API 579-1 Local Metal Loss on Elliptical Heads

[IrwinL]

Hello all,

As I am reading thru Part 5 of API579-1, I run into a question on the Level 1 assessment for elliptical heads. Hope you guys can help me out here.
In Level 1 assessment procedure (5.4.2), it says level 1 can be used to evaluate type A component, which includes elliptical heads. However, in the procedures Step 8 where it shows the requirement on remaining thickness ratio (Rt) and longitudinal flaw length parameter (λ), I can only find the details on cylindrical shell (Figure 5.6) and spherical shell (Figure 5.7). How do you deal with other components (e.g. elliptical heads)? Just ignore the Rt and λ and compare RSF with RSFa?

Any help is appreciated. Thanks in advance!
IrwinL

 

[Cashe]

Use the equations to calculate R_t. (Eqn. 5.40~). The lambda values are different for Cylindrical and spherical components, but I've really noticed no difference unless you are dealing with a very small diametered pit. I use cylindrical for most cases. I've never come across any spherical components before.

 

[GD2]

I agree with Cashe. The graphs are identical except the range values for Lamda. The difference should be minimal whichever option you use. I think the intent of the code is to tell the reader about the different vessel type - Cylindrical Vs Spherical without going into head details.
My take is in alignment with Cashe. Use the cylindrical shell rule for cylindrical vessel and spherical rule for a spherical vessel.

GDD
Canada