SJones:
Thanks, but upon further reflection, I might not be completely right about erosion resistance being expected to increase with hardness. Perhaps it depends to some degree on the nature of the material and the geometry of attack of the erosion.
We did some work recently on frac sand separation for starting up gas wells. A client was experiencing extremely fast erosion rates in well production piping and asked if there was some theory that could be applied towards predicting the corresponding expected reduction in service life. I did some analysis and concluded that, in general, the solids loading profile (in terms of solid particle size distribution) followed a sigmoid (S-curve) function. For a typical particle size analysis, as you increased the solids fraction in the gas stream for a given particle size - especially after correcting for stream void fraction - it became clear that the kinetic energy carried by the particles began to exceed that carried by the "gas" by a multiplying factor of about 4 to 5 at 10% solids by volume. We had some data in the form of a research paper on the corresponding accelerated wear rate for a particular elbow made of a particular alloy, and at least in "order of magnitude" terms my findings were in the ball park.
I took it a bit further and attempted to rationalize things in terms of material fracture toughness and the angle of particle impact. I concluded that there are two modes of abrasion resistance: resistance to scratching and resistance to impact. Accordingly, I concluded that for a 90-degree elbow, probably the latter effect would dominate. I have not been able to put numbers to it yet, but if I hypothesize that abrasion resistance generally increases with toughness (loosely correlated to the area under the stress-strain curve to rupture at UTS), a material might have "toughness" by having either more ductility at a given yield / UTS, or higher hardness corresponding to higher yield with shorter elongation to UTS. If that is true, then resistance to impact abrasion might be better afforded by higher ductility (probably corresponding to "softer") material, whereas resistance to scratching / gouging abrasion might be better afforded by a less ductile (probably corresponding to "harder") material. In very poor and imprecise engineering terms, highly ductile material might be expected to sustain millions of little plastic "dings" and deformations without having material fragments start to break free from the surface, although it might "wear" more rapidly at more acute angles of particle attack. Conversely, harder materials might be expected to behave in the reverse manner to that.
If one believes that, as I do to a certain extent, then erosion resistance of a tee with inflow from the branch might indeed be higher for a softer material than it is for a harder material. Regardless, the resistance to erosion in terms of service life comes down to some function of the rate of kinetic energy transferred as the solids (and gas) are decelerated against the material, and can be expressed in units of power. That makes sense, since the more powerful the "sandblaster", the faster you can "blast stuff".
So, I might not be completely right at all.
I think, too, that the analogies I drwa reflect the "cowboy engineering" side of me.
Regards,
SNORGY.
