PICKLING OF STEEL
71
Approved: PICKLING OF STEEL by Melvin Kaufman A Thesis Submitted for Partial Fulfillment of ·the Requirements for the Degree of Bachelor of Science in CHEMIC AL El'.TGINEERING In Charge of Investiiation Head. of Major Pepartm.ent Virginia Polytechnic Institute Blacksburg, Virginia 1962
Transcript of PICKLING OF STEEL
Approved:
PICKLING OF STEEL
by
Melvin Kaufman
A Thesis Submitted for Partial
Fulfillment of ·the Requirements
for the
Degree of Bachelor of Science
in
CHEMIC AL El'.TGINEERING
In Charge of Investiiation
Head. of Major Pepartm.ent
Virginia Polytechnic Institute
Blacksburg, Virginia
1962
II.
III.
-ii-
TABLE OF CONrrENT'S
0 • • • • • . " • • • • • INTRODUCTION • • • •
LITERATUHE REVIEW • • • • • • e • • • • o • •
Pickling Procedures for Various Ferrous Metal Products ••• • • • • •
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2
2
Pickling Solutions • • • • • • • • • • • 4
Concentration of Acid 4
Pickling Inhibitors • • • • • • • • 4
Pickling Temperatures • • • • • • • 5
Theory and Mechanism of Inhibitors •••••• 0 • • • • • 5
Advantages and Disadvant;ages of Using an Inhibitor. • • • • • • • 6
Pickling Defects .. • • • • • • • • • • • 7
Blistering ••••••
Hydrogen Embrittlement
Overpickling .. • • • •
• •
• • • • • • •
o· • • • • • •
7
7
7 Picklepitting • • • • • • • • • • • 8
EXPERIMENTAL •• .. . . . . . . • 0 •
Purposes of Investigation ••• • • • • •
• • • • •
9
9
Plan. of Experimentation. • • • • • • • • 10
Preliminary Investigation • • • • • 10
Description of Experimental Work • • • • • • • • • • • • • • • 10
... iii-
Determination of the Most Efficient Pickling Bath •- . . . .
Determin~iti.on of the Effect Of Adding.an Inhibitor to-the· Pickling Solution ••••• • • •
Determination of the-Life of, the Inhibitor •• o •••• • • •
Determinatior1 of the Frequency Factor and the Energy of ·· · Activation for the Pickling of' Steel in 18.;l Per Cent· , Sulfuric Acid Solution ••••
J:iilaterials • • • • • • • • • • • • • •
• •
• •
Page
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11
ll
12
12
Apparatus • • • o • • .• • -• •• -. -. '• 'o • • 14 Method of Procedure • • • • • • • • • • • 16
Preparation of-the Pickling Baths _ • • , • • • • • ·• • i. • • ·• 16
Determination.of the Most-Efficient Pickling Bath • • • • • 16
Determination of the Effect of Adding an Inhibitor to,the" Pickling Ba:th • • • • • • • • • .. 18
Determination of' the Life of the .Inhibitor. • • ,. • • • •· • • • 18
Maintenance of Constant ·Acid Concentration •••••• • • • •
Data and Results • • • • 0 • • • • • .. •
Sample Calculations • • • • • • • • • • •
19 20
45
Loss .in Weight of Sample • • • • o - • 45
IV.
v.
DISCUSSION
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Calculat;ion of the Initial Concen·tration of Sulfuric Acid i.n the Pickling Bath
Calculation of the·Frequency Factor and Acti va:tion Energy ••••••••••
• • • • • • • • 0 • • • • •
• • • •
• • • •
- • • 0
Discussion of Results• • 0 • • • • • • •
Page
Condition of the Samples before Pickling ••••••• o • 48
Procedure . •· . . . . . . . •· . . . 49 Reproducibility of Results. • • • • 49 Effect of Agitation • • • • • • • • 49 J<~.ffect of the Rodine· 82-A
Inhibitor ••••••• • • 50 Evalua:tion of Results • 0 • • • • •
Recommendations • • • • • • • • • • • • •
Limitations • .. • • • • • • • • • • • • • CONCLUSIONS . . " . • • ...... - .. • • • •
VI. SUMMARY • • • • • • o • •·· •· •· • e • • • • •
50
52
54 56
5~ 61 62
63
VII. BIBLIOGRAPHY. • • • • • • • • • • • • • • • • VIII. ACKNOWLEDG.MENTS • • e O • • Cl • • • e •
IX. VITA • ••• ••• • • • • • 0 • 0 e • • • •
Table II.
Table III.
Table IV.
'l'able v.
Table VI.
Table ·vII.
Table VIII.
Table IX.
Table x.
Table XI.
LIST OI1' TABLES
Pickling of Steel in Sulfuric Acid ::1olution • • • • • • o • • • •
Pickling of Steel in Ferric Sulfate-Sulfuric Acid Solution •••••••• • • • • 0
Pickling of Steel in Sulfuric Acid-Hydrochloric Acid Solu·tion • • • • • • • • • • • 0 •
Pickling o.f .Steel in Citric Acid-Ammonia Solu·tion • • • • • • •
Pickling of Steel in Phosphoric Acid Solution • • • • • • • • •
Pickling of Steel in Hydrochloric Acid Solution o ..... o •••
Determination ·of -the .Effect of an Inhibitor on a Sulfuric
• •
• •
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27
29
31
33
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Acid Picklina Bath • • • • • • • • 37 f_--,
Pickling of S·teel in Spent Inhibited Sulfuric Acid Solution • • • • • • • • • 0 • • •
Utilization of Inhibitor and Acid by Pickling Steel in Inhibi"t,ed Sulfuric Acid Solution o ••••••• • • • • •
Determination of the l?requency Fac·t;or and Activation Energy for the Pickling of Black Stovepipe Bteel in 18.3 Per Cent Sulfuric Acid Solution
Results of thEi Pickling of Black St;o·v-epip0 St,eel in
• • • •
Acid Pickling Baths •• • • •••
40
41
43
Table XII. Results of the .. Pickling of Steel i.n Inhibited and · Uninhibited Sulfuric Acid Solution • • • • • • • • ..
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Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure ;1.
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LIST OF :F'IGURgs
Pickling or Steel in 18.3 Per Cent Sulfur-le Acid Solution .. • • . • • • • •.•.. • • • •
Pickling of' Steel in Ferric Sulfate-Sulfuric Acid Solution • .. • • • •. • • .• • • • •
Pickling of Steel in Sulfuric Acid-Hydrochloric Acid Solution • • • •. • •. • . •. • •
Pickling of Steel in Citric Acid-Ammonia Solution •. •. • ..
