Internal gear Pump Material for acids ( corrosive, toxic)

[bmw318be]

For acid such as sulfuric acid what is the suitable casing construction material ?


Is Ss316 or ss316 L could have corrosive resistant


Is alloy 20 is more superiour in term corrosive resistant compare to stainless steel ?


What kind of failure of pump usually when it react with acid ?

 

[SMIAH]

Call KSB.

 

[LittleInch]

See also this thread on something similar

http://www.eng-tips.com/viewthread.cfm?qid=346087

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[DubMac]

Alloy 20 IS better than 316ss for corrosive services; also MUCH more expensive. Of course you must look at what concentrations you have. You might want to look at non-metallic pump for acid services.

 

[ccfowler]

For sulfuric acid or other severely corrosive applications, I strongly prefer to avoid metallic contact with the fluid. Such pumps and piping systems may cost significantly more initially and require due special attention, but all the bother of corrosion can be effectively eliminated.

That said, if the expected service life of the system is short, such as for an experimental or demonstration application, then these greater costs are likely to not be justified. If there are system requirements for fluid purity, then the corrosion of the pump and piping system could introduce unacceptable trace contamination into the pumped fluid. Careful attention to acid concentration, temperature, and the potential for localized variation in concentration can play a major role in determining whether an all non-metallic system may be justified even for a relatively short service life system.

The corrosive attack rates can vary dramatically with differing concentrations. This is particularly evident with sulfuric acid where the corrosion rate for commercially pure sulfuric acid on carbon steel is very modest but very severe for lower concentrations.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[ccfowler]

To elaborate a bit on my previous posting, I offer a quite unpleasant example of varying concentration of the pumped corrosive fluid. In this case, commercially pure sulfuric acid. Since the nomination al corrosion rate for carbon steel is very modest, that material was chosen for most of the system. Unfortunately, the piping system, in particular, saw long periods of stagnant or laminar flow, so the concentration had plenty of time to stratify with higher concentrations at the bottom and lower concentrations at the top. This was most obvious on horizontal pipe runs. Since the lower concentrations result in much greater corrosion rates, the end result was rapid development of pin hole sprays of sulfuric acid.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[bmw318be]

For composite material what are the materials are that could have corrosive resistant ?

Any advise using alloy c for pump construction to handle sulfuric ?

 

[ccfowler]

I repeat, if possible, avoid metallic contact with corrosives whenever a choice is possible. I would pursue finding least costly means of this before considering metallic options.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[ReliableJester]

bmw318be,

It really depends on the concentration and temperature of the sulfuric acid that you want to pump. For example, carbon steel would be a fine material of construction for sulfuric acid piping if the sulfuric acid is 94%-98% concentration and <100°F as sulfuric acid within that range isn't very corrosive to steel. However, I wouldn't recommend this material for a pump, even if your acid is within that range. The reason being is that sulfuric acid likes to act a little strange when higher velocities/higher turbulence is involved. The corrosion rate of steel by sulfuric acid is greatly increased in high velocity/turbulent regions, especially at higher temperatures. And I'm not talking about erosion due to the higher velocities/turbulence, the corrosion of the metal in a high velocity/turbulent region is notably more prominent than the 94%-98% sulfuric acid in a lower velocity/less turbulent region.

I have a system that circulates ~100°F 94%-98% sulfuric acid through carbon steel pipes. Recently we started having issues of leaks forming in the pipe elbows. Ultrasonic thickness readings of the pipe showed the pipe to be in good condition, but visual inspection of the elbows showed that they were seeing a significantly higher corrosion rate (again corrosion, not erosion) than the rest of the piping system. Upon further research I came across the studies that showed how velocity/turbulence affected the corrosion rate of sulfuric acid on steel.

So, in conclusion, the wet end of a centrifugal pump is a very turbulent region, so that become important when selecting a material of construction for sulfuric acid. I have had success with both Alloy 20 and Hast. C in turbulent 94%-98% sulfuric acid service (~100°F). As for 316L (CF3M when cast) I have no experience with it in said service, but it is possible, that it may see issues with high velocity/turbulent sulfuric acid, when typically it would not any other time.

I have also attached a link to a PDF version of the NorFalco Sulfuric Acid Handbook that may be of use to you, either now or possibly in the future. However, it does not mention the velocity effect on corrosion rate, so keep that in mind when reading their corrosion charts, additional research may still be needed.

And finally to ccfowler's point, non-metallic pumps/systems should also be considered, as they could result in a cost savings. Also, make sure to consider how you plan on sealing the pump, you may want to consider a mag-drive pump in this service as well, but understand there are pros and cons to everything and there is usually never a "perfect" solution to every problem.

I hope sharing my experience has helped. Good luck.