I
Corrosion Control with
38
I N D U S T R I A L AND ENGINEERING C H E M I S T R Y
The pressure pipe installotion at left, fabricated from Hetron and believed to bc the largest of
g[urs-runfarced polyustn in the m d d , cantaim marc than 12,OOOfeet in diameters 2 to 74 inches. For mare than 2 yeors, it hos handled saturated NaOH and K O H brines containing chloriw with prcrnrrc surges up to 100 p.s.i. and tcmperaturcs to 200' F. Lower left shows installotion &ch h a been in u t chloriw uruiu for about 2'/, years at 180' F. At right is D tank fabricated in sections and iworpwot'ng Mod cables hclicolly wound around the exterior. This unit has been in service with sohrrolcd NaOH and KOHat 775' F.for more than 4'/,ycarr
Glass-Reinforced Hetrons WALTER A. SZYMANSKI
R O B E R T C. T A L B O T
Laminates .f these highly chlorinated resins as materials of construction for corrosion control answer many problems ranging from storage tanks and process vessels to jire-retardant and decorative architectural materials class of reinforced polyester resins, trade-marked Hetrons, is giving excellent service as a material of construction for corrosion control in equipment such as storage and process tanks and vessels, piping and tubing, ducts, stacks, and scrubbers. Their chemical resistance is good, heat distortion points high, and they are inherently fire-retardant. In addition, ease of handling, workability, and light color has led to ease of visual inspection and consistent quality. Hetron resins should not be confused with isophthalics, bisphenol A, hydrogenated bisphenol A, or general purpose resins. They are based on the reaction of hexachlorocyclopentadienewith maleic anhydride which forms a highly chlorinated anhydride or its acid:
A
The acid contains a double bond but it does not copolymerize with monomers such as styrene and is therefore more properly a modifying dibasic acid. When this acid is allowed to react with dibasic acids and dihydric alcohols, an unsaturated polyester chain results. Commercial Hetron is a mixture of this unsaturated resin and a liquid monomer. Then further reaction of the resin and monomer in the presence of a free-radical initiator such as methyl ethyl ketone peroxide causes the resin to thicken and gel. The reaction is exothermic and on further curing, the gel forms a crosslinked thermosetting solid plastic with little or none of the original unsaturation left. The cross-linked polymer of a dibasic acid and dihydric alcohol without the saturated modifying acid is generally not good for producing glass-reinforced materials of construction. It is the highly chlorinated dibasic acid in Hetrons which produces useful resins. VOL 5 6
NO. 4
APRIL 1964
39
Fabrication
1
i
i
I
0 25
1
I
0 50
EXPOSURE TIME, YR.
0 75
2 1 .o
Figure 7. Resistance of Hetron laminates cured at room temperature. 1, caprylic acid at 778" F.; 2, mixed esters of fatty acids at 7 78" F . ; 3, underground clay soil at ambient temperature; 4, 53 02. per gallon of each of sulfuric and chromic acid; also 70% hydrochloric acid plus 30% acid juoride salts at 720" F.; 5, 6, 70 and 50% sodium hydroxide, respectively, at 75" F.; 7 , 8, 7 0 and 28 to 30y0ammonium hydroxide, respectively, at 75" F.; 9, 10, 70 and 48% of hydrobromic acid, respectively, at 75" F.; 11, cooling tower water at ambient temperature; 12, chemical plant atmosphere; 13, 75% hjdtochloric acid in saturatedferrous chloride at 240' F .
Figure 2. Resistance of Hetron laminates cured at room tempeiatuie 14, 80% sulfuric acid at 75' F.; 15, 707, acetic acid at 75" F.; 1 6 , glacial acetic acid at 75" F.; 17, 18, 7 0 and 85% phosphoric acid, respectively, at 75' F.; 1 9 . water, saturated sulfur dioxide, air, and traces of sulfuric and hydrofluoric acids, plus H&Fe at 770' F.; 20, 21, 70 and 357, nitric acid at 75" and 740" F.: respectively; 22, methyl isobutyl ketones plus 74% hydrochloric acid at 758" to 203" F.; 23, toluene diisocyanate at 750" F.; 24, 23 to 30% hydrojuorosilicic acid at 75' F.; 25, 37y0 formalin at 750" F.; 26, 36% hydrochloric acid at 75' F.; 27, 2070 hydiochloric acid plus organics at 740' to 750" F.; 28, phosphate salts plus hydroffuoric acid at 75" F.; 29, 3 to 6% chromic, 7 to 3% nitric, and 7 to 3% hydrofluoric acids at 75' F.
