Document pervO6gRVvKrMbB75beyxbVpa

FILE NAME: Philip Carey (PC) DATE: 1972 Feb 1 DOC#: PC039 DOCUMENT DESCRIPTION: Patent - Corrosion-Inhibiting Thermal Insulation for Stainless Steel United States Patent Mueller US) 3 ,6 3 9 ,2 7 6 145J F e b . 1 , 1 9 7 2 1541 CORROSlON-INHiBITlNG THERMAL INSULATION FOR STAINLESS STEEL (72) Inventar Arttor P. Mstote, Cmcinasti, Ohio 1731 Atognee: Parates Ctrpraatom, Ciftcfamati, Ohio 122] Fikd: Nev. 4,1*7 (21) AppI.No.: B6J74 ffilunn itlf T 1tn>t1irt%iinm 163 J Continuation-m-pert of Ser. No. M6391, Jely 31, 1969,abanooed. (52| UJ5.CL......................,,...... 252/42,106/286,161/170, 161/193, 161/205,260/29.7 P. 260/29.7 R 151] IuLCL..............C4b 43/64, C04b 35/16, C04b 43/02 158] Heid of Search................252/62; 106/286; 260/29.7 8. 260/29.7 P, 29.7 K; 161/170.205,193 156) 2,625.512 2,903,409 3,043,790 3,103,254 3.169,927 3,244,632 3.383,230 SeferHKU O 4 UNITED STATES PATENTS 1/1953 9/1959 7/1962 9/1963 2/1965 4/1966 5/1968 Powell....................................252/62 Morse............................. --252/62 X Sanders...............................260/29 7 Sledman.................................181/33 Matsch...................................252/62 Schuht et ai.............................252/62 Streib et al............................106/286 3,450347 3322,067 3323/385 6/1969 7/1970 1/1970 Samsetai...... ............ - ..... 252/62 X MacArthur........................ 252/62 X Shannon................................ 252/62 Primary E u w iv r-H in iM Aiwher Attorney--Mclvihe, Scramer. Faster A Hoffman {57] abst&a c t Molded thermal msutatioa material for we is comert with awtstemtic stainless steel chemical-processing equipment, to inhibit Areas corroaioa crocking thereof, consists of at least 60 percent by weight of oetoiar expanded perthe, bonded by a dried, inorganic, water rotofcfe binder. The binder com oti of a a&a/or proportion of a mixture of sodium wbcstc and potatourn tUc*tc and a mfcor proportion of tedium hexametapbosphate, and the molecular retioof (he silica to the al kaline oxide is at least 3.6 to 1.0. The potassium stfacale cos sets of at least about 40 percent, by dry weight, of the total sSkatc in the dried binder, and the total binder constitutes at least about 20 percent, by weight, of the total insulation com position. In the manufacture of the molded insulation, the mixture of perlite and the binder, in slightly damp condstioa, tt placed in the mold cavity and subjected to light molding pres sure, sufficient to compart the material into the exact configu ration of the mold cavity without expelling water from the mixture. The molded insulation is removed from the mold and oven dned at a temperature of about 250* F. 13 Claims, Ne Drawings 3,639,276 ... 1 2 CORROS10N4NHI3ITING TSEKMAL SWSULATKJW PtDR STAINLESS STEEL The composition the binder material which te effective to produce these highly desirable results consists chiefly of water CROSS-REFERENCE TO RELATED APPLICATION soluble alkali sttcate (a mixture of potassium and sodium), with a minor proportion of water soluble phosphate. This This application is a continuation-in-part of a copendis^ ap> three-component binder imparts 0 the molded partite junta plication, Set. No. 846,591, filed July 31, 196. now aban tkm improved properties in certain respects, that are not ob doned tainable with any angle component, but only with the com posite mixture in the range of proportions herein dadnmed. SUMMARY OF THE INVENTION Although the binder solution is a mixture, m terms of its effec This invention relates to a molded thermal irouiatica 10 tive bonding action in the molded perlite insulation, it must be material generally suitable for use in insulating heated indut- regarded as a single binder material, specifically a phoaphate- trial processing equipment, including petroleum-cracking modified soluble alkali sdicate, which becomes substwrtiafiy towers, stills, chemical reaction vessels, boilers, storage tanks insoluble upon simple drymg of the molded perlite and binder and piping having surface temperatures as high as 1,300* F. IS composition. The molded insulation may be in the form of blocks or slabs, A further object of this invention is to produce from esStdar or hemicyhndrica! pipe covering sections. expanded perlite and the soluble alkali silicate-phosphate Austenitic stainless steels are used extensively for the fabri binder a precision-molded thermal insulation by a simple, cation of processing equipment in the petroleum, chemical, direct molding process. The method involves pressure com and soap and detergent industries because of their excellent 20 paction of a loose mixture o f the expanded perlite and a minor resistance to chemical attack. Austenitic stain tm steel is proportion of a selected inorganic fiber, previously moistened defined as a chromium-iron alloy to which sufficient nickel with a predetermined amount of the alkali silicate-phosphate has been added to retain the austenitic phase (solid solution of solution, without expulsion of water from the mold, followed the alloying elements in face-centered cubic iron). A typical by merely drying the molded piece. When the new insutatioa analysis of one type of such stainless steel shows 179 chrnnu- 25 is thus produced it is found dial the finished, dried, molded um, 129 nickel and 2.39 molybdenum. product has substantially the exact shape and dimenskmf of However, austenitic stainless steel has one serious weak the mold cavity m which it was formed The shrinkage and ness, in that it is subject to stress corrosion cracking under cer tain conditions; and this has caused many equipment failures ^ with resultant high cost for equipment repairs or replacement, warpage of the molded product during drying are negligible, therefore the insulation need not be molded oversize, and can be used without requiring any machining to specified finished and for loss of process production It has been well established dimensions and provides an exact fit for the piping or other that the conditions which tend to induce stress corrosion surface on which it is to be installed. It is a special advantage cracking are: ( I ) the presence of stress in the metal, (2 ) the o f the process (hat no ceramic firing or