Material Needs to be Reviewed for Acid Slurry

Is the pump a centrifugal pump?

Is it wearing out primarily due to abrasion or corrosion? It says it's good for high Cl environments, but what about H₂SO₄? Here's the datasheet.

There is a somewhat incomprehensive chemical/Material of Construction (MOC) database at the Cole-Parmer website that may give some clues:

http://www.coleparmer.com/techinfo/chemcompresults.asp

If abrasion is the primary cause of wear, then elastomers to line the pump head are often used, depending on the type of slurry.

Have you called any pump vendors?

I entered the following string in Google:

+"extreme environment" +"slurry pump"

Click on it to see results.

Good Luck!

Thanks for the prompt reply, Actually, they are wearing out mainly due to Erosion. It's a centrifugal Pump and I just viewed the Impeller last week, it was all rotten after 1100 hours.

You have double extremes, 99% acid plus abrasion due to slurry. So pump body, impeller and sealings shall not only be compatible for acid to be handled but it should be hard enough to withstand abrasion attack from slurry. So external surfaces of these parts should be nio-hard or lined with very hard coating (contact special coating suppliers like Devcon, Chesteton, Demech etc.).

GA, and another way to resist abrasion is with resilient (elastomer) coatings on impellers, pipe linings, and the like.

Yeah, like I already said.

probably a porcelane coated impellers will do and as the pipes

If you need valve for such application for both corrosion an abrasion.We'll suggest you to use FUV ceramic lined valves which can well slove for both problem.You may refer to the property of our advance ceramics which used to line to valves.

Abrasive and corrosive at the same time is always very difficult.

There was a pump company that had an alloy called R55, which is similar to Hastelloy 'G' or Illium 'G', which was resistant to H2SO4, but could also be hardened to 300 Brinell. However, CD-4MCu can also be hardened to 300 Brinell, is much cheaper, and is the usual material for this type of service. An alternative material favoured in some areas is 30% Chrome Iron, which may or may not be better.

A method that used to be used was to make the pump in an alloy such as those above, and then add a rubber lining. When the rubber wears off the pump is still resistant for a while. It just extends the life of the pump with minimal outlay, but doesn't do much for pump performance and efficiency.

To be honest, you might struggle for any improvement. It might be best to consult one/any of the few remaining pump manufacturers that specialize in difficult applications and special materials.

How can sulphuric acid be 99% if the Litrite is 40%?

Why is such a potentially corrosive mixture being pumped? What might be done to neutralise it before sending it? Would it be better to dry it and send it either pneumatically or on a coveyor system?

Why haven't ceramics been tried ?

Is the particle size too large?

Can the temperature be lowered?

The Sulphuric Acid Conc is 99% and solid contents are 40%. Its basically a leacing process to extract cobalt from laterite ore using acid. Temp is 100 deg C, there is nothing else we can do to change any of the parameter except changing the pump specs.

That response suggests of a lack of imagination in the Process Engineering Department.

Yes, may be :)

Have a look at http://www.weirminerals.com/products__services/centrifugal_slurry_pumps/horizontal_slurry_pumps.aspx

Not the easiest pump to maintain but reliable.

Try to search some pumps used on HCl plants, ahm usually i should say NaOH producing plants. I have some worked experience before, ceramic coated pipe interior(what should be the other term for "interior"- annulus perhaps) as well as pump impeller surface coated with ceramic.

Well, it's okay not to change the process parameter (neutralizing) because as common sense will tell, you will probably have a bigger cost (700 hours of neutralizing treatment & cooling-is not wise) compared to just replacing the pump with enough spares on the warehouse. Well, you can estimate or have comparative cost for that, if you like and find out which choice is better off either nuetralizing or just buying some spare pumps or parts.

Gallagher used to make a centrifugal pump with a viton liner that was used a LOT for pumping sand and acid slurries down oil wells. (it is called gravel packing but no gravel is used, it is relatively fine sand.) But ever since they were bought out by Weir, they have been trying to kill off the design but all the major oil service companies keep insisting that they still supply them (it works better than anything Weir makes currently) so Weir bends them over and charges a ransom for them, but they get what they need even if they charge an arm and a leg for them. I don't recall the model number off the top of my head (I have it at work) but if you want to contact Weir and are willing to pay the ransom, that might be one alternative for you.

