I have to check a piping for thermal shock.

4" Hot oil line @ 170 deg C, (uninsulated) has a potential of
exposure to water @ 6 deg. C (external)

Material CS, sch 40.

Any suggestions ?

Regards,

It is advisable to change the atmospheric temp as 6 degC or add another temp case at 6degC and check the stress range for two temperatures.

will it account for the sudden change in the temperature ?

PKU's suggestion is correct - you can look at the steady-state to steady-state effects by either revising the installed temperature from 20 C to 6 C, or by defining a 6 C temperature case and an algebraic thermal stress range case from 170 C to 6 C. But this does not account for local effects during the transient.

CAESAR II looks at temperature changes as though the temperature profile is fully developed. If you go very suddenly from 170 C to 6 C, you are going to have localized effects that are beyond the capability of CAESAR II (just lke a peak local stress due to a discontinuity).

Just like a peak stress at a discontinuity, you will have to do a hand calculation to evaluate the thermal transient effects. Since most of the thermal shock effects will be radial rather than axial, there's nothing you can do with CAESAR II to evaluate them. CAESAR II considers every element to be a line element with the stiffness properties of a 3D element, but has no capability to evaluate differential elements within that line element.

I had a fair Idea that it was not a CAESAR question, more a
stress question.
I thought someone might have come across this situation earlier and might help.
Thanks anyway

check ASME section III NC as I recall you may find some direction on this topic....

Hi SRI,

Without getting to deeply into arcane sciences, most people who are speaking of "thermal shock" to piping are addressing the significant change in metallurgical properties that may occur when the pipe wall metal is rapidly heated or rapidly cooled. E.G., if a hot pipe is suddenly cooled ("quenched") there may be (depending upon the material) a significant loss of ductility and the pipe will become relatively "brittle". Similarly, some materials can become embrittled by sudden (or even lengthy) applications of heat. The metallurgical implications can be studied by doing some "homework".

There usually will be "symptoms" left behind that can be detected. Recovering from a refinery fire usually involves hardness testing of the pipe material thought to have possibly been affected by the temperature changes. Perhaps you should look into this topic via a "Google search".

Regards, John.

Material is CS. I would assume something like 106 B. Cooling from 170 should not cause hardening effect. If the material temperature drops down to 6 C, which most propably will not happen, the impact values can go down drastically if the material is not designed for low temperatures. You may get some surface cracking. Cold outer surface compared to hot inner results in high stresses. If there are fatigue issues then any crack is no good. Pipe deformation is a small possibility if the cooling is one sided.

One that I would check is where the generated steam goes. I have a resent case where we had to put in large line with bursting disc to get rid of steam instead of blowing up 3 m diam vessel (http://www.jat.co.za/worksamples.htm). Smaller line would have been enough but the issue came up late and there was free nozzle.

I know of a boiler drum that was destroyed by the "thermal shock" resulting from feedwater impingement on the drum inner wall after the owner decided that it wasn't worth the money to repair the feedwater heater. I guess he was wrong. Boiler drums are a whole hell of a lot more expensive than heat exchangers.

From a fatigue standpoint, if you can calculate the change in the outside surface temperature from the water impact, you can calculate the stress from the contraction, which can be estimated as simplistically as E-alpha-DT. From stress range, you can calculate the fatigue life. But the heat transfer problem is complicated by the fact that the water will be hitting a surface at at temperature above its boiling point. Further, depending upon how the water is impacting the surface, you may have bowing and other issues. And if it is rain you are thinking about, what number of cycles are you going to estimate (other than an endurance limit)? If it is rain, you should use a rain shield.

Its deluge water...
To avoid the complication I think we would finally end up cladding the piping.