high-temperature fur presence of moisture on the metal surface, (3) the presence of 35 nace treatment of the molded product is needed to render the chlorides in solution, and (4) a temperature range generally of binder effective, since this is accomplished by simply 50* to 200" C. (22* to 392* F.)V Dana. Stress Corrosion evaporating the water content at relatively low temperature. Cracking or Insulated Austenitic Stainless Steel. ASTM Bul~ trim, Oct 1957 ASTM STP No. 264, Stress Corrosion Further objects of this invention are to provide a molded thermal insulation for the temperature range up to 1.300* F., Cracking of Austenitic Chromium-Nickel Stainlew Sleek, 40 that it hard, strong, and resistant to mechanical abrasion 1960 Ashbaugh, External Stress Corrosion Cracking of Stain stresses; that is of low density and has high-thermal-insutatioa less Steel Under Thermal Insulation, Material! Protection, efficiency, that is resistant to deterioration and structural dis May 1965. Thus, thermal insulation systems when installed on stainless integration by absorbed water, even at steam temperatures; and that can be produced at a low cost. steel surfaces exposed to environments containing both *- h is a special advantage of this alkali silicate-phosphate chlorides and moisture may act as collecting media, trans binder composition that it is entirety inorganic, and thus the migrating and concentrating chlorides on the heated metal perlite-binder combination is not appreciably affected in surface, thereby inducing stress corrosion cracking. strength by deterioration in the temperature range from This invention affords protection against stress corrosion 25O-40O* F., in which range organic binders are largely which has two phases: first, the insulation itself is inhibited destroyed and lose most of their bonding strength. against the corrosion-inducing effect of any trace amount of Expanded perlite has previously been used in the manufac chloride ion which may be present therein as a contaminant of ture of preformed (molded) thermal insulations for industrial the materials of its composition. Beyond that, the binder used use on surfaces in the general temperature range for which the provides a continuing inhibiting effect, after the insulation has ^ product of the present invention is suitable. In particular, been installed upon a stainless steel surface, that prevents the reference is made to U.S Put. No. 2,884,380, issued Apr. 28, ttrcss-corrosion-inducmg effects of any concentration of 1959 to Cook, Fleming end Heilman, the patented product chloride ions from environmental sources which may gain ac having cellular expanded perlite as its majot ingredient, with a cess to the stainless steel, as from a marine atmosphere, or composite binder. The primary binder is the inorganic from chloride-containing chemicals used in the plant mineral. Bentonite Clay, and the secondary binder is an or processes. ganic material selected from the group: emulsified asphalt, With the foregoing considerations in mind, it is the principal polyvinyl acetate, polyvinyl alcohol, acrylic polymers, starch object of this invention to provide a molded thermal insula and carboxymethyl cellulose. tion, composed predominantly of finely divided, cellular ex Reference alto is made to U.S. P at No. 3,408,316, issued panded perlite, bonded into monolithic form o f prociae dimen- 6S Oct. 29. 1968 to Mueller and Asher, which also relates to a siont by an inorganic, water-soluble binder This binder is of perlite insulation made with a composite mineral-organic such composition that the molded insulation is not only self- binder. The mineral is Bentonite Clay and the organic binder inhibited, but further, makes available to the surface of the includes a low. and StaMe-viscotity modified *trch and a stainless steel with which the insulation k in contact, an in phenol-formaldehyde thermosetting resin. This patent also hibiting film of soluble silicate-phosphate that prevents the 70 gives detailed information regarding the chemical and physi strew corrosion-inducing action of chloride ion from occur cal characteristics of raw perlite, deposits of perlite ore of ring, by transmigration when moisture is present. This new suitable quality in the Uniteid States, pulverization of raw per corrosion-inhibiting insulation may of course abo be installed lite to proper sieve analysis before expanding treatment, con on heated metal surfaces other than austenitic Stainless steel ditions of the expanding process, and the physical charac with satisfactory results. 73 teristics of expanded perlite. 3,639,276 3 4 The perlite insulation products of the above-reference Expanded perlite within the limits of the following specifica patents have no corrosion-inhibiting effect when installed on a stainless steel surface All thermal insulating materials contain tions for sieve analysis has been found entirely suitable for the manufacture of the new insulation. soluble chlorides in varying amounts, up to 1.000 parts per million, and these patented perlite insulations may contain 5 Percent retained by vottune trace amounts of chlorides, generally in the range of 50 to 170 ASTM kturttWd Mi*vf No Mm Mu p p m (parts per million). Further, neither the expanded per lite nor any of the binder materials disclosed in these patents ha* a specific corrosion-inhibiting effect when an excessive concentration of soluble chloride is present on the stainless 10 steel surface. 