Pipelines, Piping and Fluid Mechanics Engineering - NEMA Force Allowed on the Flange

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Pipelines, Piping and Fluid Mechanics engineering - NEMA Force Allowed on the flange

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NEMA Force Allowed on theflange

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farhad2474(Mechanical)2 Feb 08

2:04

Hi

I recently involved with a compressor

it has 16 flange at output. I am

going to do stress analyze the pipe is

connecting to this compressor. The

venders catalogue mentioned that

this compressors flange can

outstand 10x NEMA forces . I would

be appreciated if some body tell me

what mean it is (10 x NEMA).

Best regard

farhad

DSB123(Mechanical)2 Feb 08

6:05

farhad2474,

If what you write is correct

then the Vendor is saying that the

allowable loads acting on his flange

can be 10 times the NEMA quoted

values. This seems to be a very robustcompressor if that is the case. I would

check and ask for definative

allowables from the Vendor rather

than accepting catalogue information.


8:15

hi ;DSB123

thank you for you answer . Really iam right. They wrote like this in the

meeting with my company .I wasnt

involve that time.so please tell me if

you know a bout 10x NEMA .

best regard farhad

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JohnBreen(Mechanical)2 Feb 08

10:39

farhad2474

You will need to get a copy of

NEMA Standard SM-23. PLEASE

NOTE THAT THIS IS A

STANDARD FOR STEAM

TURBINES. On steam turbines, the

inlet is the smaller and hotter nozzle

and on compressors the outlet is the

hotter and smaller nozzle. You will

need to read and understand this

Standard. Then using SM-23 you

will have to calculate the loadings (a

function of nozzle size and

temperature)that are within the

allowable limits of the

Standard. Your compressor is said to

be able to accommodate loadings that

are an order of magnitude greater

than the NEMA Standard maximum

allowable loadings. This is a

surprisingly robust compressor.

You should also read and understandAPI Standard 617, Centrifugal

Compressors.

I concur with DSB13, get the actual

allowable loadings in writing from

the compressor manufacturer to cover

your employer's liabilities.

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LSThill(Mechanical)3 Feb 08

12:34

Piping Stress Analysis Design

Criteria for Compressor with Steel

Nozzles and Castings

Steel Centrifugal Compressor Force,

Moment and Stress Limitations

1. With Limitations are not

provided by vendors, the following

limits are guidelines which are

reasonable for design.

2. At operating temperature, using

the hot modulus E resultant

bending moments are permissible up

to a value which would cause abending stress of Sh/4 in a

connection having a section modulus

equal to the connecting piping for the

same size where the connection is 4

NPS or larger. On smaller size

connections a stress of Sh/3 shall be

permitted. (Sh is as defined by

ASME B31.1 or B31.3 current issue,

for the material of construction.)

3. NEMA SM 21 & 22 X 1.85

a. Most compressor vendors specify

1.85 times the NEMA SM 21 & 22

standards as their allowable load

limits. Generally, this indicates that

do not have test data to substantiate

allowable loads. There are several

methods of circumventing thisproblem. The best method is to

present the piping loads to the vendor

prior to purchase and making the

loading part of the contract. If the

equipment has been purchased, the

loads should be presented to the

vendor for review for possible

acceptances. Reference to API 617

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MJCronin(Mechanical) 4 Feb 088:20

farhad,

John Breen gives good advice....get

the allowable loads in writing from

the compressor vendor.

You may be surprised at how many

operating problems are blamed on"excesive piping loads" during the

startup phase, when the true fault

usually lies with the compressor

vendor.

With regard to the point about

NEMA SM-23 being STEAM

TURBINE loadings, yes this is true,

but my experience has been that the

major compressor vendors will not

develop thier own set of acceptable

loads.

They, as a group, prefer to play the

game of "submit to us your loadings,

then we will charge you a extra to

review and approve them"

Over the past 30 years, they see thisas being a "seperate profit center" and

a trap that all AEs seem to fall into.

My opinion only..

