ASME B31.3 Chapter IX Elbows 1

[Ben A]

Can anyone offer some guidance here, I seem to be stuck in a loop following paragraphs around.

We intend to use an ASME B16.9 Elbow for a project being designed to B31.3 Ch IX (high pressure piping). Design pressure is 915 Barg.

I'm currently stepping through the Code like this:

K303 - components to listed standards are acceptable (B16.9 is listed), as long as they are in accordance with K302.2

K302.2 - Components without listed pressure/temperature ratings to be rated as be K304 (B16.9 only rates components as suitable to the matching straight pipe)

K304.2.2 - Elbows not in accordance with K303 to be designed to K304.7.2

K304.7.2 - essentially means we'd need to do FEA on the component.


We would like to avoid having to go down the FEA route for cost and time reasons, but K304 doesn't give any other guidance for Elbows. As ASME B16.9 is based on straight pipe pressure requirements, is it acceptable to base the calculations on the K304 straight pipe section rather than elbows? I note from the Code Cases that B16.9 fittings proof tested to the design pressure are acceptable, and also that in the non-high-pressure section of B31.3 it specifically allows doing this.

Thanks in advance for any help

 

[alchemon]

Why don’t you just go find out what the pressure and temperature rating is from the MFG’er of the fittings you want to spec/use?

 

[XL83NL]

Because such ratings don’t exist.

 

[alchemon]

Every decent fitting book I have ever seen has a section in the back verifying that the fitting is at least as strong as the connected piping in accordance with the rating as defined by the applicable pressure code.

 

[Ben A]

Why don’t you just go find out what the pressure and temperature rating is from the MFG’er of the fittings you want to spec/use?

Because we are the fitting manufacturer...

Our manufacturing and design process is based on the requirements of ASME B16.9, which does not give specific pressure-temperature ratings. Rather, it is based on the idea that the fitting will be stronger than the attached pipe. The rating of the pipe would be ascertained from whatever Code the pipeline is being designed to.

Some of the standards for fittings in Table 326.1
(e.g., ASME B16.9 and B16.11) state that pressure–
temperature ratings are based on straight seamless pipe.
Such fittings shall be rated as calculated for straight
seamless pipe with the same allowable stresses as the
fitting and the nominal thickness corresponding to the
wall thickness or class designation of the fitting, less all
applicable allowances

This is my standard 'get out' in B31.3, however this provision is not present in the Chapter IX high-pressure section of the code. So I guess my question really is can I give my fitting a pressure-temperature rating based on the straight pipe equivalent and then verify it against Chapter IX that way?

Sorry if I'm rambling, I'm fairly new at this!

 

[XL83NL]

Every decent fitting book I have ever seen has a section in the back verifying that the fitting is at least as strong as the connected piping in accordance with the rating as defined by the applicable pressure code.

Fitting book? Codes and standards determine such things, if thats what you mean. Manufacturer's dont (assuming were talking B16.9 here). They just manufacture fittings.

 

[alchemon]

A fitting book - aka a catalog of the standard available fittings that the manufacturer can provide. I realize that the advent of the internet has made these books more like “click a button on the website”.

The manufacturer is responsible for ensuring that their product, if it is “listed” (with a relevant “standard specification”) is at least as “strong” as the connected piping of the same size, WT, and grade that is to operate under the specific guidelines of the individual pressure code. The actual pressure rating of the piping is though defined by the relevant pressure code.

I have normally seen this as a series of tables in the back of their catalog. For example, for ASME B31.8, for a B16.9 6” sch. 40 weld 3R-90, Y42 the pressure ratings will be the same as for 6” sch. 40 X42 piping - differentiated by the various design factors (which varies depending on “class” of pipeline). Meaning that the fitting’s pressure rating is at least the same as the piping. However, for actual operating conditions this is limited/determined by the applicable pressure code.

 

[alchemon]

“This is my standard 'get out' in B31.3, however this provision is not present in the Chapter IX high-pressure section of the code. So I guess my question really is can I give my fitting a pressure-temperature rating based on the straight pipe equivalent and then verify it against Chapter IX that way?”

Your application of the code is correct from the standpoint, that the pressure rating is defined by the pressure code itself, as normally it varies depending upon specific conditions and criteria within the code. Also, you are correct that we ascertain the rating of the fitting from the pipe itself.

As previously noted: most catalogs that I have seen contain such information, in writing - from the manufacturer. I have no experience in manufacturing fittings, but I have looked at enough catalogs of them to know - that there is some provision and requirement for burst testing to verify your assumption that the fitting is as strong as the pipe. I would suggest that you research this before you publish information that indicates that your actual manufactured fitting is as strong as the pipe itself.

