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Anonymous Poster #1

Silicon Carbide Rotary Face Damaged

06/27/2020 7:19 AM

A sudden failure of newly installed mechanical seal on hot ammonia pump failed (Seal failed the moment pump motor was started), on investigation seal hard/rotary face ( silicon carbidewas found badly damaged. There was no leakage during two hour alignment activity while the pump was pressurised at15kg/cm2 Please comment. and discuss. Picture of damaged face and soft face are attached.

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Anonymous Poster #2
#1

Re: silicon carbide rotary face damaged.

06/27/2020 7:26 AM

Looks like it’s f###ed.

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#2

Re: silicon carbide rotary face damaged.

06/27/2020 7:36 AM

Where are the pieces that are missing from the seal?Were they found inside or outside of the seal area?

It almost looks like someone drove a screwdriver into the seal from outside.

This looks like impact damage to me.

Contamination of the seal area could have occurred or it could have been damaged during installation,which would be my first guess.

I have seen similar damage when a seal was improperly installed using improper tools or techniques.

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#3

Re: silicon carbide rotary face damaged.

06/27/2020 7:40 AM

There is no way I can arrest someone for doing that.

I hope you’ve got a spare?

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#4

Re: silicon carbide rotary face damaged.

06/27/2020 7:41 AM

Looks like the seal was fractured before or during installation....

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#5
In reply to #4

Re: silicon carbide rotary face damaged.

06/27/2020 7:54 AM

I concur.

Maybe the pump and motor assembly was craned into place by the motor lifting lug alone (for instance) with mass of pump cantilevered on shaft/seal interface.

Since the OP indicates around 2 hours spent verifying alignment and such, then logically the failure was already present before that time.

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#6
In reply to #5

Re: silicon carbide rotary face damaged.

06/27/2020 8:35 AM

Motor was not removed from skid volute of single stage overhung centerline mounted pump was also there ay skid. Only the pump (bonnet and bearing housing)was removed and istalled .

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#7
In reply to #6

Re: silicon carbide rotary face damaged.

06/27/2020 8:55 AM

Could have been a material flaw that surfaced under stress....the seal could have been dropped at some point...who can say...a repetitive failure would tell us more...

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#8

Re: Silicon Carbide Rotary Face Damaged

06/28/2020 4:18 AM

As others have said, I would suspect mechanical' damage during installation. It looks like there was enough face area intact to prevent leakage while stationary but as soon as the pump was started the hydraulic forces would part the faces.

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#9

Re: Silicon Carbide Rotary Face Damaged

06/28/2020 11:01 AM

Greasing or oiling the seal's mating surfaces and the mating shaft surface is essential when assembling.

That looks like it may have been assembled dry and then it tore out a section on startup because the seal surface and the shaft surface were not greased or lubed prior to installation.

Seals have a pre load that bears on the effective seal area which is delivered by the spring so if that seal was perfectly dry and devoid of lubrication when installed, then the image you show is the kind of damage I would expect to see on a seal and shaft that were completely dry on startup.

This article explains pre lubing is essential.

I also note you say that you have 15kg/cm2 pressure but this article also mentions that "rubber oil seals are not suitable for dry running applications or high pressure" so please check that you are fitting the genuine manufacturer's seal for that purpose, seeing as it's in what sounds like a high pressure application.

https://newdealseals.com/en/rubber-seals/oil-seals/

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#10
In reply to #9

Re: Silicon Carbide Rotary Face Damaged

06/28/2020 11:59 AM

Suction pressure is 13 kg/cm2 dry running possibilty not there.

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#11
In reply to #9

Re: Silicon Carbide Rotary Face Damaged

06/29/2020 4:26 AM

This is not a rubber lip seal.

The seal faces of a mechanical seal of this type should NOT be lubricated during installation.

Sometimes lubrication is recommended for the fitting of the elastomers such as O rings etc.

The spring load on a mechanical seal is extremely low and is required only to keep the seal faces together, particularly under no, or very low, pressure. It is the hydraulic forces on the seal that keep the faces from parting (too much) during operation.

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#12

Re: Silicon Carbide Rotary Face Damaged

06/29/2020 3:15 PM

If I had to guess,I would say it looks like someone hit it with a screwdriver, twice,in an attempt to seat the seal,which was installed crooked and improperly by an inexperienced person.I have seen exactly this type of damage before because of this problem,mainly on small pump seals.Metal tools should not be used installing the seals,and they should be pressed in,not driven in.

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#13

Re: Silicon Carbide Rotary Face Damaged

06/30/2020 2:05 PM

What thrust bearing this pump has?

Is the thrust bearing well secured against excess end play?

With excess end play, the shaft assembly can rattle back and forth, especially during startup. This can cause the faces to damage.

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#14

Re: Silicon Carbide Rotary Face Damaged

07/13/2020 3:53 PM

I have seen EXACTLY this type of seal fracture cause by thermal shock. Once even a tiny flake breaks off the hard (and brittle) seal, the cascade damage can be spectacular.

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