Steam Turbine Data 2

[micvanzyl]

Dear All,
I'm evaluating the vendor data required for pipe connections to turbine nozzles.
Each page contains to tables.
The upper table (In the bottom right hndd corner) there are summations for applied moments. I don't know what Z*Fy or y*Fz mean in the following:

SIGMA(z*Fy) + SIGMA(y*Fz) + SIGMA(Mx)

The lower table includes values for Actual pipe actions which I don't know the reason for stating them ( I know they are probabely paseted in wrong columns).

Please let me know any other general data I shall check to preform this job.
I've attached the preliminary information I've got to have your ideas.


Thank you
Mic

 

[StressGuy]

You probably need some clarification from the vendor, but I read the tables as follows (I'll just use the first page for an example)

The blue numbers in the upper left are the displacements that the various nozzle connections will impose on your piping system. You need to include these movements in the stress model.

The red numbers in the upper right are the individual allowables that your piping system can impose on each nozzle connection. You need to check the six forces and moments from your stress run at each nozzle connection against these numbers at both installed (cold) and operating (hot) conditions.

The equations below are an additional constraint on the loads. I'm concerned that you don't understand the summation equations. Pretty much any rotating equipment standard (ANSI, API, NEMA) has summation equations similar to these. In this case, the vendor has imposed restrictions on this collection of nozzle loads with regard to the maximum combined Fy and Fz forces, along with the Mx moments. You will need to develop a spreadsheet to run these summations based on the forces and moments that you get from the stress report.

Which brings up the lower left blue numbers. These are the locations of the nozzles relative the the point of resolution the vendor wants you to check against. The X and Z column heading are misformatted. These are the values you use to solve the summation of Mx equation in the upper right.

Finally, the lower right portion of the page is for you to fill out. Then vendor wants to see your results as documentation that your piping design imposes loads that are less than what the restrictions are in the table above.

I don't see anything on the documents you posted indicating what XYZ system the vendor is using. You are going to need to know what the vendor thinks is up (typically Z or Y). Based on the values given to nozzle locations, I suspect they are using Z as the vertical axis system.

You have an extremely complex turbine system and it will take a experienced senior stress engineer several hundred hours to do all of the work to solve the piping design for the vendor requirements. Your questions suggest that you are working on a problem that is well above your level.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[micvanzyl]

Dear Edward,
Thank you for your kind explanations.
The coordinate system is missing in the supplied data and I'll ask for it in future correspondence. However, you're most probabely right as I look at the nozzle displacements.
I haven't faced a turbine system yet and that's why I wasn't familiar to the extra constraints supplied by the vendor.
Would you please let me know if there are any concerns regarding system dynamic analysis? At the moment, I'm thinking of siscmic loads and the system modal analysis.

All the best
Mic

 

[StressGuy]

Well, I've been at this for about 15 years now. I've worked a number of different types of rotating equipment piping systems - but I don't think I've yet worked a steam turbine as complex as what you have presented.

There's nothing inherent to a steam turbine that would call for a dynamic analysis. Seismic requirements depend on the geography of the installation and should be defined as part of the project standards. Modal analysis typically comes into play for reciprocating compressors. Impeller based systems are effectively continuous flow and not likely to excite low frequency mode shapes.

Your biggest challenge by far with this unit is going to be getting the combined load limits satisfied. While you have six force/moments to satisfy for each nozzle, odds are good that you will have to be well below those for each nozzle in order to get the three resultant equations to give you a summation less than the imposed allowable. Just taking a look at your Fy summation for hot loads on the first sheet - the allowable is +/- 60kN. If you add up the five Fy allowables (assuming they all end up with the same sign), you get 113.2kN. You are going to have to iterate each of these five lines until you come up with a set of Fy values whose sum is less than 60kN. At the same time, you have to get the Fz and Mx summations to also get below 60kN and 250kNm respectively. It is about like trying to solve a Rubik's cube.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[micvanzyl]

Dear Edward,
Thank you very much for your helpful advice.
Actually my biggest concern was regarding the inherent considerations (if any) I need to observe for such an equipment. That's great if I can treat it like other normal rotary equipments I've worked out so far.
I don't know the nozzle sizes yet; if the allowable loads are low compared to the nozzel sizes, then it seems this Rubik's cube can be never solved

All the best
Arman

 

[rmw]

I can't open the file on my home computer and I probably won't think to do it at work (too busy working).

But, that said, are there any values on there for "cold spring"?

rmw

 

[micvanzyl]

rmThank you for your reply.

 

[stgrme]

Chances are you will not be able to satisfy all the restraints on forces and moments. I suggest you make a reasonable effort and then, if you have a few points which exceed the vendors limits, submit your analysis for review by the vendor. In many cases, the vendor will accept your variances.

Best of luck!