AUTHORS W a l t e r A . Szymanski is Sales Engineer, Polyester Resin Sales, Durez Plastics Division of Hooker Chemical Corp., N o r t h T o n a w a n d a , N . Y . Robert C. T a l b o t is Senior Corrosion Technician with the Hooker Chemical Corp., N i a g n r a
Falls, N . Y .
40
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
I n fabricating a piece of equipment, a laminate is formed by combining controlled amounts of resin and an appropriate free-radical initiator with controlled amounts of glass-fiber (in some instances synthetic-fiber) mat, cloth, roving, other fibrous material, or a combination of these. For corrosion service, the most common method is by the contact hand lay-up wet process where a layer of catalyzed resin, reinforced with a 10mil Type C (chemical grade) glass-surfacing mat i s applied over a mold, which is surfaced with a release agent such as polyvinyl alcohol or ~ 7 a x . T h e glass mat prevents cracking due to shrinkage As the resin-rich layer begins to gel and cure, a minimum of two layers of I1/2-ounce Type E (electrical grade) chopped-strand random glass mat, saturated with catalyzed resin, is applied. These layers are closest to the corrosive environment, and their resin richness imparts chemical resistance. Glass content in these layers averages about 25yc,. Reinforcement of about 30y0 or more can result in fairly rapid deterioration of the laminate structure. Structural strength is provided by applying additional layers of resin-saturated mat, cloth, or woven roving. At least one layer of I1/a-ounce mat is used between plies in this part of the structure so that no two plies of fabric are adjacent. T h e exterior may then be finished with a resin-rich layer incorporating ultraviolet screeners, which help to retard sunlight degradation. All products are then allowed to cure at room temperature to a Barcol hardness of 40 to 50. No postcuring is required. During lay-up, care must be taken to ensure that all portions of the laminate are thoroughly and uniformly wet out and that air is removed by working the resin into the fibers by methods such as hand pressure and tension, rollers, doctor blades, or reinforcement. This also controls uniformity of wall thickness. For conLTenience and color coding, small amounts of pigments or dyes are permissible, if they do not obstruct visual inspection. As the structure cures: it contracts slightly and recedes from the mold surface, thus allowing the mold to be pulled away. Some fabricators use collapsible molds. Generally, the glass supplied is already finished with a methacrylic Chrome complex or silane to improve its bond to the resin. I n this type of fabrication, quality depends to a great extent on workmanship. Therefore all products should be purchased only from reputable fabricators and, before installation, each item should be critically inspected. As a minimum, the specifications should call for unfilled and unpigmented resin in the chemically resistant part of the laminate. This area remains fairly clear during curing and therefore facilitates visual inspection for defects. Additives, fillers, or anything that can mask defects which affect serviceability should be avoided. Defects such as voids, resin-poor areas, pitting, or air entrapment can and do cause early failures. e
Properties
Chemical Resistance. Because the final structural laminate is a nonhomogeneous combination of resin and glass, testing for chemical resistance is more complicated than for most other materials of construction. Except for chemicals such as hydrofluoric acid and strong alkalies, fibrous glass is generally quite resistant, but perhaps because of its increased surface area, it is not as resistant as bulk glass. Therefore when a laminate containing this material is exposed to a corrosive environ-
T Y P I C A L PROPERTIES O F GLASS MAT-REINFORCED HETRON LAMINATES Tensile strength, p.s.i.
X lo3 X lo3, R.T. Flexural strength, 180° F.
20
Flexural strength, p.s.i.
35
Flexural strength, after 2 hr. HzO b o i l
35
Flexural modulus, p.s.i. X
25
lo6, R.T.
1.8
1 .o
Flexural modulus, 180' F.
1.7
Flexural modulus, after 2 hr. HzO boil Compressive strength, p.s.i. W a t e r absorption,
X lo3
yo b y wt.
45
0.13
2 hr. b o i l
lzod Impact, ft.-lb./in.
14.5
Flammability, ASTM D-635
Self ext.
Flammability, ASTM D-757, in./min. Glass content,
0.1
% b y wt.
H e a t distortion point (264 p.s.i.1, casting,
33
F.