20 VI SO 100 100 u t v* 3 IS ts n 43 m 2 $ 5 it DETAILED DESCRIPTION OF THE INVENTION This invention will be described by presenting two typical 15 Thus, the expanded perlite used is characterized by particle compositions, one of which (I ) contains asbestos fiber and the size grading such that from 60 percent to 90 percent by other (II) contains no asbestos fiber, but does contain as a fibrous reinforcement a small amount of fine glass fiber m the volume passes the No. 20 test sieve and is retained on the No 50 test sieve form of chopped, spun glass roving. The various criteria used In the composition of the silicate-phosphate binder solution in the selection of the ingredients, the method of preparing the 20 it has been found that it is necessary to use alkali silicates hav hinder solution, the manner of mixing the composition and the ing a high-molecular ratio of silica to alkali oxides. This ratio molding of the end product are described in detail Thereafter should be at least 3.6 to 1.0. If the alkali content is greater the preferred ranges of compositions, both with and without than this, it exerts too much fluxing action on the perlite parti asbestos, and broad ranges satisfactory for certain purposes cles and causes fusion and failure of the molded insulation at \m1I also be set forth Finally, some test results of the typical 25 temperatures much below the designed ! ,300 F. service limit. examples will be stated Also, the higher-alkali-content binder remains quite soluble Generally, it has been found desirable, and in some cases es after drying and the water resistance of the insulation is sential. to include in the molded perlite insulation a small greatly reduced. The composition of a typical example, above amount, up to about 10 percent by weight of a heat-resistant set forth, used a commercial sodium silicate solution having a inorganic fiber such as asbestos or fine fiber glass Asbestos 30 weight ratio of SiOj/NajO of 3.75 (molecular ratio 3.88) The fiber helps to prevent edge cracking of the molded perlite potassium silicate used had a weight ratio of 2.50 for SiO|/K,0 piece during drying and fine glass fibers have a similar effect, and a molecular ratio of 3.92. fine glass fibers, such as chopped spun roving, add toughness The water-soluble phosphate which is usee in the composite to the molded insulation and provide a mechanical reinforce hinder solution is preferably sodium hexametaphosphate, ment that tends to present the breaking apart of a piece that 35 ( NaP03)6 another phosphate which gives equivalent results is ha*, become cracked or otherwise damaged in handling In the so-called "glassy phosphate.*' a structurally similar some cases n may be desirable to produce the ness perlite in polyphosphate which has up to 21 phosphorus atoms per sulation as units of relatively small dimensions (insulating mole Other soluble phosphates such as sodium bricks) for special conditions of installation and where such pyrophosphate, and phosphoric acid, give unsatisfactory small pieces are to be produced the inorganic fiber may be 40 results omitted Confirming the advantages of the composite soluble sil icate-phosphate binder disclosed herein, it was found that T5 PiCAL EXAMPLE 1-COMPOSITION CONI AINING when sodium silicate was used alone as the binder for the per ASBESTOS lite insulation the molded pieces showed warping and cracking As a typical example of the practice of this invention, a 45 when dried, and the insulation did not meet the soaking heat molded thermal insulation has been produced having the fol test at 1,200" F. because the perlite fused at a temperature of low mg composition. about 1,100 F Perlite insulation bonded with a mixture of sodium and potassium silicates also showed warping and Pcrt.cn! v>fnjv Dr\ Heigh 50 cracking and was not serviceable at 1.200 F. The combina tion of the two alkali silicates plus sodium hex ametaphosphate, in the proportions disclosed herein, used as I puniteti pcritlc. hull, dcruit) 2 M h /cw 1 the perlite binder, produced an insulation that was free from h"* warping and cracking had very low shrinkage al 1,200* F. with SoHlum htitcatc e tfh i JUtMi 3 7 3 /1 O mIm Ic. uliiit'polMfch W eifh t r-ho 2 5 /1 0 S sjtum H tw m 0|>htA plM i(>iN j^ O ,ilt 1 3 55 noTtehnedsehnocryt atosbfeusstioosn,fiabnedr winasthseercvoicmepaobsleitiuopntsoer1v,3e0s0a*sFpecial 103 purpose, that of preventing edge cracking of the molded per 4 1 lite piece during drying. Long asbestos fiber if included in the S hort inioMlc sshevlok fib er 17W g rad e ) S u u-nc huiudK'nc polym er latex I Nauftftex 2752 > composition has been found objectionable because of its ten 4 4 60 dency to cause balling of the moistened perlite mixture, so J I that it does not compact uniformly in the mold, thus making T o u t 100 0 the molded insulation weak. An extremely short fiber grade such as Canadian Grade 7 does not have this objectionable ef CRITERIA WITH RESPECT TO THE INGREDIENTS fect, and does prevent edge cracking and makes the molded 65 insulation somewhat less brittle. For the manufacture of the new thermal insulation, an ex Any short fiber grade in the 7 Group of the Canadian panded cellular perlite of very low-bulk (loose fill) density, m (Quebec Asbestos Manufacturers' Association i.e., the range of 1.8 to 3.5 pounds per cubic foot is used The best Q.A.W.A.) Standard Classification may be used. Generally combination of properties of the finished molded insulation is the shortest grades. 7T or 7W, will be selected because of their obtained when the bulk density of the expanded perlite is in 70 low cost and easy workability in the perlite insulation mixture. the range of 2.0 to 2.5 pounds per cubic fool. The bulk density Another kind of short asbestos fiber that gives exceptionally can he maintained within this desired range by controlling the good results is short Amosite asbestos of fiber length sieve analysis of the pulverized raw perlite ore and the tem equivalent to that of the Canadian 7 grading perature and rate of heating of the perlite particles in the ex While the binder composition for the expanded perlite is pansion process 75 completely inorganic it may be desirable to include in the 3,639,276 S 6 composition a very small amount, in the range of 3 to 5 per easily airborne and thus earned into the hmgt and there cent by weight, of an organic material as a plasticizer for the become permanently embedded in the atvelar regions Withia molded insulation. For this purpose a synthetic rubberiike the human lung tissue, asbestos fibers are virtually indestructi latex dispersion such as styrene-butadiene polymer latex is ble and are not expelled or absorbed. The result in many cases suitable, and various other rubberiike polymer dispersions S is the lung disease termed "aebestosts.'' which often develops may be used. This very small amount of organic plasticizer eventually into lung cancer. Asbestos is is a special type of makes the dried molded perlite insulation leas brittle, and pheumoconiotii (dust ibirair of the hmg) and hat often been more