To use fittings or not to use fittings, that is the question
To use fittings or not to use fittings, that is the question
(OP)
Philosophy opinions please.
If you were to route a vapour vent line with 3/4" tubing approximately 10', 10', 5' (x,y,z) would you forget swagelok fittings and bend the tube between the endpoints or would you use the elbows to accomplish the same? Additional info; end points are facing 90ยบ apart (i.e. one faces north the other faces east)
I guess really its a debate between;
A) min bend radii vs. fittings leak
B) spaghetti look vs. "clean" look
C) ???
Discuss.
If you were to route a vapour vent line with 3/4" tubing approximately 10', 10', 5' (x,y,z) would you forget swagelok fittings and bend the tube between the endpoints or would you use the elbows to accomplish the same? Additional info; end points are facing 90ยบ apart (i.e. one faces north the other faces east)
I guess really its a debate between;
A) min bend radii vs. fittings leak
B) spaghetti look vs. "clean" look
C) ???
Discuss.





RE: To use fittings or not to use fittings, that is the question
B) I don't think this is an issue. You can make a mess either way - and I am sure I have done it both ways.
C) Less fittings to lose or forget if one bends the tubing?
But, that's just me.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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RE: To use fittings or not to use fittings, that is the question
Reason:
- less fittings therefore less installation cost
- less work therefore less installation cost
- less leaks therefore less operational downtime loss
- less leaks therefore less maintenance
- less maintenance therefore less operational cost
RE: To use fittings or not to use fittings, that is the question
RE: To use fittings or not to use fittings, that is the question
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: To use fittings or not to use fittings, that is the question
Of course, you can always buy the tube bender from Swagelok...
RE: To use fittings or not to use fittings, that is the question
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: To use fittings or not to use fittings, that is the question
the advantage of fittings is that the installation is easy to maintain.
also... making it a one piece item it makes it cumbersome to set in place.
i vote for fittings... the cost of measuring, bending and installing 25ft of tubing in man-hs may be more than the cost of setting 3 pieces of tubing with 2 intermediate fittings.
you will have to surely give some slope back to the tank to drain condensates on the horizontal sections and will need to bend the horizontal sections near the fitting.
cheers
saludos.
a.
RE: To use fittings or not to use fittings, that is the question
All of the working tubefitters whom I've met cannot make two bends in a single plane and hit a specified center distance between the end legs. Most of them didn't know what the marks on a tube bender are for; none knew how to use them.
If there's any chance the tube will have to be rodded out someday, then it should be assembled with elbows anyway.
If you specify bends, most working tubefitters will make the tube in three pieces, each piece having a bend at one end, and the other end made long and trimmed to suit in the field, with two straight couplings. If you insist on making it in one piece with two noncoplanar bends, prepare to throw away at least two pieces that don't quite fit.
Mike Halloran
Pembroke Pines, FL, USA
RE: To use fittings or not to use fittings, that is the question
all working for us!
Note that your total length is over 20', which is the longest standard length you can get tubing in- unless you want to use coiled stuff AND you have a coil straightener. So you're in for one fitting anyway. That means one bend can be saved by using a 90, making fitting easier.
In general terms: if you've got a decent tubefitter, bend the tubing and save the lossy, expensive elbow fittings. The fact that you don't need elbows, plus the ease of assembly/disassembly/reconfiguration provided by means of the compression connections, are the two principal reasons to use tubing in the first place.
If you don't have a good tubefitter, go with the elbows- or buy a piece of stainless overbraid flex and route it along some support. That is, provided the tubing will meet your pressure/temperature/inertial conditions.
RE: To use fittings or not to use fittings, that is the question
Related question;
When you design do you do so without regard of personnel who will perform the task, or do you limit your design and give up on cost/performance for the sake of wider installation margins? (i.e. idiot-proofing)
RE: To use fittings or not to use fittings, that is the question
The answer to your question is yet another question: are the people doing the work known to you and working under your direction, such that you can assess their competence and supervise their work and ensure that your design intent is faithfully executed? Or do they work for somebody else- and your only interaction with them will be via drawings and specs? The answer to that question will determine, in part, the level to which idiot-resistant design is necessary.
All design is an optimization amongst what's commonly available, what's commonly done, the experience and competence of the folks at hand, and what is minimally necessary or desirable from a materials minimization or functional or cost-minimization perspective.
Those things said, you must be careful not to over-specify out of fear or ignorance. If you're not a tubefitter yourself, making decisions on behalf of the tubefitter without speaking to him/her is a good way to cost yourself more than the necessary amount of money- both in your own time and in their time (and probably materials) wasted. Choose good folks to do the work, then give them acceptable alternatives to choose from. They'll select the optimal choice with far greater skill than you might hope to accomplish in isolation.
RE: To use fittings or not to use fittings, that is the question
It's sad on my part to read about recent experiences that show that installing fittings onto pipe is more desirable from a do-able and professional point of view. My experience (although not recent) shows totally opposite results. pennpiper points out some good features about bending; however, one of the most important - from a design and hydraulic aspect - is absent: bending a tube or pipe significantly reduces the pressure drop in a system.
