Material melting, or is it wearing away? see picture

[USAeng]

This is a nozzle in a coal fire power plant with opposing burners so the fire is pointed at eachother on both sides. Attached is a picture of an igniter nozzle that has been melted according to the customer. The nozzle used to narrow down to more of a tip at the end so what you see is the nozzle minus about 1.25". I am trying to figure out if it is melted or if the material has been worn away / corroded from leftover coal dust and coal ash byproducts. Also I am hoping to get some new material to make some of these from that will last longer for them. I am thinking good-better-best 304-310or347-inconel 600 series.
Temperature is an average of 1600-1700F and could reach 2000F. Thanks for any opinions.

 

[metengr]

Based on the photo and from what I have seen over the years with large power boiler coal nozzles, this is local melting. I would recommend you use either 310 stainless or RA333 for this service.

 

[racookpe1978]

Probably a mix of all those.

There are "blobs" and "sags" where softened metal have been drawn together by surface tension. That would be a symptom of melting - but also of softening which begins sagging and drooping. But the melting didn't happen everywhere, and the tip didn't just "melt off". If it had, you wouldn't see the crystalline-like surface, sharp breaks, cracks and the hard edges where the tip vibrated (?) and broke off.

Vibration could break off sections. (Wind from fans or other nozzle air/coal dust flows?) but the sagging would probably come first.

If the nozzle tip were softened or degraded first, would that have plugged cooling air flow through and around the tip? Were there ever auxiliary small air flow openings in the lost section that would have kept the end of the nozzle slightly cooler? Seems like you need to drop that tip temperature to about 1450 or so.

 

[blacksmith37]

Look up "hot corrosion", vanadium slags, metal dusting. Occasionally these problems can be fixed with 444 stainless, (but not for high stress applications).

 

[arunmrao]

It is localised melting,scaling outside,, erosion wear I am unable to make out(perhaps blame my eyesight),feel it with your fingers around for any smoothening of surfaces. As suggested change over to 310 or RA 333 for overcoming this issue.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[USAeng]

thanks a lot guys... this makes me feel much better about my choice of steel... very good information

 

[mrfailure]

The exfoliation on the outside of the nozzle confirms wall loss from corrosion attack. Looks like wall loss initially from hot corrosion; the loss of integrity at the nozzle tip compromised the flame direction, resulting in subsequent melting

 

[blacksmith37]

Ooops... points off for the old guy; I meant 446, a ferritic that forms sigma for strength (but not toughness), very good for soot blowers, thermowells etc.. I saw the 333, one of my favorite alloys and got distracted. The absence of Ni in 446 makes it much more resistant to hot corrosion,etc, than 310, and cheaper. If money is no object, 50:50 (Cr, Ni) will be great (but product form can be a problem.)

 

[USAeng]

Thanks again... I will check into that 446 price compared to the 310... and the comments on the modes of failure are good... I thought about the heat of the flame at the nozzle being an issue but you are prob right about the change in direction of the flame being a problem

 

[EdStainless]

are these now machined from bar?
Ever thought of casting them?
That opens up alloys that you don't want to have to machine.
High carbon versions of 45Cr55Ni and such.

For me, I would try 310 first.
If you are getting wear still then look at Co based alloys. I like the low carbon ones.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[arunmrao]

If a cast option is considered then ASTM A 297 grade HW,will be a wonderful option. I have made such parts,in this grade successfully.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[USAeng]

we will be making small quantities so we will prob. machine from bar stock... I will check out the 310 first and see how that works.

 

[CalvinKelly]

What alloy are you using now?
It looks melted to me. Usually if it looks melted, it is melted. And if it is melted you'll have a hard time finding something else that doesn't also melt.
In my experience, coal nozzles supposedly running 1700-1800F have been known to melt (Texas, during a 1980's heat wave).
310 sounds as good as anything. 253 MA is stronger.
RA333 is absolutely my favorite alloy but does have about 100F lower melting point. Bar not available but tube can be fabricated from plate, see HypeR Alloys, Roseville MI.
Yes, I am a retired Rolled Alloys metallurgist.
As in, my signature below is no longer correct but I do not know how to successfully change my profile.

James Kelly

http://www.rolledalloys.com

 

[unclesyd]

If your size requirements permit you might be able to get centrifugally cast material in several of the above mentioned metals in near net shape. I know there are many variations of 310 SS like the HK alloys available
If you could post your size requirements perhaps Calvinkelly might offer some additional advice.