resistant to the disintegrating effects of abrasion stresses, confused with silicosis. The effect of the embedded asbestos as in the tumble test. While the new perfhe insulation can be made completely from mineral and inorganic materials, the 10 fibers it to produce pulmonary fibrosis--scarring of the lung tissue--and progressive deterioration of the king function. preferred compositions with asbestos fiber (typical composi Many organizations ate attacking the asbestos problem, tion l> contain at least about 3 percent by weight of such an including the U.S. Public Health Service (HEW), Mount Sinai organic plasticizer. The compositions in which chopped spun School of Medicine (New York City), London School of Hy glass roving is used instead of asbestos fiber do not require any IS giene and Tropical Merhcine. American Medical Association, organic plasticizer, as m the formula of typical composition II. British Medical Research Council. New York Academy of TYPICAL EXAMPLE li-COMPOSITlON CONTAINING FINE CLASS FIBER 4 Sciences, American Cancer Society, several State Departtnents of Health, the International Association of Heat and Frost Insulators and Asbestos Workers, and several manufac As a second example of the practice of this invention, using 20 turers of asbestos-containing insulation products. In Great a perlite composition containing chopped spun glass roving as Britain, asbestos has been established as a compensable in the inorganic fiber, s molded thermal insulation was produced dustrial disease. Very recently, the Environmental Protection having the following compositions: Administration of New York City has act restrictive roles for h rrd f >c*nk. Dry wifiht feani* 25 ttihoensaaftecsopnrsatyruacptipolincastiitoens,otfoanpyreavsebnetstaoisr-cpoonlktaiitnioinagbiynsfuilnae asbestos fibers. E i p a tM ptrfat. bttk 2 3 16 fi Sudawoi Mfaca*. Mltcv/hPda rMto. 3 75/1 0 Referring to the composition o f typical example I of the new perlite insulation, the asbestos fiber content is very small, only T3 30 4.4 percent by weight, so that the hazard of fine airborne II* asbestos fibers being inhaled by insulation workmen is POlAMU MtkCBt. MhC*/p4Hah rM 2.3/1.0 Ssdwi ktiaifeti6plwphwU Ctwippc* ftat fo v f t," minimal With the composition of typical example II, which I4I 1* contains no asbestos, this hazard is completely eliminated. 40 The fibers of chopped spun glass roving are of much larger J |(K4 W" krtftb Tout 1000 35 diameter than asbestos fibrils and while they may caute tem porary irritation of the respiratory membranes if inhaled, they do not induce a pneumoconiosis nor cause permanent lung damage The other ingredients of the new perlite insulation- It will be noted that this composition contains no asbestos cellular expanded perlite, sodium and potassium silicates, and and no organic plasticizer material and is 100-percent inor 40 sodium hexametaphosphate--are likewise noninjurious to the ganic. human hing if fine particles of dust from the molded insulation When fine glass fibers are included the composition as a are inhaled. heat-resistant, inorganic reinforcement for the molded perlite insulation, chopped spun glass roving is selected as the most 43 suitable form of glass fiber for this purpose. The individual PREPARATION OF THE PRODUCT The preparation of the new modified silicate binder solution fibers of the roving are of very small diameter, in the range of is quite simple. The quantity of sodium hexametaphosphate to about 0.00036 to about 0.00039 inches, and have been spun provide the specified proportion in the binder formula is dis together into a roving and then chopped to a specified length. solved in water. To this solution is added, with agitation for It has been found advantageous to use a mixture of fiber 30 about 13 minutes, the specified quantity of sodium silicate, as lengths, generally in the range of K to Vi-inch length. Some solution. Then the specified quantity of potassium silicate, as chopped roving as short as one-eighth inch may be included, solution, is added with further agitation for about 3 minutes. If but it is less effective as mechanical reinforcement than fibers an organic plasticizer is to be included, as in example I, there the 14 to Mt-inch range. Some longer fibers, up to I inch in is then added to this mixture of soluble silicates tn d phosphate length, may also be included, but fibers longer than one-half S3 the specified quantity for a styrene-butadiene polymer latex, inch are more difficult to mix uniformly with the perlite and with further agitation for another 3 minutes. More water is binder and they tend to ball up and cause the mixture to com pact unevenly so that the product is less uniform in density and strength. HEALTH HAZARDS OF ASBESTOSX'ONTAININO PRODUCTS added to adjust the concentration of the binder solution for spraying, and the binder mixture is agitated for another 10 60 miInnupterso,dauncdinisgtthyepnicraeladexyafmarpuleseI. the short asbestos fiber and the expanded perlite were weighed and then thoroughly blended dry. This dry mixture was then sprayed with a mea During the past 10 years there has developed much new sured quantity of the binder solution, separately prepared, knowledge and. consequently, greatly increased concern re 65 containing the specified amounts of sodium silicate, potassium garding the health hazards to workers in the asbestos-produc silicate and sodium hexametaphosphate. The styrene-bu ing and consuming industries and to those who install or use tadiene polymer latex was also included in the hinder solution asbestos-containing products, that may result from the inhala for convenience in application. The moistened mixture of per tion of fine asbestos fibers into the lungs. Preventive measures lite, asbestos and binder was than further agitated and blended such as increased ventilation, dust suppression and removal 70 to complete the distribution of the binder solution over the from the working area, and the wearing of face mask respira surfaces of the perlite particles and fibers. The completed mix tors while fabricating and installing asbestos products such as ture, ready for molding, was a loose, bulky, granular mass that thermal insulations have substantially reduced this hazard. appeared to be slightly damp, but not visibly wet. The The individual crystalline fibril* of chrysolite asbestos sue moisture content was about 90 percent of the weight of dry extremely fine, about I millionth of an inch in diameter, are 75 tokds. 