Pickling . of' Steel in 18. 7 5 Per Cent Phosphoric hcid. Solution ••••••••••
Pickling of Steel-in 20.5 Per Cent Hydro chJ.oric Acid Solution • .. • • • • .. • • •
Pickling of Steel in Spent Inhibited Sulfuric Acid Solution • ., 5 • • • .~ , • •
Determination of the Frequency Factor and Activation Energy for the Pickling of.Black Stovepipe S·teel in 18 .3 Per Cent Sulfuric Acid Solution ., • • • .. .. • • • •
.,. . .
.. . . • • •
• • •
• • •
• • !It
Page
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I. IN'l'RODUG'fION
Pickling is a cheap method for cleaning the
surface of a piece of metal with lit-tile attack on
the metal itself. In the industrial piekJ.ing of iron
and iron produc·ts there are seven solu·tions most
commonly used as pickling baths.
Pickling inhibitors are agent~s ·that may be added
to an acid pickling be.th to diminish the attack of the
acid on ·the metal areas :from which the seal<-; has been
removed, wi'thout appreciably rertarding the rate at
which the acid removes scale or rusto
'rhe purposes of' this invr:lstigation are: to
determine which pickling bath will remove the most
surface oxide.in the least amount of time; to
determine the effect of the addi·tion of' an inhibitor
to the pickling bath; to de-te:rmine the life of the
inhibitor; and to determine the frequency factor and
energy of act;i vatio11 for the pickling of steel in
lf!.3 per cent sulfuric acid solution.
· II. LITEHATURI~ fil~VIEW
~'Pickling is thG term applied to the chemical
removal of surface oxides from metal by im.rn.ersion in (1) .
an acid solution" • Many different pickling baths
with regard to type, strength., · and tempera·ture of the
acid solution are possible. ~l1!1e bath to be used depends
on ·the mat;erial to be pickled, the character of the scale
involved, .and t~he surface desired after the pickling.
Pickling Procedq.res for Various
Ferrous M<:rtal Produc·ts
'When low ... carbo.n s·teel is pickled for enameling,
galvanizing or tinning, special precautions·are
necessary to insure a surface that., is chemically clean
as well as free from scah1. In pickling low-carbon
steel, inhibitors or foaming agent,s may b~ twed in
·the bath, but only v.ri th careful and proper
precaution, because some inhibitors leave a thin but
very tightly adherent surface film, which clings
persistently to the metal even after careful rinsing.
Pickling teriq:i~1ratures are generally between 150
to J.60 °F. 'l'his range of temperatures pri:;duces a.
better quality finished product than wo,uld be gotten
a-t higher temperatures, where time and pickling
capacity permit, an acid concentration of five or
six per- cent is advisable.. Ho1,1ever, where
comparatively low temperatures ar•e employed, it is
customary to compensate for decreased therm.al
activit~r by re,ising the acid concentrat,ion ·to about
10 or 15 per cent. Vigorous mechanical agi·tation o . .f
the bath is always advisable. When the solution is
allowed to remain stagnant, gas pockets may form.,
keeping -the acid out of contact with the metal and
arresting the pickling solution on these localized
areas. When the steel is galvanized, these
scale ... retaining areas remain uncoated. Agitation
.offers the f·urther advantage of securing; uniform
ac:td concentration throughout; the bath, assuring a·
more nearly uniform :ra:l:ie of pickling.
-4-
Pickliri« Solutions
Sulfuric, muriatic, nitric, and hydrofluoric . (?) acids, or mixtures of them £l.re generally used -~ •
Sulfuric acid is ·{jhe cheapest pickling acid and the . ( l}
one most commonly employed • .Muriatic acid is
used for special purposes, such as etching before
galvanizing or tinning, and soni,atimes for pickling
stainless steel. Nitric acid is used in the pickling
of_stainless steel and is occasionally employed to
oxidize scaled su~fa.ces in order to facilitate
pickling~ Hydrofluoric acid is sometimes added to
the bath to accelera:te pickling, and is used
occasionally in pickling cast:Lngs to remove sand._,~
Concentration of Acid.. ri'he concentrat:i.on used
depends upon the kind and t,empt~ra.ture of acid, the
type of material being pickled, and the surface
desired.
Pickling Inhibitors. Pickling inhibitors are
agents that may be added. to an acid pickling bat,b. to
dimini$h the attack of the acid on the metal areas
from which the scale has been rem<.>ved, without
appreciably retarding the rate a;!; which the ac:l.d
removes scale or ru.st; and to diminish the severity
of hydrogen embri t'clement
Pickling Temperatures'. An increase in tempera·ture
greatly increases· the a.cti vit,y of the pickling bat,h.
Over-pickling is likely to occur at high temperatures~
The choice of an inhibitor is an important factor in
est,ablishing the limiting temperature, since some
iriliibitors fail rapidly at~ high temperatures.
Although a temperature of 170 to 190 °Fis
sometimes satisfactory when the time cycle is
short, pitting may result if the pickling period is
prolonged. With many high-carbon and alloy S'teels,
a pickling temperature of 140 to 150 °F has been found
satisfactory for efficiency, surface quality, and life
of the inhibitor.
Theory and f~Iechanism of Inhibitor.§.. '!'here are
three theories concerning inhibitors. 'rhe firs·t
theory is that an inhibitor is a negative catalyst
selective in action, retarding the react.ion of acid
on metal but not on scale. In practice, no inhibitor
corrtinues its original effecti ven.ess una.bated
throughou.t the entire pickling cycle. However,
inhibit~ors lose efficiency so slowly that the loss
can hardly be attributed to reactions in which the
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· inhibi'l;or plays· a major part as reagen-t. The effect
seems an.a.logous to the poisoning of a ca.ta.lyst. The
second the?ry.states t.hat inhibitor action seems to·
be associated "1rith an increase in the hydrogen over
voltage at ·the ma'tal {cathode) surface. A protective
coating of hydrogen, maintained on the metal surface,
helps to protect the metal from direct contact i:.-d·th
the acid, thus diminishing the a:ttack.
'£he third theory states that a thin layer of
inhibitor material is e.dsorbed or plated out on the
surface of the metal. However, if such a. layer exis•ts, it is so extremely· thin as 'to · escape
detection in many instances.
