CSAZ662 Commentary and Implications of using very conservative minimum-design-temperature

[USER10]

In CSAZ662 Commentary part it is stated " it is common industry practice to use –5 °C
as the minimum design temperature for buried piping and either –30 °C or –45 °C (depending on the
local climate) as the minimum design temperature for above-ground piping" .
I think that this practice is not safe as minimum temperature of buried pipes in many northern cities can be much lower than -5°C.

I called a pipeline eng friend who works mostly in projects in Alberta and Northern British Columbia but not in the arctic zone to discuss the above commentary. He stated that in cold cities (where temperature of ground at 3 ft deep is expected to be lower than -5 °C) he just just ordered pipes with proven notch-toughness at -45 °C as most suppliers have already these pipes. In other words, he does not usually bother to determine the minimum design temperature for a specific area for buried pipes and further to carry out proven notch toughness tests at such temperature. My question : is that a good practice...? and what are the implications (e.g cost, materials, pipe performance) of using pipe with proven notch toughness at –45 °C while real minimum temperature could be much lower than that (maybe two or three times lower than -45 °C)>?

Thanks in advance for your thoughts on this subject

 

[brimmer]

Underground piping does not get to the temperatures you are suggesting. If it did, all our water pipes would freeze. Remember, product flow keeps the pipes at warmer temperatures. I have never seen a petroleum product pipeline go below 0C (unless product has stopped flowing). There are pipelines melting permafrost in the far north because they give off heat. How do you get a temperature 2 or 3x lower than -45C? That's -135C.

 

[SNORGY]

Perhaps the most irritating consequence that you will run into by assuming unnecessarily low MDMTs is that it will become virtually impossible to get your stress analysis to pass, once you look at how the combined longitudinal stress limitations are treated in that Code. (Setting a needlessly low MDMT might skew your judgement towards setting a correspondingly low temperature at time of initial restraint.)

Who is right doesn't matter. What is right is all that matters.

 

[GD2]

Minimum Design temp (CSA)is determined as a combination of minimum operating temp, soil temp, ambient temp. Many times we just think about the ambient temp, which is not true. CSA Z662 had been written after lots of experiment and research. That’s why it gives to use -5C for buried pipes. This temp is also used by stress engineers as installation temp.

Above ground piping sees more extreme temp. It’s therefore common to use -45C exposed outdoor and 0C inside a room.


GDD
Canada