Dear Friends,

I read many threads here & also the ASME papar for Friction treatment, i found some queries among all of these. I hope I can get clear my doubts.

I have Two queries as below.

Problem : My system have design temp = 50 Degree C & Opera Temp = -22 Degree C. Ambient Temp as per Project code = 36 Degree C.

I have to issue Pipe Rack Load Data.
I did the analaysis with Mu=0.3, take out Restarint Output & after that I changed the Friction Multiplier as = 0.0 in Static Load Case.Hence, considering Friction Factor =0 throught the system.

I compared both restraint summary,as per Technical Paper & thread's discussion, Without Friction Factor is conservative. But i found that with friction factor Forces/ Moments are very high. Even some cases without friction factor loads are high,some nodes have the same values & some nodes are have less value than with friction system.

Although my design temp & ope temp are nearer to ambient temp,expansion effect is not so much. But I still feel that for Pipe Rack load data, With friction Factor is the best methodology instead of without friction factor.

Since, the frition factor plays a key role for forces / moments, i am not able to understand why some nodes have less loads than without friction factor file.

Problem 2)One of my system connected from Pump to Tank via Pipe Rack. I would like to know the load case for Tank settlement. I did analysis as below. Please review the load cases if i m right or wrong.

l1 = W+P1+T1+D1+D3+H (OPE- D1= PUMP)
l2= W+P2+T2+D2+D3+H (OPE- D2=PUMP)
l3= W+P1+H (SUS)
l4 = W+P1+D3+H (D3= SETTLEMENT TANK)(SUS)
l5 = L1-L3 (EXP)
l6= L2-L3 (EXP)
l7 =L1-L2(EXP) (THIS IS FOR TEMP DIFF)

I followed as per above load cases.

For Case - 4 what will be allowable?
Are Nozzle Load check against the load case L4?

I hope ur guidance will sort out my quries.

when u applay friction factor the load will distribute through all your frictional support,hence the load u get on anchor bay point will be lower than the the case with out friction .

Azley,

I agree with arun when he talks about load on supports. Without friction your supports don't have any load in expansion direction, what may have some trouble in case of calculate it. And the load that goes for anchors is the sum of load friction caused by expasion of pipe. So, in case of Pipe Rack I believe the best methodology is using friction coeff.

And for problem 2, the settlement is due expansion of tank? Is yes, maybe is better delete D3 from settlement and keep this calculation for L1-L3 and L2-L3. The nozzle is verified by 3 loads, SUS, EXP and OCC. And how D3 is due temperature is better keep this load only in EXP case and SUS only for own weight.

Hope had helped.

Miyamoto

Dear Miyamoto san

I agree & thanks for ur reply.

However, I am not able to understand ""And how D3 is due temperature is better keep this load only in EXP case and SUS only for own weight.""

D3 is how to consider in EXP case?
I checked with TR of COADE, but EXP case is not found.

Can you throw more ur light for this one?
It helps me.

Arun Thanks, for Pipe Rack Load Data, I will check with Friction Coeff only.

Azley,

1)
For rack piping analysis we consider Expansion/operating case without friction for
1. Checking stresses
2. checking interference of pipes at change in direction(i.e displacements)

For loading point of view you shall consider operating case with friction.

2)
In case of tank settlemet your load case L4, as per me it is under primary stress so sustain allowable as per code.

3)L7 load is is wrong.
When you are going to consider stress range it is differen between max and min tem not diff of operating and design.

Dear Devendra & Richard sir

I noticed as below,request to look & reply my doubts

Comparison of one same system with friction & without friction for stresses & Loads.

1) For Stresses -

The SUS and EXP - Output ratio values are not have major differ. near to equal.

PURE OCC (WIND) + SUS - Without Friction Factor output is very higher for stresses. But allowable are same in both files.

However "Allowable FOR EXP LOAD CASE are reduced in the file of without Mu system compared to File with Mu" ----- Please explain.

2) The "EXP" Load Cases summary as per below. (Thermal OPE - SUS)

with Mu

Code stress - Less
Allowable - Higher
AXIAL STRESS - Higher
BENDING STRESS - LOWER
Torsion Stress - Higher

With out Mu

Code Stress - Higher
Allowable - Lower
Axial Stress - Lower
Bending Stress - Higher
Torsion Stress - Lower

Considering friction factor in analysis the displacements are less than
Without considering friction factor file, because supports like Guide, limit stop & Rest supports are start to acting for absorbs the relative direction expansion of piping.

So, is it affecting the allowable in case of EXP Load Cases? This is not understood.

2) Loads

Loads at only REST SUPPORTS, REST SUPPORTS WITH GUIDE, ANC locations, some nodes have higher loads in vertical+horizontal direction than each other file. Can you help,why these both are have deficiencies.

In my knowledge that with friction factor LOADS ARE HIGHER than without Friction Factor for same system.

Let me correct if I am wrong.

Dear Devendra,

L7 is correct as per my opinion, T1= 50Degree & T2 = -22 Degree.

SO,as per CODE 31.3, for full thermal stress range it is required.

Dear Azley

Sorry,It was my mistake about load case I7 .

there is no relation ship between allowable stress of material and friction...

Dear Arun & other experts

It shall be corrected your sentence - relationship of material is always encounter for allowables.

I agree with "friction & allowables - have no relations in any code formulas" but you can take a trial of your any system long run pipe rack or any one.

You observed that the value of Allowables in case of EXP load cases,are differernt than the in both with friction & without friction factor files.

The allowables are reducing in " without friction factor CAESAR II file".

Consider TWO EXP Load Cases (DESIGN & OPE TEMP - SUS) - The ratio of reducing value will be same of with friction & without friction factor.

search for "liberal stress"

Dear Danb

Thanks, I had experianced for the same as per Code" Liberal Stress"

I checked with that one also, the summary is as below.

Without Liberal stress

- With friction - Allowables are same.
- Without friction - Allowables are same.



But,if you consider or Tick mark the " Liberal Stress Check" in special execution parameters, than check.

With liberal stress

- With Friction - ALlowables are more.
-Without Friction - Allowables are less.

I request to try for the whole system of any piping system as trial.
If anyone experianced such matter.

Dear Danb

These are only I am talling for EXPANSION cases.

Check the "Code" equations for allowable expansion stress, there are two:

First Equation:
Sa = f(1.25Sc + 0.25Sh)

Second Equation:
Sa = f(1.25Sc + 1.25Sh - SL ) We refer to this equation as the "liberal allowable". This is our term, you won't find it in the Code.

Note in this second equation that the allowable depends on the magnitude of the Sustained stress "SL". So as "SL" increases, "Sa" decreases.

If your Expansion allowables are changing with friction, then since Sh and Sc are constants, SL must be changing with friction. Compare the results of you two Sustained cases (witha and without friction).

when u applying a liberal stress your allowable stress range will be
SA(Liberal) = f[ 1.25 Sc + .25 Sh + ( Sh - Sl) ]

as you said ur allowable are changing only when activating Liberal so we can reach a conclusion its only due to changes in 'SL'
it may happend due to (HOT SUSTAINED)
eg: your support is lifting in no-friction case which cause ur SL incraeses as this support is not taking load , which results (Sh-sl)get reduce and allowable also

i hope it clears ur doubt

Dear Arun and Richard Sir,

Thanks for ur help.