Advanta.e:e~ and Disadvantages of using an
Inhibitor. The advantages gained from usi11g an
inhibitor are as follo,ws: reduction. in,metal loss,
saving of pickling; acid, prevention or minimizing of
scrap losses from overpickling, and a 'decrease in
blistering and in hydrogen embrittlement. The
disadvantages incurred in.using an inhibitor are:
increased pickling time, possibility of residual
surface film, which may interfere with subsequent
operation, and. added eost of the inhibitor.
-7-
Pickling Defects
Some of the more common defects brought on by
pickling are presented. in t.he .follO'wing paragraphs.
Blistering. 'rhis is a t;roubl~some defect on
sheet and strip steel. Blistering is brought about
by gaseous inclusions forming gas pockets just beneath
the surface of the steel during rolling. Hydrogen
generated in the pickling operation, penet;rates these
pockets and lifts the surface, causing a blister.
Properly selected inhibitors may minimize blistering
but cannot prevent ito
Hydrogen E;mbritt;lement o Hydrogen embrittlement
is a result; of ·the penetration of t~he steel by
nascent hydrogen. Inhibitors are valuable in
mini.mi zing this effect.
Overpicklingo This error causes porosity of the
transverse surfaces and a roughening of the whole
surface, accompanied by a discoloration and decrease
in size and weight. Overpickling can be avoided by
removing the metal from the bat;h promptly when the
pickling has been accomplished. Inhibitors aid in
preventing overpickling, but are not a guarantee
that it will not occur.
Picklepitt;ing. Eleetroly·tic pitting is the most
prevalent and troublesome type. It is characterized
by a patchwork of pitted areas irregular in shape.
Caused by an electric potential between the scaled
areas and th<:: clean steel, electrolytic pitting occurs
on.ly where the scale has been removed from small areas
before the pickling or at an early ~rtage in the
process.
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lII. EXPERIM1£N'l'AL
The :follm•ling s·ections contain the purposes
of this investigation, the plan of' experimenl-;ation
by which this investi:gation wiis carried out, the
matt1rials and apparatus _used, the method of procedure,
data and results, and a sample of tl'w calculations
perfonaed ..
Purposes of Inves·tiga:tion
The purposes of this investigation are: to
determine which pickling·bath·will remove the most
surface oxide in the least amount of time, to
determine the ei"'fect of the addition of an inhibitor
to the pickling bath, to determine the life of the ·
inhibitor, and to determine the frequency factor and
energy of activation for ·t:.he pickling of steel in
18.J pGr cent sulfuric a.cid solut,ion.
Plan of. Experimen ~at.ion .... , .. ' .. -:-i---
'I'he f ollowi.ng paragraphs contain the plan of
experimentation by which this investigation was
carried out.
trelimina.ry In.vestiga:tion. A brief study of the
available literature was to be made by the author in
order to fam:tliarize himself with the more general
principles of the pickling of iron and iz•on products.
Description of . "BxRerimental Work. 'l'he
experimental worl<: consisted of determining which
pickling bath is most efficient, determining the
effect of the addition of an inhibitor to a pickling
bath, determining the life of the inhibitor, and
det~ennining the frequency factor and energy of
activation for the pickling of steel in sulfuric
acid.
Determina·tion of the Most f~fficient Bath. The
most efficient pickling solution was, to be determined
from a plot of loss in weight versus time. The loss in
weight, expressed as milligrams per square iuch, is
the loss in weight of a steel coupon after being
immersed in a pickling bath :for a three .. minute
interval. The coupon was to be immersed as many
times as was required for the weight loss to become
constant. Then the coupon was to he immersed one
more time for approximately JO.minutes.
Determinati()n of the Effect of Addj.ng an
Inhibitor ·to the Pickling ,Batq. 'l'he effect of'' adding
an inhibitor to a pickling solution was to be
determined from t wo plots of the loss in weight of
the steel coupon versus time. The time of immersions
chosen we:r-e 1, 2, 4, $, 16, and 32 minutes.. A plot
would be made to represent t,he piekling o.f the coupon
in an uninhibited pickling bath, and a eecond plot to
represent; the pickling of the coupon in an inhibited
pickling bath.
D~t~1·minution of the Life of t;he Inhibitor. From
the plot of t,he pickling. of the steel . coupon in the
uninhibited pickling bath, the time required to remove
the surface.oxide from the steel coupon may be
obtained. Then each of four steel coupons a.l:"e
immersed in a freshly-prepared inhibited I;>ickling
bath one at a time for this amount of time. Then a '
plot, of loss in weight vers.us time for a fifth steel
coupon will be m.ade. The length of immersion in the
pickling bath will aga;in be 1, 2, 4, B, 16, and 32
minut)es. 11.'his proc.edure will .be repeated until the
amount of surface oxide removed, and the rate of at;tack
on the metal itself, are approximately the same as
obt:.ained using the uninhibited pickling bath. It will
be necessary to replenish the amount of acid in the
pickling bath so that; the acid remains at full
strength.
Determin<'ltion of' the · Ft"equenc;z Factor and the
.Energy of'. Activation for the Pickling: of Steel Yl . 18 • 2 Per Cent Sulfuri.c Acid q,2.lu_!;l,2,4. The frequency
factor and the energy of activati1;,n for the pickling
of steel in 18.3 por cent sulfur:lc acid solu·tion will
be determined using the Arrehenius equation once the
rate of attack on the base metal is known.
Materi~
Under this. heading thei"'e will be found the
malieriais used during this investigation.
Acetone. Impure. · Supplied by the J. 'l'. Baker
Chemical Co., Philadelphia., Pa. Used to dry sample.
Ammo11\'-!.m Hx;droxide. · C. P. , code 1293, lot
E501006. Supplied by General Chemical Division,
-1.3-
Allied Chemical and Dye Corpe, New York, N. Y.
Used as a component of the pickling solution.
Citric Acid. 1•1anufactured by J. T. Baker
Chemical CQ., Philadelphia, Pa. Used as a
component of the pickling solut,ion ..
Distilled '.'later. Distilled f:rom Virginia
Polytechnic Ins·titute tap wat;er, Blacksburg, Vi:rg:i.nia.
Used to wash t.he sample,.
Ferric Sulfate. Lot No lJlJ-1-2. · Supplied by J.. ·r.
Baker Chemical Co., Phillipsburg, N. J. Used as a
component of the pickling solution.
Hu;drochloric Acid. Assay (HCL) - 37,7 per cent,
lot No 6041. Supplied by J. ·r. Baker Chemical Co. ,
Philadelphia, Pa. Used as a component of the pickling
solution.
