Boron Coating on Centrifugal Slurry Pump 1

[HenryBell]

I am designing a booster system for a slurry service that utilizes centrifugal pumps.

Some general info: 400gpm, 300 TDH, 1% catalyst fines in slurry, 0.008" max particle size, 645-660F slurry temp.

The client has requested that wear rings be eliminated from the design which leads to hot pump clearances. The client also requested carbon steel with boron coating for the barrel, casing, and impeller. I was told that in the Boron coating process the pump parts mentioned are heated to ~1900F and that they require re-machining afterwards.

Typically how thick is the Boron coating? Only 1 of the 4 vendors that were sent bid packages brought up Boron thickness as an issue. He thinks the Boron coating will be too thin after machining. This vendor particularly favors (high velocity) Sume coating instead, saying that it is up to 3x thicker than the Boron coating.

The other 3 vendors have not mentioned anything after the proposal was sent. Should I worry?

Sincerely,

Henry

 

[ChickenSoop]

Interesting application.

I don't have your answer, but what is the pH? If neutral, why not consider high-chrome iron slurry pump?

How are you sealing the pump - seal or packing?

 

[JJPellin]

I don't have an answer to your question, but have some limited experience with Boron coatings. We used to use them for bottoms pumps with abrasives. We used them because it is one of the few coatings that can be applied to blind area. That is to say, many coatings can only be applied line-of-sight. Hidden areas inside a pump volute or impeller cannot be coated with some processes. I believe that the machining needed for Boron diffuser coatings is because of distortion from the heat. So, the only areas that need to be machined are fits and faces that probably don't need to be hard surfaced. The way that I believe Boron diffusion coatings are applied they don't build up a surface thickness but affect the material properties to some depth. Please correct me anyone if I have my facts wrong. We ended up changing to a harder surfacing process because Boron was not hard enough.

 

[unclesyd]

The company that provided our Boronizing doesn't exit any more. We never worked with this company but did consult with them.

Here is one company who offers Boronizing. The second company is the one that has the technology.

http://www.crmcbandassoc.com/products/borongas.html

http://www.vaporkote.com/default.htm

 

[stopsunset]

I have experience with Boron diffusion.If I understand the process correctly, it's not really a coating becuase the the boron actually diffuses into the metal(approx. 80 mils)rather than puddling on top of it. We modifies our FCC slurry pumps in 2000 by using this process on the wetted parts.We haven't touched the pumps since.It was a tremendous success!

 

[Woodlands]

for carbon steel, boron diffusion alloying (nicknamed TMT) changes the surface microstructure ~.011 to produce a homogenous depth throughtout the part (except where you mask it off). It is a heat treating process and many refinery customers use for erosion/corrosion protection in that service versus thermal spray coatings, which are limted to "line of sight" application and are really just a mechnical bond versus the weld overlay's which are very "stressful" versus the high chrome irons, which are used in the miing indusrty and by some pump manufacturers, but are suject to problems when you have a thermal transient. There are several vendors in the US that do this process (TMT, Vapor-KOTE, SMS), but in many cases it is better to colloborate with the pump OEM, as it has been proven that flow distrubances caused from a variety of reasons such as off peak flow, suction or discharge recircualtion, injection flows from flushed wear rings, etc., can cause consideration acceleration of erosion not matter what type of protection you have. It is a time consuming process because area's that need to maintain a tolerance must be machined after the TMT process because the parts distort during the treatment, therefore stock must be left on these surfaces (or added to it) prior to the process. The flavor of the month for this application calls for carbon steel base alloy for impeller, cover, and case, ringless design with direct stellite weld inlay on the case ring area prior to the TMT, and DLD coating on the impeller wear area after the TMT.