had survived all the years it took the heater to die a natural death, and were not part of the failure mechanism that occasioned the need for retubing. So, the seal weld in and of itself is quite strong as well, but in reality it is the expansion that is designed keep the tube in the tubesheet.

Speaking of tube expansion, the major FWH manufacturers, if given their choice, (sometimes customer specs govern) will use explosive expansion. It is much faster than the other methods we have discussed, given the ability to shoot whole rows or combinations of rows at once. It is very consistent, notwithstanding the negative comments on the website we discussed, and produces good results.

I have one other thing to throw out, that is my opinion and only my opinion, although others share it with me. I want the readers to be aware of the potential problem.

For HP Hx's, with thicker tubesheets, and with heavier wall tubing of the harder tube materials, (Stainless steels, carbon steels, etc.,) I don't recommend tube hole grooving. Let me state categorically that with softer tube metallurgies, brass alloys, Cu/Ni alloys, etc., grooving is mandatory!!!!

The consideration I want to present is the potential for cracking in the tube after expansion due to the sharp corner (bevelled or not) of the groove. With full length expansion by whatever method, the grooving is not necessary to obtain the full tube pullout strength.

Unclesyd, I do, however, like your 3 groove approach. I do agree with the concept that if two are good, three have to be better.

You and I may just have to agree to disagree on the above points, but I am sure you will agree with me that the forum readers need be familiar with the reasoning behind either approach.

rmw

 

[unclesyd]

On our exchangers there were no tubesheet preparation other than drill, ream, and cut the serrations. There were no other preparation on tubesheets, no groove or bevel, etc. Several aspects of the preparation of the tubes and sheet contributed getting a good weld. We keep the holes very clean and burr free and as stated we polished the tube ends. If the HX was a multipass we touch up the grooves if possible. On rebuilds we cut down the bundle and the tubesheets were hydroblasted, penetrant tested, chemically cleaned or sand blasted, mostly the CS. Most SS bundles weren’t repairable we could only save the tubesheets. Generally we only pulled tubes for inspection.
Some of the SS welds were autogenous, some had filler added. CS was treated the same way. Inconels did vary in that we had slight bevel and always added filler. Titanium, the welds were autogenous. Hastalloy also had a slight bevel with filler added.
The tube welding procedure we used was not amendable to rolling after welding as we had a non-circular entrance to the tube that required us to modify a tube roller, by reducing the outer end of each roller to where it would clear the weld. Most of our rollers were 3 roll tapered and 4 roll tapered. We did start using some parallel rollers but initially we had a lot of trouble with the equipment. I have a lot of nice scribes. We always tried to roll pass the tube sheet on SS bundles, both vertical and horizontal.
One reason we rolled and seal welded was we had a lot of SS HX’s in very corrosive service that would vigorously attack the crevice between the tube and sheet. In another area we had quite a few fixed tubesheet SS Hxs’ where some were only rolled. with serrations, these were product to product where a little leakage wouldn’t hurt.
I think overall we our tube bundle program was quite successful over the years. We listened to and investigated the pros and cons of every step in our process but were never convinced that there was anything better than what was evolved in the shop.
We didn’t have any of the large BFWH heater even though we had 8 Power Boilers and 3 waste heat recovery systems.
Again as I stated the large BFWH are a different animal which I will gladly defer to your expertise.
As you are around high pressure or for that matter any water heater I will pass on another HX Anecdote which maybe familiar to some here.
I was walking, on my way to the powerhouse as I wad passed our H2 plant that has waste heat boiler as an integral component. There is a FWH on platform to side and above the doghouse of furnace. I was by but something made me look back at the plant. There 4 people, 2 mechanics and 2 leak stop people, up by the FWH, none should have been there with the plant on stream as all the valves are two levels below. I entered the battery limits of the plant, breaking a rule, climbed up a bunch of stairs and as I climbed the caged latter to platform I noticed several bolts and nuts laying on the platform and water dripping from the flange. I hollered for them to get off the platform ASAP, though in a lot tougher language. I made sure they got right off leaving everything on the platform. As I followed them I got to the top of the stairs and had to sit down, my legs wouldn’t support me. This was the scariest moment in my 42 years in a chemical plant. I got to area supervisor an as I told him to crash the H2 plant, he was on the phone. Later I asked him why he acted so fast and he said that I looked scared. The bolts were failing from caustic embrittlement. The same bunch had slugged this flange the prior month. This was 24" Class 900 flange operating at 900-1000 psig and around 700°F.