I accept and design around the employment of pipe (and tube) fittings being used on my projects. But in my experienced opinion, I do it as an acceptance of not being able to achieve the ultimate in what pennpiper rightly points to as perfect piping: bending rather than welding whereever possible. What I have accomplished in the field with 2 welders and 1 pipefitter (all from Italy) would startle and astound most of the people contributing to this thread - with the exceptions of maybe pennpiper and moltenmetal. I marvel everytime I compare present USA piping projects in the field and recollect what my guys in Peru, Venezuela, Chile, and other countries accomplished with nothing more than one Lincoln DC welding machine and 2 Oxy-acetylene torches. It is absolutely astounding what human ingenuity and craftsmanship can accomplish if allowed to prosper - and cultivated as such.
The outstanding example of this that I recollect was in 1965 when I was encharged to build a CO2 combustion generation plant in Peru. I contracted 2 ex-Montecatini welder-fitters who had participated in installing an ammonia plant in Callao, Peru and stayed there when then fell in love with local belles and started their own metal fabrication shop. They were both classified as "maestros" in iron working. This meant they were master fitters and welders as well. My plant design called for humid CO2 generation, Amine absorption at atmospheric pressure and subsequent compression and refrigeration to 1,200 psig pressure and -20 oF storage temperature. It also include a Dry Ice production process that involved CO2 recovery at -100 oF and pressures to 350 psig. I contracted these guys to furnish all the fitting and welding of 100% of the equipment involved and they assured me they could do it with nothing more than a P&ID. They insisted on bending all the possible process and utility piping that they could, up to 2". They also insisted on welding all piping butt-welded with the autogenous technique: only a metal rod and an oxy-acetylene torch. They were not only successful in welding all the piping and bending most of it, but they guaranteed that they would not have a leak - in either liquid or gas service. When they finished, I was able to startup the new plant within an hour and we were producing quality product into storage within 2 hours. They were 100% right. I didn't have a damn leak! And all the Schedule 80 piping butt welds were so damn beautiful, it almost made you cry. Some of the welds were ordered cut by me to inspect prior to startup and the penetration was 100% root - an so homogeneous that you couldn't tell where the parent metal was.
That plant produced for 30 years until they had to shut her down because of obsolescence and nothing else. I was raised as a card-carrying boilermaker through college, so I could appreciate what had been done. The piping layout and the trajectories were a thing of beauty and literally seamless. We never experienced any corrosion in that plant - on the MEA side or on the wet CO2 side as well. That's why a lot of guys cried when the unit had to be put away.
My point in telling and sharing this experience is to expound what has been said and stated by moltenmetal, pennpiper, and BigInch. I realize a lot of younger folks haven't had the opportunity to experience what I and others have, but the good news is as moltenmetal indicates: there's more than one way to skin a cat, and we have methods and ingenuity that have survived the test of time and experiment. Sure, welding techniques have improved. But human ingenuity and skill have much more potential to give than what many suppose.
If it were my plant and I could come up with the skilled craftsman, I would bend every last foot of piping or tubing under 1".
RE: To use fittings or not to use fittings, that is the question
To answer your question Molten, I know the crew that will perform the work and there are a couple of guys I trust, and a couple are suspect to me. I have no say in who gets deployed so I always have to specify to the LCD. It really bothers me that I have to either tie the pipe fitters hands or be so particular that if some minute detail is missing all work stops because of it because its expected.
Sorry bit of a rant there.
RE: To use fittings or not to use fittings, that is the question
Well said!
RE: To use fittings or not to use fittings, that is the question
Anecdotal:
I have had the pleasure of working around some very skilled pipefitters and welders at our site early in my career.
One part of our polymer process is heated by vaporized heating fluid which encompasses a large area with several thousand bends in lieu of fittings except flanges for valves. Our entire system was fabricated over a period of several years by two fitters and two welders working on slabs. The max size in the bends is 2" with the majority be 1" and 1 1/2" schedule 40 CS.
All the original ammonia piping in and around the storage area was bent pipe.
In our original hydrogenation facilities all piping was bent on site with the only flanges being for valves and connection to compressors and reactors. The piping was 2" with 1/2".
I made a call to a mechanical supervisor on a current large piping project going on to see if he had any one could bend pipe. He unqualified answer was no. In fact he said that in removing some of the above mention bends his people were amazed that under all the insulation there was no fittings. He also stated that he has one instrument mechanic that can bend tubing and make it look pretty. He is kept busy in the pilot plant and is about to get hired by the site. The pilot plant stays away from fittings for all the reasons mentioned in previous post.
While speaking of bends I've been in the process of trying to get a sample of some SS pneumatic instrument tubing that is going to be removed to show people what can be done by skilled people. The area I want is where the tubing comes from a central control room and joins a pipe rack. This junction has the tubing going in 5 directions. Over the years I have been asked several times what type machine was that done on.
There is currently no incentives for anyone to learn some of the trades/skills that were once quite common. Over the years I picked on some aspects of pipe bending and straightening of structural steel and being able to recover Austenitic SS components that were mechanically bent. All these skill have stood the company in good stead and not once did I get an attaboy from management. So why did I use these skills, The only reason was personal satisfaction and a few compliments from some trades people.
RE: To use fittings or not to use fittings, that is the question
If you have a skilled welder, then definietly fittings.
You work to the strength of your crew.
If you have both, then I guess it goes to personal preference and the situation at hand?
Personally, if I can bend the tube, I would - personal preference.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?