Pipe to Pipe welded Joint in a reactor shaft-blade assembly 1

[plantprowler]

I've seen some Glass Lined Reactors where the agitator shaft & blades are all fabricated from what seems to be heavy steel pipes (they avoid sharp turning radii where the glass coating will crack). Which are finally coated with the protective glass & baked etc.

My question is about the blade-to-shaft joint. Essentially they had to weld a small diameter pipe (blade) to a large diameter pipe (the shaft) at right angles. Would this lead to one continuous hollow cavity or would the blades be a separate cavity.

My engineering sense says the metal wall of the shaft would still remain as a barrier but just wondering whether for fabricablity etc. one may prefer to gouge out the wall area underneath where the blade will be welded to?

From the drawing I have it isn't obvious how that welded connection would be.

 

[SwinnyGG]

If I'm reading correctly your'e wondering if, when the smaller tube is attached at a right angle to the larger tube via full perimeter fillet weld on the outside, the wall of the larger tube will melt away leaving a hole connecting the internal volumes of the two parts?

Unless something very weird happens, the answer to that question is no.

 

[plantprowler]

Thanks @jgKRI

Yes. You interpreted correctly about the " leaving a hole connecting the internal volumes of the two parts"

That's exactly what I want to know.

OTOH, melting is one possibility but I was more thinking about whether there'd be some fabricablity / welding reason to do a perimeter weld after removing the intersecting part of the larger pipe on purpose. i.e. In the same way you'd gas cut out the portion say if this was a pipe-tee for liquid transport applications.

 

[plantprowler]

To follow up, in a second vessel I took an actual photo. See below. Here the blades look like flattened pipe-like sections.

My question is the same: Would the blade + shaft be one connected cavity? Or separate ones.

 

[JohnGP]

I've not had experience with glass lined fabrications, but don't see why you would need to open up the shaft intersections to make just one cavity. With galvanising there needs to be a through path, but don't think this applies here.

 

[r6155]

Consider a shaft like a solid round bar, no holes in the shaft.

Regards
r6155

 

[SwinnyGG]

whether there'd be some fabricablity / welding reason to do a perimeter weld after removing the intersecting part of the larger pipe on purpose

No. Drilling or cutting holes in the central shaft tube does not make the fabrication easier, faster, or cheaper- just the opposite, it will add significant cost and time.

Are you asking this question because these rotors are produced so that the internal volumes of all sections are linked in the way you describe, or because you're looking for improvements?

 

[plantprowler]

Thanks @jgKRI

Context is that we are wondering if there's a corroded spot on one blade whether material can travel and damage other blades straight without any restriction. Or if there will be a barrier (at least temporarily)

 

[SwinnyGG]

You're worried about flaking or other damage inside of the tubes?

Unless you have evidence of this I would put the probability of significant corrosion on the inside of a fully sealed, welded, and glass coated assembly as very very low. Even if there is loose material inside the tubes, it's going to be transported to the tips of the fins by centrifugal force. The likelihood that it would ever touch the wall of the central shaft, let alone enough contact to wear a hole into the internal volume of the central shaft, is very very very low.

 

[glsinfo]

The blades to shaft contains a vent hole. So, yes the possibility exist for fluid to enter the blade and the shaft (& other blades).

 

[plantprowler]

@glsinfo

Ah! A vent hole! That's the most plausible explanation. Makes total sense.

Just out of curiosity: Why do we need to vent the blade cavity to the shaft cavity? What's the reason?

 

[glsinfo]

The vent is for off gassing during the firing process (for fusing glass to steel)

 

[plantprowler]

@glsinfo

Makes a lot of sense. I think you have figured out the exact answer to my puzzle. Thanks!