CSA Z662 - Reducing Flanges Interpretation

[302Hugo]

If there is one thing I hate about being an Engineer it is interpreting Codes, lol. I am being asked more and more from the field on if tapped flanges, centerline or off center, can be used. I feel I have a decent understanding on the requirements laid out in B16.5/B31.3. However, I am a little puzzled on the interpretation in regards to this in CSA Z662 although I think I am reading it correctly. Can anyone help me out or provide feedback? Also note that my question relates to threaded flanges only, as well the use of these reductions are for installing drains at the end of a header, and are not used as a branch connection or pipe reduction.

Table 5.3 states that B16.5 flanges can be used (with limitations) in CSA design. So that would tell me that reducing flanges are OK to use as long as it meets the B16.5 requirements, correct? I don't get any indication that reducing flanges are a nonstandard flange in B16.5, so I would not have to follow Clause 5.2.6.3, correct? However, in the new '15 edition there is a new clause 5.2.6.4 that blatantly states that blind flanges cannot be used as a reducing threaded flange, excluding in pressure testing. However, it doesn't state anything about not being able to use a hub flange as a reducing threaded flange. So this tells me that I am good with using a properly designed hub flange reducing flange, correct?

In regards to using an off centered tapped flange I beleive I would again have to look at it as a closure. And Clause 4.3.13 Pressure design for compenents - Closures, tells me that I can follow SEC VIII. Which is the same for B31.3.

I know it all comes down to interpretation, but typically there is a "right" answer. So if anyone can provide me feedback on this it would be much appreciated.

 

[302Hugo]

I hate to bump this thread but I haven't received any feedback.

 

[LittleInch]

It's not easy to understand what you're on about. for the avoidance of doubt, what do you mean by a "hub flange" or a "hub flange reducing flange"

The new clause ( it would be good to see the entire clause) seems a little onerous, but quite clear. trying to find ways around code requirements are often convoluted and usually not worth it.

A few drawings or sketches or photos might bring the post to life a bit....

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

 

[302Hugo]

Thanks for the feedback LittleInch.

I don't want to sound rude, but I would hope that anyone who can answer my question would know what a hub blind flange is...maybe it was just confusing because I didn't specify "blind"? Sorry if so. To be clear a hub blind flange is basically a blind flange with added girth on the non pressure size. See the attached rough sketch. A hub flange reducing flange, would just be a reducing flange made out of a hub blind flange.

I am in no way trying to find ways around code requirements. I haven't met a soul yet that has been able to read the codes and say "I now know exactly what it means". There is a reason why the main codes have commentary and interpretation addendum published. I just haven't worked in this area of the code enough to be able to confidently say that is the meaning.

After reading through my OP I think my main question is "Is a reducing flange considered a nonstandard flange in B16.5/Z662?". From what I can tell it doesn't seem to be because in B16.5 it doesn't state anything about nonstandard flanges and in Z662 in Clause 14.3.5.1 it states that nonstandard flanges are those not manufactured to a standards listed in 14.3.4.3 (which B16.5 is). I am confident in this answer but maybe someone with more experience working in this area of the code can provide feedback to ease me? So I think my answer then becomes; if they are nonstandard than I have to follow Sec VIII and if they are standard I can follow the reducing flange criteria of B16.5 (excluding tapped blind flanges because of clause 5.2.6.4).

FYI below is Clause 5.2.6.4 from Z662. It begins to say that blind flanges may be drilled and tapped, which IMO and basically by definition turns it into a reducing threaded flange. Then the last sentence says "blind flanges shall not be drilled and tapped for use as reducing threaded flanges". So which is it? For me that is very confusing, although I assume they are considering a blind that is drilled and tapped for the pressure test purposes is not a "reducing flange".

"Blind flanges may be drilled and tapped for instrumentation and pressure testing purposes to a
maximum size of NPS 1. Blind flanges may be drilled and tapped greater than NPS 1 up to and including
NPS 3 for use as vents and drains during pressure testing only. The tapping criteria of ASME B16.5 shall
be followed. Blind flanges shall not be drilled and tapped for the use as reducing threaded flanges."

 

[LittleInch]

Well yes it was confusing about the rather important missing word and is certainly something that helps to have a drawing or sketch, but tbh, I've never come across hub blind flanges like you draw and as seen in the various images and they appear to be specifically not included in ASME B 16.5. (e.g. Materials required for flanges and flanged fittings are listed in Table 1A with the restriction that plate materials shall be used only for blind flanges and reducing flanges without hubs. They therefore appear to be simply things people make, but have no specific standard or code attached to them as far as I can see.

So Is a reducing flange a no standard flange - IMO, No, but only when it complies with the dimensions as shown in table 6 or table II-6 of Appendix II.

however a standard like 16.5 won't say anything about other flanges, it will simply state this is the design of flanges and blinds. Other more comprehensive specs like Z662 or B 31.3 will refer to other non standard items, but the main flange code won't. You can't say "oh this flange is OK because 16.5 doesn't say anything - that's twisted and incorrect logic. You need to be able to say "this flange is OK to 16.5 because it complies with section x, table y and figure Z"

My reading of that clause is quite clear. It says you can drill and tap flanges for certain sizes and very particular purposes (Instrumentation and pressure test purposes) up to 1" diameter and slightly bigger for drains and vents for hydrotest. Other than that you're not allowed to use blind flanges, with or without the mysterious hub of indeterminate dimensions, as a screwed reducing flange. I think you're trying too hard on this issue. Take a step back and look at the intent of the clause - it is blindingly obvious to me - No tapped blind flanges (except instruments and testing).

