UG-36(c)(3)(-b)

[loilfan]

We are looking to modify a pressure vessel so that it has a finished opening 1 7/8" diameter in a 3/8" plate. A pad is placed on the inside of the shell and is threaded in place by a threaded flex hose hooked up to the nozzle. The opening will not be near any discontinuities or welded joints.

If you remove the pad and the flex hose, all we have is a single hole as if it had just been drilled out. i.e. If I did the reinforcement calculations, all I could have for available reinforcement is A1 (Area available in Shell).

I do not consider UG-36(c)(3)(a) to apply since the connection has not been welded, brazed, or flued. Does UG-36(c)(3)(-b) apply even though the threading for the connection is in removable components? Or is the intent that the threaded, studded and expanded connections are only in the shell?

 

[SnTMan]

loilfan, UG-36(3)(c)(b) states threaded connections. If it is indeed intended to apply to tapped holes in the vessel wall I see no real difference between a tapped opening and an un-tapped one.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[rww88]

While it may not directly address your question, I am willing to forward excerpts from a textbook that I am writing that deals with this topic. It is too voluminous to post here, so if you are of interest, indicate the best way to send this material to you. Best regards.

 

[loilfan]

SnTMan, the wording in the Code doesn't distinguish the opening as tapped or un-tapped, which is essentially the basis of my question and a better way to frame it. To make this all easier, I'll re-write my question as: does UG-36(3)(c)(b) apply to un-tapped holes?

If it's a tapped hole or studded connection, then there would inherently be a minimum thread depth required. Similarly with the expanded connection. my concern is that the Code assumes that there is some additional material perpendicular to the shell in which the connection takes strength from.

For example, in UG-36(c)(3)(a) welded, brazed, or flued connections would all have material that extends perpendicular to the opening and additional reinforcement in A2 is possible.

rww88, I am interested in seeing what you are writing - thanks! However, I'm not sure how to connect. I can't find a Private Message feature on this site and we shouldn't be posting our email addresses.

 

[SnTMan]

Well, I gotta ssy, I don't know the exact meaning of the words "threaded, studded and expanded connections". They no doubt apply to some class of work with which I am not familiar. If a person knew the details of these types of connections it would seem clear whether or not UG-36(3)(c)(b) can be applied to a simple drilled hole.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[rww88]

In my humble opinion only, I believe the intent of UG-36(3)(c)(b) is provided by a re-write of the paragraph: "threaded, studded, or expanded opening connections whose drilled pilot hole for threads, or formed pre-hole for expansion, that is cut in the shell or head, is not greater than 2-3/8 in.(60 mm) diameter." From the aforementioned textbook: "Not to be confused with the internally threaded insert type opening connection such as a half or full coupling, a tapped opening is one in which the sidewall of a hole in a host shell component is cut with internal threads with a tap. This type of opening is employed when low-cost, easier, and more rapid appurtenance connection/disconnection is desired, contrasted to that required of a bolted flange or weld end connection, and where minimal developed host shell component flexural strength is required. This tapped opening allows an externally threaded appurtenance to be connected through mechanical engagement."

 

[SnTMan]

rww88, that is more or less the interpretation I took for my 14 Feb 18 02:29 post. That is, a hole tapped thru the vessel wall. The meaning of "studded connection" still eludes me, though

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[loilfan]

Thanks for sharing your work, rww88!

I take "studded connection" to mean something like this link where the vessel wall has sufficient thickness for the minimum thread engagement of the bolts.
One could argue that it is a welded connection and would instead fall under UG-36(c)(3)(a).

https://forgedcomponents.com/fci-as...nnections/fci-studding-outlet-specifications/

Just to confirm, you both think that the intent of UG-36(3)(c)(b) applies only to openings in which there would be sufficient depth for threading?

For example, If I wanted to put a NPT 2 tapped hole in the shell wall, I could only use this if I have a shell that is at least 0.7565" thick. 0.7565" is the Effective Thread Length from Table 2 of ASME B1-20-1 and ASME B16.11 Table I-5 for threaded couplings. Any shell thickness less than 0.7565" for a 2.375" opening (NPS 2 OD) would then not be sufficient?

i.e. my 1 7/8" hole in 3/8" plate wouldn't be inherently thick enough and would require additional reinforcement.

EDIT: As per david339933 below, use Table UG-43 instead for my example.

 

[rww88]

Definitions of studded connection:
1. Flanged end or outlet connection in which thread-anchored studs screwed into tapped holes replace the holes for bolt studs.
(Source: API SPEC 6A, Specification for Wellhead and Christmas Tree Equipment, Twentieth Edition, October 2010 (Addendum November 2012)).
2. Connection in which thread-anchored studs are screwed into tapped holes.
(Source: API Specification 16A, Specification for Drill-through Equipment, Fourth Edition, April 2017.)
(Source: API SPEC 16A, Specification for Drill-through Equipment, Third Edition, June 2004 (Errata/Supplement November 2004)).

