threads seizing... ideas why?

[USAeng]

we have a 1 1/4-12 unf 1B and a 1 1/4-12 unf class not specified on drawing but with a pitch limit of 1.194/1.193

the material is 1144 steel and the temp is about 1000F

customer is complaining about parts not being able to be taken apart after in service for some time

Any ideas why these threads would be seizing? Thanks

My initial ideas are to explore different materials and to go to a course thread.

 

[KENAT]

What is the material of the other part?

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[USAeng]

on one the material is 1144 on both parts

on another there are 3 parts with 2 being 1144 and then a tip that is threaded that may also be having a problem seizing that is 316 ss. I wish I knew more exactly what was seizing... the customer has just complained and all I have to go by is the salesman coming back and saying that he is upset that parts cannot be taken apart...

 

[KENAT]

I was kind of thinking galling but I'm not so sure now.

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[USAeng]

one thing I just read in the machinist handbook is that they say for high temp, high strength applications they recommend series 8 threads for anything over 1"... I wonder if the type of thread we are using is bad for this application?

 

[USAeng]

I wonder if we have the external threaded part hardened after machining if that might help as well...

 

[stanweld]

No doubt the threads in the 1144 material will deform due to Creep. This material was never intended for use at 800F to 1000F

 

[MiketheEngineer]

If you heat it up to 1,000 - does it come apart easily??

If so, that may somehow explain the problem

 

[btrueblood]

Is there corrosion or oxidation build up on the threads?

Is there combustion product build up on threads (soot/coke)?

Diffusion bonding might be occurring.

 

[desertfox]

After tightening the joint and then heating are the threads under external load? just wondering whether the threads are deforming whilst at 1000F whilst under external load.

desertfox

 

[USAeng]

I dont know if there is any stresses that remain after being torqued down... perhaps then the heat relaxes the material and it deforms which makes it hard to get apart.

 

[USAeng]

there are no external forces though

 

[SnTMan]

Any anti-seize used?

 

[USAeng]

does anyone know if the series 8 threads would be an improvement?

I was thinking of maybe using some steel with some Mo and Cr in it too...

I think that antiseize is used during assembly at our shop... but I doubt the customer reapplies when servicing at the boiler front

 

[hydtools]

So the customer can disassemble for the first servicing? Is it after the customer reassembles that the thread seizes?

Ted

 

[KENAT]

Trouble is wouldn't the high temperature affect any antiseize that is used?

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[desertfox]

The joint is made cold, then heated to 1000F and if the two parts aren't heated uniformly together you get differential expansion and bingo the threads deform against each other and make it hard to undo.

desertfox

 

[unclesyd]

Was the AISI material quenched and tempered at 1000F prior to use.
Actually a little higher temper might be beneficial.

We have multiple B 16 fasteners that operate at 600F and are subject to periodic heating to 1000F for 4-6 hrs at a time. Our standard thread lubricant is a water based DAG, Colloidal Graphite, applied by dipping prior to use and reuse. There are very few problems with breaking a joint. All bolts and studs 1" and above are 8 threads.

Here is a another high temperature thread lubricant, Thermo-O-Plate 220, we use especially on finer pitch threads and the higher alloy threads with elevated temperatures.

http://www.henkelna.com/cps/rde/xch...tredDotUID=productfinder&redDotUID=000001F4C5

http://www.socousa.com/home/Chemola/Maint/tp220.htm

 

[USAeng]

New update... just was informed that the customer has temperatures that are ranging from 1300-1500F... what does not make sense is that they have product in the area made of alloy carbon steel that seems to last. Does 2.25Cr steel last ok in that temp?

 

[desertfox]

Hi USAeng

Thats probably still to high a temperature for 2.25Cr steel, have a look on this link:-

http://books.google.co.uk/books?id=...m=8&sqi=2&ved=0CFEQ6AEwBw#v=onepage&q&f=false

Is it possible that you could provide a sketch or drawing of your threaded joint along with some technical information like bolt preload, how the joint gets heated up, material properties etc.

desertfox