I have two questions:
1- As per piping stress analysis specification, the piping flange and pump nozzle flange misalignment should not be more than in 1.5 to 2 mm in axial, transverse and angular direction.
My question is what is the criteria for this misalignment when there is expansion bellow in the line. In my case, as shown in figure, the nozzle flange is misaligned around 90 mm in vertical and 40 mm in axial when i check it from Caesar in WNC case after removing the nozzle anchor.


2- Actually we are facing an issue with a hot oil pump. The pump shaft coupling is misaligned (dont mix up with above mentioned misalignment) after some passage of time and pump seal is started leaking. After analysis through Casear ii, it is found that pump suction piping loads in y-direction are slightly more than the 2 times of API-610 nozzle allowable loads. Other loads including discharge are within 2 times of API-610 and qualifying the Appendix-F equations. Temperature is 330 C and suction line size is 10".
Are the piping loads responsible of this leakage.

Hi Ali,

1.I wont recommend Exp. Joint for 330 C ,they are prone to leak. Suggesting to provide enough flexibility in suction & Disch. pipes ,which should be taken care before freezing Pump locations (Area)

2.Have u qualified the Pump Vendor allowable loads ? ( or u considered the 2 times API directly.)In case ur loads exceeds the given allowable the u need to convey ur loads to the Vendor fro his acceptance.


3.Displacements in WNC are too high which will definitely create problem of misalignment due to which there must exists the Vibration which will cause the Mech-seal ( metallic Bellow type)to damage.

Rg,MVS

Hi MVS,

Thanks for your reply. Actually the piping and pumps are lying in a skid and the skid was provided by vendor. Our part was above the anchor support as shown in figure. Piping between anchor to pump was within vendor scope.

The issue is pump is getting shaft misaligned and subsequently causing seal leakage. Now in order to identify the issue, i have modeled the skid part in caesar ii and found that loads are slightly greater than 2 times of API. (pumps are API).

Now the question... Is high piping loads causing shaft misalignment ? or something else..

The issue persists since commissioning. As around one year has been passed, so Pump skid Vendor is not cooperating

Is that (really) a full anchor at the top of your vertical run? Is the this the skid boundary? What sort of expansion joint assembly do you have (e.g., untied, tied, hinged)?
Also, pushing your nozzle load limits up to 2 times Table 5 requires the "approval by the purchaser and specific direction to the piping designers for its use". Are you the purchaser?
Yes, high piping load can cause misalignment.

Hi Dave,

Yes.. it is a really full anchor. See image below.
Again yes.. its a skid boundary between vendor and us (EPC contractor).
Its a untied welded (no flange) metallic expansion joint.
Yes.. we are the purchaser.

Actually we purchased the entire skid from vendor and the integrity check of inside piping and pump was vendors responsibility.
Now the pump were purchased in some earlier dates than installation . Moreover initially the leakage problem was not highlighted. So the warranty has expired and vendor is not in mood of cooperation in this matter.

Now the problem came to engineering division( where i work) to analyze and find some solution. So when i analyze the inside skid piping with vendor provided stiffness values of expansion joint, the piping loads are slightly more than 2 times of API...
Just to inform that the allowable loads values mentioned on pump GA is one times of API.
Now i have to find root cause and some remedial measures.

Hi Ali,
Wht type of Mech-seals u r using?( it must be Metallic Bellow)

Ali Raza Bashir,

If you made the calculation just only from the anchor until the pump, with the untied bellow, pressure and temperature, and check the pump's allowables, you'll see that the system doesn't work.

Ask for the vendor's stress calculation (s).

Regards

@ MVS... Yes it is a metallic expansion bellow without any tie-rod and welded connection. Its just below strainer..not visible in picture due to insulation.


@ RBDF..Actually, system is okay w.r.t code compliance... but the piping loads are higher on pump nozzle. One thing more, i have not given any value of effective area during expansion bellow modelling in Caesar ii.

