Tube Leakage!!

[azammakda]

Hello everyone!!
We have a chiller unit installed with a screw compressor.
Recently we have done plugged the copper tubes and did the pressure test. The pressure was holded up for a day.
Started the compressor with new expansion valve and drier, but the new tubes have been leaked only after 3 days.
What can be the possible causes of tubes leakage ? Is there a same reason for first time and second time tube leakage ?

[passandscore]

You could have froze up the secondary refrigerant causing it to rupture the tubing. What are you cooling? Water, Glycol, Brine?

Other tubes may not have leaked during your pressure test but are compromised by what ever caused your problem.

[azammakda]

Water
But we have an anti-freeze switch installed on the compressor.

[CV_Geardrive]

Hi,
Too many causes for such failure.
Questions: Where are the leaks? In tubes, in supports or in tube sheet?
What brand and model is the chiller?
What is flowing inside the tubes? Water or refrigerant?
Regards,
CV

[azammakda]

Answers: Leaks are in the tubes. The defects are pin holes and (longitudinal) cracks
Refrigerant is flowing inside the tubes
What you want specifically while asking brand and model. Plz specicify

Regards

[hookster]

Longitudinal cracks in the tube bundle normally indicate a hoop stress fracture this is caused by circumferentially generated forces.
The usual cause of excessive circumferential force in a tube is from freezing and water expansion.
Over pressure would have to be significant to cause tube failure.

Your case appears strange as you say they are refrigerant tubes. Is this condenser leaks or evaporator?
Is it maybe not a vibration issue? I have seen chillers roof mounted and chiller frame unable to withstand fluctuations and the air cooled tube bundle returns fail repeatedly.

I think CV asked for the make and model so we can all try an identify circuit and construction etc.

Although there are some known chillers on the market with inherent failures! One nicknamed the SIEVE springs to mind

[NewmanRef]

Answers: Leaks are in the tubes. The defects are pin holes and (longitudinal) cracks
Refrigerant is flowing inside the tubes
What you want specifically while asking brand and model. Plz specicify

Regards

The tubes installed are definitely refrigeration grade copper? Not water pipe? What pressure did you test at? What refrigerant are you using?

[goshen]

Hi
what type of plugs are you using? what type of unit?
you usually need conical plugs and it is actully pretty tricky on some 5/8 tubing to plug sucsesfully.
you may need to machine them to fit , if you are testing and leaks are springing in other tubes , i would say either your evaporator is gone, or you have a freez up problem , either way test the avaporator isolated from system at a higher pressure and let it sit 24 hours then check it .assuming your leaks are in the evaporator.
good luck

[CV_Geardrive]

About cracks, I agree with hookster. Water freeze and expand.
About pin holes I suspect debris in the water loop.
Debris hit the tubes and accumulates somewhere or everywhere in the evaporator obstructing water flow.
Then we have freeze up.
Is there adequate water filtration in the inlet of evaporator?
What is the nominal water pressure drop across evaporator and what is the actual water pressure drop?
What is the nominal Dt in the evaporator and what is the actual? (Before failure)
Does the water pump discharge water to evaporator? If yes what is the distance between pump and evaporator inlet? What pressure do you have in the inlet of water pump?
If you let us know the model and the manufacturer of chiller you may receive useful information.
CV

[azammakda]

Longitudinal cracks in the tube bundle normally indicate a hoop stress fracture this is caused by circumferentially generated forces.
The usual cause of excessive circumferential force in a tube is from freezing and water expansion.
Over pressure would have to be significant to cause tube failure.

Your case appears strange as you say they are refrigerant tubes. Is this condenser leaks or evaporator?
Is it maybe not a vibration issue? I have seen chillers roof mounted and chiller frame unable to withstand fluctuations and the air cooled tube bundle returns fail repeatedly.

I think CV asked for the make and model so we can all try an identify circuit and construction etc.

Although there are some known chillers on the market with inherent failures! One nicknamed the SIEVE springs to mind

The evaporator leaks. The vibration readings are normal.

[azammakda]

The tubes installed are definitely refrigeration grade copper? Not water pipe? What pressure did you test at? What refrigerant are you using?

