8031086423 Orbit Reference

Steve’s Steve’s Handy Guide to Orbits By Steven M. Schultheis, P.E. Houston, Texas U.S..

Basics ! The "lots usually sho# $ revolutions. %ro& 'ey"hasor dot to 'ey"hasor dot is one revolution. !  nor&al orbit should be sli(htly sli (htly elli"tical #ith one 'ey"hasor dot, and lo# vibration level. ! )istorted, or t#isted orbits are usually due either to rubs or to runout. ! Multi"le 'ey"hasor dots indicate a subsynchronous vibration. ! ll the "lots "resented are un*iltered and unco&"ensated. ! + live in the U.S.. so all units are &il "". Multi"ly &y units by -. *or &icrons ie / &il ""0-. &icron

+nstabilities ! The *irst one is a 1.234 *re5uency co&"onent due to an aero instability in a co&"ressor. ! The second is a very lo# level instability due to oil #hirl on a &otor #ith "lain 6ournal bearin(s. ! The third is another aero instability in a co&"ressor. ! The last one is actually due to sur(e, notice the #ay *ro& revolution to revolution the a&"litude chan(es drastically.

ero +nstability

7o# level oil #hirl

ero +nstability

8o&"ressor Sur(e

8asin( 9ibration Orbit ! The next one is a casin( vibration orbit *ro& an +) %an. O:, it is 'inda *u;;y, but you can see that the &otion is "ri&arily vertical, and the a&"litude is "retty hi(h at 1.- i"s4 i&"eller eye seal rub in a co&"ressor induced by unbalance.

=ubs continued ! The sixth sho#s hi(h vibration (oin( throu(h the critical a*ter a rub induced bo# causes the turbine to tri" o** line. ! The seventh sho#s a rub induced bo# on a turbine durin( startu" due to i&"ro"er #ar& u". Most li'ely rubbin( on the hi(h  "ressure "ac'in(.

=ub durin( thrust  bearin( *ailure.

=ub on /st sta(e #heel #hen the dia"hra(& bro'e loose and &oved into contact.

/>4 rub due to eye seal contact. The s5ui((ly trace is due to electrical noise. ?otice t#o distinct sets o* 'ey"hasor dots indicatin( t#o vibration cycles  "er revolution, or />4.

Orbit plots at the 1500 cpm critical speed of the turbine during trip due to rub induced bow. Vibration amplitudes are 9 mil pp on the outboard and 8 mil pp on the inboard.

Outboard

+nboard

=ub induced bo# in a turbine

=unout ! Scratches, nic's, din(s, &a(netic s"ots, chro&e, and other sur*ace irre(ularities a**ect the "roxi&ity si(nal and cause noise errors. ! The *irst one is a "u&" #here + installed te&"orary  "robes on an untreated sur*ace. The orbit #as not &uch use, but the bode "lots, s"ectru&s, an  "osition "lots hel"ed dia(nose the "roble&. ! The next t#o "lots sho# very distinct scratches on the sha*t sur*ace.

Hi(h runout level on sha*t &a'es un*iltered orbit &eanin(less