Thermal Shock changing material hardness
Thermal Shock changing material hardness
(OP)
I have a finned cooling coil constructed from 304L stainless steel. It is installed in an oven that is operated at a temperature of 175°C. During the cooling cycle, chilled water is pumped through the coil. At the beginning of the cooling cycle, water is fed into the coil at the full rate of about 12 gpm. This imposes a thermal shock on the coil and occurs approximately 8 times per day. After operation of approximately 2000 hours, some failures have occured which have been verified as chloride stress corrosion cracking. My question is this: If the coil was properly annealed, is it possible that stress could be developed in the material from the thermal shock? The material analysis showed rockwell hardness in the area of C34. If the coil was properly annealed it should have been in the area of B78.





RE: Thermal Shock changing material hardness
RE: Thermal Shock changing material hardness
If you have significant thermal shock it will show up as distortion of the component. Absent this I wouldn't be too concerned about thermal stresses. The unannealed condition of your 304 is sufficient to acccount for the problems.
RE: Thermal Shock changing material hardness
Your condition of thermal cycling would if anything led to either fatigue or corrosion fatigue (appears you had 600 to 700 cycles), but this would have been determined in your failure analysis.
RE: Thermal Shock changing material hardness
Here's some quantification of my earlier response. 304 with a hardness of 34Rc has to have been cold-worked around 50% ( at room temperature ). That material should have a yield stress of about 120,000psi. It qualifies as 1/2 hard temper material. This cannot have happened from thermal gradients. It sounds like mixed steel or improper processing.
RE: Thermal Shock changing material hardness
For some background on this particular HXer problem, see Thread338-42610
goomba,
1) were you able to obtain the water analyses or more info on the third party additive package? A number of water treatment chemicals become pitting initiators when boiled down (as during your furnace heating cycle).
2) Am curious, did your management shoot down earlier suggestions from mcguire and myself?
RE: Thermal Shock changing material hardness
RE: Thermal Shock changing material hardness