Nozzle load and Moments (API-676)

[techky]

Hi Guys,

I have a PD pump (Internal Gear) with Cast Iron construction. As the understanding goes, the nozzle loads (Forces and Moments) are not compliant to API-676.
The pump footing lies on the bkt which is offset from the pump casing by 400mm. Now, the piping is already fabricated based on API-676 & there is customer's requirement for API-676 nozzle loads & inability to change / modify the same at any cost.
I proposed for introducing expansion joints on suction and discharge side which was turned down.

Is there any ways to modify on the pump / piping with less impact on cost & design.

Your advise will be well appreciated. Feel free to ask me for any-more technical info as required. Thank you

 

[TenPenny]

If I understand what you're saying, the pump is not designed to meet API676 nozzle loads. But your post leaves out some information: what are the allowable nozzle loads on the pump, and what loads are going to be imposed by the piping?

Has anyone checked to see if the pump can take the loads in this particular case? That part isn't clear from your post.

 

[nickelkid]

How do the OEM allowable loads for the CI pump compare to API?

Is a dimensionally equivalent pump available with a higher load capability?

Just putting in expansion joints may not be a solution. They also need to be installed correctly, which may also require pipe/support alterations.

 

[techky]

TenPenny,
As per API-676 guidelines, for NPS 4" (Fx, Fy, Fz, Mx, My, Mz)- (1300N, 1300N, 1300N, 700Nm, 700Nm, 700Nm) respectively. Again this is Min. The construction is CS.
Our CI Pump construction for NPS 4" (Fx, Fy, Fz, Mx, My, Mz)- (2000N, 2000N, 2000N, 650N, 265N, 300N).
So as you can see, the Forces are way ahead than the API-676 mentioned Min. values.
There is a lag in the Moments.

I don't have the allowable loads imposed by piping. But the customer's requirement is to meet the moment of 700Nm at all X, y, Z axes. though I did ask for the resultant moment value if it can be met at-least.

As per the pump manufacturer, the pump can't take upto 700Nm but it's possible to withstand slightly higher than the tabulated values (650N, 265N, 300N).


NickelKid,
Agreed that CI is not to be compared with API.
But I believe that should there be any modification be done on piping, that's not drastic but very limited things need to be changed / modified. Am I right in my assumption?

 

[nickelkid]

Can the CI pump take higher loads than published by the OEM? I imagine it can.

Is the CI pump good for nominally 2.5 x Allowable Moment? Being CI I would be hesitant going that direction.

It appears that API limits govern for forces and OEM limits govern moment for the design. Right?

As far as the extent of piping modification required, we lack considerable information to comment. As mentioned, what are the current resultant loads of the pipe design. What is the configuration, materials, operating temp, load cases, etc…

 

[techky]

Hi Nickelkid,

Can the CI pump take higher loads than published by the OEM? I imagine it can.
I believe the same too. But the question is if it can match the API-676 moments for the same NPS. For forces, yes it can.
The moments primarily depends on material properties & the distance btw the bracket and nozzles. So for pumps with foot below casing have an advantage to take higher nozzle loads.

Is the CI pump good for nominally 2.5 x Allowable Moment? Being CI I would be hesitant going that direction.

It appears that API limits govern for forces and OEM limits govern moment for the design. Right?
API limits govern min. required moments as well. But you are partly right to say that moments are more under control by OEMs. It differs based on couple of design factors.

As far as the extent of piping modification required, we lack considerable information to comment. As mentioned, what are the current resultant loads of the pipe design. What is the configuration, materials, operating temp, load cases, etc…
I don't have this info now. I'll try to get this for our discussion.