Phosehoric Acid. Lot No 9127. Supplied by J. •r.
Baker Chemical Co., Philadelphia, Pa. Used as a
component of t;he pickling solution.
Potassium Nitrate. Lot No 0310, code 2122.
Supplied by General Chemical Division, Allied Chemical
and Dye Corp., New York, N. Y. Used as a component of
·the pickling solution.
-14-
Supplied by Arnchem
Products, Inc., Ambler, Pa. Used as inhibitor.
Sulfuric Acid. Assay ( a2so4) ... lot No 90628.
Supplied by J. •r • Baker Chemical Co. , Philadelphia,
P8.o Used as a component of the piclr.J.ing solu·tion.
Under this heading there will be fi,und the
apparatus utilized during this investigation.
Basin. Supplied by Blacksburg Hardware Co.,
Blacksburg, Va. Used to contain water in which
pickling solution was heated.
Beaker. Capacity 250 ml, pyrex. Supplied by
Fisher Scientific Co., Pittsburgh, Pa. Used to
containing pickling solutions when tests were being
run at room tempera-t~ure.
Beaker .. Capacity 800 ml, pyrex,. Supplied by
Fisher Scient;ific Go., Fi t~tsburgh, Pa. Used to hold
wash water.
Cla"UJ2S. 'l'wo required. Supplied by Fisher
Scientific Co., Pittsburgh, Pa. Used to hold
condenser and flask to ring stand.
... 15-
Condenser. Supplied by Fisher Sci,m.tific Co.,
Pit;tsburgh, Pa. Used t;o condense vapors from pickling
solution when tests were run at elevated temperatures,
c. c., tem.peratures greater than 120 °F o
Flask. Capacity 250 ml. Supplied by Fisher
Scientific Co., Pittsburgh, Pa. Used to hold pickling
solution when tests were rD.n at~ temperatures gr.eater
than 1:20 °F'.
Graduated Cilinder. Capacity 50 ml. Supplied:
by Fisher Scientific Co., Pittsburgh, Pa. Used to
measure volume of' acidic components of pickling
solu·tions.
Gradunted Cylinder. Capacity 100 ml, pyrex.
Supplied by Fisher Scientific Co .. , Pittsburgh, .Pa.
Used to measure volume of~ distilled water used in
pickling solution.
Hot Plate.. One hundred and .fifteen volts.
Supplied by Fisher Scientific Co., Pittsburgh, Pa ..
Used to heat ·water £or heating pickling solution.
Power Station .. Type 220-C, 115V50 ... 6025A
Supplied by General Radio Co., Cambridge, Mass.
Used to control current to hot plate.
Ring Si?_anq. Supplied by Fisher Scientific Co.,
Pittsbu:t·gh, Pa. Used for moun-ting condenser and flask.
Rubber Tu.bing. Supplied. by l1isher Scientific Co.,
Pittsburgh, Pa. Used to supply wa:ber to, and remove
water from condenser.
Stove Pipe. Per cent carbon 0.095. Supplied by
Brm.°",.1 ts Hardware, Blacksburg, Va.. Used as sample for
pickling.
Thermometer. Engraved, 0-300 °:F'. Supplied by
l1~isher ~,cient;ific Co., Pittsburgh, Pa. Used to
measure telllpera·ture of pickling solution.
Method of Procedure
Th0 procedure by which this investigation was
carried out is presented in the following f)aragraphs.
_f'.reoaration.q_f' the Pickling Bathq,. The pickling
baths were prepared according·to specified
concentrations.
Det~tminat;ion of the Mos·t Efficient, Pickling
Batho Af·ter preparing the pickling bath according
to the specified con.centrat'ion, and bringing the
pickling bath to the desired temperature thei steel
coupon. was immersed f.or three minutes. 'rhe coupon
was weighed before immersion .. After three minutes the
coupon ws.s · immersed in. distilled ;;•Jater to remove any
loose scale which might be clinging to the coupon.
'rhe coupon ·wa$ ·then dipped :in acetone to remove the
water, and dried in· a~r. After the coupon was dry
it 1.1as weighed to determine t.he loss in weight. This
procedure was repeated until the loss in weight became
constant.. Then the coupon was iinrnersed for
appro:x;imately ,30 minutes, washed, dried, and
weighed again. 'l'he la.st step was hr~lpful in
determining wh\~dier e.11 the surface ·oxide had been
removed, and for measuring the ra·te of attack on the
bare metal. rr:.he plots of ·the loss in weight versus
time were made for all the pickling baths used. A
straight lint~ beginning at the last poin.t on the
curve, ;.,md tangent to the curve is drawn until it
intersects the vertical (loss in weigh:t;} axis. 1'he
point of in1;ersect:Lon. :represents ·the amount of scale
removed. '£he ;intersection of a st;raight line drawn
from the point o·f tangency with the horizontal (time)
axis represents the time required to remove the surface
oxide. By comparison of results the most efffcient
solution was det,ermined.
Determination of the Effect of.Adding an Inhibitor
to the Pickling J3atq. 'l'.he pickling; bath being studied
was 18.5 per cent sulfuric acid solu-tion because the
only inhibitor available was Rodine f?2-A. This
inhibitor is used only for sulfuric acid. This
solution was prepax·ed by mixing 22 milli.li·ters of
97 per cEmt sulfuric acid with 173 milliliters or dis·tilled water. 1'he inhibited pickling bath,
containing 0.25 per cent inhibi·tor, was prepared by
mixing 22 of sulfuric acid, 158
millili tt-irs of distilled water, and 20 milliliters
of a solution containing 5 milliliters o.f the
inhibi·tor, Rodine 82-A, and 200- milliliters of
distilled water.
Using the same procedure Sts in the previous
section, a st.eel coupon was cu.t .in hal.f and immersed
in the baths., rrhe t,imes of immersion were 1, 2, 4,
8, 16, and 32 minutes. Using the loss in weight data
obtained two curves were plotted, one for the
inhibited bath and one for the uninhibited bath.
'rhe effect of ·the inhibitor on the bath can be
determined from a comparison of the tv.Jl') curves.
Dete:r•;nination of the Life of the Inhibitor.
The pickling bath used to determine the life of the
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inhibitor was of the same composition as the inhibited
bath USE}d in the preced:1.ng section.
F'our samples were immersed, one at a time, in ·the
bath for that length of •time required to remove the
scale. The time was determined in the preceding
section. The weight of the samples, and the pickling
bath were noted before and af·t.er immersion of the
samples. Then, using a new sample, a 'test was made
on the solution and the loss in weight of the sample
versus time curve was drawn. The times of immersion
for the last sample are 1, 2, l1-, 8, 16, and 32 .minutes.
