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Magnetic Drive Pump Leak at Containment Shell

Magnetic Drive Pump Leak at Containment Shell

Magnetic Drive Pump Leak at Containment Shell

(OP)
Hi everyone,
We have experienced weak acid pump failure (again). This pump type is magnetic drive pump (Innomag C4 3x1.5x10) The fluid pumped is nitric acid 40% with temperature of 55 degC and differential head of 1700 kPag. This is the assembly of the pump:



The start up went well however we saw abnormal spike on the electric current of the "A" pump. Shortly after we saw NOx fume and decided to switch to "B" pump & it ran normally up until now. After inspecting the A pump, we found the following pics:


Containment shell worn out due to scratching with magnetic outer drive.


Worn out outer magnetic drive


Broken wear ring

This failure mode happens after the pump was changed from C3 to C4 type. Prior changing, the failure mode was different (broken casing and scratching impeller with intact containment shell). After changing, the pump last a year before breakdown, while before changing, the pump only last 1 month before breakdown.
I would really appreciate for any thoughts or comments. Thank you.
Best regards,

Yosep

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)

Here are the summary of the failures. The yellow-coloured texts are the failures that happen when the pumps were still C3 type, while the green-coloured are failures of C4 pumps.



RE: Magnetic Drive Pump Leak at Containment Shell

Hi,
Did you check with the vendor?
Is this the right the technology for your operating conditions and material (40% Nitric acid)?
Is your solution clean, free of particles ( abrasive) ?
My 2 cents
Pierre

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
Hi Pierre,

We already checked with the vendor various times. By design this pump is capable to pump nitric acid 40%. We also have reported the failure of March 2021 and their response was due to a manufacturing defect. However, a manufacturing defect should not be the root cause because the failure mode kept happening until now.
Thank you.
Regards,

Yosep

RE: Magnetic Drive Pump Leak at Containment Shell

Hi ,
You need to investigate the reason why the coating is gone ( abrasion, temperature, Operation (overheating) , acid concentration (variation) , impurities with the acid ) .
It seems to me that the temperature is already high !
Is it a continuous process or batch process ? Some info about your process could help (simple PFD for example) and description of the operation
My 2 cents
Pierre

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
Hi Pierre,

The process is continuous. Two pumps with one as standby pump. Attached below is the process flow diagram of the system.


Pump tag number are 12P007A/B. The pump has duty to pump nitric acid condensate from 12E007 to 12C003 column. They are equipped with kickback line for minimum flow as well. We put temperature transmitter on the discharge of 12E007 prior entering 12P007. So far, the temperature transmitter did not show any abnormalities. Range of the temperature was 53 - 55 degC.
Best regards,

Yosep

RE: Magnetic Drive Pump Leak at Containment Shell

Can you provide a bill of materials for the pump? It appears to have leaked which causes exposure of the iron based components of the mag drive resulting in that brown color and the running. Did it leak through the seals or did the coupling perforate?

RE: Magnetic Drive Pump Leak at Containment Shell

Tug et al,

See the links below for details.

I am particulalry taken with the "revolutionary thrust balanced design". This eem to use some small orifices and a balance chamber to avoid thrust.

The bearings seem to be alpha sintered silicon carbide.

What do the bearing surfaces and wear rings look like.

A potential issue for me is that the internal rotor is clearly now impacting the containment shell which means you bearings are shot.

https://www.flowserve.com/sites/default/files/2016...
Sectional drawing in section 8
https://www.flowserve.com/sites/default/files/2016...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
@TugboatEng

Hi, attached below are the bill of materials of the pump



I have also attached below the working principle of the magnetic drive pump (YouTube video):
Link

I agree with you, there's a leak inside the outer magnet and the blue-paint lining has completely eroded. The liquid being pumped should not enter that area. For comparison, the picture below is the new spare of the containment shell:


The pump has no couplings as it is mag drive type. The seal was completely destroyed but I am not sure whether the nitric acid entered the outer magnet area through the seal first or through the eroded containment shell.


