Bad, Epoxy secured Guy Fittings!! 2

[Flareman]

I've been using and specifying Guy ropes for structures for a number of years. I generally use bridge strand with a bridge fitting for tensioning.
My preferred attachments to the structure have always been Open Socket fittings which I believed to be wedged with hot, poured zinc.
Recently, I have become aware (after the fact) of two different applications in which the open sockets were secured with epoxy (???) and which both failed in service. Fortunately neither occasion led to a dramatic structural failure because of the intrinsic strength in the structure and the non-concurrence of design winds.
I am addressing this with the rope supplier(s) but I would appreciate any knowledgable feed back.
I always specify proof testing of ropes and fittings at loads greater than maximum design/operating condition.
Thanks for any help.

David

 

[robert99]

Hi David - My name is Geoff from Calgary AB. We have experinced a number of cases of epoxy and Zinc failures over the last few years. A few years ago we prooftested two bridle lines (1-1/8) for a drilling rig that where epoxy filled. The bridle lines passed the prooftest (2x safe working load) and where put into service. The lines where put under load and lifted the mast 4x when one of the lines failed causing overloading on the other line which failed as well. During discoveries it was found that during the process where the wires are broomed and the socket filled with epoxy the rigger did not use a proper kit and the sockets where only partially filled. The epoxy tends to flash off very quickly and if the rigger does not pour epoxy in immediatly it tends to get hard and is difficult to pour.

We have also found socket failures on Incinerator Stacks in Gas plants in Alberta and British Columbia. These stacks are refractory lined with 3" of a light weight 2600 degree F castable. The stacks are also cladded with aluminum cladding with about a 2" air space. The air space is open to the enviroment and works like a chimney effect to cool the steel.

Most of these stacks that we have found have been in service for over 25 years and have lived past there life cycle. Over this period of time the refractory has lost its "R" factor and has become very dense. The guy lines that are attached to the stack in most cases are zinc filled. What is happening is the heat transfer from the stack to the socket has increased and the zinc now tends to creep. The first occurance of this was to a stack ata Suncor facility in central Alberta where the operator discovered the guy line laying on the ground one morning. We repaired the socket using epoxy and with in a few days the socket failed again.

We have sinced started a maintenance program in inspecting socket assemblies on all stacks. Since the first failure in 1984 we have replaced zinc filled assemblies on several Incinerator Stacks in Alberta and BC.

Part of the group of companies we belong to is a wire rope equipment supplier. We have seen a number of poured assemblies fail under proof load and again this primarily due to poor assembly.

Thanks
Geoff Robertson

 

[wiff]

Also consider the performance of epoxy at elevated temperatures. You'll probably find the zinc poured fittings outperform the epoxies.

 

[meca]

This is a very interesting discussion, that I find very useful. My company designs guyed stacks, and I have never heard of zinc or epoxy melting. Actually, I have never heard of epoxy being used before this email thread.

In the case of high temperature stacks, maybe it makes sense to use a wire rope with wire rope clips rather than structural bridge strand with an open socket. I realize the cost may be more, but you would be using a mechanical joint which is less susceptible to temperture. The wire rope is also more flexible which would be more forgiving for thermal expansion, but there is a trade-off in that it permits higher lateral displacements.

Regards,

Chris

http://www.mecaconsulting.com

chris@mecaconsulting.com

 

[Flareman]

Gents
Thanks for your input. Particularly the feed back from Geoff. Like Chris I had not heard of Epoxy use until now. I am surprised that you report some zinc failures too. I can only think of 1 in 30 years and I still don't know how that occurred.
My discussion with the supplier (of the latest problem) leads me to believe that, as you say Geoff, temperature is the root problem with the the epoxy. I think it's taken them by surprise too but their reaction lets me know I'm not the only complainee.
My current intention is to say NO EPOXY in the future because (with Flares) there's always a high temperature potential.
We always have assemblies proof tested of course and I'm interested in your remark Geoff that you have replace a few zinc filled assemblies. With what? New zinc? How does the zinc wear? Should I specify a particular inspection at year N? We already recommend regular inspection and retensioning but, of course with a flare, there are very limited opportunities to get up to the guy attachment and look, and taking off a guy is no small matter on a tall stack.
I know that there are now crimped (swaged) fittings available too for smaller ropes. I had tended to stay away from these in favor of the zinc as it seemed to me that there would be an inherent weakness at the crimp although I'm now told that may not be the case and the fatigue life may actually be better. Any thoughts?
Chris, the reason I stay away from clips is because of the need to use lower strength rope, wear on the independent core (and the fact that theres a risk of getting fiber core instead of IWRC) and the difficulty with making the bends in larger diameter strands. In the main, the only drawback of the bridge strand is the need to get the length right which doesn't give us a problem (although as an aside, we did have an engineer some years ago who added a few feet "for good luck&quot.

David

 

[RHK]

I have used "Wire-lock Resin" which is a two-part adhesive on a couple of applications where I had to thread the wire rope into the structural steel and back out again. There wasn't enough room to thread the socket through this. The beauty of this was removing the socket only required a modest amount of heating to break the bond between steel and resin and allow recovery of the socket for use on the next special lifting task.

The Wirelock brochure I have is at least 10 years old, if not 20. It has a warning that Wirelock should not be used about 115 degrees C. But it also comments "A series of creep tests confirm, however, that Wirelock is much more efficient than zinc at 130C."

Russell Keays

 

[robert99]

Hi Guy's - David your question in relation do we still use zinc...yes. In the case of Incinerator Stacks and the end attachment we installed 1200mm spacer plates to the guy lug on the stack and cut off the end attachment, shortened the rope and resocketed the socket assembly back on using zinc. In most of these cases the zinc creeped anywhere from 5mm to 25mm. These where all large diamwter stacks usually 6-8 ft. in diameter x 300+ feet high with operating temperatures of 1000 degrees F to 1300 degrees F.

Last year we resocketed zinc filled sockets on a large pipeline crossing just outside of Calgary. The crossing was over 600 ft long with 1-7/8 dim. main support cables. The bridge was installed in the early 60's and is subject to severe wind loading. The zinc in these had creep fromm 10mm to about 13mm in one case. Again in this case large spacer plates where installed and the sockets repoured using zinc.

We currently inspect all socket assemblies on all guy supported structures for zinc creepage. We currently do not encourage the use of epoxy on any socket asembly, however it is widely used in the industry, especially for bridle lines. We have seen to many failures under proofload, including the spalling of the epoxy when the lines are put under proof load. We have had pieces of epoxy the size of a quarter spall off the top of a epoxy filled socket.

Geoff