Document peV35mgv6rOBLmGMQXkayQGZX

for Long Service By STEVS HONKA Auociote Editor Round Glass Lucs omen ceramics, gloss U'{j^ Gloss` th. in, * mostly above wa.t.o..r...l.i.n. e. ; " ,',<'0k, "l,h ' 0 ` Pint wi.h sChhuot i.o. il*tZoo ond ,S. bottom cocks ,,la.. 6TMki does not deform before failure.' tujjg lures only from tensile ilressei,1^^ from shear or compression. Stretnljg curve is straight line lo the brlu&a point. Class has high degree of "notdHgl sUSvity." Tiny surface scratches, briST or Imperfections cause failure, .'33 carelul when handling gage gtfff Keep them in wrapper until res'dj^ Install. If you must put ibero'.'jfcjr place on soft, clean surfaces. Gloss can be beat-lreoted to rauejM endurance limit. This is fcnowi/Sgl "tempering." First, glass tcmpcFifiM' is raised high, then it's chilled.*pUl sets up residual stresses that are ia^ in interior and compressive at luftt And it's at surface where tension qkdj tiaru. Tempering also tends to tUj* harmful effects of surface bruisqfta fiyrMlco, protecting gloss from stoam end - turns opaque before failure I. u..d lo, blowVi,nlgyeidolw'n l,llhm."Ollho.,' Cut gloti to right length by rcvolv Ing between cutter* until It break* A1 R|,oTMm ' bn*."bl<g>lwa.s0,Ul,hb."rcokpSenTpcolTMck,. Ploce top washer, and then nut* (rot ^ hown); bottom washer; then Install PL------------scratches. Bui tubular gage glium* not as "adaptable'' to tempering.sijjl glasses. "<Rmove old gosket but don't scrape Corrosion is tough on gage glauiffi ,PO,, ^ ^'nl IU,*0Ce * ff0 caused by alkalinity and teropeniw 'Most corrosion (thinning) on labile1 glasses is sbovo water lino at upperbSj Here steam condenses and contmutSij flows down glass, eroding It. Bsjj| water with pH of 11.5, for ezsinpA, attacks glass 30 times faster thso vtgj with pH of 8.5. That shows importiwj of low pH if you have gltii-thiojjg problem. Rate of attack from lemf^S lure increases 100 limes from 26Sluj. 500 F. Solution then U to use flat |)M protected by mica so water does.lM contact glass. (wj Of course, water in gage is ww than vraler in boiler. Some condcnijt^ formed in boiler connection above i*Q flows into gage end lowers alVsliw^ This condensate dissolves some silitlil glass because of decomposition. Silica content Increases as cww*fj| sate flows down over glass. Bote of rosion below water level depends^ silica remaining in gsge water. R*,,e:Jv water attack above water level is letfAi distance increases from top end of Wa to bottom. Boiler water, not treated^ Add grophlle to washer so nut does not twin gloss; hand lighten only 0 Heot slowly by blowing steam al fop. v Open cocks from floor; close d3ln silica removal, corrodes glass. ' For over 300 psi. t'a best to use :._s gfasi, protected with mica. Pfe*"lJ| limits for tubular glass decrease glass length. Ruckling stress is ih*! K.1.hew gosket, mica, new clean suit of eccentric column loading- ;!, ''V^A.j^Oloti, another gasket; place clomps Flat Glass On Htcn-PRC&sunr: boilers above 1000 psi, there have been many costly gage* glass failures running into thousands oi dollars. But fault-has been from gage design, as well as from method of in* stalling glass, rough handling and gloss Remove clomps, glass gaskets, mica. Graphite the threads, run them down imperfections. At Corning Glass Works, I saw a nail driven into wood with a flat glass. This is possible because high residual stresses push out against the outside high com* prcsslve*stress, which was set by tem* pering. Here are failure causes, ways to prevent: " ' (I) Never reuse gage glasses. (2) Use special' glasses only for high-ternperature service. (3) Under extreme pressure, gage metal tends to bulge out, so gage bends if designed poorly--starts s crack because gloss won't bend. (4) Scraping gasket off metal raises burr --causing high unit loading. Always polish gage surfaces perfectly smooth. Polish surface perfectly smooth or the tiny high spots wilt couso failuro (5) Numerous scrapings to remare gaskets create high end low spots. Level old surfaces. (6) Pulling up unevenly on bolts loads glass unevenly. (7) At* bestos is "lumpy" In gasket, causing high spots. Use only best gasket mate* rial. (8) Many foflurei occur on high pres* aurea when starting up because glass was not heated gradually. Don't open gage cocks until new glass has chance to heot by conduction. Then oraek top* cock only. Alto, cool down slowly. (9) Don't blow down oftener then needed. (10) Use two vstves for blowing down. Keep one throttled for slow flow through glass, blow with other valve only. (II) Lubricate contact surfaces of glass with molybdenum disulfide only. This does not crystallize, allows travel between glass and fitting. (12) Don't use cover piste if ft has permanent d* flection, il it's of poor design, or if clsmping-device design is poor. (13) Mice discoloration means that mica has failed end water contacts glass. Don't wait for glass to fail--change it. High pressures and temperatures In newer boilers (oround 2000 psi) briog new problems. Fist glasses ore strength* ened by tempering, but residual stresses or strain set up may release st high Glass mustn't touch metol. Use only molybdenum disulfide on high temp temperatures. Over long periods, glass loses much strength that was added by tempering. So when ordering glass, con sider pressure and temperature. PUNT OPERATION AND MAINTENANCE SECTION PlANf OPERATION AND MAINTENANCE SECTION