ER calculation per API 6A section 6.4.2.3.2 figure b

Hello everyone!

I've checked all the threads about QTC and didn't find any answer, so I start a new thread here.

My confusion is how to understand 'the larger of the two indicated dimension' in note d in API 6A section 6.4.2.3.2 figure b. For example, we have a tubing head like the middle sketch in figure b, then the larger of the two indicated dimension means the larger of the flange thickness (FLG TOP and FLG BTM) or the larger between the flange thickness and the wall thickness (as described in the right sketch in figure b)?

Hi Leung,

As per API 6A section 6.4.2.3.2 figure b - it is the the larger of the two indicated dimension means the larger of the flange thickness T2 d (FLG TOP and FLG BTM).

The assumption is that, as heat is transmitted in all directions equally during HT, the least cross section has to be considered in any given area of the component.

With that assumption, in any complex part, try to divide it into simple parts and calculate the least cross section thickness through which the heat can be transmitted throughout the area of the part. Then find the maximum (M) of all the least CS thickness. Then find the equivalent simple configuration (Cylinder/Square/Hollow Cylinder) of that maximum (M) part. Then using the formulae given in 6.4.2.3.2 figure a. multiply 'M' by that factor.

Mostly in spools it is hollow cylinder, so Equivalent Round size to be 2*M