'l1his procedure was repeated until ·the rate of attack
on the base metal, the amount of scale remov·ed, and the
time required to remove the scale was approximately
the same for this pickling bath as for the
uninhibited bath.
M:aintenance. of Constant Acid Concent,ration .•
During the determination of the life of the inhibitor
it was necessary to keep the concentration of the
sulfuric acid. at 18.5 per cent.
The acid concentration of the pickling bath,
af·ter sa,mples had been immersed for a length of
time, was det;ermined using a pH meter and 1.0 N
sodium hydroxide solution. Ten milliliters of the
... 20 ....
pickling bath solution was titrated with one milliliter
volumes of sodium hydroxide and the pH read on the pH
meter. Each point is plotted on a curve of pH versus
volume of sodium hydroxide added.. The ·titration wa.s
considered complete when a sharp break in the curve
appeared. A straight line drawn from the peak of the
curve intersecting the horizontal (volume of sodium
hydroxide added) axis represents the a.mount of sodium
hydroxide added. Using this data, the normality, and
then the concentratie>n of the acid in the pickling bath,
was computed.. 'l'hen the amount of acid required to
re·turn th<~ acd.d concentration to 1$. 5 per cent was
calculated.
Data and Results
'!'he experimental data and results obtained during
this invest,igation are presented in the form of. tables
and graphs as indicated in the following paragraphs. Table I presents the data obtained during the
pickling of steel in. 18.J per cent sulfuric acid
at 73 °F, 77 °F, 79 °F, 106 °F; 126 °F, 140 °F, and
14-4 °F. The table indicates ·the area of' each sample
pickled, the time of immersion, and the loss in weight
o:f ·the sample. Figure l is the graphical representation
of t;he l.oss in weight of the sample versus ·time.
Table II presents the da.-ta obtained du.ring the
pickling of steel in ferric-sulfate-sulfuric acid
solution at, 82 °Jl and 160 °F. This table indicates
the area of each sample pickled, the time of immersion,
and the loss in weigh·t of the sample. l1"'igure 2 is the
graphical :representation of t,he loss in weight of the
sample versu.s time.
Table III presents the data obtiained during the
pickling of steel in sulfuric acid-hydrochloric acid
solution at; 80 °F. 'l'his table indic,).tes the
concentration of the mixed acid pickling bath, the
area of the sample, the time of· immersion, and the
loss in weight of' the sample. J?igure 3 presents the
data in graphical form.
'I\:1ble IV presents ·the data obtained during the
pickling of steel in a citric acid-ammonia solution
at 210 °t. This table indicates the area of the
sample, the acid and ammonia concentrations, the area
of the sample being pickled, the time of immersion,
and the loss in weight of the sampl 1~ o Figure 4
presents the data.in graphical form,..
Table V presents the d1..::i.ta obtained during the
pickling of st~eel in 1$. 75 per cent phosphoric acid
solution. 'fhj_s table indicates the area of t;he
samples being pickled, the temperature at which these
tests WE~:i:·e run, ·the time of immers:Lon, and the loss in
weight of th.~ samples. F'igure 5 presents the data in
graphical formo
Table VI presents the d~'rta obtained during t,he
pickling of steel in 20.5 per cent hydrochloric acid
solution at 79 °F o rrhis table indicates the area of
the sample, the time of irrunersion., and 'the loss in
weight of ·the sample. Figure 6 presents the data in
graphical form.
'l'able VII presents th.f:~ data obtained during the
pickling of steel in bot,h inhibited and uninhibi·ted
18 .3 per cent sulfuric acid solution at 78 °F. ':ri1e
inhibitor being tested was Rodine 82-A. 'rhis table
indica·tes the area. of the sample, the acid and
. inhibitor c,)ncentration, the::: area of the sample, and
the loss in weight of the sample. Figure 7 presents
the dat;a in graphical form.
'£able VIII presents the data obtained during the
pickling of steel in. spent inhibi·ted 18.3 per cent
sulfuric acid solutton. at 78 °f. This table indicates
the acid and inhibitor concentrations, the area of the
samples, the time of immersion, the loss in weight of
the sample, and the length of utilizat,j.on of the bo:th
before the sample was immersed in i't. F'igure 7
pres<:mt,s the data in graphical forme
Table IX presents the data obtained during the
utilization of the inhibitor and acid in inhibited
sulfuric acid concentration at 78 °F. This table
indicates the acid and inhibitor concentrations, the
length of utiliza·tion. the area of the sample, the loss
in weight of the sample, and the loss in weight of the
pickling bath.
Table X presents the data used to determine the
frequency fact;or .and ·th.e energy of acti vatic>n for the
pickling of black stovepipe steel in 18 .3 pE!r- cent
sulfuric acid solution. This table indicates the
reciprocal tem.perature, and the rate of attack on
the bare metal. Figure 8 presents this data in
graphical form and is used to dei~ermine the frequency
factor c.md energy of act.i yation. o
'l'able XI presents the results of the pickling
of black stovepipe steel in acid pickling baths.
'rhis table indicates t,he pickling bath used; the
temperat,;ure at which the tests ~,iGre run, th~) amo1.mt
of scale rem.ov·ed, the time requirt?d to remove ·the scale,
and the rate of attack on the base met.al.
irable XII presents the resul·ts of the pickling of
black s·tovepipe steel in inhibi't;ed and uninhibited
lJ.3 per cent sulfuric acid solution. 'I'he table
indicates the condition of the pickling bath, the area
of the sample, the temperature a.t w'hich the test was
run~ the amount of scale removed, the time required ·to
remove the scale, and the rate of attack on the base
metal. . 6
The frequency fact;or was found. t,o be l.2x10 -1 sec
and the energy of' activation to be 6000 calories per
gram mo1.
'
,1')';{'1,$[%;1;,_ il:~~~
f'~lf~~'t;m~ t ~, ~t
"' ,,~.-.,,s;c~-~-•. 'Ii' -171>1 i\~d (~~e,~tl ·t,~~~i- l
l
·~ l '''fl'; -i~-!ft ,,i,,;J,~."1' -
:20«iJ """""·
•:i>j ,ttr11 ~,,,-.~•N ,..;.~
l_ 'l ·7~ :-•· ,if ..... J"l.-,iS ~-
11.1'0 ·--1., •. io
'1i'(J i?'.H\t_ ,;lit;jt·~·~ -1:t,.M:)
-2'-0 .•. :21i ..,-..
