Inwardly flanged vs outwardly flanged 1

[Konrad]

Hello,
HW-711.1 SecIV allows welding a flanged tubesheet with a lap joint. Whether it has to be a single or double weld, depends on a word that I don't understand. An outwardly flanged tubesheet can be welded with single fillet lap joint, and an inwardly flanged one- must be welded with double fillet lap joint. What is inwardly and outwardly?

There can be two shapes of dished heads:

This complicates further depending on the way they are attached to the shell:

Now which are inwardly and which are outwardly flanged?

Thanks

Konrad

 

[CodeRef]

My thoughts......
Inwardly flanged means the flange is toward pressure while the outwardly flanged means the flange is away from pressure.
As your sketches show, it depends where the flange is placed irregardless of whether the dish is concave or convex to pressure.

flange 1a is outward while 1b is inward
flange 2a is inward while 2b is outward

There are three kinds of people in this world; those who can count and those who can't.

 

[doct9960]

Konrad,

The way I interpret HW-711...the flange is a "straight flange" similar to your sketches 1, 1a, and 1b. Therefore, your sketches 2, 2a, and 2b are out of the picture.

Sketch 1a is the outwardly flanged tubesheet. You will make sense of this when you read HW-711.1(b)..."the joint attaching an outwardly flanged head or tubesheet is wholly within the shell and forms no part thereof"

Sketch 1b is the inwardly flanged tubesheet. HW-711.1(c) says..."inwardly flanged heads or tubesheets are full fillet welded inside and outside". It is easier to do the fillet welds if the head or tubesheet is configured like that in your sketch 1b.

 

[Konrad]

doc9960,
Why do you think that my sketch #2 is not a flanged head/tubesheet? Would that mean it's exempted fom double weld requirement or that it's not permitted at all?
Konrad

 

[doct9960]

Konrad,

To tell you the truth, I have not encountered a head/tubesheet like that on your sketch #2 before. I am only familiar with flat, semi-elliptical, hemi, F&D, flanged only, or dished only heads. Also looking at your sketch #2, it would fail first at the bend radius at the flange. By the way, what is technical head/tubesheet term for your sketch #2?

Also, HW-711.1(e) mentions "straight flange" and HW-715(a)(1) mentions of skirt length, which I interpret as a "straight" flange. In Fig. HW-715.1 shows permissible and not permissible head attachments. I don't see a configuration that is similar to your sketch #2.

If you are to use your sketch #2b as an inwardly flanged head/tubesheet, you can only do a fillet weld on one side. I am not that knowledgeable on welding, but it looks like the weld that you can do on the other side is not fillet weld anymore. It will look more like a butt weld???

 

[Konrad]

Well, I think that CodeJackal's understanding is backed with some sense. I asked myself a question: why did they say that "inwardly" is less safe than "outwardly", and required more welding on the inwardly flanged body? I think the answer is in the fatigue due to alternating pressure. 1b, if welded from outside only would cause quite strong bending of the weld due to bulging head when pressurised. 1a would cause only shear stress in a single outside fillet weld, regardless of pressure value or alteration. That's why they require to put additional inside weld in 1b. Head #2 is more stiff at the rim, giving less problem of this nature, but less problem is still a problem. So thinks my AI, although he admits that it's not clarified enough in the Code. Well, it's not an engineering handbook- it's just a set of requirements to be followed.
Konrad

 

[ukinam]

konrad,

some questions on your thingamajig (sketch #2):
1. what's the material?
2. what are the dimensions and thickness?
3. what are the design conditions (DP, DT, etc)?
4. how do you intend to fabricate it?
5. what is ONE/TUV/BV or OneBeacon's say on this? (assuming they are your AI)

 

[Konrad]

ukinam,
No, I'm not intending to use this shape. But it's quite widely used, for instance as bottoms of LPG portable containers. Just my thoughts about inwardly/outwardly flanged dish began on shapes #1 and #2- but apparently it doesn't have anything to do with shape of the dish.

 

[doct9960]

Konrad,

Think of the terms inwardly & outwardly this way:
inwardly = straight flange is pointing towards the inside of the boiler
outwardly = straight flange is pointing towards the outside of the boiler

It's as simple as that.

 

[unclesyd]

In the good old days we used the details/figures in UW-13 (Sec VII 1) for installing the type 1 (as above) head. The only use I've seen of of the type 2 head (as above) has been on some gas cylinders.

 

[ukinam]

konrad,

doct9960's explanation is more logical. The ASme code was developed by North Americans. If you look into the meaning of 'inwardly' and 'outwardly' in an American/English dictionary and combine those meaning to the word 'flanged' (e.g. inwardly flanged), you will make sense in what the ASME people are trying to imply.

If you consider your Sketch 1A as 'inwardly flanged', you can never do a double fillet weld. How do you intend to do a fillet weld on the inside...between the head and the shell?

 

[Konrad]

ukinam,
No, I don't consider 1a inwardly flanged. This is not what anyboby said here, including the North Americans. The issue begins clear after browsing an inch of paper forward and opening the book on Page 139, HLW-411.2(a) and (b)- they're linked to sketches which leave no doubt, and noone cares what shape has the head in the center. I'm sorry I didn't find it earlier. Now I know what is inwardly flanged and outwardly flanged. Thanks, everyone.