3,639,276 7 8 Typical example II was produced in exactly the (ante way, except that the asbestos fiber was omitted and the chopped spun glass roving was blended dry with the expanded perlite, also, the styrene-butadiene polymer latex was omitted from the binder solution. In malting the molded insulation the water content of the moistened perlite mixture (to be later removed by drying the molded piece) will be in the range of 0.8 to 1.1 times the weight of the dry solids and usually is between 0.9 to 1.0 times the weight of dry solids. . A weighed quantity of the slightly damp mixture was placed in a mold cavity and subjected to light molding premure, suffi THE BROAD RANGES cient to compact the loose material into a monolithic molded If it is desired to produce a molded perlite irmiUtioe having mass having the exact configuration of the mold cavity, but excellent ftress-corrotion-mhibitmg properties, tart not without expelling any water from the mold. The molded piece 15 requiring mechanical strength, water rcritunce or service was then removed from the mold, dried in an oven at a tem perature of about 250* F., and tested. The dried molded insu lation showed no shrinkage or warpage and had the exact dimensions of the mold cavity in which it was formed temperatures ns high as posicrsed by the insulation of the preferred compositions, this can he accomplished using asbestos-containing compositions within a somewhat broader range, as follows: GENERAL CONSIDERATIONS - wi t cow jw tue* Ns*> Dry *H)>I fercrM It has been found that particularly good results are obtained when the potassium silicate is at least half (50 percent) of the total soluble silicate in the binder composition. The sodium hesametaphosphate should be at least 20 percent by weight of the total silicates in the composite binder and may range from 20 to 40 percent, but preferably from 20 to 30 percent. To ob tain the optimum physical properties of the molded perlite in sulation the total amount of the composite silicate-phosphate binder should be at least 20 percent by weight o f the insulation composition. The dry solids content of the combined soluble silicate and phosphate binder materials in the binder solution is usually about 20 percent by weight The water-dispersed styrene-bu tadiene polymer latex, if used, is not included in this figure since this material does not function as a binder in the molded perlite insulation product. Preferably the new molded perlite insulation is produced at a density in the range of 10 to 12 pounds per cubic foot. It can be molded at higher density up to 14 pounds nth some sacri fice of thermal insulating efficiency, or as low as 9 pounds with somewhat lower mechanical strength. THE PREFERRED RANGES Referring to the composition of the above typical example I of the new perlite insulation, some variation in the proportion <Up--4nd porter. fe fc de--By 25 1 J .S f e f e . A. to d m m mfcfie a p t-- mm Mbcube Sodwm hewrene-- 4uwp--m Ife trt nhewlow fiber Styrene butadiene ptey-- r teln 30 mn *0 t 4 i 0 0 Mm n 14 18 6 i A molded perlite insulation having excellent stress-corro sion-inhibiting properties, but with somewhat lower capabili ties as to water resistance, mechanical strength and service 35 temperatures than possessed by the insulation product* of the preferred compositions, can be made using glass-fiber-rcm- forced compositions within a broader range, as follows. 0rond cooipoaitMMi Dry eight Percent 4 0 ---------------------------------------------------------------------------- Mm. Mm C-- andnd prrlnc. hulk 4en*My 1 I b J < 6 A A- *0 Tl Snrtn-- wtetme futaauwR -- c-- 3 1 S 19 Sttfeua ferhnmeuphtnp--tr Chipped apoofl gi.se* rtn^, ) 0 V ' bo 1" length 0 >0 of each of the components is permissible Optimum results arc TEST DATA obtained within the following preferred ranges: 50 When the molded perlite insulation products of the above Preferred rnmpuHwn typical examples I and II were tested, in comparison with the requirements of L'.S. Military Specification M1L-I-2781E for Or) weight Prrcewl Insulating Block, the following physical properties were shown. Mm- Mm . 55 Expanded perlite, fe ll denwty 2.0 to 2 3 tb./c. A. 69 n Sudiun Mhcefte 12 Pagc*HMR UlKMt 12 Sodium behtimeupfetapfeMe Short gdesitH fiber 4 4 * 60 St) *rnc-hwiiadaeoe poiymer label 3 4 Density, tt./ru. n..................... Flexural siren*tti (transverse modulus): The potassium silicate is preferably at least 40 percent of Dry, lbs. prraq. >o.................... W et. Ibo. per sq. In .......................... . the total weight of silicates in the binder competition. 65 It is ot course to be understood that within the above per K(Irrte eoeitnf heat for t hewn at M W *?.: cent ranges, if one ingredient is at the minimum or maximum Los* in wrkrhl. percent.............. of the range, then the percentages of the other ingredients U m a r ahrtnfcaae, peroeni............... Resistance to abrasion (Mrabk te), must be adjusted accordingly to total 100 percent. W rteht lorn, partent. Referring to the composition of the above typical example II 70 Alter H minutes........................ After SOm inutet.......................... (containing fine glass fibers instead of asbestos), optimum Water absorption, alter M houn Un- results are obtained within the following preferred ranges for mersten. prirent l>yweight. Water oisorption, after 2 hour boil- each of the ingredients. lf water Immersion, percent. Tn**> sample I H it. t t l gMntmaraUii M lb-I-77ftK MA maximum. 74.0 021 I times density. 44 awl (No require. mit.) IV a s ISA marimlm. in L l 2A martaenm. n o 4.0 M maximum . 