Document 5kb2mrzbJmDjjqy1YkeppJ3zV

How Scale Formation Ruptures Metal CLEAN BOILER SURFACE, Mt, absorbs littla heat, posses most on to wotar. As scale builds up, right, picture changes SCALE COATINO forces Steel to absorb Increasing amount of heat, ond so tubo metal weakens and softens under temperature SCAll BUILO-UP, uncontrolled, in o firotube boiler, can leod o bulge like this one lets go, It touches off a violent exploslofc. to bagging and bulging like (Ke extreme cote above. Once Today, groper water treatment tools con positively proven! I; DANGER! Boiler Scale At Work RUPTURE Of METAL from too high o local lemperolure. obove, represents the final sioge In domage from uncontrolled sealo Sensible, fasting control of boiler scale requires a background of cauios, cures. Here's first of 3-part series to give you these data By PAUL BRINDISI, Chemfari fnffinecr, Cairo taboretorf** Mucn op your ability to acquire end maintain the best possible internel conditions for your boiler depends on how successful you are in staving off scale formation. First, you need to he familiar with how -scale forms, and specifically how it pertains to your par* ticolar boiler design and operation. And what is even more Important, you must then conscientiously enforce Iho proper steps to prevent scale formation. Rarely ever do KU-or-raist schemes produce a satisfying or lasting solution. Nor can slipshod supervision in sure favorable results. In fact, the leu you leave to mere chance and the more you set up controls over the physical and chemical factors governing scale deposits, the surer you are of preventing scale boihl-up. But lei's get down to coses. What are these factors? How do they influence scole formation? What effeci do they hove on boiler operation? What must you do to remove scale? Here are the pertinent onswera, whoso details will follow in later articles. factors. Hardness bestows the scale* forming property on water. It consists of the calcium and magnesium com* pouods contained in a water. Except for felting rein, all natural waters possess hardness to some degree. And rain water in making its course over and through the soil absorbs mineral salts to give it hardness. The amount of solids it absorbs depends on (!) chemical composition of the esrlh'a strata in any one particular locale (2) ease with which its constituents are apt to enter Into solution. As a rule, the longer water remains In intimoie contact with the ground, the more minerals it dls* solves. Subterranean waters, therefore, generally carry more dissolved solids -than surface waters. Since calcium sod. magnesium salts are quite soluble, it follows that underground waters usually possess higher hardness content than surface waters. We con roughly classify mountain. streams as having from a little below : 10 ppm to 60 ppm of hardness (**. CaCO). Surface supplies fall wilhia s 50-160 ppm range, and well waters from 150 an to nearly 2000 parts. Sea water, having hardnesses that run well up iato . the thousands, is ruled out as not leas' ible for boiler feedwater use. Calcium is most always the largest single mineral element found in naturil' waters. It usually predominates over magnesium by 2 or 3 to l. Together, as total hardness, they constitute the big ger group of dissolved solids in notursJ; waters. They appear most frequently 94 ENGINEERING AND MANAOEMENT SECTION sown In the form of bicarbonates, sulfates nd chlorides, and generally in this or der of greatness.' A fair amount of sim ilar sodium salts will also be included. A small ta a goodly portion of silica will most always be present. Other dis solved Solids, such as the nitrates of cal cium and magnesium along with com pounds of iron and manganese a well i alumina, normally appear in much lesser proportions. Still more minerals are contained, but their minute quanti ties bear no Influence on scale develop ment. *<ol formation. Your row water asy look crystal dear and be quite lor drinking ond other purposes, et with (he above-mentioned mineral mpuritice it is sure to be for from ideal tor your boiler. Why so? Because your oiler Is of itself helpless to cope with the disposal of these chemicals. While the wotcr is distilling off as virtually a pure vapor, some dissolved solids are continually precipitating out of solution. Left untreated, they go on to accumu late to damaging proportions, photos, right. Unless eided-by chemical means, no amount of blowdown will dislodge these deposits once they attach them selves on the boiler metal. This scale-forming process occurring in a boiler can be likened to a snowfall. The crystals first alight sparsely, then with greater number and become inter linked, soon to blanket the whole of <hc affected area, and eventually pock into a thick foyer. With scale, however, the result more often is a dense, hard, very adherent incrustation that defies either mechanics! or chemical removal. While these physical traits are typi cal of scale in general, the chemical composition differs with eaeh esse. All chemical components of scale are poor conductors ol heat. Their relative pro portions, and hence the texture of the composite, determine how much re sistance the scale offers to the transfer of furnace heal to the water. The sili cates, for example, have a greeter in sulating effect than the sulfates, ond the sulfates more than the carbonates. Operating Troubles. By far the worst damage scale inflicts is the -rupture of boiler tubes, photos' right, with the heavy loss o( production, time, labor and money their replacement entallo. Let us consider a segment of boiler tube, and with the aid of the three sketches see how its failure occurs. Just like any other beating utensil, the metol tube acts as a container only. It merely serves as a medium ol trans fer. It won't be victimised by the heat opplied as long as it can pass'the heoi JANUARY 1MJ ENGINEERING AND MANAOEMENT SECTION as