Currently, we are performing 3 monthly visual inspection of the pump's internal parts during plant online condition and we always find a tiny deposit of nitric acid on the containment shell. (the date stamp in the photo below is wrong, it is on March 2021, 2 months after the incident above happened).


We have no idea what's causing this problem as this pump is stated compatible with the fluid.
Really appreciate any thoughts on this.
Best regards,

Yosep

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
@LittleInch

Hi LittleInch,
Thank you for your response. Does it mean that "thrust balanced" system is the culprit of this failure? Based on the video, it seems that the containment shell does not move when the thrust balance was activated.


If the internal rotor scratched the containment shell during its axial movement, there should be wear in the inside part of containment shell, yet it did not present.


The picture above also shows a dent in the balance shaft, possibly because of friction with the other parts due to thrust balancing system?

Best regards,

Yosep

RE: Magnetic Drive Pump Leak at Containment Shell

"tiny deposit of nitric acid" .... Hmmmmmmm

MJCronin
Sr. Process Engineer

RE: Magnetic Drive Pump Leak at Containment Shell

That's a very interesting video you linked to.

I'm just speculating that maybe the impellor assembly is moving too much bac and forth or can move very suddenly causing the containment sheath to crack or get stressed and allow a little bit of fluid out.

Do the pumps see any form of surge or shock loading?

What do the wear rings look like?
What do the bearings look like?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Magnetic Drive Pump Leak at Containment Shell

And I would like to see data showing that that particular resin is good at this temp in this acid.
I am concerned that the fiber is so visible, there should be a substantial layer of pure resin on the wetted side.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Magnetic Drive Pump Leak at Containment Shell

I would say it is highly likely that magnetic particles from your process fluid are accumulating on the magnets and wearing through the containment shell.

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
@LittleInch
Yeah, the axial movement corresponds to the suction pressure of the pump, in this case - the Cooler Condenser 1 pressure. We put a pressure gauge in the suction of the pump and so far it does not fluctuate too much. It stays on 430 kPag. However, when the pump running, we often see fluctuations of the pump motor's ampere. You can see the example below. Yet we are not sure whether we should worry about it or not because the fluctuation is so small, below 1 A.

Red line is the amps of A pump, blue for B pump, and black for the discharge flow from the pump to the Absorption Tower.

Below is the picture of the back rotating wear ring


and below is the front rotating wear ring


below is the bearing bushing photo from the backside of the impeller



@Compositepro
We had suction strainer removed from the pump because of the action of the past RCA which stated that the strainer created turbulence flow that would impact the pump. However, the manufacturer of this pump said that this pump could handle solid particles up to certain size.

RE: Magnetic Drive Pump Leak at Containment Shell

Hi,
What about the control valve downstream , do you notice any corrosion , erosion ,.... which may come from the nitic acid solution?
Pierre

RE: Magnetic Drive Pump Leak at Containment Shell

There is a big difference between "particles" and "magnetic particles". Particles will pass though without any issue. Magnetic particles will stick to the magnets and accumulate until they destroy the pump. You need a good magnetic separator, not a strainer basket. Every car has a crude one on the oil drain plug. In fact, the deposits on your magnets look just like those on a drain plug magnet.

RE: Magnetic Drive Pump Leak at Containment Shell

Compositepro is correct .... "magnetic particle (rust) seems to be killing this pump over and over.... IMHO

What did FLOWSERVE tell you about the need for a magnetic strainer upstream of your pump ?

I do not see one on your PID

MJCronin
Sr. Process Engineer

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
@Pierre
Hi Pierre, so far we do not have any big issue on the downstream control valve (LV12005 as in P&ID below)


@Compositepro & MJCronin
So far during our discussion with Flowserve they did not mention about the need of magnetic strainer upstream of the pump.

FYI, we just have performed a pressure test of 13 bar on the containment shell that has been in service for 2.5 months. The leak is confirmed coming from the inside of the containment shell.