310
These tanks, fabricated from Hetron 72 by the wet hand lay+ technique, have handled demineralized water at ambient temfierature f o r more than 2 years
ment, appreciable loss of strength can occur, presumably by degradation of the bond between the resin and the glass fibers. T h e strength loss can continue with length of exposure, or it may level off. With appropriate safety factors, however, laminates which level off to a constant value or which lose only 5 to 10% can be used quite successfully for industrial applications. In testing suitability of a laminate, field exposure is preferred and in laboratory tests field conditions should be simulated as closely as possible. But equally important, test samples should be representative of the production technique and of the chemically resistant part of the fabrication. Usually, the structural-strength part of the laminate need not be tested T h e samples used are generally laminates about 1/8 inch thick containing about 25% glass mat in two 11/2-ounce layers with a IO-mil surfacing mat on each surface. Cure, following normal shop practice, should be at room temperature. Testing castings or laminates which have been postcured, for example, at 1 hour at 100' C. followed by another hour at 150' C., is not representative of actual fabrications and has no practical meaning. T h e most satisfactory method of testing is to expose, under constant load, one surface of the corrosion-resistant part to the corrosive environment and then measure the synergistic effect of load and environment on strength characteristics of the laminate. However, this procedure is complicated and time consuming and, except in special cases, is usually not practical. Fortunately a more practical method which is relatively easy and quick has proved satisfactory. Here, several samples, about 4 by 5 inches, are exposed to the corrosive environment. Cut edges should be coated with resin to seal off exposed glass fibers. Samples are removed after different lenqths of exposure, and changes in strength, usually flexural, are recorded. In addition, changes in hardness, thickness, weight, and appearance of the laminate and environmental solution can be recorded as desired. For the data in Figures 1 and 2, which s h o ~ 7typical results of such evaluations, samples for flexural testing were cut from the center of larger test specimens to eliminate wicking, which occurred in varying degrees a t the exposed edges. I n most cases, curves are based on a t least three points with a n average of three results a t each point. After the exposure times noted, all samples appeared in excellent condition. T h e low flexural strength shown by samples exposed to 15% solution of hydrochloric acid saturated with ferrous chloride at 240' F. (curve 13) can be attributed to rather severe wicking through the exposed edges to the centers of the samples. Apparently this led to degradation of the resin-fiber bond. Under microscopic examination, the resin itself seemed unaffected. Additional samples with edges protected are under exposure. T o simplify the procedure for measuring chemical resistance of laminates, hardness retention values were plotted against flexural strength retention to determine if a correlation existed. After plotting about two dozen values it was found that a significant relationship existed VOL. 5 6
NO. 4 A P R I L 1 9 6 4
41
with a correlation coefficient of about 0.93. However, as additional test data was added, the coefficient dropped to a low level. Hence, the conclusion is reached that no relationship exists between hardness and flexural strength retention, at least for Hetron 197 laminates cured at room temperature. Applications
For more than 10 years, Hetron polyester resins have found jvidespread acceptance for industrial applications in corrosion control. Hooker Chemical’s Kiagara plant uses more glass fiber-.reinforced plastic in corrosion control than perhaps any other processing plant of similar size in the country. Tanks. An 18,000-gallon storage tank for concentrated hydrochloric acid (367,) at ambient temperature was recently purchased for $3500. It was made by the filament winding technique where continuous glass filaments saturated with resin are helically wound under tension around a chemically resistant laminate. This and the following method can be used to fabricate tanks in confined awas in the field. Other tanks have been used which were fabricated in sections and reinforced for strength by helically winding Monel cables around the exterior. These and several other storage and pressure equalizing tanks have been in saturated sodium and potassium chloride service at 175” F., and p H as high as 11 for more than 4l,i2 years with little evidence of degradation. Tanks have also been fabricated over male molds by the wet hand lay-up method. One handling concentrated hydrochloric acid at ambient temperature and one handling demineralized water at ambient temperature are in excellent condition after two years of service. Centrifugally cast tanks of Hetron have served satisfactorily for a number of years as water softeners, fuel tanks, and fertilizer tanks. Here, a centrifugally rotated, heated female