Try http://www.weirminerals.com/

If you need higher pressures/lower volumes, look at the triplex mud pumps that are used for oilfield use. especially the ones with TTZ ceramic liners. again sand and acid is real common in the oilfield.

If your abrasion problem is caused by the high impact speed of the slurry with the pump, why not consider some kind of (large) diaphragm pump with similar specs?

If it is only for transferring Slurry from A to B - any height difference -- go for On-Off control. Push out using Compressed air . Only keep mixing when transferring.You can transfer at lot less time too . And no pumps to wear out.

Same pipeline would do.Additional Transfer vessel will be needed-- and some Ball valves .

mm

I will try to search further info against the info given and will see where we can make allowances. Thanks very much for your help

You could look at changing the process, but this is sometimes easier said than done. It might not be possible at all, or it might just introduce other problems that are not worth facing. I have seen a number of processes where there was no choice but to accept high rates of erosion/corrosion.

The usual advice for abrasive wear is to go either very hard or very soft. I think you have three options worth considering:

1) Some plastic materials are used on abrasive duties, especially HDPE (and also PVDF). I don't know how well they might handle 40% solids, and they might not even last as long as CD4 MCu, but prices for pumps and spares would be considerably lower. You could consider the likes of Wernert Pumpen (Germany), Vanton and possibly Richter.

2) There are a few pump companies that specialize in abrasive/corrosive duties and offer very hard materials for critical components, such as ceramics, NiHard, etc. Here you could consider the likes of Duchting (Germany), Kestner Engineering (UK), etc.

3) As has been previously mentioned by others, rubber-lining (the 'soft' option) could be a good solution. There are a number of companies offering rubber-lined slurry pumps, eg. the aforementioned Weirs (the old Warmann pump, perhaps?), Goulds and Tuff Pumps (UK).

It is up to you and your pump supplier to calculate whether it is best to go for an expensive 'Rolls Royce' product (eg a Duchting pump in SiCast), giving longer life and less maintenance, or a cheaper pump with shorter life and more maintenance but lower spares costs.

Good luck, and let us know how you get on.

GA. For this application lining is must and if possible, ceramic lining may work better. Brushable ceramic lining may be offered by Stanvac & Loctite also in addition to I suggested at #3.

You could be right, and perhaps brushable coatings should be added as the fourth option. I recall many years ago someone using a brushable coating to extend the life of their pumps on acidic Titanium Dioxide slurry. It seemed to work well, but I can't for the life of me remember what the coating was.

Materials, and particularly coatings, have come a long way since I was involved in this sort of stuff. I now know that ceramic-filled polymers are good for abrasive wear, so why not ceramic filled resins? Perhaps Corrocoat is another one to add to the list?

The problem with going "hard" instead of "soft" is that generally speaking, the harder the material, the more susceptible it is to hydrogen embrittlement from the Sulfuric acid. And rubber liners/impellers can generally be replaced a whole lot cheaper than exotic metallic ones.

That's interesting. I have to say I don't know much about hydrogen embrittlement, and never came across it when I was doing pumps for H2SO4. Perhaps the pumps corroded (or eroded) before embrittlement could set in? How long does it take to reach destructive levels? Could the embrittled surface of the metal be eroded/corroded away as embrittlement occurs, thus not allowing embrittlement to fully develop? I've heard of hydrogen embrittlement with reference to steels, but would it affect NiHard and Chrome Iron the same way?

I agree with what you say on rubber linings, but NiHard and Chrome Iron are not really exotic. To be honest, I wouldn't know which solution to favour until I had a good feel for pump costs, maintenance costs & schedules, etc.

Look at NACE MR-0175 for a good primer on embrittlement from H2S, Similar mechanism in play. Any reaction that can release hydrogen ions will drive them into the base material's interstitial spaces and can have serious effects, particularly if you have dissimilar materials that will set up a galvanic cell. Any alloy/material that can survive in high partial pressures of H2S would work here except for the erosion issue. Typically for steels, the limitation is 22HrC or less, anything higher and it will crack, and the harder the faster. Drop a 52100 ball bearing into a beaker of HCL acid for instance and watch how fast it shatters (but use a plastic beaker and make sure you wear PPE to prevent a splash burn!). Some Nickel superalloys (625, 725, 625+, C-276 MP35N, Elgilloy, etc.) are virtually immune under all but the most severe situations. But again, erosion will be an issue for virtually all of them. What is in play here is what is known as erosion corrosion. It is a hybrid condition between the two where the two mechanisms feed off each other. the erosion removes any passivated surface, the low oxygen prevents repassivation of the surface, and then corrosion sets in on the unpassivated base material. All of those exotics utilize chrome to form a tightly adherant layer of Chrome Oxide on the surface to prevent further corrosion, but erosion is constantly eroding that thin layer off and low oxygen levels prevent repassivation. And Hydrogen embrittlement can open cracks that lead to even more corrosion. It is a nasty cycle.

