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Participant

Join Date: Aug 2010
Posts: 2

Miter Bend Calculation

08/14/2010 1:38 PM

How I can make design calculations for 8 inch Carbon steel (A672 GR B60 CL-13) miter bend (90 Deg, radius= 1.5D) for water service at ambient temp.Is there any formula to make the template?

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Associate

Join Date: Jun 2010
Location: Connecticut, USA
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#1

Re: Miter Bend Calculation

08/14/2010 2:22 PM

I think you need to use these standards PFI-ES-24 (PFI ES24 - Pipe Bending Methods, Tolerances, Process and Material ) I could be wrong.

Bend under internal pressure (102.4.5):

pipe under internal pressure where I for intrados is:

and I for the extrados is:

and at sidewall I = 1.0,

R = radius of pipe bend

Bend under internal pressure (304.2.1):

pipe under internal pressure where I for intrados is:

and I for the extrados is:

and at sidewall I = 1.0,

R = radius of pipe bend

Bend under internal pressure (841.231):

For cold bends the deflection of longitudinal axis and the radius is limited according table in paragraph 841.231

Hot bends are to be designed and manufactured according ASME B16.49, the internal pressure rating shall not be less than that which is calculated for straight seamless pipe and the intrados wall thickness should be:

where the t the wall thickness of the pipe is

Elbows under internal pressure (102.4.5):

Elbows manufactured according standards listed in Table 126.1 are suitable for use at the pressure-temperature ratings specified by such standards.

Elbows not according above standards or for which design formulas and not given in the code shall be based on calculations consistent with the design criteria of this code. These calculations shall be substantiated by one or more of the means stated in A B C or D of 104.7.2 (Does this mean or allow that an elbow can be calculated according a bend with uniform thickness? Refer B31.3)

Elbows under internal pressure (304.2.1):

Elbows manufactured according standards listed in Table 326.1 are suitable for use at the pressure-temperature ratings specified by such standards.

Elbows not according above standards or for which design formulas and not given in the code shall be based on calculations consistent with the design criteria of this code. These calculations shall be substantiated by one or more of the means stated in A B C or D of 304.7.2, or the elbow can be calculated according the Bend calculation, refer 304.2.2.

Elbows under internal pressure (841.231?):

No specific design rules are listed for fabricated elbows

(Does this mean or allow that an elbow can be calculated according a bend with uniform thickness? Refer B31.3)

Miter bends under internal pressure (104.3.3):

1. Only straight pipe calculations required if:

2. Pressure shall be limited to 70 kPa if:

or

and thickness is not less than required for straight pipe

3. Pressure shall be limited to 700 kPa if:

and

and thickness is not less than required for straight pipe

4. For pressure over 700 kPa: proof test, FEA, etc required with a defined minimum for closely spaced and widely spaced miter bend

Miter bends under internal pressure (304.2.3):

1. When theta =< 22.5 deg than max. allowable pressure shall be the lesser of (t = T - c):

and

2. When theta > 22.5 deg than max. allowable pressure shall calculated as (t = T - c):

For all miter bends the R1 shall not be less than:

with A:

(T-c) =< 13 mm → A = 25

13 < (T-c) =< 22 mm → A = 2(T-c)

(T-c) > 22 mm → A = 2(T-c)/3 + 30

Miter bends under internal pressure (841.232):

1. If system hoop stress > 40% of specified minimum yield strength miter bends are not permitted. Deflections caused by misalignment up to 3 deg are not considered as miters.

2. If 10% < hoop stress < 40% SMYS the deflection of each miter shall not exceed 12.5 deg.

3. If hoop stress < 10% SMYS the total deflection angle shall not exceed 90 deg.

4. If hoop stress > 10% SMYS the distance measured at the crotch shall not be less than one pipe diameter

4.04.00 Bends and Elbows

i) Elbows shall be generally of long radius type.

ii) Bends for piping 65 mm Nb and above shall be made hot and for piping 50 mm Nb

and smaller may be made cold.

iii) Bends shall be made in accordance with PFI-ES-24. Bends shall be supplied with

the minimum tangents except where the piping layout necessitates shorter lengths

in which case the tangents shall be suitably reduced after the bending operation to

suit the requirements of the piping layout.

iv) Heat treatment of bends shall be done as per material specification and PFI-ES-6.

v) The finished bends wall thickness at any point of the bend shall not be less than the

straight pipe wall thickness. All bends 65 mm Nb and larger shall be ultrasonically

examined as per PFI-ES-20.

vi) Where examination of bends indicates that wall thinning has resulted in thickness

less than the minimum specified, repair by weld deposition shall be allowed only

where the length of the affected area is 150 mm or less as measured along the

outside arc of the bend. Repairs in excess of this amount shall not be allowed. All

repairs shall be carried out only after approval of the Employer.

vii) Circumferential butt welds shall not be used in the area of the bend. Longitudinal

welds, where bends are formed from welded pipe shall be located on the bend's

neutral axis

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Guru
Engineering Fields - Piping Design Engineering - New Member Egypt - Member - Member since 02/18/2007

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Location: Cairo, Egypt
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#3
In reply to #1

Re: Miter Bend Calculation

08/15/2010 1:23 AM

Dear CNCNuckingfuts,

Good effort with my rate "Good Answer".

