RE: [PipingDesign] Thick and High Pressure Pipe

In petrochem, the two code cited overlaps in some cases (like fired boilers application serving the Utility). What code to use is really up to the owner of the facility/plant. The two are almost alike with one signifcant difference - the factor of safety. The Power Piping uses 3:1 and the Process Piping uses 4:1. What does it mean -?, the b31.1 will require a much thicker pipe sched than those of b31.3. thicker pipe cost money.

Remember the stress redduction factor of 1.0 for 7000 cycles in b31.3 - that is meant for a 20 year life (S. W. Spielvogel say so). Using a thicker gage in B31.1 translate to a longer life than 20 years .

It is also reasonable to assume that using bigger factor of safety will result in a more reliable piping system - at a cost (thicker pipe last longer and has more strenght to most extent).

So whcih one to use? The answer depends on the life of the plant your looking at and the level of reliability u wanted to achive. This is not a rule but merely an opinion as a user of both b31.1 (nuclear power plant ) and b31.3 (ethlene, gl;ycol and polymer)

_________________________________________-------------------

Christopher wrote
> First don't mix Code rules. Don't use Div 2 in Div 1 construction, for
> example.
>

Again i agrred but only for the fab/construction of new equipment. Let us consider a new pressure vessel. your purchase spec (from the point of view of end user) should clealry state whtwer its going to be fabricated either to Div 1 or Div 2 rules. It can not be both as Chris W. has stated.

You then commission the unit and while in-service, a damage on the shell was noticed. How to you assess the damage on the shell after getting all the results from the ndt. We'll, you use div. 2 appendix 4 as an acceptance criteria because there is nothing in either api 510 or div 1 that will guide in the assessment (as far as determining the level of stress is concern).

The use of Div 1 or 2 or any code requiring an engineering evaluation assume that the user is competent enough and have sufficient expereince to perform such analysis. Else hire the services of a P.E.

> ----------
> From: Christopher Wright[SMTP:chrisw@skypoint.com]
> Reply To: PipingDesign@yahoogroups.com
> Sent: 20 June, 2001 5:19 PM
> To: ?
> Subject: RE: [PipingDesign] Thick and High Pressure Pipe
>
> >This now leads to the question when should one use the b31.1 or b31.3 (
> as
> >oppose to what's the difference between b31.1 and b31.3 or between Div 1
> >and 2 - is Div.3 out?)
> In general, you use the original design code for the system. If nothing
> in the original Code applies you are pretty much on your own. No code
> provides rules for every detail and the intent in such cases is to
> provide details which will provide the same design margins as used for
> the original code.
>
> That intent means several things:
> First don't mix Code rules. Don't use Div 2 in Div 1 construction, for
> example.
> Second, you have to understand the original code fully to understand the
> original design margins.
> Third, you'll probably have to do some careful engineering design and
> analysis to make sure your new detail does in fact have the same margins
> as the original.
>
>
>
> Christopher Wright P.E. |"They couldn't hit an elephant from
> chrisw@skypoint.com | this distance" (last words of Gen.
> ___________________________| John Sedgwick, Spotsylvania 1864)
> http://www.skypoint.com/~chrisw
>
>
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Received on Thu Jun 21 01:35:00 2001