How to determine allowable rapid temperature change in piping at our plant?
How to determine allowable rapid temperature change in piping at our plant?
(OP)
Good morning all. We are looking at using a thermal oil for heating some equipment at our plant. The oil is kept at 350F in a main building and is currently used for one of our processes.
The piping to the new equipment is run outside and is insulated. Can someone point me in the right direction on how to determine if we are OK with pumping this hot oil into a potentially cold pipe? We are located in Ohio where temps get down to about possible -20F.
We want to provide verification that we do not have to spend electric cost to constantly circulate the hot oil through the piping to maintain temperature in this heating loop.
Here is piping specs
Thermal fluid piping shall be seamless carbon steel ASTM A53 Gr B standard wall
All pipe flanges shall be forged carbon steel ASTM A105, ASME B16.5, Class 300 welding neck, raised face, with Std WT bore
If anyone is curious about the oil it is Paratherm HE - specs attached
We use spiral wound gaskets on all flanged connections. Pipe size is 3"
If anything is unclear let me know. Thanks
The piping to the new equipment is run outside and is insulated. Can someone point me in the right direction on how to determine if we are OK with pumping this hot oil into a potentially cold pipe? We are located in Ohio where temps get down to about possible -20F.
We want to provide verification that we do not have to spend electric cost to constantly circulate the hot oil through the piping to maintain temperature in this heating loop.
Here is piping specs
Thermal fluid piping shall be seamless carbon steel ASTM A53 Gr B standard wall
All pipe flanges shall be forged carbon steel ASTM A105, ASME B16.5, Class 300 welding neck, raised face, with Std WT bore
If anyone is curious about the oil it is Paratherm HE - specs attached
We use spiral wound gaskets on all flanged connections. Pipe size is 3"
If anything is unclear let me know. Thanks





RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?
OK after searching we find E to be about 29.5x10^6 PSI and coefficient of thermal expansion to be about 6.5x10^-6 in/in°F.
The yield strength of the piping is 35,000PSI so do I divide the 35,000 by the multiple of the numbers above to get max temp differential in the ballpark of 182°F?
RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?
If you find the thermal shock load (dT/dt) at -20degF on the piping is in excess of what is permissible, would electric heat tracing of these pipes be a lower operating cost?
RE: How to determine allowable rapid temperature change in piping at our plant?
The A53 pipe itself can work at these lower temperatures, but impact testing should be specified in the PO to be conducted at whatever the lowest temperature is, or test even lower at lowest temperature -5 additional degrees F or so.
RE: How to determine allowable rapid temperature change in piping at our plant?
If this is acceptable, you'd still need to account for impact testing requirements in case Operations have somehow missed out on keeping this line warm.
Just took a look at this fluid's physical props - its off the curve on viscosity at 30degF !
So, what happens at -20degF if for some reason this trickle warming operation was missed out - would this liquid freeze up? No data on freeze point, and viscosity of 320cP at 30degF is worrying enough. Having to drain out this line everytime you shutdown relies on operating procedures also.
Looks like external electric heat tracing (obviously not steam tracing) is the only way to cold start to warm up reliably with this Paratherm. A low temp alarm at control room should be included.
A piping engineer should suggest what dT/dt is permitted at 30degC or so, when you begin warm startup operations with the bypass needle / globe valve.
RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?
My issue with this is that you seem to be looking for a static equation for a transient event - never normally a good way to do things. I also can't see your system so have no idea how long or how convoluted this system is. My concern would be that one section of the pipe would be heating up and expanding, whilst the other is still cold and with lower strength properties. This is very difficult to model accurately.
I think the way out is to maintain some sort of temperature in the pipe (say 30 to 40C) and then re-start over a period of 5 to 10 minutes at a low rate. You should be running this through a transient stress model / transient flow model to show temp rise over time taking into account metal thickness and heat p time as well as the hot oil.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?
We do not have transient flow software and even if purchased would not have the experience necessary to correctly use it. We may consider subbing this out unless we can determine some other way
For certain we must keep the fluid temp above a chosen number to allow pumping - we can do this
I attach a simple P&ID so you can see more what is happening. There is much more obviously but I do not think it mattered to include for the discussion
The length of piping is about 500' of 8" pipe for the main dryer loop as shown in attachement. The secondary loops (EET loop) have between 100 and 300' of 3" piping depending as there are 3 loops. There are some transitions with stepped down sizes to the 3" and back to the 8" but not shown
RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?
Piping Design Central
RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?
The drawback of using a restrictive orifice to keep the pipe warm is is that the pipe will still be 350F at one end while the other end will be far colder. You should have a separate pump to circulate oil in the new heating loop and slowly introduce hot oil into this loop with appropriate controls. Just the heat of pumping will tend to keep the fluid from getting too viscous because the heating will increase with viscosity. Thus the temperature will tend to be self-regulating.
All the discussion so far has dealt with the hoop stresses in the pipe due to rapid temperature change. In most cases dealing with the the longitudinal stresses cause by a large temperature change and anchor points are the greater challenge.
RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?
RE: How to determine allowable rapid temperature change in piping at our plant?