-MJC


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2:48

thank for answering to my question

i am going to use following Equation

for allowable load on the flang of

compressoer according to NEMA-23

Fx=50Dc

Fy=125 Dc

Fz=100 Dc

Mx= 250Dc

My= 125Dc

Mz=125Dc

Dc= (18+equivalent dimeter)/3

Am i right ?

best regard

farhad

tigny(Structural) 6 Mar 08 4:39

Farhad2474, dear all,

I would like to input a little of my

own experience in this field.

If you use a software like CAEPIPE

or CEASAR II, you should use the

analysis tools for NEMA SM23, and

enter all relevant details: equipement

centerline axis, !for all nozzles:

nozzle nominal diameter, distancefrom resolution point (= biggest

nozzle) to nozzle, calculated forces

and moments, and if needed, the

factor for allowable increase.

If the vendor's catalog gives you an

allowable of 10 time NEMA SM-23

on this nozzle, it means a check of

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only limit 1:

chapter 8.4.6.1 gives limit 1on total

resultant force and total resultant at

any connection

formulas are given for resultant

forces and resultant moments, as wellas equivalent connection size

according to your manufacturer spec.,

you can multiply 500xDe by 10

and check 3FR+MR


http:///reader/full/pipelines-piping-and-fluid-mechanics-engineering-nema-force-


Fx= 10x50Dc, Fy = 10x125Dc, etc.

If you check only the limit 1, the

overall compliance would not be OK,

as far as my experience tells me.

The NEMA, as it is presented, is

misleading because many peopleseem to check only the nozzles one

by one, whereas the intent of the

NEMA is to take into account the

dimensions of the machine (nozzle to

nozzle).

And I don't like having fixed values

from the vendor, since with the

NEMA formulas, you could increase

one componant, reduce another, and

still be within the limits. I'd rather

have him certify the allowable

coefficient.

yours truly,

tigny


Hi all,

I forgot to mention that all

calculations to NEMA should be

done with english units (pounds for

forces, foot pounds for moments),

then the results can be transfered to

SI or others.Otherwise, because on non dimension

factors in the formulas, you'll get into

trouble.

In API 617 you have formulas for SI

units (Newtons and Newton.meters),

but a 1.85 factor is already included.

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http:///reader/full/pipelines-piping-and-fluid-mechanics-engineering-nema-force-


yours truly,

tigny

robinc(Mechanical)26 Mar 08

12:10

Hi all,

Regarding the "resolution point" for

the combined moments in API 617

and/or NEMA SM23:

I understand the forces/moments are

"resolved at the centreline of the

largest connection ..." (API 617 2002

pg 2-42)

Where along this centreline is this

force resolved ... the nozzle face ... in

the vertical plane of the shaft ...

random location?

Caesar II implies that it is the nozzle

face but I can't find this explicitly

stated in either code. In my mind the

resolved forces should be about theshaft. If these loadings deflect the

shaft, then you end up with

mechanical issues.

Looking forward to either a one

sentence clarification, reference, or

long discussion.

Thanks,

Robin

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C2it(Petroleum) 27 Mar 08 9:20

Robinc,

The resolution point is not too clear.

It should always be specified and

agreed with the vendor. In a 2 nozzle

machine there is logic in using thelargest nozzle face and c.l., since that

is where major pipe loads are

imposed. Using that for combined

loads means that the moment effect

of forces acting there is zero.


Hello Robinc,

you state "If these loadings deflect

the shaft, then you end up with

mechanical issues."

I would dare to say "if loadings

deflects the pressure casing, the

bearing casing and/or the gearbox

casing, then you may end up with

mechanical issue". I suppose that if

the shaft bends, you shurely have

already rubbed everyplace in your

machine!

About the reference point: At first we

took some reference point at the level

of the fixed point of the machine

(between the fixed legs i.e. for

compressors-expanders) but to be

more consistent with NEMA SM23,API 617, and after reading the help

file from CAESAR II, and also

because of the request of one of our

clients, we now use the biggest

nozzle center as the reference point.

yours truly,

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tigny

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