1 June 2023

Horn Drop test of Steam Turbine | Turbine Fundamentals and Basics | Basic Aspects of Steam Turbine Maintenance | Part#3 | Content-18

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Horn Drop test 

1.) Horn Drop test of Steam Turbine:-

  •  By horn drop test the loading of the casing on each corner is determined. It is taken on HP and IP Outer Casing.


  • In a horn drop test a drop is measured on an individual corner of the casing with the help of dial indicator by removing the support of the individual corner and then it is compared with the opposite corner.


  • The horn  drop test  is repeated at various stages in  individual  casing i.e. first without  connection of any pipe lines the horn drop readings  are recorded then it is compared after welding of inlet, outlet and extraction pipe lines  etc.


  • As such the influence of these  major pipe  lines  are notices on  each  corner  of HP/IP casing by comparing the horn drop  test readings. 


  • The horn drop test  will  indicate the  quality of work during  assembly/welding of pipe lines with the HP & IP casing.


  • The horn drop readings are very important  in HP  & IP casing.


  • This is a very important check and may  cause serious  problem in operation of the  machine like high vibration in the machine failure of barring gear in hot/cold machine, obstruction during expansion of machine etc.


2.) Horn Drop test Procedure:-

1.) During the horn drop  test  the individual  packer  of the  casing is  removed and  the  load  of  that  corner  is  supported  over the  jacking  screws  of  the  casing . Now gradually the jacking screw is relieved with the help of Hydraulic jacks on that corner and drop is recorded. This is repeated for each corner of the casing.

2.) In case of variation in the left and right side reading the drop is adjusted by adjustment of the shims from left to right or vice versa . No addition/subtraction of shims is allowed from the outside.Correction is carried out till the equal loading is observed.

3.) Above Complete test at four corners is again repeated after joining all the Pipe lines with the Casing

4.) The variation in horn drop reading of left and right side of the casing may be permitted up to difference of 50%.

5.) If the variation is much , then no correction is made by adjustment of casing packers. The variation at this stage is caused due to piping pull /push only and hence if any correction is required then the same is to be carried out in the piping joints and its Hangers support only. Sometimes it is necessary to cut the piping joint for the necessary correction.

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