Threaded Flange on 6" Pipe

[sider]

Hi all,

we have a project requirement for screwed flange on 6" piping. How usual is this solution and what problems can be expected?

The pipe will be located 3 m above the ground.

The current issue I foresee is that during the screwing of the flange, it would be hard to match the hole's position and the required length of the spool.
Also, not sure how that can be screwed, I suppose you need immense force...not sure a person can screw that on the ladders?

BR

 

[LittleInch]

That seems a pretty large diameter for a screwed connection.

You won't get a seal on the end of a ladder and getting any sort of correct position for the boltholes next to impossible.

Any more details or options?

 

[r6155]

The piping supervisor knows how to do it.
No problems.

 

[TBP]

Can easily be done off an 8 or 10 foot step ladder, depending upon how tall the pipefitter is. More likely, off a manlift. If neither of those methods is suitable for whatever reason, build a scaffold. After applying whatever thread sealant is required (Teflon tape and/or whatever kind of pipe dope) start the flange by hand, and tighten to hand-tight. Use a chain pipe wrench on the OD of the flange to tighten it fully. Alternatively, install a couple of temporary bolts, with nuts on the flange, leaving the nuts loose enough to get a pin bar of suitable length between the flange face and the inside of the nuts, and use the bar as a lever prying against the loose bolts to tighten the flange on the pipe. While some amount of muscle power is certainly required to do this job, nothing on a superhuman level is needed - any pipefitter should be able to do it. "Immense force" should not be required to achieve a leak-free screwed pipe joint. Two-hole it like any other flange to have the bolt holes align with those in the mating flange.

 

[georgeverghese]

The things people do to avoid a plant shutdown....tell Operations Management to make this decision. They will surely blame you when things go wrong

 

[goutam_freelance]

How usual is this solution and what problems can be expected?

As pointed out by earlier experts, 6" threaded flanges are unusual.

As per B16.5 Clause 2.4.1 threaded and socket welded flanges are not recommended for temperatures above 500 deg F or below -50 deg F if severe thermal gradients or thermal cycling are involved.

Also, the pipe thickness should have the threading allowance incorporated.

Hope you have already considered these.

 

[LittleInch]

In reality you have a process requirement for a 6 inch flange. someone, somewhere has decided that a screwed one is a good / best/ cheapest / easiest option.

Reality is now biting to say that decision was a poor one. Time to reconsider your options.

 

[TBP]

As is so often the case, we don't have enough information. What type of system is this? A fire water system in a commercial or institutional building? A low pressure steam heating system in the basement of a 120 year old apartment building? A corrugated box plant or commercial/institutional laundry where there's a 1/2 inch of flammable dust (like gunpowder flammable) on beams, etc?

 

[r6155]

I have never used threaded flanges.
But they are INCLUDED in ASME B16.5 and can be used in some industries. Agriculture?.....?

 

[TBP]

I've had an ABSA inspector for pressure piping codes tell me - in no uncertain terms - that grooved piping (Victaulic) on our compressed air lines was not code compliant. She was wrong.

I've had a large mechanical piping contractor's in-house pressure piping quality inspector tell me - in no uncertain terms - that the screwed piping on the natural gas lines suppling our boiler burners was not code compliant. He was wrong.

I'd be interested in seeing a list of all the industries where piping codes prohibit the use of screwed flanges. Not company or corporate standards, but actual codes.

I'll bet the list is a lot shorter than many imagine.

 

[XL83NL]

I don't think its an issue if it is Code compliant or not, the question would be if its a good idea. 6" NPT is a terrible idea (our construction crew always tried to prevent silly process engrs spec any NPT size over 1"), but lets say you were to do it. B16.11 doesn't list 6" NPT sized fittings for example. Then you could machine your pipe to 6", but what fitting - that is Code compliant - in 6" will you use to connect the pipe's other end? Doing a 304.7.2 on such a dumb item is really the overkill

Like LI said;

Reality is now biting to say that decision was a poor one. Time to reconsider your options.

 

[r6155]

It may be a good idea if in an emergency you cannot have a welder.

 

[LittleInch]

As said B16.11 doesn't go above 4", but then also doesn't include flanges. B16.5 you need to look up "threaded" connections.

But have you thought about a victauic type coupling instead if you can't weld it for some reason?
How are you going to thread the pipe?
Is the pipe thick enough?

Goutam As per B16.5 Clause 2.4.1 threaded and socket welded flanges are not recommended for temperatures above 500 deg F or below -50 deg F if severe thermal gradients or thermal cycling are involved.

Goutam - which version of B 16.5 is that in? My 2017 version has no 2.4.1, neither does B 16.11.

 

[r6155]

ASME B16.5 2020 does not have clause 2.4.1

 

[LittleInch]

Codes rarely prohibit any thing, but give warnings instead or firm guidance. They are designed to tell you what you should do, not what you shouldn't.

Company specs or procedures can say what they like.

 

[TBP]

Ridgid - and no doubt others - have threader heads that can handle larger pipe, in place, if required. A Ridgid 141 will thread 2-1/2" through 4" pipe. A Ridgid 161 will thread 6" and 8" pipe. They can be driven off 535 and 300 machines, or by the 700 with a square-drive adapter. I believe that they can be driven via a 12-R manual ratchet handle, if necessary.

 

[goutam_freelance]

Goutam - which version of B 16.5 is that in? My 2017 version has no 2.4.1, neither does B 16.11.

Unfortunately, it is very old 1996 version.

But this does not mean this is irreverent as this was a product of the finest minds in mechanical engineering at that time.

But I have a lesson here, indicate the version whenever I quote any code.

 

[r6155]

@ goutam
You can work with an obsolete standard (asme b16.5 edit 1996), it's your problem. But you should NEVER reply in the forum like this and confuse instead of helping.
IRRESPONSIBLE.

 

[goutam_freelance]

@r6155
I do not agree that old editions are inherently wrong. So I may not follow your dictat.

 

[TBP]

I think that people posting questions on a public forum like this should recognize ANY free advice/information they get is worth exactly what they paid for it.