Ali,
No effective area means no pressure thrust in analysis. If it is un-Tied expansion joint, there will be pressure thrust. The pressure thrust (acting vertically down in your case) will create vertical load and bending moment on nozzle. This moment can cause misalignment in shaft coupling / bearing failure.
A dummy support at riser may help in your case.

Ali Raza Bashir,

I'm talking about nozzle loads not stresses,

Regards

Hi Ali,
Hope the flange,reducer & pipe spool is not supported which is considered to be hanging on the pump nozzle will have some moment acting on it.

Its untied bellow, so the thrust force will also be acting on it.

These two loads may be the reason.

regards

@kahlidmf...You are right about placing dummy support below riser is beneficial.. What i have suggested to our team is to 1- remove anchor, 2- place a dummy support with guide and stop just bend the bend and 3- relocate the expansion bellow in horizontal run near pump flange.

@RBDF... yes the vertical load Fy is higher than 2 times of API loads. Further the vendor is not in mood of cooperation. His response is very slow and he will not share his calculations.

@syedibrahim... Yes as i said earlier, i have inserted a dummy support behind bend in order to support the piping, strainer etc.
And for thrust force, I have put axial stop an guide at dummy.

Below are my proposed recommendation . Just to clarify, as per our company procedure, we use an reinforced tee at dummy and bend interface while modelling in caesar ii.

Hi Ali,

Please mention the pressure used for analysis.

The vertical leg where the anchor is removed requires a guide minimum in one direction E-W or N-S.This is because of large bore pipe.
Regards

Ali,
What is pressure? In most of the cases discharge pressure is considered till suction block valve (there is a reason for this).
What is purpose of relocation expansion joint. If you consider expansion joint in horizontal , pressure thrust will directly act on nozzle/pump casing. Are you considering full pressure thrust on nozzle or thrust because of annular area of bellow?

Regards,
Khalid

Ali,

Just seeing your sketch above, the single bellowed expansion joints are not functioning well, you have to put a trunnion at the elbow and your problem will be solved.

@ Rivera..

Thanks for your suggestion. Well, i have already proposed a trunnion/dummy below bend with axial stop and guide on it. See the above figure. Actually as per our company procedure, we model a reinforced tee at trunnion and bend interface.

@ Jailani..

The idea of putting guide at the place where anchor is removed seems logical. Thanks for advice.


@Khalid..

I am out from office since a week. I share the pressure values by tomorrow.

Hi Ali,

In my last post I asked u , what type of mechanical seat u r using at Pump gland follower ( there r many types Gland pack sealing / Mech -Seal plate/ Mech Seal having Bellow type). Please check.( Note:Expansion Bellow used in piping & Mech-seal having its own Bellow element are two different things)

Yes , definitely u have to use expansion bellow in suction piping .Further suggesting to use Bellow type Mech-seal; u may get some relief from seal leakage only after reducing the Nozzle loads.

- Removing Of Anchor @ Tie in Point seems logical & correct.( if possible use enough gap/Slot in Vertical to allow thermal movement & to minimize nozzle loads use Guide support ( Slotted plate ) at same location.)

- Can v play with Expansion Bellow stiffness /No of convolutions etc...if yes ,then try with ......

Pls share ur Analysis inputs & results ( mainly nozzle Exceeded Loads & Vendor Allowable loads) before trying below,


option-1
- Bellow( Limit -Tied) in vertical whose lateral movement will give benefit in Nozzle AXIALY & Laterally too.
-Reduce the bellow stiffness ( if bellow can be revised).
-Elbow Trunnion Rest Type with Sliding coeff. friction 0.1 & try to use the removed anchor place as guide in Horizontal.

option-2
- Bellow( Limit -Tied) one in vertical & other in Horizontal -Reduce the bellow stiffness ( if bellow can be revised).
-Elbow Trunnion Rest Type with Sliding coeff. friction 0.1 & try to use the removed anchor place as guide in Horizontal.

Option-3
If ur using Untied bellow ,u must provide Axial & Lateral Supports to allow pressure thrust & play with Bellow stiffness to meet allowable.