Pump impeller failure / distort / crooked

Inspect the impeller for physical damage on it's leading edge.

Report.

Dear sir,

kindly advice me what did you mean by inspect the impeller for physical damage on it's leading edge? For your information, all of the part inside the pump was in good shape except the impeller and the mechanical seal. Seek for your advice sir. Thanks for your attention to this matter.

Regard

Yes..i do realize the blue spot at the impeller. thanks for your advice. For your information, I just received this pictures from my friends. He ask me about my opinion. I will share with him this information. I totally agree with you that it hard to identified it if we just looking at the pictures. Thanks again sir. Have a nice day!

Just in my opinion : How about if you make a failure analizing of the Material ? Say it like Stress or Fatique ? 'cause I didn't see any fatal FOD on the blade (Photo). Thanks

This type of pump cannot be used to pump driftwood and crustaceans. Replace it, and learn from the experience. The strainer bypass valve should be removed.

While this isn't my field I have to add the following understanding that the light and shadow make it tough

If the photo is any indication (the camera ALWAYS lies btw)

every single blade was originally straight (normal to) the hub.

only the two blades at the 9 o'clock are still straight.

I agree with the comment about yanking the bypass valve (but only because preventative equipment shouldn't be bypassed)

But between the blueing on the tips and the count of bent blades (all but two or three) I don't think this was FOD (a crustracean or a bolt) but instead the pump was set up incorrectly or failed during run time and contacted other fixed objects.

Yes..i do wonder that this impeller might be straight...It is impossible to straightened the curved blade perfectly...I will suggest my friend to inspect for the remaining impeller. This is a 3 stage compressor. He just provide me pictures of first and second blade. Because he believed the impeller is not in good shape, it have break the mechanical seal. By the way, thanks for giving good advise. have a nice day!

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Hello

A couple of questions, Do you have any picture's of the seal failure, if the elastomers around one of the seal faces is vulcanised that will be another indication of excess heat and thermal growth. What is the condition of the shaft that fits into the hub of the impeller, As this is an open impeller it should handle solids easily especially as it won't be at high pressure a particle or foreign matter big enough to do the damage shown would have jammed the pump or you would have serious debris flowing around the system. If that is a bronze impeller it will expand rapidly if it is rubbing anywhere which would happen if the pump was run dry.

are there any marks inside the housing that might show that something hit the impeller from the side facing the sea? An object might have jammed it and scraped somewhere.

often things like this will have a shear pin in the drive. A shear pin is a pin made weak enough to break before the impeller breaks. the pin is also cheaper than the impeller. Another thing to add is a coarse screen on the inlet.

as not all of the blades exhibit signs of over-temp conditions..i.e. assuming the shaft didn't seize, .& is the keyway slot broken .? .... hard to see the blade root , but checking for cracks at the hub gland and blade root , if any found , might suspect eminent multiple catastrophic blade failure ,.. don't see any missing chunks out of the blades.. but i think this photo is of the trailing edge... how much flow passed between the failure and finding the failure? filter flotsam might have been purged by the flow ?

just some thoughts on the subject

I appears that this pump may not be the best one for your intended use. It does, indeed, appear that something is in the pumped media that has hit the impeller blades and has bent them as seen in the photo. Perhpas an impeller of a semi-open design would be more appropriate. That would have a back shroud that would give strength to the blades since it would not have them standing out from the hub with the cantilever action that allows them to bend so easily. Further, attention to the impeller material could be a solution. Bronze is a relatively soft metal that is prone to bending when used in this unsupported manner. If this design is to be used, consideration of a ductile iron impeller might be warranted. Although, iron in general is more brittle than the bronze, it is also stronger. Avoid thermoplastic materials as they are not suited to the conditions that have caused the failure of your pump. I would be interested in seeing the rest of the pump. Since the impeller is only 10 cm in diameter, it is not a very large pump. From the damage shown I would guess the rotative speed is probably around 3500 rpm. That would more urgently demand a semi-open impeller as I have described. Get with a good pump supplier in your area and see if he can guide you. The seal problem will be cleared up when you get the impeller condition satisfied. The resulting imbalance of the impeller when it is distorted as shown will nearly always destroy the mechanical seal. Good luck.

If i have a good eyes ,i can see some corrosion in place of lock key which supports impeller with pump shaft ,if this key not in good condition it will leads to that corrosion, more important it will allow impeller to move in axial direction while in rotation, finally impeller will hit inner casing for pump and causing this failure

Your investigation indicates there was no debris in the screens and items beyond the pump.

I would suggest that a different failure mode has happened.

In all cases the bending of the blades seems like "plastic deformation" rather than collision. This would indicate the material has exceeded its yield strength and bent.

This could happen if the vanes were operating at a force beyond the material capability. Such an issue could happen if the pump were "instantaneously" brought up to speed and the inertia of the material to be moved was sufficiently great, or if the head pressure was extreme (like an outlet pipe was obstructed).

My "guess" is that the impeller blades are too soft for the applicaiton and have simply deformed to a point where the excess load was able to bypass the vanes inside the pump housing.

Hope this makes sense, as it's the only way that I can imagine such damage without physical evidence in the downstream equipment.

Your answer, as well as that of GVA BR both have merit. If, in fact the damage or deformation was caused by the fact that there was too much load applied to the impeller blades, the solution could be, as I stated above, to use an impeller with a back shroud to give added strength to the impeller blades. It appears that this impeller is not the best design for the application.

I would like to ask some question regarding this impeller to investigate cause of damage.

1- Total head of pump.

Another thought while having calamari for lunch today.

Since you indicate the screens were bypassed, is it possible that some "high viscosity" impurity (like a jellyfish) was pulled into the pump, turned into puree and then exited to leave no evidence other than the deformation of the vanes?

Why was the strainer bypassed? Was it already clogged with jellyfish or some other aquatic contaminant?

Hi everyone,

my guess is simple, may be the pump was started in a dry condition, no fluid inside, and after suficient time for the pump to get enough velocity, i meant rotation ok!, the pump body got filled, with fluid hitting the impeller and causing the damage...

Some one wrote this before, but may gess is that If the pump suction was really out of service and someone forgot to fill with water before start the pump, and for some reason, when the fluid run for the suction sudenly, with a high velocity, it could cause a great shock to the blades.