From the aforementioned textbook:
"A common near-surface opening connection is the studded connection, often referred to as a studding outlet, studding pad, or just pad. The connection's name is derived from the fact that it has blind holes that have been tapped to receive threaded studs that are the fasteners of the mechanical joint of the connected appurtenance. (A stud is simply a threaded rod; one end assembles into a tapped hole, the other end receives a nut.) Connection shapes are prevalently circular, but can be square, rectangular, and obround as well. Because of the low profile of this near-surface opening connection, the axial line of penetration is either normal or radial orientation.
"The studded connection consists of a thick cross-section of material with a large central opening, weld-attached to the host shell component. It is typically forged and then machined to finished dimensions although machining from plate material is also performed. A boss is a parent-based type studded connection that is formed from a flat surface machined on the host shell component. Generally studded connection forging material compositions range from carbon and low alloy carbon manganese and silicon containing steels to high alloys containing chromium and nickel. Acceptable fabrication materials, including plate, are listed by specification number in the API Standards and ASME Code. The range of acceptable material compositions affords the designer the ability to make economic choices based on the strength and corrosion resistant requirements that draw a parallel with that of the host shell component.
"The studded connection forms the base for a number of different end purposes to include the compression of liquid level sight glasses, the attachment of blind flanges for inspection openings, and the foundation for agitators and immersion heaters. This type of opening connection is suitable when liquid hold-up in an appurtenant pipe line must be minimized and where available space will not accommodate a projecting type nozzle opening connection."

 

[david339933]

Min plate thickness for a 2" NPS threaded connection is 0.70" per Table UG-43.

 

[SnTMan]

Studding outlets or pads I am familiar with, but would consider as falling under UG-36(c)(3)(a) since they are typically welded to the shell. I suppose a "studded connection" could apply to a blind, tapped hole (or set of the same) in a vessel wall. But, then the distinction from a "threaded connection" is what?

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[rww88]

Question: Just to confirm, you both think that the intent of UG-36(3)(c)(b) applies only to openings in which there would be sufficient depth for threading?
Answer: Yes and No. Peruse the design example attached excerpted from the aforementioned textbook.
Warning: The material and information contained in this attachment and earlier posted excerpts have not be edited or checked for correctness.

 

[david339933]

I take it as a threaded connection is thru the vessel wall, while studded connections have requirements for thickness between the bottom of the threaded portion and the inner surface of the vessel as per UG-43(d).

 

[david339933]

Why is 2c continually added to d? Such as: A = (d+2c)tr

 

[david339933]

I see now...d is defined as 4.5" when it should be 4.6876".

 

[SnTMan]

david339933, your 15 Feb 18 19:06, I'd tend to agree. I'd find it hard to believe that a pipe or fitting threaded into a tapped hole would be considered to act contributing reinforcement to that tapped hole. For that reason, I see no real difference whether the opening is tapped or not.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[loilfan]

david339933, thanks for pointing out Table UG-43. That should be used instead of the values in B1.20.1 or B16.11. I edited my earlier post.

Per the definitions of threaded, studded and expanded connections in UG-43 (d) to (f), we can conclude that UG-36(3)(c)(b) applies for tapped holes meeting Table UG-43. For untapped holes, I would think that we can use the thicknesses required by Table UG-43 as justification for the strength of reinforcement (more material is actually available since it wasn't tapped) but that additional analysis would be required for the strength of the connection. Thoughts?

 

[david339933]

I don't think I would use thickness of Table UG-43 as justification for reinforcement. Thickness of Table UG-43 is to ensure adequate shear area of threads via a minimum length of engagement. As UG-43(e) states a built up pad,or a properly attached plate or fitting can be used to provide the metal thickness and number of threads required or to furnish reinforcement when required. What "properly attached" actually means may be up for debate.
The problem is that UG-43(e) is only applicable for threads in the vessel wall as per below interpretation. So should UG-43 be ignored in this instance? It would seem so, but it could be used as an argument for length of engagement as well as allowing a "properly attached" pad count as reinforcement as long as the strength of attachment can be shown.
I would certainly like to know how this plays out.....

Section VIII, Division 1, UG-43(e)
Date Issued: 09/06/1978
Record Number: BC-78-527
Interpretation Number : VIII-78-121
Question(s) and Reply(ies):
Question: Is it the intent of the second and third paragraphs of UG-43(e) to apply to a type of threaded connection where a fitting or pipe is welded to a vessel wall and has either internal or external threading covered by UW-16?

Reply: No. These paragraphs are applicable only to a type of threaded connection where there is a threaded hole in the vessel wall.

 

[loilfan]

UG-36(3)(c)(b) permits an opening up to 2 3/8" diameter provided it is a threaded connection. An untapped hole would only be stronger than a tapped hole provided no additional strength is claimed from the additional threaded component. The finished diameter would only be bigger with a tapped hole.

I agree with SnTMan - I don't see why a tapped hole would be acceptable for this exemption, but an untapped one would not be.

 

[SnTMan]

UG-43 (d) to (f) actually defines these type of connections fairly well, I had forgotten. All in all, I'd say my opinion is unchanged.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand