Code Boundry and S vs SA/SB 1

[PipingEquipment]

Hi,

Am planning on removing a pair of flanges connecting two vessels via a 12" sch10S piece of pipe and replacing with a pup piece of pipe (eliminating the flanges as they leak in a high heat and high caustic service), my question is since Section VIII specifies that the code is ended at the first weld does that mean the pipe I want to weld in between the two vessels can be considered B31.3? I ask because I can only find the nickel alloy in B-xxxx not SB-xxxx, and as I understand it ONLY SB-xxxx (or SA-xxxx) can be used for code vessels, or alternatively is there any way around a material not double stamped for B/SB without re-certifying it to SB standards?
Also, the Section VIII portion ends at the first weld, but is the weld included, in other words can a SB pipe (Section VIII side) be welded to B pipe (B31.3 side)? Or would the first weld have to have BOTH pieces of pipe be 'pressure vessel quality' (SB)?

Thanks for your input and help.

 

[metengr]

Here is what Section VIII, Div 1 states;

U-1(e) In relation to the geometry of pressure containing
parts, the scope of this Division shall include the
following:
U-1(e)(1) where external piping; other pressure vessels
including heat exchangers; or mechanical devices, such
as pumps, mixers, or compressors, are to be connected to
the vessel:
(a) the welding end connection for the first circumferential
joint for welded connections [see UW-13(h)];
(b) the first threaded joint for screwed connections;
(c) the face of the first flange for bolted, flanged
connections;
(d) the first sealing surface for proprietary connections
or fittings;

(a) would be applicable in your case because you would have a butt weld to the section of pipe sticking out from the vessel.

 

[PipingEquipment]

So at that first weld where the BPVC ends, can an SB (section VIII) material be welded to a B (B31.3) material?

 

[metengr]

Yes.

 

[PipingEquipment]

Thanks!