1~~:-50 ---
·---?l..,JO --
-
-
6 1
-~ 'l ':¼J'\ 19l;~;wl,Q°l;£ ....... -~,12 - 'it ~--' ,;;,,i._.;fi.-,1F
·---'Th~·· '.a\•"· -:,.~fit);}'~-
4JI~, ---)J •. 40 -· ..... -"""'""' 29.,.m -
J9.)() ,.,..,.
-
40
36 :c: (.)
~32 d (/)
ffi 28 a.. cri ~24 :E w i 20 :E <( Cl)
LL 16 0.
1-::c <!> 12 w
8 Cf) Cf) 0 ....J 4
5 10 15 20 25 30 35
TEMP. -140 Clf ~-- ARE.A---1.125 SQ .. IN.
TEMP. -144 °F ~------- ARE A - 1.5 SQ. IN.
TEMP.- 126 °f -------t
AREA- 1.5 SQ. IN.
TEMP. -- 73 °F AREA- 1.5 SQ. IN_. -
TEMP. 77 °F ~----"-l
TEMP.-79°F AREA-1.5 SQ. IN. ...__ __ _ AREA-1.5 SQ.It-,!.
TEMP.- 105 °F ~---1
AREA- 1.5 SQ. IN.
40 _4:_5 50 55 60 65 70 75 so·=: 85 TIME, MIN.
FIGURE I. PICKLING OF STEEL IN 18.3 PER CENT SULFURIC ACID SOLUTION
90
TABLE II
Pickling of Stoel 1u Ferric Sulfate-Sulfuric
Acid Solution ~-----'fype of Stjeel: Ferric Sulfate Concentration:
!?lack St~ovepipe 6 .S7 Per C(mt 3.98 Per Cent Ac:id Goncentration:
'l'est 1rempera:t;ure, °F Area of Sample, sq in.
Time
min
3 6 9
12 15 18 21. 24 50 $2
82 2.0
9 160 1.75
Loss :i.n Weight of Sample
mgm/sq in.
30.30 JJ.15 36.35 70.45
22.65 35.55 41.50 55.90 68.75
177.50
180
160
140
:r: (.) z 120 -0 (/)
a:: w a.. (/)
::i: 100 (!) ::i: w ....J a.. ::i: <t Cl) 80 lL 0
:r: (!)
w 3= z 60 tn (/) 0 ....J
20
0 TEMP.-160 °F
-----l
AREA-1.75 SQ. IN
CONC. OF FERRIC SULFATE-6.87 PER CENT CONC. OF SULFURIC ACID- 3.98 PER CENT
TEMP.- 82 °F AREA- 2 SQ. IN.
20 30 40 50 60 70 80 90 TIME, MIN.
FIGURE 2. PICKLING OF STEEL IN A FERRIC SULFATE-SULFURIC ACID SOLUTION
29 ... -
TABLE !II
Pickling of Steel; iu Sulfuric h_cid-Hydrochloric
'fy'pe of Steel: Hyclrochlo:ric Acid Concentration: Sulfuric Acid Concentration: Area o.f Sample: 'I'emperature:
'rime
min
3 6 0 ';I
12 15 18 21 2l., 64
Loss in
Black ::a;cvepipe 17.6.5 Per Cent 3.77 Per Cent 1. 5 Sq in.
80 °F
Weight of Sample
mgm/sq in..
5.10 9.15
12.30 14 .• 70 15.60
16.10 16.30 16.50 17.40
18
16 ::c <.) z 14 -0 Cl)
0::: 12 w a.. (/)
10 (!)
w 8 ..J a.. < Cl)
6 lJ.. 0
::c 4 (!)
w 3: z 2 Cl) Cl) 0 _J 0
0 5 10 15 20
TEMP.- 80°F AREA- 1.5 SQ. IN.
CONG. OF SULFURIC ACID- 17. 65 PER CENT CONG. OF HYDROCHLORIC ACID - 3.77 PER CENT
25 30 35 40 45 50 55 60
TIME, MIN.
FIGURE 3. PICKLING OF STEEL IN SULFURIC ACID -HYDROCHLORIC ACID SOLUTION
65
-31-
•rABLE IV
}:ickling _Q! Steel in Citric
Acid-Ammonia Solu'tion
'fype of Steel: Acid Concentration: Ammonia Concentration:
Black Stovepipe $.77 Per Cent 2.17 Per Cent 1..5 Sq in. Area of Sample:
'femperature:
Time
min
g 12 18 24
30 60
210 °F (boiling)
Loss in.Weight of Sample
mgm/sq in.
0.215 0.240 8.300
14,. 550 17 .L}OO
18.200 18.350
:r: (.) z -d Cf)
a:: w fl..
Cl)
(!)
:E
w _J fl..
<{ Cf)
LL 0 f-:r: (!)
w 3 z Cf) Cf) 0 _J
2
18
16
14
12
10
8
6
4
2
0
TEMR - 210 °F (B0IUNG) AREA -1.5 SQ. IN.
CONG. OF CITRIC ACID- 8.77 PER CENT C0NC. OF AMMONIA- 2.17 PER CENT
0 5 10 15 20 25 30 35 40 45 · 50 55 60 TIME, MIN.
FIGURE 4. PICKLING OF STEEL IN CITRIC ACID-AMMONIA SOLUTION
-
-33-
Pickling 2f Steel iu PhosQ_horic Acid Solution
'ry-pe of Steel; Acid Concentration:
.Black Stovepipe 18.75 Per Cent
Area of Sampl0:
l1est Temperature, °F
Tim.e
min
l 3 6 7 9
12 15 31 45 63
a Air agitation.
l r ~. . • :> .... q in.
lJ 177
Loss in We:i.ght of Sample
mgm/sq in.e
19.05 -· 20.40 21.65 --- 22.80 21.LtO --23.60 ..... 25.15
23.25 26.65 25.00 --...... 52.60 2.s.30
. 55
50
:::c: 45 (.) z TEMP..-177°F
6 40 .AREA- L5 SQ. IN. en er w a. 35 c,j
(!) 30 lt
p
LaJ t _J a. <( (/) AIR AGITATl:ON LL TEMP. 165°F 0 I- AREA- 1.5 SQ .. IN. ::c (!)
w 15 3: z (/) 10 (/) 0 _j
5
(J'--------------------------------0 5 15 20 25 30 35 40 45 50 55 60 65
TIME, MIN
FIGURE 5. PICKLING OF STEEL IN 18.75 PER CENT PHOSPHORIC. ACID SOLUTION
TABLE VI
Pickling .Qf Steel iu.Hydrochlqr!.£.~ Solution
'l'ype of Steel: . Acid Cone en t,ration:. Area of' Sample: Temperature:
Black Stovepipe 20.5 Per Cent l.J75 Sq in.
"70 OF
min
0 g 9
12
15 1g 51
7 .
Loss in Weight of Sample
mgm/sq in.
--.30.50 31.00 .31.35 31.50 31.75 31.75 31.80
33
30
J: 27 TEMP.- 79°F O· z AREA - 1.315 SQ, IN d en 2 a: w a. en 21 :i (J:)
:i uJ 18 .J a. ::E c( en 15 u.. 0
r- 12 J: (!)
w 9
z en "' 0 6 .J
0 s 10 15 -20 25 30 35 40 45 TIME, MIN
FIGURE 6. PICKLING OF STEEL IN 20.5 PER CENT
HYDBOCHLORIC ACID SOLUTION
rrime
min
1 3 7
15 31 63
-37-
TABLE VII
Determination of ~h!a :~ffect Q! §!!l Inl}ibi tOJ.:
.Q.B .si Sulfuric Acid Pickling !!ath
Type of Steel: Acid Concentration: Inhibitor Concentration:
Black Stovepipe 18.75 Per Cent
0.25 Per Cent 1.5 Sq in. Area of' Sample:
Temperature: 78 °F
Loss in Weight of Sample
mgm/sq in.
Uninhibited Inhibited
3.60 7.60
12.55 17.70 20.00
21.50
2.35 5.20
10.35 14.40 16.40 16.80
TABLE VIlI
Pickling Qi: Steel ill Sp<;1nt Inhibited
Sulfuric Solu·tion
t'ype of Steel: Temperature: Acid Concentrat.ion: Inhibitor Concentration: Area of Sample:
Time min
1 3 7
15 31 63
95
Black Stovepipe 7$ 0!4"' 1$.5 Per Cent
0.25 Per Ccn·t, 'by Volume 1. 5 Sq in.
Length of Utilization of Pickling Bath
112 min 207 min 302 min
Loss in Weight of Sample mgm/sq ine
1.45 1.00 2.40 J.liO 1.65 7.35 6.80 3.10 12.95
12.10 6 .• 10 17.25 19.20 11.65 19.40 23.25 16.00 20.60
25.75 1?.20 21.05 -·-------------------------
. :I: (.)
2
20
z 18
ci en a:: 16 lu a.. c,j 14 ~. (!)_
w 12 _J a..
10 LL 0 I- 8 :I: (!)
w 3:: 6 z Cl)
4 _J
5 10 15 20
UNINHIBTED ~--i TEMP.- 78 °F
25 30 35 40
. . . ·_ . . .
SOLUTION UTILIZED FOR 302 MIN. . TEMP. - 70 °F
SOLUTION ·UTILIZED FOR 2.07 MIN. .____--1
TEMP.- 75QF
CONC. OF SULFURIC ACI0-18.5 PER CENT
CONG. OF INHIBITOR - 0.25 PER CENT
AREA OF SAMPLES - 1.5 SQ. IN.
45 so· 55 60 66 70 75 80 . 85 90 95 TIME, MIN.
FIGURE 7. PICKLIN.-G OF STEEL IN SPENT INHIBITED SULFURIC ACID SOLUTION
TABLE IX
Utilization .Q£ Inhibitor and~ by Pickling
Steel in Inhibited Sulfuric !.£!s! Solution
Type of Steel: ·remp0rature: Acid Concentrati(>n:
Black Stovepipe 7$ °F 18.5 :Per Cent
Inhibitor Concentration: Initial vfoight of' Pickling
Solution:
0.25 Per Cent; by Volume
219 .. 5518 Grams
Length of Areu of' Loss in Weivht .:> Loss in Weight Utilization $ample of Sample of Bat}?,
min sq in. mgm/sq in. gm
28 1.500 8.40 l.9l1J6 28 1.500 10.35 0.3461 28 1.500 8.50 0.2415 28 1.375 16.80 0.2244 95 1.375 25.85 27.233ii, a
95 1.500 17.20 2.6721 8.3 1.500 2.1.05 3 .J08li
a Evaporation loss also included.
'l'ABLE X
Determination .Q.f the f.r.§.CiUengy F'actor _fil'.ll! Activation
Energy for,~. Pickling .Qf Black Stovepipe Steel
in 18 .3 Per Cent Sulfuric Acid ~ioJ.ution ,_...........-:~.___
l T
o.0033g-o.00336 0 .. 00335 0.00318 0.00304
0.00299 0.0029s
Rate of Attack on Bare Metal
mgm/sq in./min
0.090.3 0.0973 0.0532 0.1870 , 0.2770
0.4830 o. 5300
10000
1000
100
.x
10.0
1.0
0.10
3 6 9 12 15 18 21 24 27 30 33 ·
1/T x 10~ °K
FIGURE 8. DETERMINATION OF THE FREQUENCY FACTOR AND ACTIVATION ENERGY FOR THE PICKLING OF BLACK STOVE-
PIPE STEEL IN 18.3 PER CENT SULFURIC ACID SOLUTION
( .
16. l 1' H2soit
i.,, 1' u,10~ . . ,.a1 fg _ re2 (se9;3 .
17.65 % ~S04 J.77 % RCL
·. s.11 -~ Ci,tric ·· A.cid .
2.,17 1& l':Jfi3
18.15 !l!jl04, ,
20 • 5% .i:itlL
13 11
· 126 140 144 3:l-
160
210 {!li,iling)
·-16·sa · 177 · ·1,
Amoun:t &f Seale
Re1t1(r)ited
.18.50 15.00 li.60 16.75 16 .• 2s 28.10 11.1, i2.,o 27 .• 00
. '
Tim~ Requill"~Gl to h~ve Seale
41 61 JO lS 15
9 15 24 15
' "'' ~m Pe dissolved. ~q i~./rd11
o.,04S2 0~04S7 Ol02.l6
.0.093S 0.13.$; 0.241,; 0.2,se o.,s,0 3.9050
·O.)OOQ 1.1100
e.010.s
-lffld.M.ted -
Intd.hi~e& ftlli~ w.ma .Iallblt•eci 'Ailltie4 .,, .. ~t.i-M4 11t:1lt11d J02cn·
14 ,,
Au.ate et _ flu· ~dn4 it&M •f 4ttdk. feale · .w lleaft •• Ba.ft ..... ~.... -- -· 1.1111: ---
•11/fl/Sq ia. Illa -.VS4i ia./ld.a
1a.11 l.J.J,S_
21.0 a8,.J
-~ 0 .• 0341
Lff!l u·.w . .x·~.r· :n .. · ·r:·.·.•.-x·.r--,n·.·1. :··.u_· __ f u ·. r~i.-. t ··, 1· 1:;"·; __ t ... :J .. Ru .·-1 ,:,a _ ___ 1_1 --~----_. ... r··1: ·,,_·:,1··- ·u1_ n J, {··• I ".-•.;. ,,·
; ,
a W4- •••••in~oa- timlnl.shd dtle _to-e1tapo;mt,1oa,..