Leak coming with yellow mark liquid on the tissue


Pressure dropped from 13 bar to 4 bar overnight

This finding is consistent in the past year since the failure on January 2021. We always find the containment shell leak during pressure test.

My thought is the nitric acid leaked from the containment shell would start to corrode the outer magnet which was ductile iron. Overtime, the corroded parts then start to accumulate inside the outer magnet chamber and amplified the initial damage (leak). We know what was happening but we do not know on why it started and how to stop it.

Best regards,

Yosep

RE: Magnetic Drive Pump Leak at Containment Shell

Magnetic particles will always cause problems on either side of the can in a magnetic coupling. However, it is also very possible to have voids or porosity in the composite pressure seal due to a manufacturing defect.

RE: Magnetic Drive Pump Leak at Containment Shell

I'm still hung up on the photo you shared of the nitric acid that leaked through the containment shell. Any kind of particle accumulation would tend to for a wear ring pattern, no? This leak is in a single point. The fact that the leak is a singular point rather than in a ring shape indicates to me a chemical attack rather than physical phenomenon.

I would recommend you request coupons of this resin from the manufacturer and test it yourselves in your process fluid to see if it is actually resilient. How sure are you of the purity of this nitric acid stream? Any possibility of other contaminants (chlorides?) that may change the potential corrosive nature of this stream?

Lastly, is this containment shell resin fully resistant to HNO3 throughout the entire material? I.e. is the structural winding the same material as the "resistant" internal layer?

RE: Magnetic Drive Pump Leak at Containment Shell

Going back to the beginning - the fauilures started when the y moved from a C3 type pump to a C4.

The key difference for me is this moving shaft. does it cause mechanical damage?
Does it cause a pressure spike in the fluid coming around the back of the rotor and overstress this casing?
Is there a difference between a C3 and a C4 casing?

how are those containment shells made? they look a bit "manual" with the mesh staying visible.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
@TiCl4
Hi there. We are absolutely agree with your statement. Yesterday I have sent the containment shell to external lab for failure analysis. Whether the containment shell was damaged because of chemical attack or because of friction with impeller due to thrust balancing. I will update it later in this thread.

@LittleInch
Hi LittleInch. As far as I know, both type of pumps (C3 & C4) has thrust balancing system. The key difference is the size of suction & discharge flanges. C4 has slightly larger size with suction is 3" and discharge is 1.5". While C3 is 2" and 1" respectively. All other parts are the same, including the containment shell.

Best regards,

Yosep

RE: Magnetic Drive Pump Leak at Containment Shell

The failure lab/forensic analysis will give us the answer ....

While the "nitric acid deposits" are suspicious, I agree with TiCl4 that circular grooves on the containment shell are the hallmark of a magnetized particle failure. The single point leakage without circular grooves makes no sense to me

Were your replacement containment shells purchased from FLOWSERVE or were they repaired shells from some local fiberglass vendor ?

Strainers with magnetic inserts are relatively cheap ....Why are you so reluctant to add one to your system ? ... aside from a modest pressure drop, there is no downside

MJCronin
Sr. Process Engineer

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
Hi MJCronin,

We got the replacement from Flowserve USA via our local distributor. We never repair the broken containment shell. Our current approach is as soon as we find any leaking, however small, we replace the containment shell immediately. - a costly approach but necessary to avoid plant shutdown.

Anyway, our other site in different country also has the same problem with this magnetic drive pump. We use the same spec. They installed a drain to help indicate that a leak started coming, a lagging indicator. But they still do not understand the root cause of the problem.


For magnetic strainer, I assume that it was because different failure mode prior changing to the new type, but it is definitely worth a try. I will try to propose a MOC later on about that.

Best regards,
jsasada

RE: Magnetic Drive Pump Leak at Containment Shell

Hi Jasada,

I encountered a similar failure of magnetic drive but it is with external gear magnetic drive.

Can you check the following

1. NPSH margin during the operation
2. Suction Pressure
3. Vibration
4. shaft Alignment
5. Keyway tolerance

In my encountered of containment can and drive magnet assembly failures is over time when the pump would run continous 24hr x 7 for 1 month.

