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Niyama is just the thermal gradient divided by the square root of the cooling rate, and it helps to detect micro porosity. 

I attached a ppt where this is explained but basically the lower the niyama values (high cooling rate or low thermal gradient) the higher the possibility of micro porosity.

Remember that Niyama works under a certain range depending on the different materials.


This range is not necessary to know in Micro Porosity result. This result is based on dimensionless niyama so no range known is needed. This result is based on niyama and also in other parameters like pressure... (I attached a paper that talks about it)


Best Regards




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Hello Pau,
Your document said that "As the Niyama value decreases further, the amount of micro-shrinkage increases until it becomes detectable on a standard radiograph.". So that, the Niyama criterion can detect the macro porosity too, right? If it is true, so why should we use the Porosity to define the area have macro porosity?

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