Welding an olet on a welded cap 1

[gazepdapi]

Hello everyone,

Just a quick question....is there any standard that prevents me from welding a threadolet/flexolet on the end of a welded cap or even limits the size of the tap as well? I've looked through some applicable standards but can't seem to find anything.

Thank you!

 

[pennpiper]

"is there any standard that prevents me from welding a thread-o-let/flex-o-let on the end of a welded cap"

No!

Sometimes its possible to do all the right things and still get bad results

 

[zdas04]

Some company standards will limit the size of any weld-in connection to less than half the nominal diameter of the line (you can put a 4-inch o-let on an 8-inch line, but not on a 6-inch line), the same rules say that you can't use a reducing fitting for more than half (I can use an 8X4, but not an 8X3 concentric reducer). These company rules are pretty common and can be a bigger pain than they are worth to try to change.

Absent company nonsense, the code seems to like o-lets at lot. I've done some reinforcement calcs for lines with them and it is easy to see why.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

Interesting. I've had a look through some relevant codes (B 31.3, B16.5, B16.9) and can't find anything which says it can't be done (not unusual), nor can I find anything which says it can be done.

The best I can find is actually the flange code , B16.5, where fig 14 shows connections ( but these seem to be connections onto pipe) and Table 6, which gives allowable dimensions and sizes for drilling centre holes in blind flanges (nearest to your requirement). This would help in showing that your sizes are similar, but isn't an exact match.

Other than that the fall back position is that you need to check your strange thing against ASME VIII or justify it as a branch fitting under B31.3 - however there is a lot of mention of it only applying to connections to "run pipe".

The fittings code says nothing about welding anything to the fittings - but then people make elbowlets and similar connections to attach to elbows....

I would wonder why you can't use a concentric reducer, but also I guess it depends on relative size ( weldolet to cap) and wall thickness / pressure rating.

So I can't find anything which says you can or cannot do what you propose. However, messing about with pressure containing fittings which don't specifically ALLOW you to drill holes in them leaves you open to liability if it fails in service, unless you check the design to some other recognized pressure vessel code such as ASME VIII or PD5500.

Quite often the design codes don't state negative things, only how to do things. If your design doesn't fit the code then it is not compliant and you need to qualify it some other way.

Assuming you're doing this to B31.3, there is considerable latitude for doing things outside the definitions "...and their validity accepted by the Owner".

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

 

[BigInch]

Nothing prohibits welding an O-let to anything. zdas mentions a common limitation to branch sizes of 1/2 the main run's diameter. Normally these O-let taps are between 1/2" to 2", but in any case keep them below zdas's limits.

 

[KevinNZ]

I have had inspectors band any welding to fittings. But there is noting the codes to prevent it and there are even pictures in the codes of stuff welded to fittings (e.g B31.1 Fig 127.4.8 (E) (b))

 

[zdas04]

Inspectors need someone (preferably an engineer) to pour cold water on their heads about once a week to rein in their power grabs. They cannot ban anything. Ever. If they think they can then they need an education at the toe of a boot.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[DekDee]

IMHO "banned" is incorrect terminology.
The Inspector is perfectly entitled to prohibit something if there is written justification.
The Inspector may be a representative of the Engineer and the Project Specifications may determine if something is prohibited or not.
The Inspector may be a TPI and the relevant code / standard may determine if something is prohibited or not.
The Inspector may be a representative of the Owner and the Project Specifications / Codes & Standards may determine if something is prohibited or not.
It is the Inspectors role to ensure that prohibition is enforced.

What is not allowed (and what I think zdas04 is alluding to) is Inspectors who make up the rules themselves and try and prohibit (or ban) something based on their opinion.

kevinNZ,
You need to be careful thinking that just because it is addressed in the code it is acceptable.
Project specifications can be more stringent than the code and the responsible Piping Engineer may have decided he would not allow welding onto fittings.
Therefore, if the Inspector told you welding onto fittings was not allowed, prohibited, banned (whatever you want to call it) - he was perfectly justified.