The magnetic drive assembly shifted its position and shaft touching the containmrnt can wbich create heat to the SS316 containment can. The debris from shaft rubbing of containment can would enter the magnet cavities which damage the magnet overtime and jammed the magnet.

If the pump stop then it would stalled as the debris create friction inside magnet assembly.


RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
Hi BMW,

Would you like to share the pictures please? I am curious with your failure events.

We have confirmed that:
1. NPSHr is below the NPSHa
2. Suction pressure is 350 - 400 kPag
3. Vibration level are normal throughout the time, (0.1 - 2 mm/s)
4. Alignment always performed during pump installation
5. We also always measure the keyway tolerance prior installation.

Best regards,

jsasada

RE: Magnetic Drive Pump Leak at Containment Shell

Hi Jasada,

Sorey for the late reply.

Please refer to attached

https://1drv.ms/u/s!AshU1On9Vy6fiv1Uqq8m0Ck6cLSL9g

from the pump photo the motor is frame B35, however it was not bolted.

1. How many KW the motor power and RPM .

2. This normally no alignment is done since it is flanged coupled,

3. Another question, how your permanent magnet is sticked into the hub ? Are they using silicon, this worth investigation of the melting temperature of epoxy.

4. Please share the drive magnet photo

RE: Magnetic Drive Pump Leak at Containment Shell

Are your techs checking clearances before putting the pump in service? Have you sampled the chemical stream for chlorides, heavy metals, etc.?

While I don’t think it’s a contributor does anyone have technical info on Aramid and Carbon fiber reinforced ETFE? From my recollection Aramid isn’t great with nitric

RE: Magnetic Drive Pump Leak at Containment Shell

Looking at the system into which the pumps are integrated, there could be another origin of the troubles. How do you start up the pumps? If I see it correctly on the P&ID the (continuous) by-pass with the orifice back to the sump ends in the liquid phase. That could cause gas to be trapped during start-up, if also used to prime the pumps.

RE: Magnetic Drive Pump Leak at Containment Shell

@jsasada

I am currently working on the same exact incident investigation with an Innomag C3-2x1x10 mag drive pump. The process seems to be identical yours. These pumps are our reflux acid pumps for our nitric acid absorber column. 42% nitric acid. Absorber runs around 85-90 psi. We have had multiple failures with this same pump and all have resulted in damage to the containment shell.

Link

We thought at first, that the magnetic drive coupling was either not set properly or the set screws became loose allowing the coupling to move forward tearing apart the containment shell. However, I assembled this pump and found that the coupling would touch off on the pump casing and not touch off on the containment shell.

A key piece of evidence is the pump shaft that is embedded in the containment shell. See linked attachment. Comparing the damaged shell to a brand new shell, I could see that the pump shaft was recessed 0.500 inches deeper into the containment shell. Looking closer I could see that the carbon steel casing that is embedded in the containment shell had been pushed out toward the magnetic coupling. This carbon steel casing houses a composite insert that houses the SiC pump shaft. These components are very rigid.

What we think caused this failure was that the sleeve bearings were starved of lubrication, eventually heating to a point where the sleeve bearings seized on the pump shaft. Considering that the sleeve bearings are housed in the magnetic coupling of the impeller, this would put a lot of torque on the pump shaft and in turn the carbon steel housing in the containment shell. The carbon fiber//ETFE material encases this carbon steel housing. We believe at some point this eventually ripped the ETFE of the containment shell, allowing the pump shaft and carbon steel housing to spin freely. Axial forces eventually pushed this housing and pump shaft toward the magnetic coupling eating away at the composite shroud that houses the pump shaft. Since this pump shaft is bored all the way through, this allowed nitric acid to find a way to the drive end of the pump. See attachment

We have no process data to show that the pump was ran dry, but transient conditions most likely are a factor (shutdowns, startups, etc.) IMO, momentary dry running is unavoidable.



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