B31.3 - elevated temperature considerations and questions

[XL83NL]

Im designing a B31.3 pipe spec for a 900 deg C / 1650 F system (low pressure).
The current idea is to use alloy 800H as it has better strength opposed to the 'straight' 800 grade.
While designing, I stumble on a few problems.


1) Determining flange rating for UNS N08810 in the 1500F-1650F range; ASME B16.5 app. A (2009 edt) provides some direction for calculating flange ratings, however, when I use ASME II-D stress values of SB-564 UNS N08810 flanges beyond 816 deg C (i.e. range where B16.5 stops), I run into the problem that the first calculated value of say 850 deg C gives me a higher pressure than that of 816 deg C; this is because the one for 816 deg C is limited by the ceiling pressure. I thus need the ceiling pressure for 750 deg C but it's not listed. How could one soundly engineer the ratings for temperatures beyond that´s what listed max in B16.5 (i.e. 816 deg C)? The obvious problem are the non-listed ceiling pressure for T > 1500 F. Can VIII-1 app 2 help? If so, whats a suggested approach?

2) Based on other threads, literature and colleague's experience, Im thinking about using Hastelloy X or Inconel 718 studbolts. Which type of nuts could be good for these studbolts? Can I use 'regular' 8MA nuts? Their rating dont go that high, then again, I dont think the nut will be problem ...

3) The W-factor from B31.3 in table 302.3.5 is limited to 1500 F. What are good considerations and literature to review, in order to do the math & homework for the factors in the range 1500 - 1650 F? Can e.g. the material mfr's like Special Metals provide help? Or Becht's article on weld joint strength reduction factor (

http://dx.doi.org/10.1115/PVP2005-71016)?

Or .... ?

Is there maybe some good piping book on these kind of subjects for high temp piping?

Any help is highly appreciated!

 

[XL83NL]

Anyone who has some thoughts?

 

[BigInch]

You can interpolate betweeen listed temmperatures, but you cannot extrapolate any allowable stress for temperatures outside the listed tempeature ranges. The codes do not permit utilization of materials at temperatures any higher than the maximum given for that material.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[XL83NL]

Thanks BigInch for the answer. However;

-I think I've read somewhere that extrapolation is possible, although I forgot the reference. Will see if I can find the reference.
I do agree with you if you're 'saying' extraploation may not be good engineering practice, however per ASME B31.3:2010 table 302.3.5 general note (a) it seems not to be permitted.

My question was what more I can do to determine the factors, besides doing numerous creep tests to determine my own data.
Can I do some literature review? There must've been people before me who needed to have W-factors for piping design.
Im definitely not the first. Ive seen topics here before on high temp piping.


-I think Im not beyond the Code's allowable wrt upper temperature range, as there's the exclusion in para 323.2.1. Second, last time I checked ASTM B407 N08810/08811 was listed up to and incl 1650 F (~900 C) in B31.3:2010. So dont see a problem there.
For flanges I repeat my question; yes, maybe a problem. But how to design flanges joint with B16.5 flanges @ 1650F? VIII-1 app2.?

 

[BigInch]

Unfortunately I'll have to leave you there. My interpretation, and equally as fortunately, my customarily lower temperature design requirements, do not force me to look past the "not permitted" clause. Maybe somebody else can direct you to the hi-hi temp zone.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[XL83NL]

That's unfortunate. Thanks though BigInch!

 

[vpl]

If you're really wanting to design to the Code, use ASME B31.1. It covers the temperatures you have. Otherwise you're on your own because you're definitely outside the B31.3 limitations and you cannot extrapotate no matter what you think you remember.

Patricia Lougheed

******

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[Duwe6]

". . . and you cannot extrapotate no matter what you think you remember." VPL

Exactly correct!

The reason you can't/aren't allowed to extrapolate is that material strength curves go asymptotic "somewhere" on the high-temp end, and the material creep problems get exponentially worse "somewhere". When you multiply one uncertainty times a second uncertainty, any answer you derive is pure garbage.

Interpolation between known strength/temperatures is allowed because the Strength-Temperature curve is 'reasonably' linear between two adjacent [known] points.

