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UG-46 requirement for vessel

UG-46 requirement for vessel

UG-46 requirement for vessel

Hi everyone,

We are having a vendor fabricating a 48" dia. vessel for us.

We have an issue with a manhole for inspection purposes.

According to ASME VIII UG-46; all vessels greater than 36" in diameter shall have a manhole, except when the shape of the vessel or use of a manhole is impractical in which case 2 handholes are needed with an equivalent area for each at 4" x 6".

The vendor is telling us a manhole is impractical thus they are using N3 and N4 nozzles (6" dia. each)as shown in the attached picture as the inspection holes.

The reason why it's "impractical" is not clear but I thought I would ask this quick question here to see if it's even worth looking into this. Apologies for the poor photo resolution -- i'm having trouble uploading a clearer image.

RE: UG-46 requirement for vessel

Try to get a written explanation from the vendor.


RE: UG-46 requirement for vessel

It is likely impractical because they didn't put that cost into their bid.
Get the reason in writing.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: UG-46 requirement for vessel

The average LinkedIn user/member wrt this subject (specific the ASME PVP group) may very well be below ET’s userbase’s level of expertise, I get that - but didn’t you already got enough input over there?
Bear in mind that some frequent posters here also post there, however typically with a bit more reticence I’d say. Here’s a good example

- You never get what you expect, you only get what you inspect.

RE: UG-46 requirement for vessel

I will repeat what I said on LinkedIn ..... You get what you ordered, Rubje ... .... If you forgot to order something in your RFQ, it's not the duty pf the fabricator to considerably increase his price for what you might have overlooked.... its gonna cost you, the vessel purchaser, more later ....

"I do not understand why the purchaser DID NOT specify the necessary manway when he first defined all features and characteristics of this tiny pressure vessel !!!.... It appears to me that the purchaser tried to "slip in" a MW into the scope when it was forgotten by the engineering newbie when he specified the vessel.

I stand with the fabricator in his claim"

Sr. Process Engineer

RE: UG-46 requirement for vessel


I'm confused by your message. I only posted regarding this inquiry on this message boards.

Did someone else ask a similar question on linkedin?

RE: UG-46 requirement for vessel

Here are some limitations/comments regarding inspection access to your ASME vessel: (all of this is IMHO !)

1) ----- Acceptable vessel designs to provide inspector access include:

a) Manways - these are the most common method of access b) Small access shell hatches-for that purpose c) vessel body flange for vessel - most expensive option and rarely used d) Planned nozzle access through LARGE (8-12")diameter process nozzles when adjoining piping spool is removed - This is the most awkward solution

2) ------Manways are expensive, especially in materials other than carbon steel. Manways and access through the manway must be carefully laid out considering the location of vessel support lugs, nozzles, manway davit (if present) etc... Under EN standards, manways are limited in diameter to half the diameter of the vessel. This means that a manway for your stubby vessel is limited to about 600 mm diameter

3) -------Since you seem to quote ASME rules, I suggest discussions with your AI to ask about what is acceptable to them

Keep us posted about your progress and final vessel access solution

What are the materials of the vessel ?

What are the design pressures and temperatures ?

Is ASME VIII the Code of Record ??

Is there access around the vessel in the final layout drawings ? Despite what your psychotic MBA master may tell you, the location of ANY MANWAY ON ANY VESSEL cannot be finalized until the General Arangements are complete ... Otherwise, vessels are ordered and installed with unusable manways that open up to a building colmn

My thoughts only...

Sr. Process Engineer

RE: UG-46 requirement for vessel

Without Manhole, the end circumferential joint is welded from the outside. I suggest RT 100% on this weld.


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