Only, I'd like to add that the texts you are derived are paragraphs from ASME B31. Where Para. 102.4.5 is extracted from ASME B31.1, Para. 304.2.1 is extracted from ASME B31.3, and Para. 841.231 is extracted from ASME B31.8 (note that the 1st letter of para. no. is the code section no).

Note. Miter Bend is a recognized and familiar term in Pressure Piping Code ASME B31 and not considered as an "odd term" as derived in Post #2 of our friend Tornado. Where the miter bend is a bend fabricated from one segment (piece) or more of pipe by welding.

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Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Ketchikan, AK, USA
Posts: 15370
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#2

Re: Miter Bend Calculation

08/14/2010 4:50 PM

"Miter bend" is an odd term. "Miter" implies two or more pieces of pipe cut at an angle and welded together to make one or more sharp turns adding up to the total change of direction. "Bend" implies a smooth turn in a circular arc. Can the intention be clarified?

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Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
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Posts: 15370
Good Answers: 600
#4

Re: Miter Bend Calculation

08/15/2010 2:07 AM

If we are discussing true miters, a two-piece miter consists of two pipe sections cut 45° and then turned to form a 90° joint. A three-piece miter is three pipe sections cut 22.5° and then turned to form two 45° joints, which add up to a 90° turn. Etc.

The template for a miter joint is a sine wave with wavelength equal to the circumference of the pipe, and amplitude equal to pipe diameter x sin(cut angle). This is usually laid out by drafting techniques (developments and intersections) rather than by formula.

Mitering = angular cuts and pieces welded together. Bending = forming into a smooth arc. The processes and formulas involved are different. Whether or not ASME or some other code recognizes the term "miter bend," it is still an odd term because it combines two unlike techniques, and leads to confusions such as this one, in which we don't know if the OP is mitering or bending the pipe.

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Anonymous Poster
#5
In reply to #4

Re: Miter Bend Calculation

08/16/2010 5:59 AM

Sorry Tornado, have to take issue with this statement - "Bending = forming into a smooth arc". I have not seen this as a definition of bend or bending in any dictionary, ever. Take it from Mr Galala - this is the accepted term in piping, so absolutely no confusion whatsoever, unless you insist on using the wrong definition of the term "bending".

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Power-User

Join Date: Apr 2008
Posts: 138
Good Answers: 2
#6
In reply to #5

Re: Miter Bend Calculation

08/16/2010 9:00 AM

In design terms it is known as "Pipe Bending or "Tube Bending". Sometimes the term "Bend Radii" is also known by many. I never heard of a "Miter Bend" on a pipe ot tube. There may be difference? Miter is used when cutting a piece of metal, wood, plastic or whatever flat material that has an edge chamfered to an angle of some sort.

You can find formulas for Pipe or Tube Bending on any Pipe or Tube Supplier's catalog or if you Google it, you can find under "Pipe or Tube Bending Formulas"

Also check the "Machinery's Handbook" under "Pipe and Tube Bending"

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Guru
Engineering Fields - Piping Design Engineering - New Member Egypt - Member - Member since 02/18/2007

Join Date: Feb 2007
Location: Cairo, Egypt
Posts: 1746
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#7

Re: Miter Bend Calculation

08/16/2010 10:32 AM

To whom it may concern, the attached figure (extracted from ASME B31.3) indicates the difference between Pipe Bend and Miter Bend.

...........................................

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Anonymous Poster
#8
In reply to #7

Re: Miter Bend Calculation

10/24/2010 4:22 AM

Dear Sir

Please tell me, how to weight calculate mitre bed from ms pipe.

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Anonymous Poster
#9
In reply to #8

Re: Miter Bend Calculation

10/28/2010 4:43 AM

1.5 x D (10.69x (D-t)t lb/ft

by Anand, Hyderabad

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Users who posted comments:

Abdel Halim Galala (2); Anonymous Poster (3); CNCNuckingfuts (1); hernaju1 (1); Tornado (2)

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