Going past the known curve is "going off the deep end" engineering-wise. An engineer that does this is Willfully Negligent, and will be held personally financially [and possibly legally - jail] responsible for any and all consequences. [USA jurisprudence] He/she has documentation that they knew better than to do something this egregious. Me, I like my bank accdount, house, and car. Although the courts should leave your family one car.

 

[XL83NL]

vpl and Duwe thanks for the contributions.
Maybe I was wrong, and I didnt read anything on extrapolation, but on interpolation.
Both your replies make sense, you're right in that it shouldnt be extrapolated.

Ill have a more deeper look into B31.1. Does B31.1 also address a solution for my problem on B16.5 flange ratings @ 900 C ?


However, my first question still hasnt been answered I think; what can I do to determine W-factors beyond that whats listed?
Is there literature to review, maybe it's addressed in another Code line sect III, or anything else?
It doesnt seem plausible to me no one has ever made a piping system for these kind of high-temp applications.
And even though some may not have been acc B31.3, those high-temp piping systems have to got to have some provision for the weld joint strength reduction of those systems at elevated temperatures.

Although all replies so far have contributed to this thread, and though I agree with anyone who says extrapolation is free trip to jail, so far it seems no one has been able to answer my original question(s).

 

[vpl]

Maybe you need to go back and rethink your questions in terms of different codes and materials. Just saying.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[BigInch]

The decision begins with reading the scope of each code. Each one covers a different type of system, so I don't see how you can switch from power to process, or process to power, depending on what temperature you want to try to reach.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[XL83NL]

Some more background info ...
The piping system will be part of a very small plant, may only be 1 or 2 mtrs long, and may run for testing purposes during only a very short period (few months, max year(s)). Therefore, it´s not that exciting, however, to my engineering judgement, it still has to be soundly designed and engineered, with good consideration to all given design conditions and possible failure modes. Given the plant's function, I think piping will best fit in B31.3, as there are no boilers or fired heaters which heat the process gas.

Although I agree with BigInch; I quickly checked B31.1, and for as far as I can see now, I cant see the benefit of using B31.1 over B31.3 for my specific problem. B31.1 allows 1500 F for USN N08810/-11, and doesnt allow to go beyond that; B31.3 lists values up to 1650 F (and even allows to go beyond that).

I also read Becht's paper, and though it's pretty valuable for background reading, it didnt help me further WSRF's up to 1650 F.

I've also gone through the EN 13480 piping code a few months, but it's still a pretty new code, with little history. Second it seems to be a combi of several other piping codes (it even has parts in it literally taken from sections of B31.3). Therefore Im not feeling to go that way.

I still think B31.3 is may best option, based on above arguments and previous posts.

But Im still stuck ...

 

[BigInch]

Speaking of EN codes, you do realize that you will have to use whatever code is approved for use by the country in which you will install this thing.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[XL83NL]

I do realize that.
But typically, client specs for these kind of projects the company I work for does, dont put any specific requirements, like design codes, on piping, as dont our own contracts. We're in a, say, very unique business.
Second, most of our work done falls under the PED Directive, 97/23/EC, so in view of that Directive, you're not stuck to a specific code. In stead, as long as the contract doesn't specify any specific requirements, you can choose any code you want (and even mix codes - although I wouldnt recommend that), as long as you're fullfilling the essential safety requirements of the Directve, where applicable.

So, in terms of regulatory requirements or national jurisdiction, there's nothing holding me back from picking a desired code, except from any possible contract requirements.

 

[BigInch]

You're correct. When you mentioned EN, I thought it might be a PED project.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[Patafian]

Regarding WSRF

I think that you may need not use any weld strength reduction factor.
As the piping is intended for short operation max. one year you are below 10 000h.
If do not assume continuous operation you may come to 5000h or even less.
On the other hand if your stresses are not to close to allowable and you do not have a longitudinal seam you do not need to consider WSRF.

Regarding extrapolation

Extrapolation of creep strength for temperatures above values listed in standards is generally not permitted.
European standard EN-13445 says that such extrapolation falls outside its scope. It allows extrapolation of time independent strength parameters ie. yield strength.