0 10.0 as maximum. t i t t i l (No require- ment.) >*17 lo. Preferred compxmtMA n wtyc. Dry htipH N iccm 75 1The tret prrlinrii showed no UurUirei delrriot stk>M or physical dlelnuwratkui ot the moldrd (mulatto In UlU teat. Thermal conductivity measurements o f the insulation the perlite insulation redisaoivet or colloidally dispertes aa ex product of the above typical example I gave the following tremely small amount of the excess dried silicate-phtosphale values, in B.t u per hour per square foot per degree F. per binder between the perlite panicles and deposits a microscep- inch of thickness. icaily thin protective film on the surface of the metal. This film 5 contains the alkaline cations. Sodium, (Ns* ), Potassium. ( K* I C tHKh*ctrv tty X*) F. m m krN f. " 0.44 and the anions SiO ,_and PO,_. phis the dispersed sitics of die 5w rr. ywrf. ' as DM soluble silicates (SiO,). The excess binder maintains a reacr- voir, and the minute amounts withdrawn do not affect the ` A< would be expected from the fact that the insulation 10 bond strength of the mutation. products of example I and example II arc closely similar in ADDITIONAL PROPERTIES composition and nearly of the same density, the thermal con The new perlite insulation of this invention has quite ex-' ductivity values for example II are substantially identical with traordmary properties in respect to its behavior in the those of example I, within the normal phn or minus 5 percent presence of monture or liquid water. Thus, it is not water- reproducibility variation of thermal conductivity measure 15 repelient and water is readily absorbed and transmigrated ments on insulation materials for high-temperature service. within the molded insulation. Yet even after 24-hours immer The new perlite insulation of the above typical examples sion and when fully saturated with water the molded insulation was also tested for its corrosion-inducing potential by the test retains almost two-thirds o f its original dry flexural strength; methods of Military Specification MIL-l-24224 (Naval Ships even soaking wet the flexural strength still exceeds the Engineering Command of the Department of Defense) for 20 requirements of MIL-4-278 IE. Even more remarkable is its thermal insulations to be applied on stainless steel. The test behavior when immersed in boiling water. Thus, after more results showed that the new perlite insulation Is fully inhibited than 100 hours of such immersion, the test specimen was mill against inducing corrosion and meets all requirements of the intact, showed no evidence of structural disintegration, and above specification, with-an ample margin of safety. The test after drying to remove the absorbed water, was capable of giv method involves " wickmg" (transmigrating) of distilled, 25 ing satisfactory service as thermal insulation. Although all the deionized water through the insulation specimen in contact ingredients of the composite silicate-phosphate binder solu with a stressed, heated specimen of austenitic stainless steel tion were water soluble when applied to the perlite before for a period of 28 days, to concentrate any soluble salts at the molding, the binder after drying has become highly water-rc- surFfraocme othf ethaebmoveeurletshualttscoituilsdatphpearerebnyt itnhdautctthcernacekwinpge.rlite in 50 tpieturlmitet panardticreletasiunnsdaerstsreovnegreawndatepreresxipstoesnutreb.ond between the sulation has very low density; high-thermal-insulation efficien cy; adequate strength for handling and installation, whether dry or wet; good resistance to abrasion; high resistance to From the viewpoint of the effectiveness of the new perlite insulation, is exerting a positive corrosion-inhibiting effect on stainless steel, the fact that R readily absorbs and trans smtreurcsitounra, ladnidsihnatesgnraetgiloignibwlehecnorsruobsijoecntepdotteontbioailliwnghewn aatpepr liimed 35 tmhiagtrawtehsenmeoxiscteusrseiveis mcoonisstiudreereids padrevsaenntta,gaesoufsro. mThsipsilelnagsueroesf on stainless steel. water on the outer surface of the insulation or from steam Referring to the above "corrosion-potential" test of the in leaks, the transmigration of moisture through the insulation sulation, it has been proposed to accelerate this test and also will dissolve a sufficient amount of the excess soluble silicate simulate the conditions under which chloride ions from exter 40 and phosphate of the binder content, and transmit it to the nal sources, as well as from the substance of the insulation, metal surface to form the protective silicate-phosphate film concentrate on the surface of the metal. This is done by wing as the wicking test solution a positive, corro*ion-inducing ion, thereon that will inhibit the corrosive effects of any chloride ion concentration. namely, 1500 p.p.m. of sodium chloride, in the place of The invention having now been described in detail, and the deionized water. This test is run for 6 days and determines the 45 ranges of composition within which the improved corrosion- extent of any inhibiting effect against stress corrosion afforded inhibiting thermal insulation may be made having also been by the insulation. When tested in this way, the new perlite in set forth, the limitations intended are only those set forth in sulation showed that it afforded complete protection against the following claims. corrosion induced by the chloride ion under such conditions. The embodiments of the invention in which an exclusive It will of course be understood that in order to be effective 50 property or privilege is claimed are defined as follows: as a corrosion inhibitor the insulation must be installed so that 1. A molded thermal insulation consisting of at least 60 to it ts actually in contact with the stainless sleet. Transmigration about 75 percent by weight of finely divided, cellular ex of moisture will then supply sufficient soluble silicate and panded perlite having a bulk density in the range of about 1.1 phosphate from the insulation to the metal surface to produce to about 3.5 tb./cu. ft., bonded into a monolithic mass by a a protective Film; but if the configuration of the insulation is 53 dried, inorganic, water-soluble binder consisting of a major such that there are large voids with no contact, as with some proportion of a mixture of sodium silicate and potassium sil fittings, this may not occur.' icate and a lesser proportion of sodium hexametsphosphate, THEORY OF OPERATION said sodium bexametapbosphate being from about 20 to about 40 percent by weight of the total silicates in said binder com The results above described were unexpected and not fully 60 position, said soluble silicates each having a molecular