It might have been better drafting to start with the prohibition - NO tapped flanges, then list the allowable exceptions, but either way it is quite clear to me that other than the specific items mentioned, if you are to follow Z662, you can't tap blind flanges.

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

 

[LittleInch]

Pressed send by accident - Looking back at your OP, you seem to be taking the view that because a code doesn't say you can't do something or use something then you can - "However, it doesn't state anything about not being able to use a hub flange as a reducing threaded flange."

IMO that is fundamentally incorrect. Codes cannot list all the things that don't apply, they can only list the things that do. If what you're trying to do or the thing you're trying to use isn't there, then the code doesn't cover it - Simples.

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

 

[XL83NL]

Im not familiar with CSA Z662. but Ive used reducing flanges before on B31.3 applications, and they B16.5 isnt very clear on it, I believe it is written in B16.5 how they shall be designed/designated.
Also, weve used a lot of high hub blind flanges, especially in those applications where we e.g. want to use a tubing connection to piping, and where the pipe size is almost the same as the tube size, e.g. 1" pipe to 3/4" tubing. The high hub versions are then used when acc. table 6 the reducing outlet size (i.e. tube size) is greater than allowed. To me, high hub blind flanges are pretty clearly defined B16.5, however the exact hub height is somewhat tricky to derive.

 

[moltenmetal]

A hubbed blind flange is a forged blank from which a threaded or socket welding flange may be manufactured. That we can (readily) find hubbed blind flanges on the market is, to us, an indication that this is the case in practice.

B16.5 is not to my knowledge, clear on whether or not a threaded reducing flange must be forged in near net shape, i.e. including hot piercing of the forging to form the rough opening prior to machining- but I sincerely doubt that this is how reducing threaded flanges are produced. Our own company assumes that a flange which has the dimensions of a B16.5 threaded or socket-welding reducing flange listed in the code, may be manufactured from a hubbed blind by machining- and in fact, we assume that this is how most of the threaded reducing flanges sold to us are manufactured. The vendor stocks hubbed blinds and machines threaded connections to the required size, then applies the required markings. It is the same with socket welding reducers and socket welding reducing flanges, swaged nipples and many other components- there are too many size combinations required for most vendors to consider it sensible to stock them all, so blanks are stocked and machined to required dimensions on request by customers.

Threaded reducing flanges below a certain size ratio may be produced from an ordinary blind flange without hub. However, only one connection is permitted and it must be on centre. Otherwise, you must resort to using ASME VIII appendix 2 to design the flange.

Note that it is not clear to us that a reducing weld neck flange can be manufactured by this method. In that case, again unless I'm mistaken, a near net forging is required, including piercing. It is not permitted to merely forge a lump in the rough shape of a weld neck flange, and then to bore the hole and machine the weld neck to the required dimensions.

I've never read CSA Z662 and have no idea whether or not it provides requirements beyond those of B16.5 or B31.3 with respect to this issue.

 

[LittleInch]

XL83NL,

I had a pretty good look at B 16.5 and couldn't find anything to do with hub type blind flanges. Do you have a reference in 16.5? or any other ASME spec?

I assume you mean something like this??

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

 

[moltenmetal]

Because we're talking about a) flanges outside the ratio of sizes permitted in B16.5 to be made from an ordinary blind flange and b) threaded connections, i.e. outlet sizes 2" and smaller (and generally smaller even than that), we're talking about flanges essentially with the dimensions of an ordinary threaded or socket welding flange of that class- with a hub height nowhere nearly as high as the one in your pic, LittleInch.

 

[302Hugo]

LittleInch - No offense and I appreciate your feedback but when you state "the mysterious hub of indeterminate dimensions" I get the feeling you may not not have the experience I am looking for to answer this question? You are correct there is no specific code (that I know of) that outlines the design of hubbed flange. As XL83NL and moltenmetal point out the hub flange is a common fitting to which B16.5 flanges can be made from. And now that I read things again I think I may have confused my question even more by not keeping the term as "hub flange". Flanges with the hub requirements are littered all over B16.5. Clause 2.8, 6.8.2, 7.5.4, Table 6 and Fig 4 for example. Yes, the picture you posted above is a hub flange although this specific flange would likely be made into a hub welded flange and not used for a reducing flange...although it could be machined to suit. You say that a hubbed blind flange and a typical blind flange should be looked at one in the same, but I disagree. They are clearly 2 different fittings. A blind flange has no hub and can be made from a hub flange if the face is squared off, as 6.4.4 states.

