Document kDOqbMmyQ19rzk2O8omgm0gzb

PLAINTIFF'S EXHIBIT CO LO RAD o APPARATUS SALES DIVISION ROCKY MOUNTAIN DISTRICT . . TELEPHONE KE 4-7171 March 24, 1958 101604 Valmont Ho. 3 Unit 25,000 KW Turbine No. 32395 Valmont Ho. 4 Unit 25,000 KW Turbine Ho. 34688 Mr. A. A. Woodward Superintendent of Steam Production Public Service Company of Colorado 38th and Holly Denver, Colorado _> Dear Woodle: Confirming our conversation of March 2, our turbine design engineers have removed additional machines from the recommendation that the fields be prewarmed before bringing up to operating speed. Ike release of additional units has been brought on by the knowledge of the causes of failures of fields that have occurred. Industry now knows the importance of the transition temperature to the brittle or ductile characteristics of the steel and to possible presence of thin silica layers within the forging. For this reason it is not necessary now to prewarm the Cherokee Ho. 1 uait if the field is at 75F or above. Of course, Arapahoe No. 1 and NS. 3 and Zual Ho. 1 have net had the prewaraing requirement. We are now in a position where we can determine if the subject turbinegenerator sets could be taken off of the field prewaraing requirement by the use of sonic tasting sad by trepanning.. Elaboratffiggjg^if thin silica inclusions were present in your present rotor, the flexing^H^K. rotor would now have opened these areas up so that they would be readily eflHjpid on sonic testing. By means of trepanning into the field poles or coxgpifllllng, we eaa obtain a sample to check the actual transition ~ temperature of the metal in the field forging. These tests could indicate any one of the following three recommended steps: 1. To remove this particular field from the list of those fields for which we recommend prewaraing before bringing to speed. 2. We would recommend that the field be kept on the prewaning procedure. WAD00038 GENERAL^ ELECTRIC Mr. A. A. Woodward -2- March 24, 1958 3. If sonic indications have increased very appreciably and it is not possible to bore then out or trepan them out, we night recom mend no further use of this field. (I aight add that in this field re-examining prograa that we have found but one field in the third category.) We are now in a position with technicians to aake sonic tests and do trepan ning operations in the field in your plant. The present rates are as follows: Sonic Test Equipawnt - $30 per day plus transportation expense to and froa job site. (Usual tiae for : cheeking field - one day.) Factory Sonic Technician - $12 per hour straight tine rate, $18 per hour tine and one-half rate, $24 per hour double tine rate, plus travel and living expenses. (Usual tiae required - one day at job plus one day each way for transportation.) Trepanning Equipment $100 per week or any fraction thereof plus transportation. (Usual tine 5 to 6 days.) Trepanning Expert District technician is available out of our San Francisco office and his rate would be $12 per hour straight tine plus travel and living expenses. (Usual tine required - 6 to 7 days.) In spltsgjjy. the above comments, I would like to recommend preheating the fields, eapeetnlly on larger dianeter fields, for the benefits derived from protecting the insulation from so much abrasive action when the unit is at speed due to coil expansion. If you should desire more copies of the paper I left with you - Why Do Generator Rotors Burst?. GER-1462, please let me know and I will obtain them for you. Very truly yours, WAD00039 CHMc:jm C. H. McCabe Manager - Installation & Service cc: Mr. W. S Pullen - Denver Engineering - Turbines Mr. M. I Cleveland - Sehenectadv