ratio of understood. Presumably there may be some reaction between silica to alkaline oxide of at least 3.6 to 1.0, said potassium sil the soluble silicates and the surfaces of the perlite particles icate being at least 40 percent by dry weight of the total tU~ forming an insoluble or difficulty soluble compound, or icate in the dried binder, said composite binder being at least depositing a silica film at the interface, during the drying of about 20 percent by weight of he total insulation composition, the molded insulation. Another possible explanation might be 65 said dried composite binder constituting a reservoir of streaa- the reaction between the metaphosphate and part of the sodi corroeion-inhibiting compounds for en austenitic stainieK um oxide in the silicate solution to form an orthophosphate. steel surface on which said insulation is installed, whereby thereby increasing the silica/soda ratio and making the film moisture transmigrated through said insulation to said steal plelsasnaetaisoinlys sthoeluabcletu. aRl ebgeahradvleiosrs oofftthheemvoalldideidtypoerfliatneyinssuuclhatieoxn 70 sSu*rfVac-eadnedpPoOsits- tahneiroenosnaandflideri,scpoenrsteadinsinilgicKa,*SaiOndj,Nwah*icchatiisoenfs, confirms the superior results of the composite silicate- fective to inhibit strets-corrosioit cracking of said stainle phosphate binder. steel. The mechanism of the formation find maintenance of the 3. A stress-corosion-feihlbiting molded thermal insulation cncn'v.hivs'-inHihhinp ft'''- v*'. thy- `' - T * * < -w-w^ws -- " ' - . ;if - * -, ^ - i- V - . - - " '1- " % < ; ' 3 , 6 3 9 , 2 7 6 - _ n ' V 12 a bulk density in the range of about 1.8 toabout3J lb ^ c u .lti being of free flowing contistency and readily sprayabte for ep- fro about S to about U percent offsodium tiNcaie hating a fheatioa to said expanded perlnc, and said binder composi nsoieeular ratio of silica to odium oxide of at lea 3.6 to I JO, tion being a corrosion mb&ttor for austenitic stntntem steel from about 6 to about IS percent of potassium tikcate bavins . B arbees cm which the perlite insulation bonded therewith is a molecular ra t of (Sica to potassium oxide of at least 3.6 to 1.0. from about 3 to about 6 percect of lodium hexametaphosphase, from about 3 to about 6 pereeot, by weight I . A binder composition for a ptewure-molded mass of fine- 1y divided, ceUuter, expended perlite thermal insultting of short asbestos fiber bating a gradstkw r r nfnm inn to matartel, oootieang of a water solution of a mixture of sodium Croup 7 of the Canadian Standard Fiber Clwlfficintinei g and potassium silicates, said sakates cadi having a mofeewter (Q.A.M.A.), and up to 5 percent of a styrane-butadteite ratio of silica to alkalme oxide of at least 3.6 to I.O.andsodt- polymer latex as a plasticiser, said mixture of sibeatfs and twe hexametaphosphate disaoived in said mixed sttcaie solu sodium bexametapboaphate constituting a composite binder tion, mid potassium silicate being in the tm jt a t shout 40 to for said expanded perlite to bond the pardelca imd fiber* bite a about 60 percent of the local weight of tohtbte tificatas in the monolithic molded asms, said thermal insulating material i* bender composition, u id is showing no significant change from mold dimenskxis, having a amaler proportion than the soluble aheates, i t the range of tow density and higb-themssi-insulating efficiency in the tem about 20 to 30 percent of the total weight of said tMctues. said perature range from about 100* F. up to about 1,300 F., hav hinder solution containing abont 20 percent by weight of dis ing high flexural strength both dry and wet, and being highly solved solids, stud binder solution being of free flowing con resistant to structural deterioration by boiling water. 20 sistency and readily spreyable for application to said expanded 3. A stress-corrosion-inhibiting molded thermal loeuiation perlite, and said binder composition being a corrosion iehibi- for austenitic stainless steel, consisting of from about 63 to or for austenitic stainless steel surfaces on which the perlite about 70 percent by weight of cellular expanded partite having insulation bonded therewith is teetaScd. a bulk density m the range of about 2.0 to 2.3 8>./c*. f t , from 7. A binder composition for A pressure-molded mess of about I to about 12 percent, of sodium silicate having a 25 finely divided, cellular, expanded perlite therms! insulating molecular ratio of silica to sodium oxide of at least 3.6 to 1.0, material, ronsiatitig of a water solution of s mixture contamiag from about 8 to about 12 percent of potassium silicate having equal amounts by weight of sodium and potassium silicates, a molecular ratio of silica to potassium oxide of at tea 3.6 to said sodium silicate having a silica/soda weight ratio of about 1.0, from about 4 to about 3 percent of sodium hex- 3.73 to 1.0, said potassium silicate having s tilica/potasb ametaphosphate, from about 4 to about 5 percent of short ^0 weight ratio of about 2.30 to 1.0, and sodium hex asbestos fiber having a gradation conforming to Group 7 of ametaphosphate dissolved m said mixed silicate sotetion ia s the Canadian Standard Fiber Classification (Q.A.M.A.), and minor proportion of about 20 percent of the total dry weight from about 3 to about 4 percent of a styrene-butadiene o f said sahestet, said binder solution containing about 20 per polymer latex as a plasticizer, said mixture of silicates and cent by weight of dissolved solids, said binder sotetion being of sodium hexameuphosphalc being st least about 20 percent by free flowing consistency and readily tprayabie for application weight of the total composition and constituting a composite to said expanded perlite, and u id binder composition being a binder for said expanded perlite to bond the particles snd corrosion inhibitor for austenitic s inless steel surfaces oa fibers into s monolithic molded mass, said thermal insulating which the perlite insulation bonded therewith is installed. material showing no significant change from mold dimensions, ^ S. A molded thermal insulation according to claim 1, con having a density in the range of 10 to 12 ib./cu. f t and bigb- taining as mechanical reinforcement for the asonoiithic mast thermal-insulation efficiency