Shell DEP vs ASME VIII div 1 and 2 nozzle types for Volumetric Inspectio

[TomRob142]

DEP 31.22.00.31 lists 100% UT or RT for Category 1 vessels, with a note to indicate that this only applies to ASME VIII Div 1 UW-16.1 F-1 to F-4, or ASME VIII Div 2 table 4.2.13, otherwise no volumetric inspection is required (PT/MT only). This feels like it could lead fabricators to offer nozzles outside of these types in order to minimise the NDT scrutiny of welds, and results in only requiring MT/PT for Cat 1 vessels. Am I right in thinking that the only penalty incurred by the vessel designer/fabricator is a reduced joint efficiency for the nozzle to shell weld, since no RT/UT has taken place? It feels like the DEP should be directing users to utilise those nozzle types are are readily inspectable by RT, to achieve improved joint quality, and not giving fabricators a route to minimise the level of NDE on main pressure boundaries.

On the same subject, what is the difference between Div 1 UW-16.1(G) and Div 2 table 4.2.13 type 7, the latter being deemed inspectable by rad but the former not?

 

[david339933]

Am I right in thinking that the only penalty incurred by the vessel designer/fabricator is a reduced joint efficiency for the nozzle to shell weld, since no RT/UT has taken place?

There really is no penalty as the efficiency of the nozzle to shell weld is not used in any calculation for the other joint details. The most common nozzle weld details are those other than UW-16.1 f1-f4.

 

[TomRob142]

Although I can understand your point on nozzle joint calculation, how do we mitigate this in design software, where we must select the RT level at the package level, should we still be able to select RT-1 even with nozzles that have not been volumetrically inspected? The only calcs that I can see that include joint efficiency are for the pressure thickness of shells, however Cat D joint (nozzle to shell joint) efficiencies are covered in table UW-12 which adds to the mystery.

If anyone has experience on whether thickened neck self reinforced nozzles as per Div 1 UW-16.1(G) and Div 2 table 4.2.13 type 7 nozzles are in fact the same and are possible to inspect by rad then i'd be interested to hear more. I appreciate that the dimensions of the thickened portion may be key, however this is not how DEP 31.22.00.31 reads, as it classes them as not requiring UT/RT in any case.

 

[david339933]

RT-1 can still be used in this situation. If you use UW-16.1 F1 - F4 you need to RT the nozzle to shell weld to have RT-1, per UW-11(a)(5).

 

[r6155]

@ TomRob142
There is no mystery.

See ASME VIII Div.1 Table UW-12 Note (8).
(8)There is no joint efficiency E in the design equations of this Division for Category C and D corner joints. When needed, a value of E not greater than 1.00 may be used.

Regards

 

[TomRob142]

@r6155 Yes I also saw that comment - but I took a corner joint to cover set on nozzles and not set-through nozzles, where joined with a full pen weld. Mandatory appx 3 suggests otherwise, and that a corner joint is defined as follows;

(c) corner joint: a joint between 2 members located in intersecting planes at approximately 90 deg.

which makes the note (8) statement relevant to the post.
Would love to know why joint efficiencies for cat D welds are listed in table UW-12 at all, and are not listed as Not Applicable? Still a mystery to me!