2" LWN in lieu of 2" CPLG for Sec8 UG-46(f)

[ConstantEffort]

Do two 2" LWNs satisfy the Sec 8 Div 1 inspection opening requirement on a 36" ID vessel?

My vessel falls under UG-46(f)(2):
"All vessels 18 in. (450 mm) to 36 in. (900 mm), inclusive, I.D. shall have a manhole or at least two handholes or two plugged, threaded inspection openings of not less than NPS 2 (DN 50)."

I read this as, vessel shall have one of these three:

1) manhole
2) two handholes
3) threaded inspection NPS 2​

Others read it as shall

1) have an opening not less than NPS2
2) it can be a manhole, two handholes, or a threaded inspection opening​

Under my interpretation, a pair of 2" LWNs with a 2" finished opening would not qualify as a threaded inspection opening of NPS2. It would also not meet UG-46(g)'s definition of a handhole (2" x 3" minimum opening).

Under others' interpretation, it is NPS 2 or larger and it is reserved as an inspection opening.

Others' argument makes sense to me, the opening on the 2" LWN (2.0in) is larger than that of a 2" 6000# coupling (1.7in), but I just cannot get my brain to read the code the way they are reading it.

 

[marty007]

I've never gotten a 100% clear interpretation from people on this one either.

One difference I see between a 2" coupling and a 2" LWN is the radial offset from the vessel, and in turn the amount of the inside surface of the vessel that will be visible. The 2" coupling puts you much closer to the vessel, giving you a steeper viewing angle down the longitudinal axis of the vessel.

I'm also very curious to hear the perspective of other forum memebers.

 

[GenB]

ConstanrE. You are comparing a 6k coupling with a LWN. Its the ID what counts and the I'd of the LWN is less than the threaded 2 in. I guess if you use a larger, say 2.5 or larger ID LWN may be acceptable to the AI. Check the ID if it is 2.375 in. Also keep the face as short as possible to the vessel. This is a complicated issue,the shall is a must have 2 openings per Code...

 

[ConstantEffort]

GenB,

I did mess up the ID of the 2" coupling. I looked at the bore of a socketweld coupling and assumed it was the same for a threaded coupling. Thank you for catching that.

So that lends more validity to my stance that a 2" LWN would not equate to a 2" coupling.

Good enough for me, unless someone else can reply "yeah, we always use 2" LWN handholes and our AI loves them!"

 

[Duwe6]

Why not 3"NPS pad flanges, so you can actually see some of the interior? LWN is like looking down a gunbarrel, and a 2"NPS cplg [the intent of Sect-VIII], is not much better.

Will admit to some prejudice; I inspect them and fix them, but have only built a few. And a cplg is cheaper and easier to install. But it is close to useless to evaluate the interior.

 

[gr2vessels]

Does it really make any difference the 2" or 3" opening in a vessel? There is black pitch dark in a 4" opening, let alone the smaller ones. You can't see anything inside anyway. If you need to use a borescope, then why would you spend money on fancy large openings, when you can do with the cheapest and the smaller one on market, provided the nozzle thickness conforms the code. Use the most cost effective nozzle and if the LWN is cheaper but you need to cut it a bit shorter then do it. BTW, is it really a 2" NB handhole?! Must be very, very small hand...but once inside the nozzle, how would you look inside, past the hand? Perhaps a manhole could be practical if you need extensive inspection and NDE tests inside the vessel, but otherwise, small holes for borescope.
Cheers,
gr2vessels