The Effects of Hostile Environments on Coatings and Plastics

9 Typical Uses and Durability of Various Plastics in Hostile Environments

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 22, 2016 | http://pubs.acs.org Publication Date: September 29, 1983 | doi: 10.1021/bk-1983-0229.ch009

A. A. BOOVA Atlas Minerals & Chemicals, Inc., Farmington Road, Mertztown, PA 19539

Plastics are finally gaining a position of eminence as premier protective barriers against hostile environments in the various process industries. Plastics are proven viable alternatives to such formidable corrosion barriers as rubber, glass, carbon and graphite, brick and ceramics, wood, metals and various alloys. Prior to World War II, European process industries such as steel and metalworking, chemical and petrochemical, pulp and paper, etc. were more aggressive than their U.S. counterparts in the use of plastics in hostile environments. Plastics were recognized as possessing: a) b)

c)

d)

E x c e l l e n t chemical r e s i s t a n c e to many o r g a n i c and i n o r g a n i c a c i d s , a l k a l i e s , s a l t s and s o l v e n t s . High strength i n r e l a t i o n to weight f o r producing p i p i n g and equipment o f e x c e l l e n t s t r u c t u r a l integrity. S u f f i c i e n t f u n c t i o n a l i t y to permit formulating f o r a multitude o f end p r o p e r t i e s , i . e . , chemical and/or thermal r e s i s t a n c e o r both, c e r t a i n p h y s i c a l properties, e t c . The p r o p e r t i e s to permit ease o f molding, forming and f a b r i c a t i n g , and

when compared to various metals and a l l o y s were found to be very cost e f f e c t i v e . Polyethylene and p o l y v i n y l c h l o r i d e and epoxies and phenolics were the most popular thermoplastic and thermoset m a t e r i a l s , r e s p e c t i v e l y , o f that p e r i o d . Today i n d u s t r y makes a v a i l a b l e a host o f e x c e l l e n t chemical r e s i s t a n t p l a s t i c s f o r a multitude of a p p l i c a t i o n s . T h i s paper w i l l discuss f a b r i c a t e d p o l y e t h y l e n e , p o l y v i n y l c h l o r i d e and polypropylene f o r s p e c i f i c i n d u s t r i a l a p p l i c a t i o n s . 0097-6156/83/0229-0141$06.00/0 © 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, David P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

142 Design

Criteria


The s e l e c t i o n o f the proper p l a s t i c f o r a given c o r r o s i o n environment i s not a simple process. I t r e q u i r e s c a r e f u l a n a l y s i s of the p r o p e r t i e s o f the p l a s t i c contemplated. Equally importantly, i t r e q u i r e s c a r e f u l a n a l y s i s o f what i s to be p r o t e c t e d (tanks, exhaust systems, p i p i n g , e t c . ) and the environment to which they are being subjected. The f o l l o w i n g "check p o i n t s " w i l l be o f a s s i s t a n c e i n e s t a b l i s h i n g the environment to which the p l a s t i c w i l l be subjected and the subsequent p l a s t i c s e l e c t e d . A) B)

C) D)

E)

F)

I d e n t i f y a l l chemicals and t h e i r c o n c e n t r a t i o n s . pH, a l though h e l p f u l , does not provide s u f f i c i e n t i n f o r m a t i o n . Maximum and minimum temperature exposure, i n c l u d i n g any a n t i c i p a t e d thermal shock. Is the p r o t e c t i o n r e q u i r e d indoors, outdoors, o r both? Mother Nature i n t r o d u c e s many challenges f o r p l a s t i c s , i . e . , sun, wind, r a i n , freeze-thaw, e t c . P h y s i c a l f a c t o r s such as p o s i t i v e and negative p r e s s u r e s , v e l o c i t y , abrasion, impact, v i b r a t i o n , e t c . Is the a p p l i c a t i o n one o f c o n t a i n i n g (process v e s s e l s , storage tanks, scrubbers, e t c . ) , conveying (pipe, v a l v e s , f i t t i n g s , etc.) or exhausting (hoods, ducts, stacks, e t c . ) . I f the p l a s t i c i s t o be a f a b r i c a t e d i n s e r t f o r an e x i s t i n g s t r u c t u r e , provide a l l p e r t i n e n t dimensional data and the m a t e r i a l of which i t i s c o n s t r u c t e d , i . e . , s t e e l , other metals, concrete, wood, e t c . Is process obsolescence imminent or i s long term prot e c t i o n required? A s i g n i f i c a n t c o n s i d e r a t i o n profoundly a f f e c t i n g economics.

Table I enumerates the v a r i o u s p h y s i c a l and thermal propert i e s o f these p l a s t i c s . These f a c t o r s are minimum requirements f o r the design engineer. Tank design i s the most c h a l l e n g i n g f o r the design engineer. Experience has proven to be the most p o s i t i v e as w e l l as the most expensive f o r many f a b r i c a t o r s o f t h e r m o p l a s t i c s . Much o f the design information from which formulas are d e r i v e d i s p r o p r i e t a r y and j e a l o u s l y guarded. As can be a p p r e c i a t e d , design f a c t o r s can be voluminous when one considers the a v a i l a b l e p l a s t i c s , creep p r o p e r t i e s o f these p l a s t i c s a t v a r i o u s temperatures, a l l o f which must be determined as a f u n c t i o n o f time. The myriad o f government mandates has r e q u i r e d p l a s t i c s f o r most i n d u s t r i a l a p p l i c a t i o n s to be s e l f - e x t i n g u i s h i n g and/or f i r e r e t a r d a n t . The p l a s t i c s i n d u s t r y has been responsive to these mandates as w e l l as those imposed by in-house standards of many


9.

BOOVA

Uses and Durability of Various Plastics


THERMAL AND

143

TABLE I PHYSICAL PROPERTIES

Type I Property PVC 6,800 T e n s i l e Strength, p s i . 10,000 Compressive Strength, p s i F l e x u r a l Strength, p s i . 14,000 F l e x u r a l Modulus, p s i . 500,000 Impact Strength IZOD 0.88 ( f t . l b . / i n . notch) 3 E l o n g a t i o n % (at y i e l d ) C o e f f i c i e n t o f Expansion 4.0 (in./in./°F. χ 10~ Thermal C o n d u c t i v i t y (Btu./hr./sq. f t./in./°F.)x 10" 1.33 Maximum Useable Temp. (°F.) 150 5

4

Linear Polyethylene 4,000 2,500 2,000 80,000

Homopolymer Polypropylene 5,200 6,000 6,000 230,000

2.5

4.0

25

20

7.0 3.17 180

3.9

to

6.1

1.3 200

companies. Polypropylene, f o r example, i s a v a i l a b l e i n three f i r e r e t a r d a n t grades. B r i e f l y , they are d e s c r i b e d as f o l l o w s : V-0

Grade

-

V-l

Grade

-

V-2

Grade

-

S e l f - e x t i n g u i s h i n g with no d r i p p i n g of sheet upon i g n i t i o n . S i m i l a r to V-0 Grade except i n t h i c k nesses of l e s s than 1/8". It i s highly u n l i k e l y that t h i s grade would be used for f a b r i c a t i n g self-supporting structures. S e l f - e x t i n g u i s h i n g with some d r i p p i n g p e r m i s s i b l e , however, the d r o p l e t s must be s e l f - e x t i n g u i s h i n g .

Flame r e t a r d a n t p r o p e r t i e s are not without s a c r i f i c e to chemical r e s i s t a n c e , formulation f l e x i b i l i t y and p h y s i c a l p r o p e r t i e s . For V-0 and V-2 grades, f o r example, p h y s i c a l p r o p e r t i e s are reduced approximately 20% and 10%, r e s p e c t i v e l y . P o l y v i n y l c h l o r i d e , polyethylene and polypropylene have e x h i b i t e d outstanding v e r s a t i l i t y to a multitude of h o s t i l e environments i n the v a r i o u s process i n d u s t r i e s . Table I I provides a general i n d i c a t i o n of the chemical r e s i s t a n c e that might be expected from these three p l a s t i c s .



144

TABLE I I CHEMICAL RESISTANCE


Environment

PVC (TYPE I)

Polyethylene

A c e t i c A c i d , 50% Aniline Chromic A c i d , 15% E t h y l Acetate Ethyl Alcohol Hydrochloric Acid H y d r o f l u o r i c A c i d , 50% Hydrogen Peroxide N i t r i c Acid

R N R Ν R R R R R (Up to 68%)

R R R

Phosphoric A c i d Sodium Hydroxide Sodium H y p o c h l o r i t e Sodium S u l f a t e Sulfuric Acid

R R R R R (Up to 96% Cold)

R R R R R

R R R R R

Polypropylene

R R R C C R R R R (Up to R (Up to 40% Cold) 60% Cold) R R R R (Up to R (Up to 50% Cold) 60% Cold)

Toluene R Ν C

= Recommended = Not Recommended = Conditional

I t i s to be noted that Table I I does not i n d i c a t e r e s i s t a n c e at a s p e c i f i c temperature. Concentration and temperature are the most s i g n i f i c a n t f a c t o r s c o n t r i b u t i n g to the success and l o n g e v i t y of any p l a s t i c f a b r i c a t i o n . Fabrication Polyethylene, p o l y v i n y l c h l o r i d e and polypropylene a r e e a s i l y worked u t i l i z i n g o r d i n a r y wood or metal working hand and power t o o l s . Being t h e r m o p l a s t i c , these m a t e r i a l s can be e a s i l y thermoformed as w e l l as cut, sawed, d r i l l e d and tapped. In the heat forming process, e l e c t r i c ovens are g e n e r a l l y used which can main t a i n good thermal c o n t r o l . Of the three t h e r m o p l a s t i c s , p o l y propylene r e q u i r e s the more f i n i t e thermal c o n t r o l . Table I I I provides approximate time and temperature r e l a t i o n s h i p r e q u i r e d f o r thermoforming these three p l a s t i c s . When forming c y l i n d r i c a l stock f o r subsequent f a b r i c a t i n g i n t o ducts, s t a c k s , tanks, e t c . the sheets are removed from the oven and formed on mandrels. The sheet i s h e l d on the mandrels with a cotton canvas u n t i l c o o l . P o l y v i n y l c h l o r i d e w i l l c o o l f a s t e r than polyethylene and polypropylene, consequently, expe d i t i n g the next step i n the f a b r i c a t i n g process.


9.

BOOVA

TABLE I I I TEMPERATURE RELATIONSHIP

TIME AND Plastic 4

f

Sheet Size χ 8' χ 1/4"

PVC Polyethylene Polypropylene 4 Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 22, 2016 | http://pubs.acs.org Publication Date: September 29, 1983 | doi: 10.1021/bk-1983-0229.ch009

145


f

χ 8' χ

PVC Polyethylene Polypropylene

Temp., °F.

(°C.)

Time, Mins.

250 270 340

(120) (130) (170)

20 40 45

250 270 340

(120) (130) (170)

30 60 80

1/2"

The three p l a s t i c s lend themselves w e l l to heat welding. The three types of welding most commonly used a r e : 1. 2. 3.

Butt Welding E x t r u s i o n Welding Hand Rod Welding

Butt welding, sometimes r e f e r r e d to as f u s i o n welding, i s used when f a b r i c a t i n g l a r g e q u a n t i t i e s of f l a t stock as w e l l as l a r g e diameter or r e c t a n g u l a r o b j e c t s . Butt welding equipment i s p r e c i s e and h i g h l y automated. The equipment a l i g n s , holds and welds the p l a s t i c at p r e c i s e temperatures thus i n s u r i n g welds of outstanding s t r u c t u r a l i n t e g r i t y . Butt welding g e n e r a l l y e l i m i n a t e s the n e c e s s i t y to chamfer sheet edges p r i o r to welding. Weld s t r e n g t h i s at l e a s t 95% of the t e n s i l e s t r e n g t h of the v i r g i n sheet. E x t r u s i o n welding i s done with guns that u t i l i z e r e s i n p e l l e t s o r r e e l s of small diameter welding rod. E x t r u s i o n weld ing with p e l l e t s i s used on e s s e n t i a l l y h o r i z o n t a l s u r f a c e s . Guns using rod are f u n c t i o n a l f o r h o r i z o n t a l , v e r t i c a l and over head welding. These guns g e n e r a l l y u t i l i z e rod of 1/8" and 5/32" diameter. E x t r u s i o n welding cannot be used on stock t h i n n e r than 3/8" because the heat generated causes excessive sheet warpage. Sheets are g e n e r a l l y chamfered on both s i d e s to a t o t a l angle of 60° to accommodate welding the f u l l depth of the sheet. Weld s t r e n g t h i s at l e a s t 85% of the t e n s i l e s t r e n g t h of the v i r g i n sheet. Hand rod welding i s g e n e r a l l y done f o r s m a l l p r o d u c t i o n runs and i n t r i c a t e shapes where the other methods of welding are not practical. Sheet edge chamfering i s the same as f o r e x t r u s i o n welding. Weld s t r e n g t h i s at l e a s t 75% of the t e n s i l e s t r e n g t h of the v i r g i n sheet. P o l y v i n y l c h l o r i d e welding can be done with hot a i r , however,



146

polyethylene and polypropylene y i e l d best r e s u l t s when welded with i n e r t gas. Repeated l a b o r a t o r y s t u d i e s have proven that n i t r o g e n welding w i l l provide the strengths a l l u d e d to above, notwith standing of course the s k i l l s of the f a b r i c a t o r s .


Applications P o l y v i n y l c h l o r i d e , polyethylene and polypropylene have e s t a b l i s h e d an enviable record of success i n combatting c o r r o s i o n i n i n d u s t r y . These p l a s t i c s possess outstanding v e r s a t i l i t y to h o s t i l e environments. The inherent d i f f e r e n c e s i n r e s i s t a n c e to temperature and impact represent the most s i g n i f i c a n t f a c t o r s to the u l t i m a t e p l a s t i c s e l e c t e d f o r a given end use. Of the three p l a s t i c s , polypropylene homopolymers o f f e r the broadest range of chemical r e s i s t a n c e combined with e x c e l l e n t p h y s i c a l p r o p e r t i e s . Outstanding chemical r e s i s t a n c e with l e s s p h y s i c a l and thermal demands would favor the use of p o l y v i n y l c h l o r i d e . Polyethylene e x h i b i t s e x c e l l e n t impact c a p a b i l i t i e s but due to i t s lower load bearing q u a l i t i e s , i t s use w i l l g e n e r a l l y be l i m i t e d to small p a r t s and equipment. I t s low f r i c t i o n waxlike f i n i s h makes i t a t t r a c t i v e f o r use i n a n t i - s t i c k a p p l i c a t i o n s . The f o l l o w i n g are t y p i c a l a p p l i c a t i o n s as w e l l as a b r i e f d e s c r i p t i o n of the design of the v a r i o u s p a r t s and equipment. The r e s p e c t i v e a p p l i c a t i o n s r e q u i r e uncompromising s t r u c t u r a l and p h y s i c a l c a p a b i l i t i e s with r e s i s t a n c e to h o s t i l e environments c h a r a c t e r i s t i c of the chemical, s t e e l and metalworking i n d u s t r i e s . S t e e l and Metalworking I n d u s t r i e s A.

S e l f - s u p p o r t i n g Tube P i c k l i n g Tank (Figure 1) P i c k l i n g S o l u t i o n - 20% S u l f u r i c A c i d at 180° F. M a t e r i a l of C o n s t r u c t i o n - Polypropylene Homopolymer Tank S i z e 32 Long χ 5' Wide χ 4 Deep S h e l l Thickness 1" Stock A l l Corners - Molded to approximately 4" r a d i u s R e i n f o r c i n g - E x t e r i o r Only - bottom and s i d e s with h o r i z o n t a l and v e r t i c a l s t i f f e n e r s of 3/4" and 1" t h i c k polypropylene homopolymer stock. 1

B.

1

Insert f o r E x i s t i n g Carbon S t e e l Tube P i c k l i n g Tank (Figure 2) P i c k l i n g Solution 12% N i t r i c and 5% H y d r o f l u o r i c A c i d s at 130° F. M a t e r i a l of Construction - Polypropylene Homopolymer Tank Size - 50 Long χ 3 Wide χ 4 Deep S h e l l Thickness 1/2" Stock A l l Corners - Rectangular to match e x i s t i n g tank I n t e r i o r E x i s t i n g Tank - Protected with three coats v i n y l coating. Sponge rubber approximately 1/2" 1

f

f



9. BOOVA


Figure 1. Self-supporting-tube pickling tank.

Figure 2. Insert for carbon-steel-tube pickling tank.

American Chemical Society Library 1155 16th St., H.W. Washington, O.C. 20036


147

148

EFFECTS OF HOSTILE ENVIRONMENTS t h i c k a p p l i e d to i n t e r i o r to provide cushion and p r o v i s i o n f o r expansion of the polypropylene i n s e r t . R e i n f o r c i n g - 1/2" t h i c k v e r t i c a l s t i f f e n e r s on the i n t e r i o r o f the polypropylene i n s e r t .


C.

Covers f o r 80" Continuous

S t r i p P i c k l i n g L i n e (Figure 3)

Covers prevent a c i d s p l a s h and provide confinement o f fumes f o r subsequent exhausting. P i c k l i n g S o l u t i o n - 8% H y d r o c h l o r i c A c i d a t 220° F. M a t e r i a l o f C o n s t r u c t i o n - V-2 F i r e Retardant Polypropylene Homopolymer Tank Size - 372 Long χ 10' Wide χ 5 Deep Cover Thickness - 3/4" Stock A l l Corners - Rectangular R e i n f o r c i n g - Underside of covers u s i n g l o n g i t u d i n a l and transverse s t i f f e n e r s of 3/4" and 1" s t o c k . Outside o f covers are r e q u i r e d to c l e a r span. 1

D.

f

Polyethylene Dipping Baskets (Figure 4) S o l u t i o n s - P l a t i n g S o l u t i o n s a t 140° F. Material of Construction - Polyethylene, Linear S i z e - 24" χ 24"" χ 24" S h e l l Thickness - 1/4" R e i n f o r c i n g - 1/2"

Chemical Process I n d u s t r i e s E.

Chemical Hood, Cabinet and Sinks (Figure 5) S e r v i c e Conditions - Fume and Splash C o n t r o l o f hazardous and h i g h l y o x i d i z i n g chemicals M a t e r i a l of C o n s t r u c t i o n - P o l y v i n y l C h l o r i d e , Type I Size - 60" Wide χ 30" Deep χ 60" High S h e l l Thickness - 1/4" Stock A l l Corners - Rectangular R e i n f o r c i n g - 1/2"

F.

Dyestuff F i l t e r Nutch (Figure 6) S e r v i c e C o n d i t i o n - A c i d Pigments M a t e r i a l o f C o n s t r u c t i o n - Polypropylene Homopolymer S i z e - 60" Long χ 36" Wide χ 24" Deep S h e l l Thickness - 3/4" Stock A l l Corners - Molded to approximately 4" radius R e i n f o r c i n g - E x t e r i o r Only - Bottom and s i d e s with h o r i z o n t a l and v e r t i c a l s t i f f e n e r s of 3/4" t h i c k polypropylene homopolymer stock.

Summary F i g u r e s 1 through 6 are p i c t u r e s of the aforementioned



9.

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Figure 3. Covers for continuous-strip pickling line.

Figure 4. Polyethylene dipping baskets.


149



Figure 5. Chemical hoods, cabinets, and sinks.

Figure 6. Dyestufffilter nutch.



9.

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151

i n s t a l l a t i o n s which serve to i l l u s t r a t e the v e r s a t i l i t y of p o l y v i n y l c h l o r i d e , polyethylene and polypropylene. On h i s t o r y , p o l y v i n y l c h l o r i d e and polyethylene have had over twenty-five years of s u c c e s s f u l a p p l i c a t i o n s i n the United States with the successes expected to continue f o r years ahead. The success that these two m a t e r i a l s enjoyed i n Europe dates back to the pre-World War I I e r a . Polypropylene f a b r i c a t i o n i n the United States i s i n i t s infancy when compared to the other two t h e r m o p l a s t i c s . In the l a s t f i v e years, polypropylene has gained tremendous momentum f o r r e s i s t a n c e to h o s t i l e environments, p a r t i c u l a r l y where impact and s t r u c t u r a l i n t e g r i t y are paramount. One need only to recogn i z e that the cover on a continuous s t r i p p i c k l i n g l i n e , r e f e r r e d to i n Figure 3 r e q u i r e s that a 300 l b . man may walk s a f e l y across t h i s p i c k l e l i n e . T h i s t r u l y i s c o n f i r m a t i o n of the tremendous confidence that i s being placed i n thermoplastics f o r not only r e s i s t i n g h o s t i l e environments but as w e l l f o r t h e i r a b i l i t y to perform s t r u c t u r a l l y . The process i n d u s t r i e s (chemical, s t e e l and metalworking, to mention a few) w i l l continue to depend h e a v i l y on the use of these three custom f a b r i c a t e d thermoplastics to a s s i s t them i n combatting c o r r o s i o n . RECEIVED March 3,

1983


The Effects of Hostile Environments on Coatings and Plastics

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