I dont know about what grade you are talking but these are copper tubes.
The test pressure was about 5-6 bar. The refrigerant is R-134a

[azammakda]

Hi
what type of plugs are you using? what type of unit?
you usually need conical plugs and it is actully pretty tricky on some 5/8 tubing to plug sucsesfully.
you may need to machine them to fit , if you are testing and leaks are springing in other tubes , i would say either your evaporator is gone, or you have a freez up problem , either way test the avaporator isolated from system at a higher pressure and let it sit 24 hours then check it .assuming your leaks are in the evaporator.
good luck

We are using conical brass plugs. The plugs are prepared locally. But the plugged tubes did not leak. There were new leaked tubes found in the evaporator.

[azammakda]

About cracks, I agree with hookster. Water freeze and expand.
About pin holes I suspect debris in the water loop.
Debris hit the tubes and accumulates somewhere or everywhere in the evaporator obstructing water flow.
Then we have freeze up.
Is there adequate water filtration in the inlet of evaporator?
What is the nominal water pressure drop across evaporator and what is the actual water pressure drop?
What is the nominal Dt in the evaporator and what is the actual? (Before failure)
Does the water pump discharge water to evaporator? If yes what is the distance between pump and evaporator inlet? What pressure do you have in the inlet of water pump?
If you let us know the model and the manufacturer of chiller you may receive useful information.
CV

How can the accumulation of debris leads to freeze up ?

There is no such filter at evaporator inlet. I dont know much about pressure drops or nominal Dt (what is Dt?) as i belong to maintenance team but i can tell you the discharge pressure of pump that supplies water to evaporator i.e 3.6 bar (observed on PG installed on pump discharge-reliable reading/PG )
Yes the water pump discharge water to evaporator and it is roughly 35-50 ft away from evaporator.

Model: its a chinese made evaporator and hanbell compressor.

[CV_Geardrive]

Dear Azammakda,

I have one comment.
Evaporator without water filter in inlet equals to an evaporator successful failure.

To be honest with you, I believe that you are dealing with a problem which is much greater than your knowledge and experience.
So, in few words I suggest the following.
A) Installation of water filter in the inlet of evaporator.
B) Replacement of evaporator with a new one and if possible certified.
C) Consult a qualified technician to assist you in evaporator replacement, do all necessary works to have the unit ready for start and finally to assist you in re-commissioning the unit.

With best regards,
CV

[Magoo]

The anti freeze stat should be in leaving water, continual tube failures could be caused by many issues, low water turbulence areas due to corroded partition baffles, SST too low, water flows too low, low fin tubes stress fracturing, the list goes on and on. Cathodic corrosion in chilled water circuit usually at support baffle sheet points. Test the chilled water for PH.

[azammakda]

Dear Azammakda,

I have one comment.
Evaporator without water filter in inlet equals to an evaporator successful failure.

To be honest with you, I believe that you are dealing with a problem which is much greater than your knowledge and experience.
So, in few words I suggest the following.
A) Installation of water filter in the inlet of evaporator.
B) Replacement of evaporator with a new one and if possible certified.
C) Consult a qualified technician to assist you in evaporator replacement, do all necessary works to have the unit ready for start and finally to assist you in re-commissioning the unit.

With best regards,
CV

I can believe lack of experience only !!
Your suggestions are quite obvious. These steps have already been taken.

Thanks

P.S: All the activity was been carried out under the supervision of qualified technician !!

[azammakda]

The anti freeze stat should be in leaving water, continual tube failures could be caused by many issues, low water turbulence areas due to corroded partition baffles, SST too low, water flows too low, low fin tubes stress fracturing, the list goes on and on. Cathodic corrosion in chilled water circuit usually at support baffle sheet points. Test the chilled water for PH.

The chill water is demineralized water. The PH is same as that supplied in typical boilers.
Water flow might not be a possible issue because there are water flow switches installed for compressor trip.

Thanks for suggestions!!

[mark957]

1) Vibration due to high flow rates of the liquid secondary
2) Vibravioni due to the mechanical configuration of the chiller
3) PH aggressive secondary fluid
3) galvanic currents electrostatic
4) Freezing of the secondary fluid

Hello and good luck