Patafian

 

[XL83NL]

@Patafian, thanks. I believe WJSRF's also apply to circumferential butt and girth welds, as Becht's paper on WJRSF's reads:

The weld joint strength-reduction factors apply to longitudinal and spiral welds in design for internal pressure, and to girth weldsin the design for sustained longitudinal forces and moments, such as due to weight and internal pressure.

However, please correct me if Im wrong. And as Ive indicated before, B31.3 says it's the designer responsibility to whether or not this should apply to other welds (e.g. circumferential). [B31.3 also mentions that W, for values beyond that whats listed, is the desginer's responsibility; I know this doesnt provide me with free ticket, and I wont extrapolate. It's B31.3 saying you need to do your own creep tests, for example].

Given the design conditions of the line, Im trying to be conservative. On the other hand, given the expected short use/life of the line (and e.g. by selecting a pipe spec with only seamless components), there may be some justification to exclude the WJRSF. I shall have a second review of Becht's paper ..

Assuming this question is answered, this still leaves me with 2 other questions ...

 

[Patafian]

XL83NL

I do not know Becht's paper.

My approach is based on European standard for piping EN 13480 which says:

5.3 Time-dependent nominal design stress
5.3.1 General
For welds other than circumferential welds in welded pipes and fittings, the creep strength values of the base material shall be reduced by 20 %, except where ensured creep strength values have been determined for these pipes and fittings. This reduction is valid only for dimensioning.

This in my opinion literally excludes girth welds.

Considering bolts. Is there any chance to assume the lower temperature for bolts?
I expect that whole flange joint is insulated but maybe with thinner insulation or
maybe exists some experience showing temperature drop.

 

[XL83NL]

Im just not sure when it comes to the (relatively) new eurocode for piping, looks a bit like a huzzle or mix of different codes (note that at some parts it literally copied B31.3).
I would like to base my assumptions on 'ASME', e.g. like Becht's paper, (of course) B31.3, etc... Given that, I start finding reason to exclude W for my calcs, when I go for seamless.

I might assume operating conditions for the bolts, with some heat drop, and put that they will not see more than 750 deg C. That will provide some 'air to breath'.
However the greatest challenge remains the 900 C flange design. Maybe a custom VIII-1 app 2 calc can help me out?

 

[moltenmetal]

XL83NL: with the depth of skill and knowledge represented on this forum, it astounds me that nobody here is aware of and willing to communicate what is being done by people who make commercial steam reformers- devices which definitely operate continuously under pressure in the temperature range you're talking about. There are thousands of them all over the world, for syngas, hydrogen and ammonia production, so SOMEBODY out there must have done the mechanical design for one in sufficient detail that they can comment?! Unfortunately, not having been involved in a commercial project of that type, I can't provide that insight, but surely SOMEONE out there can do so!!!!

These devices do avoid flanges, so I don't know what you do with respect to the B16.5 flange or the bolting, aside from designing things such that the flange and/or its bolting are lower in temperature, i.e. tolerating some heat loss from the process which, given the nature of your unit, may not be tolerable.

We have used materials well beyond their code-established upper temperature limits for units of limited service life and limited hazard upon failure due to both size and contents, i.e. similar to yours. We didn't just roll the dice on this, throwing away the design safeguards embedded in the codes to be replaced with guesses or nothing- that would be totally irresponsible. Rather, we worked with our client, the people who would be using the unit and to whom any injury associated with premature failure would occur, to develop a program of inspection and replacement (i.e. mandating a maximum service life), and a suite of other safeguards to render the unit safe to operate. These units were generally small enough that the regulatory bodies in question, where they existed, were not involved in the decision-making process. These folks are notorious for repeatedly asking "Where in the code does it say you can do that?", closing their minds completely to other options.

The other option is secondary containment, i.e. an inner shell operating above its code limits, inside a refractory-lined outer shell containing the heaters or burners- a "pressure furnace" if you will. If it is a test apparatus, the heaters can be electric and the outer shell can be pressure-balanced with an inert gas such that the inner shell is exposed to minimal differential pressure. For small units this is sometimes the safest solution, and depending on the regulatory regime, may be the only practical solution.