Sparking from Thermally Sprayed Aluminium Flanges.

[NeilSF]

Has anyone heard of the following occurance: Burning embers dropping from bolts upon on breaking of flanges.

Rough details are as follows.

Vessel side flange coated with thermally sprayed Aluminium
Pipe flange uncoated carbon steel.
Molycote 1000 grease

Embers smelling of 'fireworks' were observed falling from the nuts released from the thermally sprayed aluminium flange face.

 

[Goahead]

Exothermic reactions between metal (Fe) oxides and metal reducing agents (Al) are the base for the well known Thermit Welding process. Might it be that some sort of this reaction is occurring when releasing the nuts?

http://www.welding-advisers.com/

 

[unclesyd]

Goahead. hit the nail on the head. This is the reason why non-sparking tools are nonsparking around painted or sprayed Al coatings on any steel or cast iron equipment. Any type tool can cause a spark on an Al on Steel surface. It will work in reverse, striking something rusty with Al, but requires certain conditions and more effort.

We had a fire one time during a shutdown while the process people were cleaning up when an a standby operator near a drainage ditch was idly striking an Al painted steam trap with his nonsparking cheater. He lost the hair on his leg.

I was made aware of this problem in the early 50's while working for a valve company and when I went to work for a chemical company it took several demonstrations to educate management on the hazards of assuming because something called non-sparking it was. It all depends on what you are striking.

 

[EdStainless]

It isn't just the spark that results from a strike, you have to remember why a spark can form at all. When you strike there is a lot of heat at the point of contact. You can strike two pieces of non-sparking metal and easily create a hot spot that will light solvents.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[mshimko]

I concur with the above posts, and recommend a google or similar search on the topic "thermite sparking".

 

[NeilSF]

Thankyou for your replies. A thermite reaction is considered the most likely cause - but there are some contraindications.

1. This was the first time the joint had been split since construction (3 years ago) and there was little or no visible evidence of rust.
2. Thermite reactions, as my understanding has it, are difficult to start.
3. This reaction has not before been observed during the breaking of flanges, as far as we are aware.
4. Sparks were observed droping from every nut on this joint. (They droped from the space between the nut and the AL sprayed flange face - not from the torquing tool).

We are awaiting lab test results for samples of grease taken from the joint.

 

[swall]

Slightly off topic--I have seen advertisements for aluminum shot for shot blasting. I thought this would be a bad idea, now I'm sure of it!

 

[NickE]

swall- that would be so coool! think about using aluminium shot on surface rust on weathering steel! Or on old car bodies! wow! the oppertunities here in detroit are endless.

 

[Zoobie]

What about what was in the vessel/pipe? Could anything have leaked and left a residue on the flange face?

 

[IFRs]

How were the nuts loosened? With a spanner by hand? With a high speed impact tool?