I don't think I have stated that I am looking for B16.5 to tell me what kind of flange I can use? If it looks that way I am being misunderstood. I know that Z662 is what I need to tell me what the code allows...but as pointed out several times now, I felt it was not clear. And again, you are mistaken for what I am trying to do. You say that I seem to be taking the view that because a code doesn't say you can't do something or use something then you can. That is incorrect. What I am trying to do is determine what the code IS saying I can do. I sound like a broken record but commentary is there to help people fill in these blanks when they are not clear. Z662 refers to B31.3 and hence B16.5 for what is acceptable materials to use. So when Z662 in clause 5.2.6.3 says "Rectangular cross-section slip-on, special weld neck, and other nonstandard flanges" and neither B31.3 or B16.5 have "nonstandard" anywhere in their text, it makes defining these difficult.

XL83NL, Moltenmetal - Yeah be glad you don't have to work with CSA Z662. It's not bad if you are designing everything to CSA fittings but it gets pretty confusing, IMO, when you start using ASME fittings and the slight differences in specifications and parameter calculations.

 

[curtis2004]

My understanding is you can't use drilled and tapped for anything other than instrumentation, vents, drains. It shouldn't matter if it is hubbed or standard blind.

Thanks,
Curtis

 

[Gator]

I agree with Curtis. I don't see what all the confusion and typing is about.

 

[moltenmetal]

Curtis: if you can back that up with a code reference, I'll take your word for it.

If someone who actually manufactures small flanges could chime in, that would be helpful. How are threaded and socket-welding reducing flanges made? Remember, we're talking about flanges below 8" NPS in all cases. Are they made from pierced forgings, or from unpierced hubbed blinds? And if not from the latter, who is making the latter and for what purpose?

 

[moltenmetal]

Just contacted my major flange manufacturer in my area, and confirmed that they make reducing threaded and socket-welding flanges from hubbed blinds.

 

[LittleInch]

Wow, this thread is getting confused.

My point, which I think you actually accept, is that a "hub blind flange", like the one you drew in the third post, is not listed as a blind flange in B 16.5. Hence, as a "hub blind flange" it is non standard.

It may well be that the flange of the type I showed a picture of, is actually used to manufacture reducing flanges as per table 6 of B16.5. Table 6 states that the hub dimensions still need to comply with the hub dimensions of the size and class of flange relevant. Note 1 of table 6 is informative as it states that where the bore of the reducing flange is less than the minimum size stated in columns 2,4, & 6, it can be made from a "standard" blind flange, e.g. If you wanted a 2" bore from an 8" flange, this could be made from a standard blind flange.

Now it could be that this is what the Z662 code is actually trying to avoid, i.e. ALL reducing flanges should be made with an additional hub length instead of being made from a "standard" blind flange. i.e. If you wanted a 8" X 2" reducing flange, you could still have one, but it needs to be specifically manufactured, with additional thickness (the hub) and not made by drilling a blind flange, which is permitted by Note 1 of table 6 in B 16.5. It would make is simpler if it just said Note 1 of table 6 does not apply, but hey, that leaves room for interpretation.

This now actually makes sense. The wording is quite specific - "Blind flanges shall not be drilled and tapped for the use as reducing threaded flanges". To me that means "standard" blind flanges as listed in tables 8 to 22 in ASME B 16.5, not reducing flanges to Table 6 (ignoring note 1).


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

 

[curtis2004]

Molten metal,

Read 302Hugo's post with sketches and Clause 5.2.6.4 of Z662.
You can drill and tap blind flange and use it for instrumentation, drain or vent.
This makes sense because if you connect a branch to this drilled and tapped connection it will fail.
If I need a branch to be connected to a blind flange location, I will buy a new flange, reducers, set of gasket with studs and nuts.
That's what I would do in the circumstances.

Thanks,
Curtis

 

[moltenmetal]

Read 302Hugo's post with sketches and Clause 5.2.6.4 of Z662.
You can drill and tap blind flange and use it for instrumentation, drain or vent.

I don't have this code, so unless someone posts the clauses I can't read them. I made that quite clear in an earlier post.

This makes sense because if you connect a branch to this drilled and tapped connection it will fail

Within the limits permitted in B16.5 for that drilled and tapped connection, no it certainly will not! A 1/2" branch connected to a drilled and tapped connection in a 2" or larger flange isn't going to matter to that 2" blind flange, which is why the modification of the blind is permitted in B16.5 (see mandatory appendix II table 6). B16.5 makes no stipulation about what purpose the threaded connection is put to- it makes no mention of it needing to be a non-moment connection such as for a valve or instrument. That CSA standard may- I have no idea, since I've never read it. Such a distinction IS made about certain types of instrument connections permitted in ASME VIII-1.

If I need a branch to be connected to a blind flange location, I will buy a new flange, reducers, set of gasket with studs and nuts.

If you bought a threaded reducing flange to make that connection, to eliminate the need for the reducers (and the resulting potential leakage points), it would be made from a hubbed blind. That was my point, and I think it's a point worth noting. It's a frequent occurrence that people assume that codes say things that they merely feel they SHOULD say. A little commonsense and a few phone calls to people who actually make the parts in question will go a long way to clarifying those gray areas.