Galvanized 4" Pipe Tower

[goldendale]

Hi, I'm thinking of building a standard tilt-up wind tower using two 20' lengths of 4" galvanized water pipe. I plan on using a coupler between the two as well as a smaller 2' pipe inside at the joint as a gusset, maybe having a buddy who is a certified welder weld the coupler to the pipes. ( holding his breath or with the proper gear is what he told me) Does anyone out there see a problem or has a better idea? I have the two pieces of pipe already but could use only one for the lower section and the smaller diameter for the upper section. Thanks, Jeff

[ruddycrazy]

G'day Jeff,
               I have always found when welding gal I simply grind off the area where I'm welding so no gal fumes are produced or very little then paint the area with cold gal afterwards.

               I was just thinking about my tower which will be 3" heavy wall hydraulic pipe which are 6 metres long each. What I'll be doing is welding each joint to pipe welding standards then putting 4 gussets to strengthen the welded joint and have a set of guy wire holes for each section. From what I've learn over the years the only time one welds around a pipe is at a joint then any gussets etc are welded along the pipe and being very carefull not put too much heat on any side as to cause the joint to bend after cooling. As you did say your mate is a trade welder he should know the routine anyway.

Regards Bryan

[birdhouse]

jeff-
yea, welding galvo is nasty stuff.  the holding of ones breath does work.  when you say coupler, are the ends of the pipe threaded?  and the coupler would screw on?  if so, threaded ends of pipe are very weak because of the material removed in the threading process.  it would be far better to cut off the threads, and make a heavy duty coupler, or use plate steel for gussets on four sides of the joint. 

are you in goldendale, wa??? 

adam

[Royalwdg]

I agree to grinding away the galv. coating.  Vaporized zinc is highly poisoness. You could use a fan and blow it away. I also grind it to avoid contaminating the weld. Get rid of it. get a good weld and coat with a cold galv. paint.  And yes I agree to welding only lengthwize with your structure and not across.  Leave the ends of mend plates and sleeves not welded.  The edge of a cross weld will be your next weak spot.  Sleeves can be drilled from the side and plug welded from the side leavin the ends not welded. You may have to seal the top of a sleeve to keep water and rust issues out.
Dave M

[richhagen]

I'm no welder, but from what galvanized I have welded, it seems to me that you have to grind away the galvanized anyway to get a good bead.  The whitish smoke from the galvanizing is nasty stuff anyway.  I would definitely add gussets if it was me as well otherwise I would still be concerned about ihave concerns about bending or cracking at the joint. Rich

[fabricator]

By far the best way to connect two tower sections is with an outside sleeve type clamp connector, like the Dans use on their towers, I agree with Royal, welding around the couplings would not be a good idea, the reason being because of the heat affected area the circumferential weld is a point that WILL fail, as a general rule any welding on a tower is not a good idea, clamp on couplers with the guy anchors welded to them is the way to go.

[Watt]

By far the best way to connect two tower sections is with an outside sleeve type clamp connector, like the Dans use on their towers, I agree with Royal, welding around the couplings would not be a good idea, the reason being because of the heat affected area the circumferential weld is a point that WILL fail, as a general rule any welding on a tower is not a good idea, clamp on couplers with the guy anchors welded to them is the way to go.

fabricator
 Could you explain a bit more about the cicumferential weld point " will fail " in a tower application.  I just don't understand this. 

[fabricator]

Welding causes the heat affected area to change and become harder than the adjacent metal, this will cause a fatigue point in this area, in a tower application especially these areas are subject to a lot of movement and stress and will eventually fail.
As Royal mentioned longitudinal welds are not so bad as they are not bisecting the pipe, if the welds were annealed after welding, it would be ok, but to do that the entire tower section would have to put in an oven and brought to cherry red and then be allowed to slowly cool down, then the welded area and the pipe would all have the same temper.
That is why every commercial tower you see bolts or slides together, or they are joined using band clamp type connectors.

[Watt]

Welding causes the heat affected area to change and become harder than the adjacent metal, this will cause a fatigue point in this area, in a tower application especially these areas are subject to a lot of movement and stress and will eventually fail.
As Royal mentioned longitudinal welds are not so bad as they are not bisecting the pipe, if the welds were annealed after welding, it would be ok, but to do that the entire tower section would have to put in an oven and brought to cherry red and then be allowed to slowly cool down, then the welded area and the pipe would all have the same temper.
That is why every commercial tower you see bolts or slides together, or they are joined using band clamp type connectors.

Would this be related only to the guyed mono-pole tower?

[goldendale]

Okay, that makes sense to build a bolt-on coupler. I might just couple a smaller pipe to the top of the bottom 20' 4" pipe. Thanks, -Jeff PS I grew up in the oil refineries as a pipe fitter helper so this makes sense to couple it like a flange, rather than have a brittle weak joint right in the middle.