in the temperature range from of expanded perlite and binder a minor proportion of a beat- about 100 F. up to about 1,300* F., having high flexural resistant. inorganic fiber, selected from the class consisting of strength both dry and wet, and being highly resistant to struc short asbestos fiber and chopped spun glass fiber roving. tural deterioration by boiling water, 45 9. A molded thermal insuUtkxi according to claim 3, in 4. A stress-corrosion-inhibiting molded thermal insulation which said hext-iesistxnt inorganic fiber consists of up to 6 for austenitic stainless steel consisting of about 67.8 percent percent by weight of short asbestos fiber having a gradation by weight of finely divided, cellular, expanded perlite having a conforming to Group 7 of the Canadian Standard Fiber Clas bulk density in the range of about 2.0 to 2.5 pounds per cubic sification (QAM .A). foot, about 10.3 percent of sodium silicate binder having a ail- 30 16. A molded thermal insulation according to claim 8, in ica/ioda weight ratio of about 3.73 to 1.0, about 10.3 percent which said heat-resistant inorganic fiber consists of up to 10 of potassium silicate binder having a tilica/potadi weight ratio, percent by weight of chopped spun glass roving of from one- of about 2.30 to 1.0, about 4.1 percent of sodium he*, eighth inch to 1 inch length. ametaphosphate, about 4.4 percent of 7W Grade short I t . A streas-corrosion-inhibiting molded thermal uxsulslion amoaite asbestos fiber, equivalent in gradation to Group 7 of 35 for austenitic stainless steel, consisting of from about 60 to the Candian Standard Fiber Classification (Q.A.M.A), and about 73 percent by weight of cellular expanded perlite having about 3,1 percent of a styrene-butadiene polymer latex as a n bulk density in the range of about 1.8 to about 3.5 Ib./cu. ft., plasticizer, said composition being bonded into a monolithic front about 5 to about 15 percent by dry weight of sodium tit mam, said thermal insulation showing no significant change le*It having a molecular ratio of silica to sodium oxide of at from mold dimensions, having a density of about 1 1 .6 pounds least 3.6 to 1.0, from about 5 to about IS percent by dry .weight of potassium silicate having a molecular nltio of silica per cubic foot, having high-thermaMnsulatfatg efficiency in the temperature range from about 100* F. up to about 1,300 F,, to potassium oxide of at least 3.6 to 1.0, from about 3 to about having high flexural strength, both dry and wet, and being 8 percent of sodium hexametaphosphate, and up to 10 percent of chopped xpun glasx roving of te-inch to I-inch length m a highly resistant to structural deterioratioa by boiling water. heat-rextstam, inorganic fibrous reinforcement, said mixture 5. A binder composition for a pressure-molded mass of fine of silicates and sodium hexametaphosphate constituting a ly divided, cellular, expanded perlite thermal insulating composite binder for u id expanded perlite to bond the parti material, consisting of a nuyoi'proportion of a mixture of sodi cles and fibers Into a monolithic molded mass, said molded um silicate and potassium silicate in water solution, and a thermal insulation showing no significant change from mold lesser proportion of sodium hexametaphosphate dissolved in 70 dimension, having low density and high-thermal-insulating ef said silicate solution, said sodium hexametaphosphate being ficiency in the temperature range from about 100* F. up to about 20 to about 40 percent by weight of the total silicates te about 1,300* F.. having high flexural strength both dry and said binder composition, said soluble silicates each having a wet, end being highly resistant to structural deterioration by molecular ratio of silica to alkaline oxide of si tea 3.6 to 1.0, boiling water. said potamium tiheste feeinp st least um, j- *'.. .....r 1-- ** f ' 3,639,276 13 ,, 14 bout 70 percent by weight of cellular expanded perlite, hav ing bulk density in the range of about 2.0 to 2.S ib./cu. f t . from about 8 to about 12 percent o f sodium silicate having a molecular ratio of silica to sodium oxide of at least 3.6 to 1.0, from about 8 to about 12 percent of potassium silicate having 5 a molecular ratio of silica to potassium oxide of at least 3.6 to 1.0, from about 4 to about 6 percent of sodium hex* metaphosphate, and from about 4 to about 8 percent of chopped spun glass roving o f H-inch to V4-*nch length as a heat.reMstant, inorganic fibrous reinforcement, said mixture 10 of silicates and sodium hexametapbosphate being at least about 20 percent by weight of the total composition and con* stituting a composite binder for said expended perlite bond the particles and fibers into a monolithic molded macs, said 15 molded thermal insulation showing no significant change from mold dimensions, having a density in the range of 10 to 12 lb./cu. ft. rind high thermal insulating efficiency in the tem perature range from about 100* F. up to about 1.300* F., hav ing high flexural strength both dry and wet, and being highly 20 resistant to structural deterioration by boiling water. 13. A rtre*MiTOsion-inhibiting molded thermal insulation for austenitic stainless steel consisting of about 67.3 percent by weight of finely divided, cellular, expended perlite having a bulk density in the range of about 2.0 to 2.3 pounds per cubic foot, about 1 1.0 percent o f sodium silicate binder having a sMica/soda weight ratio of about 3.73 to 1.0, about 1 1.0 percent o f potassium silicate binder having a rihea/potash weight ratio o f about 2.30 to 1.0, about 4.5 percent of odium hexametaphoephate, about 4.0 percent of chopped spun glass rov ing of H-fctch length and about 2.0 percent of chopped spun glass roving of W-inch length at heat-resistant, inorganic fibrous reinforcement, said composition being bonded into a monolithic mass by said composite silicate binder, said molded thermal insulation showing no significant change from mold dimensions, having a density of about 11.8 pounds per cubic foot, baling high thermal insulating efficiency in the temperature range from about 100* F. up to about 1.300* F,, having high flexural strength both dry and wet, and being highly resistant to structural deterioration by boiling water. 25 30 35 40 45 SO 55 60 65 70