Temperature Spec Break

[Epco]

I am looking into a temporary bypass of a cooling water system to facilitate repairs on the cooling units. The current design temperature on the cooling water system is much higher than actual operating conditions (installed circa 1970). We wanted to use Victaulic fittings for the temporary piping for ease of installation and to cut down on labor time, but in order to do so we would need to derate the temperature of the temporary piping slightly to meet manufacturers specs, we would still be well above maximum operating conditions from the temperature profile we received for operating conditions over the past 2 years. I cannot find any code issues with designing the temporary pipe at the lower temperature and inserting a spec break at the tie-in point and wanted to check with the experts to see if anyone knew of any issues/code violations in doing this. Any comments would be appreciated.

 

[pennpiper]

Epco,
Your question brings up more questions. That is not new and is just the way things are.
Please give us a little more information and then maybe someone will have the "Right" answer.

- Is this a whole unit bypass or just a single piece of equipment"
- What is the line size of this bypass"
- What are the Design and Operating conditions of the system?
- How long would the bypass be in service?
- Would all of the Victaulic material be removed after the repairs are completed?
- Have you thought about installing a PSV on the system to protect the Victaulic material?

 

[BigInch]

Its OK as long as you maintain temperatures lower than the temporary's rating.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[Epco]

pennpiper,
-the bypass is only around the cooling units, there are 2 banks of fin fans we will be bypassing one bank at a time, the temporary system is sized to handle one half of the cooling load.
-The bypass line is NPS 12
-the system is designed to B31.3 - design conditions are 2800 gpm, 115psig, 140 deg F proposed, the permenant system is designed for 160 deg F, max actual operating in the last 2 years was 117 deg F.
-Bypass will be in operation for 6-8 months
-all victaulic material will be removed after the repairs are complete.
-A PSV would be appropriate if the concern were pressure related but our problem is in the fact that the victaulic manufacturer will only rate the fittings for 150 deg F which is why we will need to derate the temperature. With the maximum operating in the last 2 years at 117 deg F I did not see this being an issue as long as the spec break was indicated on the piping isometrics and the plant operators were made aware they would have to monitor the system temperature to make sure they did not exceed the temperature rating of the temporary piping. I just wanted to check to see if there was some obscure code issue that I was not aware of or had missed.

 

[Epco]

Biginch, thank-you for your resopnse, that was my thinking as well, just making sure I didn't miss something in the codes.

 

[BillBirch]

Epco,
You may want to check whether your company (owner?) has a specified margin required between the maximum operating temperature and the proposed design temperature. Some companies insist on this to cater for any uncertainties in defining operating envelopes.

I guess that you have chosen a victaulic system for its simplicity of installation in an existing plant, particularly with the elimination of hot work. I have successfully done the same many years ago. Have you considered that you may need more pipe supports than usual to maintain alignment at joints?

Also you may want to consider the following. Regarding the temperature rating of the victaulic joints - I'm assuming this is due to the performance of the elastomer seals, is the 150 degree rating for continuous service, and if so, does the pressure rating diminish with time at the higher allowable temperatures?

 

[vpl]

Epco

You should also verify that the design temperature is not based on the cooler having to respond to emergency conditions. For example, in nuclear applications, coolers do not normally see anywhere near their design heatloads. However, if an accident occurs, the heat load on the cooler goes up considerably. Derating the system to normal operating temperatures could run into significant problems, even if it was only considered "temporary." Even if you're not nuclear, you should verify that a similar requirement doesn't exist for your particular system.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[zuccus]

If you are worried about the victaulic connection, change the type of coupling you use. We typically use Victaulic style 77 flexible couplings for water service.
A quick check of the victaluic web site shows that at 12" the maximum rated pressure is 800 psi. It doesn't say at what temperature though.

I would look for a different style victaulic coupling.

Zuccus

 

[BigInch]

what's all the 2nd guessing about?

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[Epco]

Thank-you all for your response. Design issues as mentioned above were considered and the only issue I had was whether or not we were violating a code issue with the spec break/lower design temp on the temporary piping, the new design temp is still above the max operating temp so we still have better than a 20 deg safety margin on the temperature, which is acceptable to the owner. The vic fittings pressure rating is more than adequate, the temp rating of the elastomer gasket is the cause of our issues and designing to the lower temperature solves this.

 

[QuickVic]

Epco,

Curious as to what style of Victaulic coupling in 30" is in question. The EPDM gasket ( typical grade ) is good to 180F.

 

[QuickVic]

^ Correction. 230F

 

[Epco]

You are correct, the standard temperature rating for the gasket material is higher than our design conditions, so originally we had thought there would be no issue with the gaskets. The problem we ran into was Victaulic only rates their fittings for 150F with nitrile gaskets.