mold is used into which resin and chopped-glass fibers are injected to form the tank wall. Head and fittings are applied separately. Other tanks have been in service for as long as 10 years at temperatures to 200’ F. in environments such as formaldehyde, chlorine dioxide solutions, sodium chlorate solutions, alum, chlorine water, sulfuric acid, hydrochloric acid, mixtures of hydrochloric acid, phosphoric acid, and chlorine, polyvinyl acetate emulsions, pickling solutions, and chlorinated brine. Piping, Tubing, and Ducts. These items are available in a wide range of diameters with all available fittings. Fabrication methods include hand lay-up, automatic and semiautomatic machine, centrifugal casting, and filament winding. Hetron 72 pipe has been performing satisfactorily in wet chlorine for more than 61/2 years at 205’ to 210’ F. I n similar service, Hetron 197 has performed for about 4 years at 210’ F. Also, in this type of service pipe up to 14 inches in diameter, seal tanks, fans, and butterfly valves have shown excellent resistance for about 21/4 years at temperatures to 180’ F. Other 42
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
piping, tubing, and duct installations handle a variety ofcorrosion chemicals at temperatures as high as 300’ F. Other Applications. A Hetron 72 chute has handled 100 to 150 tons of wet salt with 3yoalkaline water almost daily for about 2 years with little evidence of wear or corrosion. Hetron 92 resin reinforced with glass cloth has protected insulation from weather and splash and spills of 750’ F. salt for more than 11/2 years. -4 concrete trench lined with an unfilled flexible Hetron membrane and protected by acid-proof brick has withstood chlorine water at 205’ F. for 51/2 years. Filled Hetrons have been used as chlorine cell insulators. Fire-retardant foam-cored panels with Hetron skins have replaced concrete platform walkways in cell buildings. T h e resin has been used to repair leaks in pipelines and for other maintenance repairs. Also, it has been used as a protective coating for fan impellers, agitators, pump impellers, interior and exterior tanks, concrete floors and wearing courses, and walls. Other uses include caulking compounds, expansion joints, mortar, and as a reinforcement for thermoplastic materials. Flat and corrugated panels are used extensively €or Lvindows, roofing, siding, skylights, and splash guards. Fire retardancy and chemical resistance makes these resins ideal for chemical plants in uses such as these and also for decorative purposes. A new development where these panels are combined with polyvinyl fluoride film offers even more versatility for severe weathering and chemical exposure. Other equipment in service includes mist eliminators, hoods, covers, ejectors and injectors, scrubbers, various supports, floor drains. troughs, funnels, sinks, waste disposal lines, hampers. filters, siphons, tail pipes. REFERENCES (1) Arndt, F. W., “Applying Reinforced Plastics in Corrosive Environments of the Process Industry,” C o r k i o n (November 1960). (2) Atkinson, H. A,, “Reinforced Plastics for Chemical Process Equipment,” AS.ME Publ. 61-WA-267, 1961. (3) Baker, R. E , , “Polyester Piping Chosen for Corrosion Resistance t o Brine, Chlorine,” Heating, Piping Air Conditioning (November 1962). (4) Barnett, R. E., Anderson, T. F., “Polyester Fiber Glass Equipment,” Corrosion (December 1959). ( 5 ) Coss, R. A,, Fenncr, 0 . H., “Fiber Reinforced Plastic Materials of Construction for Corrosive Environmenrs-Their Testing and Evaluation,” NACE Conf., March 14-18, 1960. (6) Dietz, A. G. H., “Engineering Laminates,” Wiley, h-ew York, 1949. (7) Fonda: A. F., “Field Joining Reinforced Plastic Pipe-Butte and Strap Technique,” Plant Engineering, March 1963. (8) Gibbs 8; Cox, Inc., “Marine Design Manual for Fiberglas Reinforced Plastics,” McGraw-Hill, New York, 1960. (9) Kinney, G. P.: “Engineering Properties and Applications of Plastics,” Wiley, A-ew York, 1957. (10) Loetel, C. E., Fordyce, H. E,, “Long Term It‘et Strength Retention,” Soc. Plastzcs Engrs. J . (January 1960). (1 1) Owens-Corning Fiberglas Corp., “Fiberglas Reinforced Plastics,” Pub. 5PL-1998, New York. (12) Modern Plaslics, “Giant Plastic Structures,” February 1961. (13) Riley, M. W., “Low Pressure Reinforced Plastics,” M a t e r . Design. E n g . (February 1960). (14) Smith, M’. E., “Hand Layup Reinforced Plastic Pipe and Duct for Industrial Use,” Tappi (April 1963). (15) Smith, W. E., Severance, W .A,, “Visual Standards for Reinforced Plastics,” M a t e r . Design E n g . (March 1959). (16) Sonneborn, R. H., “Fiberglas Reinforced Plastics,” Reinhold, New York, 1954. (17) Szymanski, 1%’. A . plication of Polvester Fabrications in the Chemical Process Industry,” NAc‘kA80nf., March 1963. (18) Szymanski W. A. “Polyester and Epoxy Resins for Chemical Plant Repairs,” Corrosion (Maich 1 9 6 b ) . (19) Szymanski, W. .4. “Reinforced Plastics in Chemical Engineering,” Plastics W o r l d (February 1956). (20) Szymanski, W. A,, “Reinforced Polyester for Chemical Plant Service,” SPI Preprint, February 1961. (21) Webstcr, R. M., “Reinforccd Plastics for Corrosive Service,’’ Cham. Eng. (June 26, 1961); Ibid., July 10.
