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.