Flat collar vs. collar on flanged connection

[MartinLe]

Consider a flat collar, like this:

http://www.erv-gmbh.at/en/flanges-collars-butt-ends/178-glatte-bunde-en-1092-1-typ-32

and a collar, like this:

http://www.erv-gmbh.at/en/flanges-collars-butt-ends/167-v-boerdel-din-2642

When to use one over the other and why?
The flat collar is welded around the pipe, the collar to the face of it. Does this matter down the road?
I don't have acces to the DIN EN 1092-1

The background of the question is that we specified flat collars and the contractor installed collars. When I raise the issue in house, I want to have asked the stupid newbie questions beforehand so I turn to you. But please leave contractor and coworker relations etc. to me, in this thread I only want to know the relevant technical diffferences.

 

[LittleInch]

Hmmm,

I can only assume that the welding of the flat collar is similar to that of a slip on flange - see this page

http://www.wermac.org/flanges/flanges_welding-neck_socket-weld_lap-joint_screwed_blind.html

and scroll down to slip on flange.

As such it seems to create quite a heat zone in a small ring with consequential issues over workmanship (i.e. potential to over heat the flat collar). The flat collar also has fillet welds which are more difficult to NDE, there are two welds, the outer weld needs to be only a certain size to prevent the flange ring from bearing on the weld instead of the flat collar and getting alignment would seem to be more problematic.

Collars on the other hand are a simple butt weld - easier to inspect and probably easier to install, which is probably why your contractor used the other type.

Personally I would always use the collar as I trust butt welds above fillet welds and unless you can't butt weld there for some reason would seem to be a better plan to me. I've never really liked slip on flanges for that reason as well.

In terms of codes, they are both the same so it comes down to preference, testing and ease of installation / construction cost.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MartinLe]

Thanks so far.
The flat collar is indeed slip on

from:

http://www.heco.de/edelstahl/flansche/boerdel-und-bunde/glatte-bunde/pn-10/technische-daten.html

I don't see the welds on the drawing, but as the front of the flat collar seems to be flush with the face of the pipe I assume one fillet weld?

 

[LittleInch]

There will be two, one at the back and one at the front. Otherwise you run the risk of either crevice corrosion getting between the collar and the pipe or simply high crack potential as fluid is able to travel between collar and pipe under pressure.

If you only have a short stub available then they look Ok, but otherwise, as I said, there's no real code difference so it comes down to cost and timing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

The collars are weld neck flanges and are bored to match the inside diameter of the mating pipe or fitting so there will be no restriction of product flow. This prevents turbulence at the joint and reduces erosion. They also provide excellent stress distribution through the tapered hub and are easily radiographed for flaw detection. A weld neck flange is welded to a pipe or fitting with a single full penetration butt weld.

The slip on flange calculated strength for internal pressure is approximately 2/3 of welding neck flanges, and their life under fatigue is about 1/3. The connection with the pipe is done with 2 fillet welds, one weld at the outside and one on the inside of the flange.

 

[rconner]

I fear there may be some confusion on this thread between what is normally considered a slip-on flange, indeed fillet welded inside and out onto the end of the pipe as others have noted, and what was actually pictured in the OP figures that appears instead may be some sort of rotateable lap joint or backing ring flange configuration (see some basic descriptions/illustrations e.g. at

http://www.wermac.org/flanges/flanges_welding-neck_socket-weld_lap-joint_screwed_blind.html)?

 

[LittleInch]

No confusion from me. I just used the example of a slip on flange because I couldn't find any drawing showing how this "flat collar" was welded onto the end of the pipe.

The OP was asking for our opinion on the difference but both end up with a backing flange ring which can rotate.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

The first one is actually a Type 32 weld on plate collar:

http://www.erv-gmbh.at/en/flanges-collars-butt-end...

The second one is a stub end used with a lap joint flange:

http://www.erv-gmbh.at/en/flanges-collars-butt-end...

These flange connections are applied, in low-pressure and non critical applications, and are a cheap method of flanging. In a stainless steel pipe system, for example, a carbon steel flange can be applied, because they are not come in contact with the product in the pipe.

 

[MartinLe]

The question is about connections with a loose flange behind a collar, yes. No misunderstanding here, I understood LittleInch as he wrote in his last comment.

bimr, in my browser your links where broken (404).

This discussion has me puzzled when flat collars are more apropriate.

 

[LittleInch]

MartinLe,

As with most things it comes down in part to cost and part practicality.

Once the cost of welding the collar (stub end) and the cost of the stub end exceeds that of the flat end and the additional welding then it might start to become attractive (depends on the material used). Also when you have a thin pipe and only a short distance available you can save a few mm by this option.

Otherwise I would always go for what you call the collar, but many would call a "stub end".

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

The links are the same that you have posted. The difference between the fittings would just be the preference of the installer. Perhaps the supplier had one of the fittings in stock. Don't see that it makes much difference.