API 661 Brinell Testing 0-3%Cr, 5-17%Cr and 25% but no 18-44% or 4% WHY?

[caper656]

I am hoping to gain alittle more on the intent of the Brinell hardness testing for what they classify as "chromium steels." I assume someone is making very specialized Cr steel pressure vessels, but why just those 3 types? It seems like the intent is check tensile/yield strength of the plate via Hardness testing and heat exchangers are largely Carbon Steel SA-516 or SA240 304L/304SS/316L/316SS. Since 304L 17.5-19.5CR and 316L is 16-18 we have always assumed these didnt classify as the "Chromium Steels" they were targeting and therefore didnt need Brinell Testing. Thoughts?Opinions?

 

I have not looked at API 661 for a long time, but I would have thought they had banished Brinell testing a long time ago. In my work I don't consider Brinell for anything, anywhere, least of all welds, for which Brinell is completely unsuited. NACE has moved away from Rockwell testing to Vickers, the only method that should be used for weld evaluations. How old is the standard you are looking at?
"Chromium steels' would refer to the low alloy Cr-Mo steels up to nominally 13% Cr steels, including 410SS and variants. It also includes the higher Cr ferritic SSs and duplex SSs. Austenitic stainless steels like 304L and 316L are not included in this category.
Hardness testing can give an approximate indication of the UTS (although nothing you can take to the bank), but it says nothing about YS.
p.s., beware of testing labs and inspection companies doing sloppy conversions from one hardness scale to another, often without declaring it.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[caper656]

I'm using API 661 7th edition which is the 2013. And I agree...just curious why or what the intent was in targeting low ally Cr-Mo original. The carbon steel I get....they want the bottom barrel, low to no spec jobs tested to something cheap that gives a "base" line for metal properties.