Vespel CR-6100 for impeller wear Ring on Boiler Feed pump 6

[amjp]

Stainless Steel wear rings tend to gall/seize when they come in contact with each other causing considerable downtime and cost.

Does similar problem of galling/seizing of wear rings occur on API C-6 pumps with Chrome wear rings.

Any experience out there replacing the Stainless Steel wear rings with Vespel CR-6100 on BFW Pumps. What are the resultant benefits (reduced clearence between rings and improved efficiency, wear rate and failure rate etc).

 

[JRLAKE]

I am pretty certain this has been discussed in detail. I would do a search.

 

[bk19702]

To echo JRBlake, you should be able to find an earlier thread on this. One of the biggest benefits with running tighter wear ring clearances is increased rotor stability (via our friend the Lomakin Effect). This can be a huge advantage in your favor when looking to improve pump reliability, particularly in an older pump design.

 

[kh1953]

A useful article regarding composites in Boiler Feed pumps.

thread407-173199

 

[JJPellin]

I can offer one reference for converting a group of BFW pumps to Vespel wear parts. We converted three old Pacific pumps (Model JB 3, 4 stage) to Vespel about 5 years ago. The pumps had a history of low flow operation, cavitation, wear-ring and bushing rubs and seal failures. These very old pumps had long flexible shafts and were originally built with packing. We believed that the conversion to mechanical seals had resulted in greater shaft deflection and made our problems worse. The tighter clearance in the Vespel seems to have helped in that regard. But, we had a number of problems anyway. Even though we exactly followed the design and installation requirements from the maker of the Vespel, we had a set of wear ring failures after a relatively short run. The impeller eye rings had collapsed down onto the rotating rings and been destroyed. Based on some information from another vendor, we think we know the cause.

Vespel has a very low coefficient of thermal expansion in the radial direction, but a very, very high rate in the axial direction. If the Vespel is cut to exactly fit the envelope where the original wear ring had been, it will grow out beyond the holder, axially, once it heats up. The unsupported projection of this ring would normally be toward the high pressure side of the ring. The OD pressure on this unsupported ring causes it to compress inward against the shaft. When the tip touches off on the shaft, it seals off the pressure drop so that the majority of the ID of the ring is now at the lower pressure and the majority of the OD of the ring is at the higher pressure. This is enough to collapse the ring. This can be avoided in a couple of ways. First, a relief cut on the OD that breaks through to the low pressure side can keep the OD from seeing the higher pressure. And second, cutting the ring shorter, so that at full temperature, it does not extend axially beyond the holder, will keep that unsupported projection from deflecting inward to start the failure process. We made both of these changes and have had no further problems.

In this group of pumps, and in a large number of other vertical and horizontal pumps in a wide variety of services, we have had very good results with Vespel and feel it has reduced vibration and shaft deflection, improved low-flow or no-flow survivability, improved overall reliability and increased efficiency. With a little care in the conversion, I would highly recommend it.


Johnny Pellin

 

[Artisi]

Johnny

A great post with good information for those who are interested and have a need.

 

[EFord]

why not check out

http://www.graphalloy.com

for bushings and bearings? Graphalloy is a graphite metal alloy and they have many years of successful experience in BFW pumps. The material is non-galling, dry-running, dimensionally stable, and is also used for high-temp applications around 750F.

 

[bk19702]

Graphalloy is a good option also, but where Vespel seems to win out (at least in my experience in the past) is in it's machinability. When you machine Graphalloy, you will end up with a mess of powder.

 

[270866]

We have several reference cases in boiler feed applications, replacing impeller and case wear rings with non-metalic wear parts. Instead of Vespel we have used PUMPTEC thermoplastic/carbon fiber material from company Createc in Germany.

Please contact Erwin Birk (+49 7541 700 77 0)or check their web side

http://www.eplastic.com.

 

[FFV5]

Vespel CR6100 is indeed a good material to replace the wear ring material in dry running pumps such as BFW pumps. It is Teflon based reinforced with carbon graphite, this gives it a good self-lubricity with low CTE that helps survive run dry processes.

Certainly highly recommended for BFW pumps!

 

[EFord]

We stick with Graphalloy for high temp pumps of all types, including many BFW pumps. The material matches housing thermal expansion and has a much larger temp range than Vespel or other plastics. It also ends up being less expensive.