inlet steam strainer deterioration

[chrissm]

Òur steam inlet strainer to a siemans HP (100 bar) Turbine has deteriorated on repeated occasions such that the strainer elements found their way to the turbine nozzle block and became trapped there. Can anyone explain why this is occuring? We have almost eliminated the strainer as being a design flaw as it is wotking good on two other similar plants. The only difference in the piping run, however, is that this plant has a 400mm to 200mm reducer immediately before the strainer while the other plants have a 300mm to 200mm reducer.

 

[rmw]

How far upstream of the strainer is the reducer? Quantify immediately before, and is the strainer centered in the flowstream, or high or low, with respect to the centerline of the inlet reducer?

rmw

 

[smckennz]

From what you have described, the problem is most likely to be due to excessive peak steam velocity caused by excessive contraction at local reducer.
Options to consider are:

Add more distance between the reducer and strainer. This will even out the velocity profile and eliminate any vena contracta effect inside the strainer body. I think this is what rmw is hinting at

Replace the reducer with a longer one having a more gentle taper.

Add a target plate inside the strainer to eliminate direct impingement. There may be insufficient space to do this without adding considerable pressure loss; the strainer manufacturer may be able to help out.

Add flow straighteners between the reducer outlet and strainer inlet. It sounds as if you may be stuck for space though.

Cheers

Steve