I am not familair with C26, but have used C-22 and C-276 for resistance to high concentrations of sulfuric acid. C276 is particularly good at 99% hot concentrations.

From what you say about failure due to abrasion, I would say it's more a matter of resistance to that than the sulfuric acid. In the past I have used electroless nickel coatings for extreme wear, and the coating can achieve hardnesses of up to 72 Rockwell B, or about 375 Brinell. Although it's a propriety process, it is relatively inexpensive.

I could be wrong, but I believe NiHard and Chrome Iron are in the region of 550-650 Brinell, which would be better than a coating, and pumps are readily available in these materials.

Concentrated sulfuric acid does not attack iron or steel at all.

(No water available for corrosion!)

So concentrations above 65% are safely transported in iron containers!

So you would need a high abrasion resistance only if steel is used.

I would try the carbide containing steels, Thyssen made these not only as castable iron-manganese-carbon alloys with up to 3% carbon but also as iron-carbide mixtures with up to 30% carbide content.

RHABE

Interesting.....and not my experience with acid wet benches used in semi-conductor processing.

An automation company I worked for in the mid 80's built several wet benches for Intel, and we had problems with hot 96% concentrated sulfuric acid corrosion with stainless steel shafting. It may not take much water to allow for corrosion, because the production area room conditions were very closely controled for low humidity.

Most engineering plastics WILL get brittle with prolonged exposure to high concentrations of sulfuric acid, so I am uncertain that plastic-lined pumps will stand up to either the acid or the abrasion.

I would agree with the hard chrome plate idea for both the impeller and the inside surfaces of the casing.

I quite agree. It's a long time ago, but I recall supplying pumps with cast iron casings and alloy impellers for concentrated sulfuric, but only at low temperatures. We were looking at special alloys before the 100 deg C mark was reached.

and three percent more water has a pretty dramatic effect too.

Note that the conc acid slurry is hot! The Cole-Parmer compatibility database shows that cast iron and 304SS have a severe effect when exposed to hot conc'd sulfuric acid. 316SS only has a "fair" rating.

"So concentrations above 65% are safely transported in iron containers!"

Sorry, I just read this again. Concentrations of 65-70% are the most corrosive for sulfuric acid. When I mentioned we used cast iron pumps for concentrated acid, that means no less than 98%, and at ambient temp. Even at ambient temp, 65% concentration would be beyond even 316ss, and would need Alloy 20 or better. 65% at 100 deg C. and you're looking at Tantalum, Zirconium and other exotics.

For abrasion resistance, high density polyethylene (HDPE) is good, and there are also other thermoplastics like ultra high molecular weight polyethylene (UHMWPE). Although soft, they are tough and won't chip off when abraded by the slurry, like hard materials.

Have you eliminated cavitation as a cause of impeller erosion? Maybe all you need is a booster pump upstream of this pump or some other expedient to assure net positive suction head (NPSH) for avoiding cavitation in the centrifugal pump.

"net positive suction head (NPSH) for avoiding cavitation"

OP is silent on this aspect. May be for such applications generally there is flooded suction (tank).

A cheap material, 'cast iron' can be used, if pump is to be treated as consumable. Ni-hard material is also a good choice. I have seen pumps made of ni-hard material for hot slurry containing very abbrasive iron slag in blast furnace giving satisfactory life. It may work for Sulphuric Acid also.

In my experience, polyethylene will become embrittled in acid service, particularly hot concentrated acids. Abrasion resistance is only part of the requirement.

I also question your statement about material not chipping off, and although it probably doesn't come off in larger pieces, ALL materials subject to abrasion will release particles over time. That's the nature of abrasion.

PVDF is routinely used in sulphuric acid pipelines. Start making enquiries in that direction, perhaps? Arrange for field trials of a suitable pump in that material, perhaps?

What are the pump requirements,

Maybe you may require a different type of pump.