 

[Ben A]

Thanks for the reply.

We don't work from a catalogue basis, we manufacture to order to customer requirements. Some customers just order 'off the shelf' components to ASME B16.9 or MSS-SP-75 spec, others provide data sheets for the pipeline and require calculations to be provided showing that the design meets the pipeline code requirements (*fairly* uncommon for an elbow, but for the majority of tees they'll want to see replacement area calculations and whatnot).

ASME B16.9 allows qualification of a fitting either by proof burst test or by calculation. Proof burst tests are not done for each possible fitting, rather three or 4 that cover the range of sizes we can make. B16.9 then allows extrapolation to similar geometry fittings (within limits), so it is the design and manufacture process that is qualified rather than the fitting itself. We have numerous proof burst tests proving our design and manufacture, some of them are older than me.

So I have confidence in what we make (the company is not new, but I'm fairly new to the field), but the ASME codes take a bit of thinking at times!

 

[LittleInch]

Going back to your OP and following this through step by step - you did a good job there - you end up at 304.7.2.

However this has three parts, a,b and c. you only need to meet "one or more"

Only part c needs FEA.
Can you meet the requirements of parts a and b??

In essence a is past experience of the component
b is performance testing.

Sounds like you've done a and b

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

 

[XL83NL]

It amazes me that for work under or acc. to Chapter IX in B31.3, you need FEA on B16.9 elbows. I can follow you on this LI, but this doesnt seem like a plausible Code reasoning to me - looks like someone has forgotten to add a certain Code section. Good question to ask the Code committee in an interpretation maybe?

 

[Ben A]

I was uncomfortable relying on a) as it's not entirely clear what constitutes 'extensive experience', and the extents of 'similar' are not exactly defined either! As a manufacturer we don't always know the service conditions, or whether reality matches the design spec we are given, I feel it would be almost impossible to compile a body of evidence to support use of clause a) at this stage (although that is something I may look record in a more useful fashion for the future).

b) I read this section as implying that the specific design had to be pressure and fatigue tested. Our existing proof tests (on geometrically similar items) are based on B16.9 only, so even if we could justify the use of those proof burst tests it wouldn't cover the fatigue aspect (I think? I don't see how a 5 minute static test would assess fatigue, anyway, but happy to be corrected if I've missed something there!).

I find Chapter IX so frustrating for the stuff we do, but hopefully that means I'm learning something.

 

[MJCronin]

I was just curious ....

What if the customer specified the design code as B31.1 ???

Would the fitting mfr have to jump though as many hoops ?

Would the results be any different for this high-pressure fitting ???

MJCronin
Sr. Process Engineer

 

[LittleInch]

I can see where you are coming from but I didn't read down to d)

(d) for (a), (b), and (c) above, interpolations supported
by analysis are permitted between sizes, wall thicknesses,
and pressure classes, as well as analogies among related
materials with supporting material property data. Extrapolation
is not permitted.

So I think you're good with a). It's clear from the experience ( has anyone come back and said your elbows have failed?) that you can look at the design of the elbows ( material, thickness, shape etc) and regard them like pipe for pressure / temperature design rating providing that you're not extrapolating for any of the key dimensions ( size, wt etc)

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

 

[Ben A]

I think I can get behind that interpretation! Next job is to persuade the customer...

It certainly makes 'sense' to me, but as I've only 6 months under my belt working with these codes I'm trying to be quite cautious about applying my version of sense to the code's intentions.

Thanks for the responses, it's given me a fair bit to think about.

 

[alchemon]

For this specific installation, maybe it would be best to do an actual burst test of the fitting design. That is what the lawyer in me would say. Of course, if it were to pass the pipeline pressure test, you "should be fine".

Sounds like you are well on your way to getting a good understanding of the codes from the MFG'ing side. It may seem cumbersome from us pipeline design engineers, but knowing and having this information is usually the difference between getting in the spec-book or not. I know of many suppliers who have came to me and asked "what do we have to do to get accepted in your spec", and I ask for some general information: what kind of fittings can you make (WT, diameter, grade, etc) and written verification of the pressure rating. And half of them leave without a reply back.

 

[31KT]

Ben : How did your FEA qualification go on the elbow designed to B31.3 CH IX. I am having similar situation where all my fittings elbows, Tee's and induction bends might have to be qualified using FEA for meeting CH IX.

 

[Ben A]

31KT: We didn't go down the FEA route, the project has been put on hold by the client. I'm not sure what the final outcome is likely to be at this stage.