Surface finish for thermal shock cracking
Surface finish for thermal shock cracking
(OP)
We manufacture nuclear valves to ASME III.
Some of our older designs have surface finishes on internal surfaces of 16 micro inch, which is hard to achieve.
It has been suggested that this was introduced to prevent cracking due to thermal shock and that this was derived from a requirement in ASME III. I have had a look but can find no such clause in ASME III.
Does anyone know if there is such a clause in ASME?
Is it good enginering practice anyway?
Bill H
Some of our older designs have surface finishes on internal surfaces of 16 micro inch, which is hard to achieve.
It has been suggested that this was introduced to prevent cracking due to thermal shock and that this was derived from a requirement in ASME III. I have had a look but can find no such clause in ASME III.
Does anyone know if there is such a clause in ASME?
Is it good enginering practice anyway?
Bill H





RE: Surface finish for thermal shock cracking
Maybe to better help your situation, I had found an equation below in a technical publication that shows the essential variables that can be used to evaluate thermal fatigue resistance between various materials;
Thermal fatigue resistance parameter = yield strength x thermal conductivity/Elastic Modulus x coefficient of thermal expansion.
Obviously, the higher the resistance parameter, the better off you are for a given thermal stress. As you can see, surface finish really does not play a significant role. In most of the components we have purchased for cyclic service, the key is to reduce stress concentration by introducing a radius at any sharp corners or openings, and removing by blend grinding any sharp tool marks.
RE: Surface finish for thermal shock cracking
RE: Surface finish for thermal shock cracking
As a side note, if you are experiencing thermal fatigue damage to the fireside waterwall tube surfaces it may be that your dwell time or cycling duty is too high. You really should not be experiencing any TF damage. We have installed several water cannons on our PC, T-fired boilers with no adverse effects.