If you ever think an Inspector is overstepping the mark and making up the rules just ask for a written reference as to where it is not allowed,

My apologies to the OP if I have hijacked the post,

Regards,
DD

 

[KevinNZ]

DD

We are the designers and write the project specifications. The inspector, the case above, just had in his mind rule a on welding to fittings, nothing in writing he can refer to.

 

[LittleInch]

gazepdapi,

Apart from what any welding inspector may or may not say, it is rare for design standards and design codes to prevent or "ban" you from doing things. They tend to list allowable items and, by default, anything not specifically included is excluded. So the design standard for a welded cap - B16.9, says nothing about allowing openings or connections. Therefore if you drill a hole in it, you are no longer "covered" by that standard.

Company or project specification may take things further and state that x,y, or Z is not permitted.

In your case, assuming you are looking at ASME B 31.3 as your design code, try section 304.4 - Closures 304.4.2 refers to openings in closures - which is exactly what you have.

Basically refers you back to ASME VIII, but does come up with the openings should not be more than one half of the internal diameter.

So basically there is an applicable standard - you just need to follow it.

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

 

[MJCronin]

Interestingly, not just any "olet" is acceptable for welding to the end of a pipe cap.

(I assume that the fitting will be welded on the centerline of the run pipe)

Bonney forge makes a special fitting,called a "flat weldolet" with special contour for this situation.

I do not know why you wouldn't use pipe reducers in this situation.

http://www.bonneyforge.com/resources/BC.pdf

MJCronin
Sr. Process Engineer

 

[gazepdapi]

Thank you everyone for your help with this...you have answered my question!

 

[zdas04]

MJCronin,
There are a lot of reasons to use a pierced blind. I use them to allow me to stack tie-in connections for gathering systems like this:

One client uses this configuration and has stacked 8 well tie ins without ever having to take the trunk down.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[DekDee]

zdas04,
With all due respect - I am totally confused.
"Piercing a blind" which I presume is a blind flange is putting a hole in something that is immediately after an isolation valve.
What has that got to do with welding a fitting onto a weld cap ?
Your scenario is for installing a fitting so production doesn't stop, the OP would have to weld his weldolet on before production even started (and as MJCronin stated - why not reducers instead)
If I have misinterpreted your post I humbly apologise.
After all, I am just one of those grubby welding inspectors who needs cold water poured on my head,
Regards,
Shane

 

[zdas04]

DekDee,
WOW, a bit sensitive are we? You perfectly illustrated my point in your post of 30 Sep. The "cold water" needs to come in the form of "what is the source of that position?" kinds of questions. I ask those kinds of questions of everyone from lease operators to senior management, and most especially of engineers. When welding inspectors start making crap up (or more often morphing something partially recalled into something else) then they need to be asked to cite references, just like you said above.

A flange is a fitting. A blind flange is a bolt-on adjunct to a fitting. In the drawing above, we put the blowdown for the line(s) on the top flange of a tee. To add another well to the system, you shut the vertical block valve, shut the pigging valve(s) from the well(s) already connected, blow the tiny section down through the 2-inch valve on the blind, unbolt the blind, bolt in a new tee (with its own isolation pigging valve), and bolt the pierced blind back on the top. My client that has a stack of 8 tie-ins at one point, took nearly a year to develop the 8 wells and never had to blow the trunk down to tie them in. Instead of a blind, this could be a weld-cap, thread-o-let and a RFWN flange. Same outcome for a bit more money.

I hope it is clear why just a weld cap, thread-o-let, and ball valve welded to the tee outlet would be less effective in this case. Same with an 8X4 reducer welded to a 4X2 reducer with a transition to a threaded ball valve (there are hundreds of thousands of doglegs like that in gas fields around the world), they just don't lend themselves to system expansions.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist