Chemical-resistant tanks and linings

CHEMICAL-RESISTANT

TANKS AND LININGS

by C. E. Zarnitz At/as

Minerals

& Chemicals

Inc.,

Mertztown,

Pa.

The dominant and most economical construction materials used in the metal-finishing industry are steel and concrete. Unfortunately, both of the\e materials are highly susceptible to corrosive attack from many of the chemicals used in the metal-finishing industry. Pickling and plating chemicals are highly corrosive and, without proper protection, the life span of steel and concrete is limited. Tanks and tank linings mu\1 be capable of: I.

resisting attack from organic and inorgamc, oxidizing and nonoxidiLing chemicals al varying concentrations. its well as from various solvents: 2. resisting broad thermal variance& including thermal shock; 3. resisting weather extreme, because economics dictate that very large btoragc and waste treatment vessels be located outdoors; 4. resisting physical abuse that accompanies processing strip, heavy parts, shupcs and castings; and 5. maximizing performance, value, and ease of maintenance.

TANKS

AND

LININGS

The type of tanks that have cxccllcd in the metal-finishing industries include lined carbon steel: lined, precast, or poured-in-place concrete: precast or poured-in-place polymer concrete: self-supporting plastics, i.e.. thermoarts and thermoplastics: and alloys. The ~KXXSS of steel or concrete-lined tanks i\ prcdicatcd on good cnginccring daign 01 the structural shell. The ultimate success of the lining, besides good engineering design, is predicated on the finish and structural integrity of the substrate. as well as on the skills and proficiency of the applicator. If the structure cannot stlstain the stress imposed by the pi-ace\\, lining failure 15 imminent. Similarly. pla\tic or alloy tank5 will Ial II good design engineering has been compromlhcd.

Carbon

Steel

When I. 2.

3. 3. 5. 6. 7. 8.

carbon

steel

tanks

for subsequent

lining.

the following

are important:

Minimum number of pieces and sufficient reinforcement must be u\ed to prevent bulging when subjected to optimum proces stress. Vertical reinforcing is prcfcrrcd to horizontal. Ledges arc eliminated, thus minimizing potential for drag-out to hang, concentrate. and corrode the cessel from the “outside-in.” Welds to rcccivc lining arc to be solid and continuous. All corners are to be ground to a minimum radius of ‘/h in.; no \hal-p right angles. Exterior reinforcing mcmbcr\ may bc skip welded. All body \cam\ must hc butt welded true and flat with variation on alignment not to cxcccd 25% of plate thickness and in no case more than ‘XX in. All outlets to bc tlangcd. Interior of vcsscl must be Il-cc of weld \plattcr. pits, deep gouges, and all welds ground smooth.

The following that will be lined

668

Tanks

fabricating

typical outlet and weld details arc suggested when with various types of Innings (see Figa. I and 2).

fabricating

carbon

steel

‘A

Stainless

Steel

Tanks

Stainless steel tanks can be compared to plastic tank& in the respect that they arc solid steel, thus eliminating the need to protect a vulncrahle cxtcrior from l’umrs and ydad~. Srainlc\~ \teels generally arc classified as straight iron-chromium alloys and iroIl-chl-ollliuI11nickel alloy,. In the metal-finishing industry, the iron-chromium-nickel alloy\. i.e.. the 300 to br series appear to he the most popular. Types 30-.7 304. 321, and 347 at-c considered generally equivalent in chemical resistance. The stainless bteel alloys exhibit excellent resistance to such oxidizing acid\ a\ nitric and chromic. They have virtually no resistance to hydrochloric and hydrotluoric ucid\. The vulnerability of \tninless steels to halogenuted acids i& easy to understand h hen you for stainless steel arc acids wch as hydrochloric and recognirc that pichlin, (7 wlutions hydrolluoric and various combinations ol nitric and hydrolluwic. Figs. 3-S provide typical outlet and weld details for the fabrication of tanks.

Portland

Cement

Concrete tank\ include\: wfficient

Concrete

Tanks

are acceptable reinforcement

w long to prevent

as food buckling

design enpinccring is practiced and and cracking: minimum ?,OOO psi

-Tank

670

Wall

/--

Steel Pad

Plate

.

compressive strength after 28 days; smooth, monolithic interior free of ridges. depressions, honeycomb, form marks, etc.; freedom from contaminants and additives, i.e., form release agents, air entraining agents. etc.; and hydrostatically tight and waterproofed on the exterior if located below grade. Self-wpporting plastic and stainless steel tanks must comply with similar structural mandates as those enumerated for carbon steel and Portland cement concrete.

Polymer Concretes Polymer concretes are a generation of materials that have rapidly matured because of their outstanding chemical resistance and physical properties. They are not to be confused

671

Table

1. Typical

Physical

Properties

of Polymer

Concretes

with Portland cement concrete or polymer-modified Portland cement concrete. The only similarity to Pal-tland cement concrete or polymer-modified Portland ccmcnt concrete i\ the use of properly graded and sized aggregate in order to optimize workability and physical properties of the composition. Polymer concretes utilize inert siliceous aggregates with binding systems hasrd on such rain5 a~ furan, epoxy, polycstcr, vinyl ester. and acl-ylic. (See Tuhlc I for typical phyGcal propertieh or polymer concrcto.) The advantages to bc derived from polymer-modified Portland cement concrete when compared with Portland cement concrctc are: I. 2. 3. 4. 5. 6.

ruhbcr,

Permits placement of concrete in thinner crush-section\. Excellent bonding to cxi\ting concrete auhstratcs. lncrcased impact rc\i\tancc. Reduced porosity. Faster \ct and cure. Improvxi resistance to salt. It does not improce resistance

Polymer modifiers \tyrcne-butadicne.

to chemicals

are generally based on \,ariou\ I-csinh and latexes, acrylic. polyvmyl acetate, epoxy, and urethane.

such as natural

LININGS There are a host of lining material\ available for protecting concrete and steel. The three basic types al-e glass-fiber-reinforced sheet and molten sphaltic\: sheet ruhher. plastics. and eln~tomers: and reinforced and nonreinforced ambient-cured synthetic resin \ystcms. Conspicuous by its absence from this li\t i\ protective coatings. This 15 not to say they can’t he used; however, 60 mil\ is usually considered to be a minimum acceptable thicknca for a material to be considered a tank lining. If a coating can he economically applied (initial cost and longevity) to ;L minimum thickness of 60 milh, free of pinholes and holidays. and cau resist the process chemicals and temperatures as well as physical ahuse. considclation should be given to their u\e. Generally speaking, coatings arc used for fume and ~pla\h protection and not neccsaurtly for total immersion proce\5 applications. A.sphn/fic, lirzir~gc are equally appropriate for application to concrete and htecl. The hot-applied. molten materials. a\ well as sheet stock can be used on concrete tanks. FOI- steel tanks. glas\-fiber-reinfc,l-crd sheet is the most dcairuble. Both type\ of aaphaltic linings. sheet and molten. are seldom, if cvzr, used without heins further protected with it chemi~al-r~si~t3t1t brick lining. Without further protection from a brick sheathing, three linings can cold Ilow and hc easily damaged from impact. abrasion. and thermal excursions. Masonry \hcathings

672

Table

II. Physical

Properties

of Asphaltic

Linings

PWp’J’~ Softening point. ‘F (‘C) Aqh. max., ‘3 Penetration 77~F (25°C). 100 g--5s~. 1 IS’F (46-Q SO ~-SW. Chemical resistance

provide a rugged, chemical-resistant other types of linings. The physical are shown

insulating barrier for protection of a\phaltic a\ well as properties and the chemical resistance of asphaltic linings

in Tables

II and III, respectively. sheet lirli~lgs, such 3s various plasti&ed plastics. Irubbers and elaatamers are most commonly wed for steel tank\. Swws~ful applications have been made on concrete: however. it is not the most desirable substrate on which to bond and cure many ot these systems. The physical propertie\ and the chcmicul resistance of sheet linings are ~how11 in Tables IV and V, respectively.

Adhrsi~,r-borzcfrd

Mrchmicrrll~

hotdetl

rigid

plrr.\ric

lirlir~~\

.fiw pwms~

or~tl po~i~~~I-ir~-pltri.r

co,~cwrc

rtrrzk.r are a relatively nw concept. Instead ot bonding with adhesives. thi\ system utilize\ anchor studs sonically welded to the back of the sheet for locking or mechanically bonding the sheet to the concrete. Ambient temperature-cured. spray- and trowel-applied .\wtheric, w.siff /ir?ir~~g .~uteru.~ arc based on the following resins: furan. epoxy, polyester. vinyl ear. and urethane. These system\ are entirely appropriate fat- application to steel and concrete. They have also been wccessfully applied to hood. certain plastics. and various metallic sub\tratea. The\e

Table

III.

Chemical

Resistance

Mrdimr Aluminum salts Cadmium salts Chromic acid, to IO% Copper \illl\ Gold cyanide Hydrochlol-ic aud Hydrofluorlc acid Iron salts Ma:nc\ium salt\ Nickel salts Nitric acld. to 70% Perchlonc acid Phosphoric acid Sodium chloride Sodium cynmdc Sodun hydroxide, to 30% Sodium salts Sulfuric acid, to 50% Trichloroethylene Trisodium phwphate Zinc salt\

of Asphaltic 7-vpP 4

R R R R R R C R R R c NR R R R R R R NR C R

C, conditional: R. recommended: NR, wt rea)mmendcd

674

Linings T,pr R R R R R R c R R R c NR R R R R R R NR c R

B

Table

IV.

Physical

Properties

of Sheet

Linings

Natural ruhhel Soft Semihard Hard NKlpV% Butyl rubber Chlorohutyl rubber Pal) vinyl chloride Plartlcixd Platicixd rigid (2 ply) Chlorowlt’onated polyethylene Fluorocnrhon\

lining

systems

utilize

wch as t’iberglass arc prcaent. These

linings

such filler

arc the most are extremely

I50 I80 IX0 I80 I85 I x.5

(66) (X2) (82) (X2) (85) (X5)

I50 I50 27s 450

(h6) (66) (135) (217)

reini’orcenxnts common; versatile

as flake

however.

glass

synthetic

and can be applied

and mica. fabrics

Fabric

reinforcements

are used whcrc

by nuintenancc

tluoridcs

pcrsonncl

with

skill\ in the painting and masonry trades. Most manufacturers of these lining systems provide training programs for plant nuimenance personnel. The physical properties and the chemical resistance of ambient-cured synthetic rcsln lining systems are shown in Table\ VI and VII. respectively.

Table

V. Chemical

Resistance

McdiwI Aluminum aIt\ Cadmium salt? Chromic acid. to 10% Copper salt5 Gold cyanide Hydrochloric acld Hydrofluoric acid Iron WI,\ Magne\um \alt\ Nickel ults Nitric acid. to 20% Perchlow acid Phosphoric acid Sodium chloride Sodium cyanide Sodium hydroxide, to 30% Sodilnn wit\ Sulfuric acid. to 20% Trichloroethylene Trisodium phwphalc Zinc salt5

of Sheet

Linings

I”

2

.i

4

5

6

K R NR R R R R R K R NK NR R R R R R R NK R R

K R NR R K NR NR R R K NR NR R R R R R R NR R R

R R NR R R R R R R R R NR R R R R R R NR R K

R R R R R R R R R K R C R R R R R K NR R R

R R R R R K NK R R R c NK K K R R R R NR R K

R R R R R R R R R R R R R R R R R R R R R

R. rrrommrnded: C. oondmonal: NR. not recommcndcd “I = nillurill ruhhcr-all pide\. ? = Neoprene. 3 = Hutyl and chlon~huiyl: -I = po,g\,oyl chlondr. 5 = chloroulton,lted polyedq lene; 6 = “,wmca, ho,,,

676

Table

VI. Physical

Properties

of Ambient-Cured

FUKlll Epoxy Polyestr1Vinyl ester

Synthetic

Lining

Resin

12s (52)

Excellent Very wad L_ VCIy good Very c-nod Good

160 (71)

I80 (82) I60 (71) I50 (65)

Urethane

“S”pgc\lcd l,m,t Wltho”, il m.,\nq

Systems

\hCillhl”f.

The tables shown above all provide the design and corrosion engineer with basic information on the various lining systems discussed. They identify specific corrosives encountered in various metal-finishing operations. Enumerated arc each of the various type\ of linings and a general recommendation for its we in the particular medium. It i\ recommended that the acceptability of specific lining\, in specific media. be verified with the manufacturer.

Chemical-Resistant

Brick

and

Tile

Linings

Historically, chemical-resistant brick and tile linings go back approximately 100 years. paralleling the development of sulfuric acid, various dyestuffs, and explosives. The use of masonry construction has grown in the basic steel, metal-working, and metal-finishing industriea. Chemical-resistant masonry sheathings are not to be construed as hydrostatically tight tank linings. They are, in fact. porous, and consequently must be

Table

VII.

Chemical

Resistance

Medirrm Aluminum xdt\ Cadmium salts Chromic acids, LO 10% copper salts Gold cynmde Hydrochloric acid Hydrofluoric acid Iron sillts Mapne\ium qalts Nickel salts Nltrlc acid, to 20% Perchloric acid Phorphorlc acid Sodium chloride Sodium cyanide Sodium hydroxide. to 30% Sodium wits Sulfuric acid, to 50’5% Trichlomethylene Trisodium phosphate Zinc salts

of Ambient-Cured

Synthetic

Resin

Lining

Systems

I”

2

3

4

5

R R NR R R

R R NR R R R R R R R NR NR R R R R R C NR R R

R R R R R R R R R R R C R R R Bis A Type R R C Bir A Type R

R R R R R R R R R R R NR R R R R R R NR R R

R R C R R R C R R R R NR R R R R R R NR R R

;> R R R NR NR R R R R R R R R R

677

Tahle

VIII.

Chemical

Resistance

of Structural

Plastics t’,~lrclll.dtwc

Pdi-/llo/‘vlcri~~

I< K R I< R K R K K R K

K K R K R R R I< R R R

C R R R R R R

C K K R K R K

NR K K

NK R R

considered as chemical. physical, and thermal harriers for protecting membranes installed behind these sheathing\. Brick sheathings contribute to the longevity of tank linings by offering addilional chemical, thermal, and physical protection. They are excellent insulating barriers and, consequently, can bc considered a\ enerpy savers.

PLASTIC

TANKS

AND

LININGS

There are a multitude of plastics availahlc for solving corrosion prohlcm? in the metal-finishing industry. The more popular and cost effective are polyvinyl chloride (PVC). Type I: polypropylene (PP); linear polycthylcnc (PE): and fihrrgla\\~l-einIbrced plastics (FRP). All of these plastics have been auccesst’~~lly used as sell-upporting tanks and “drop-in” tank liners for process and storage applications. The thermoplastics (PVC. PP. and PE) are being used for mechanical howling to concrete for similar application\. Polxvirl,12 c~h/o,-it/~~ i\ one of the oldest proven plastic< for fabrwting highly chemicnlresistant structures. (See Tahlc VIII for the chemical resistnncc of wuctural plastics.) Type I PVC is one of the bat pln\tic:, axailnhle for resistance to a multitude of strong oxld17ins enwronmcnt\ up to It\ thermal limitation 01‘ approximately 150°F (66°C). Type I PVC has outstanding structural integrity attrihutahle to its high tenGle. compressive, and flexural properties. It is one of the easiest plastics from which IO conwuct tanhs, tank liners. dipping ba\kels. and other storage and procca~ equipment. PVC is easily thcrmtrl’ormctl. wt. drilled. tapped, machined. and welded. consequently. making ic an excellent. \ersatilr, and cost-effective material from which to fabricate corrosion-rc‘\i\t;lnt equipment. Po/~~~uo~~,v/r~re has arrived. Its popularity ih nttributahlc to its cxccllcnt chemical rcG\tuncc and urpo\w\ PVC hccausc of it\ superior physical and thermal reaictance. It is available as flame and nonflamc retardant homopolymer and copolymersheet \toch. Polypropylene utilix\ fabricating techniques similar to thoac used i’or PVC. Small tanks for 678

pickling and plating, large tanks for continuous strip pickling lines, and pickling line covers have been fabricated of polypropylene. These and similar fabrications are enjoying an enviable record of success in challenging chemical and physical applications, Lirwav po/wrh$enr fabrications have performed well in the small-parts metal-finishing industry because of their low absorption, high chemical resistance. and outstanding resistance to impact. They do not possess the rigidity and tlexural capabilities of PVC or PP and, consequently. the fabrications are. significantly smaller. A new generation of PE is making significant inroads into the finishing industry. Crosslinkable. high-density PE for rotational molding is being used for tanks of 5-10.000.gal capacity. These new resins exhibit excellent physical properties and good resistance to weathering. Applications for the most part have been indoor and outdoor storage tanks and portable receiver tanks. Fiher;p/ns.v-r-rir!f~~~~ p/trsric.\ have been succea~fully used for a multitude of application\ for many years. The earliest fabrications utilized furan and phenolic resin binder system,. The more popular resin binder systems in use today are polyester. epoxy, and vinyl ester. The success of FRP structures is substantially predicated on the proper choice of resin and hardener system most inert to the en\,ironment to which the fabrication will be subjected. It i\ not enough to request an FRP tank. any more than it i\ to request a tlake-glass-remforced polyester tank. It ia important to either provide the f;lbricator M ith all chemical, thermal, and physical information pertinent to the process in order that the proper resin and hardener system might be selected. or to have in-house technical competency capable of making the proper selection of the r&n-hardener system from which the manufacturer can fabricate the deGred equipment. There arc numerous polyester resin\ available: however. for apgreasi\e corrosion environments, such as high concentrations of alkalies and a broad range of acids. the blaphenol-A fumarate resin is the be\t recommendation. Vinyl esters are epoxy-resin-based. thermosetting resins that provide chemical resistance similar to that of bisphenol A polyesters. They are considered to be slightly better in high concentrations of alkaline hypochlorites than the bisphenol A polyester. Vinyl esters exhibit outstandmg physical properties, i.e.. tensile, tlexural. and elongation that are normally associated with epoxies. The chemical resistance and physical propertie\ of epoxy resins are functions of the resins, but equally important. they arc very much functwns of the curing systems employed. Aliphatic and aromatic amine curing systems impart better chemical resistance to epoxy resins than do polyamide curing agents. Polyamides. however. impart better impact resistance to epoxies than do aliphatic or aromatic curing systems. The intention of these three examples of the resin system\ utilized for constructing fiberglass-reinforced tanks and tank lminga is to point out the necessity of knowing the chemistry of the system, or relying on reputable manufacturers to provide the technology required to make the best selection to fulfill end use requirements. Where the chemistry of these various systems contributes substantially to the physical properties of the structure. the most profound influence on physical properties is derived from the proper design and use of various reinforcing mediums, i.e.. glass fibers, glass cloth. roving, mat, veil, etc. Consult reputable manufacturers for proper design consistent with the end-use mandates for chemical, thermal, and physical properties. The chemical resistance of FRP is comparable to the chemical resistance data shown in Table VII. Table VIII summarizes the chetnical resistance of PVC, PE, and PP. The mechanically bonded thermoplastic lining system previously described circumvents many of the limitations inherent in some plastics, as well as coating. and many other elastomeric and resin lining systems. The sonically welded anchor studs are of the same plastic as the sheet and are placed at approximately 2-3 in. on centers. Sheet thickness and anchor stud density provide the rigidity necessary for a successful thermoplastic lining application. The studs. being of the same plastic as the sheet. ensure thermal and physical property similarity. The lining system is equally appropriate for new and existing concrete, as

679

I

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to 3/16”,

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680

almost