[Royalwdg]

If you took a cross section of a weld joint you would , most likely, see a small furrow or ditch along the edge of the weld bead where some base metal was consumed into the weld.  A sign of a good welder would be to not have this furrow or keep it to a very minimum.  This furrow is makes your base metal thickness less at that point. Along with hardness issues and the thinning material this is where things will fail first.  I say over build so that after all of these issues you still have disign strength above and beyond so you can get restful sleep during those extremely windy nights.   
Dave M

[fabricator]

Welding causes the heat affected area to change and become harder than the adjacent metal, this will cause a fatigue point in this area, in a tower application especially these areas are subject to a lot of movement and stress and will eventually fail.
As Royal mentioned longitudinal welds are not so bad as they are not bisecting the pipe, if the welds were annealed after welding, it would be ok, but to do that the entire tower section would have to put in an oven and brought to cherry red and then be allowed to slowly cool down, then the welded area and the pipe would all have the same temper.
That is why every commercial tower you see bolts or slides together, or they are joined using band clamp type connectors.

Would this be related only to the guyed mono-pole tower?

No, I doubt you will ever see a monopole with a circumferential weld, almost all monopoles are slip joint construction, adding welds to any tower throws wild cards into the mix, the new grid power poles you see going up these days are all slip joint construction.

[Watt]

If you took a cross section of a weld joint you would , most likely, see a small furrow or ditch along the edge of the weld bead where some base metal was consumed into the weld.  A sign of a good welder would be to not have this furrow or keep it to a very minimum.  This furrow is makes your base metal thickness less at that point. Along with hardness issues and the thinning material this is where things will fail first.  I say over build so that after all of these issues you still have disign strength above and beyond so you can get restful sleep during those extremely windy nights.   
Dave M

I understand what you are saying now.  That ditch is ' undercut '.  More a persons abilities and undrestanding of metallurgy along with which welding process.  Just saying, we build huge drilling rigs ( amongst other platforms ) which our derricks are under tremendous stresses from compression to twisting and tension and compression at once while in use or being moved.  Not to mention our cunductors from our stacks down to cement are under tremendous differentials as well.  Just saying, it can be done but most certainly agree with safety. 

[dloefffler]

A question about flanges.

How are the welds on the joining flanges of towers handled? These seem to be welded as sell as the crossmembers.

Dennis

[Watt]

What kind of tower?  If it's a pipe tower, the flange is an extension of the pipe and the flange is designed to take load transferring stress equally to the pipe.  The process to attach the flange includes, along with other things, preheating, beveling, grinding, fitting and welding.  Depending on the process and pipe thickness, multiple passes of different fillers.  Then stress relief, inspection and coating. 

[fabricator]

For the most part you won't see flanges on wind towers, engineers don't like the added complexity of adding welds into the stress equations. There are towers that have welded flanges, the huge utility scale towers have internal flanges but these things are so over built it's awesome.
A lattice tower with welded cross members is a different story as there are at least three legs and a lot of redundancy in the cross members.

[birdhouse]

oh man, does this mean i did my tower all wrong??

4" x .156wall pipe in 20' chunks.  joints have circumfrance weld, then four flanges 14" x 4" x 1/4" plate steel.  lapping 7" onto each pipe.  beveled and welded solid at all intersections. 

i hope you can see here...  still one more 20' chunk of pipe to go on.



adam

[Watt]

oh man, does this mean i did my tower all wrong??

4" x .156wall pipe in 20' chunks.  joints have circumfrance weld, then four flanges 14" x 4" x 1/4" plate steel.  lapping 7" onto each pipe.  beveled and welded solid at all intersections. 

i hope you can see here...  still one more 20' chunk of pipe to go on.



adam

I sort of doubt you will have trouble but, to be safe, keep a watch on where the points of the gussets are welded to the pipe.  Thinnest edge of the gusset I guess is what I mean. 

[birdhouse]

watt-
my gussets kinda look like this-

      ___________
    /                     \
   |                       |
   ---------------------

with a hole in the middle for guys.  i did weld extra heavy (good penetration) on the lower right and left in my "drawing"  i've read about how stress fractures can begin there and move deeper causing trouble.

adam

[Watt]

watt-
my gussets kinda look like this-

      ___________
    /                     \
   |                       |
   ---------------------

with a hole in the middle for guys.  i did weld extra heavy (good penetration) on the lower right and left in my "drawing"  i've read about how stress fractures can begin there and move deeper causing trouble.

adam

I wouldn't be too worried, just keep an eye on how the turbine tracks the wind and see if you get any twisting of the tower.  The more it twists the more I'd be worried about spreading out the stress on the lower right and lower left of that gusset. 

[fabricator]

If you'r gonna do it, that's the best way to do it, with gussets and guys attached at the joints.