RE: hello

From: <James>
Date: Mon Oct 01 2001 - 04:15:00 EDT

>-----Original Message-----
>From: A.V.Acharya [mailto:anupacharya@vsnl.net]
>Sent: 29 September 2001 18:50
>To: <a href="/group/PipingDesign/post?postID=2JObg7pXxBtF8gwaPGGxK6RzyjzfTIPR4n4_5vb3dHRBQaFI08cHtyRrdPdMvFoX5S6-3jQV4yVbEtGBEt-9k7lkHlDFFD8">PipingDesign@yahoogroups.com</a>
>Subject: Re: [PipingDesign] hello
>
>
>hye guys,
>there is a thumb rule for estimating pipe schedule
> does any one know what it is
>for cs pipes and ss pipes
> also if there are any one who can tell me how the formula is derived i
will
>be grateful
>anup

I am not quite sure if you are asking how to calculate the wall thickness requirements, but if you are here goes:

Based on ASME B31.3 1999 Edition.

Section 304.1.2 - Straight pipe under internal pressure

t = PD/{2(SE + PY)}

Where

t = pressure design thickness
P = internal design pressure (gauge)
D = outside diameter
S = stress value for material from Table A-1
E = quality factor from Table A-1A or A-1B
Y = coefficient from Table 304.1.1

Units should either be inches and psi or mm and MPa

Once you have obtained your pressure containment thickness, choose a schedule that exceeds it.

Most schedule pipe comes with a manufacturer's tolerance of +/- 12.5%

Take 12.5% from the schedule thickness, this will give you the minimum thickness that the pipe manufacturer could supply you with.

From this minimum tolerance wall thickness take the corrosion allowance; if used, typically 1 to 2mm. This will give you the final minimum wall that you could have at the end of the plant's life. This thickness must

exceed the minimum pressure containment thickness, if it doesn't choose the next schedule up.

This formula is based on hoop stress for a thin shelled vessel s = PD/2t,
plus a factor E for the method of maunfacture, e.g. 1.0 for seamless pipe
and a factor Y depending on temperature.

Other codes, B31.1, BS806 and ASME III are similar.

I hope that answers your question, if not my apologies for the long lesson
in pipe scantling calcs.

Barbara

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