Sample Calculatioll§_
'the following are the types of calculations
performed for -tnis investigation.
1.
v1here:
Loss iq Weight; of Se.mple
Wo - Wt L ::::
A
L = loss in weight of the sample, mg/sq inch ·
Wo · ;:; we•ight, of the sample· before test ·was begun, gm
Wt
A
weight of the sample after it has been immersed in the pick_l:ing bath for •r minutes ·
area of both sides of the square meter.
6.1 = 3.0
2. .Calculation of the Inttial Concentration
of Sulfuri,c ,Ac1id in the Pickling FJath
where:
(J/E N - - V
N = normality of the acidic pickling bath
G "" weight of solute,. gm
E = equivalent weight of the solute, gm
V = volume of the solute, liters.
185/49 1
-47-
J. CalcJ:!J.ation of.Frequency Factor and
A.cti vat ion Energy .
where;·
E k =
-E/RT ae or log k == log a - ---
2.JRT
k = rate ot attack on the bare metal, mg/sq in ./min
a =
E :::::
R :::
T :::
-1 frequency factor 1 (sec)
activation energy, cal/gm mol
constan·t, cal/ gm rnol/°K
absolut,e temperature, °K.
1 The intercept of the plot of log k vs T is
the frequency factor, and ·t.he slope equ.als E ------. 2.JR
IV. DISCUSSION
A discussion of results, those recommendations
the author feels might~ prove 11seful, and the
conditions under which this inves·tigati(,n was carried
out are presented in the following paragraphs.
Discussion of Result§
In this section are presented those factors
which the author feels most directly affected the
results.
Condition. of the Samples Before Pickling. The
author .feels that the cu'nount of scale removed frora the
samples by the pickling baths cannot be properly
evaluated because all of the samples were not exposed
to the same amount of corrosion. The samples were not
cleaned before they were pickled., Thus, the rate of
pickling was · af.fected. '11he effect .of' the su:ri'ace
film on the sample slowed do\'m the rate only in the
initial immersion. Once this film was removed the
pickling process proceeded normally .. The author
feels that the final results were ncrt affected.,
-49-
Procedure. The procedure devised ·ror this
investigation was weak in several areas. Having to
dry each sample in air after· each irn.mersion caused a
great deal of time to be lost o Each "{jime a sample
was remo·vecl from the pickling bath, some of the bath,
was los-t due to nctrag out," or the losfi due to the
removal of the sample. t·'Jhen tests were .run a·t high
temperatures a condens.er had. t1, be added to the flask
to prevent evaporation losses., The condenser made
immersion and removal of t,he sa.m.pl~i from the pickling
bath extremely dit"ficult.
Reproducibilit,y; of' Results. 'l'he resul,ts of this . ' . ' ..
investigation were extremely difficult to reproduce
with any degree of accuracy. The temperatures varied
by as much as plus or minus 5.0 °F, arid the volumes
of the solutions used varied by plus or minus 0.8
raillilit,ers.
Effect of Agitation. Although there was little
agitation of the pickling bath during the immersion
and removal of the sample from the pickling bath, the
rate of pickling was affected by ·chis agitation. If
the solution was agitated only slightly f'o;r a few
-50-
immersions and then greatly agitated, the increase in
the rat,e of pickling was ~very noticeable"
Effect of the: Rodine~2 ... A Inhibitor. i'he results
of the pickling of the samples in the inhibited
sulfuric acid pickling bath were too erratic ·to lead
to any valid conclusions. However, the author does
not fE)el that this inhibitor should be precluded from
further use because of th:i.s until further tests are
m.ade. 'fhe only :reason for these erratic results, at
this• point, must lie in the experimental technique
because the procedure used in testing this inhibitor
did not deviate from. the·procedu.re used in the other
tests.
Evaluation of Results. Although some of the
pickling baths tested removed more scale, and perhaps,
had a slower rate of attack on the bare metal, l8.75 per cent phosphoric acid was deemed the :most efficient
pickling solution because this solution removed the
surface ,oxide in the · 1east time; also, two tests run
wit;h this solution· produced results which agreed with
'three milligrams per square inch for the amount of
scale removed, and there was no change in the tirne.
-51-
The plots .of loss in weight; of th(~ sample versus
t~ime indicated that; the rate of removal of scale
decreased as the t,~st proceeded. 'i'his was to be
expected because most, of ·the scale was :remov·ed in the
first fe,-1 immersi<.'>ns. The rate of attack on the bare
metal, as the curves show, increased ate. constant
rate.
When the acid was used up, naturally the amour1t
of scale removed decreased. Howe,rer, the curves
indicate that the rate o:f attack on the bare metal
remained una.ffscted by the decrease in the amount of
free acid.
The erratic action of the inhibitor precludes
any discussion of results. irhe .author is unable to
account for this erra·tic . beha·vior.
-52-
Recommendations
On the basis of the information obtained from this
inv-est.igation t,he following recomm~.mdations are made:
1. The effect; of ternperature on the pickling of
steel in 18.75 pt~r cent phosphoric aci~ solut~ion
should be studied by pickling steel in thi.s solution
beginning with a room temperature and ending with a
temperature of about; l 75 °F •.
2. The effect of air agite.t:i.on on ·the pickling
of steel in 18. 75 per cent phospho:ric acid solution
at various 'temperatures should be studied by running two tests at the sam~i ·temperature; one 1Jtith air
agitation, and one without a:lr agit<;l.tion. •
. 3. ThH eff,ect of an inhibitor on the pickling
of' steel in 18.75 per cent phosphoric acid solution
at varlous temperatures should be studied.
4.. All sample:;i shi)Uld be thoroughly cleaned
before any tests are :mm so ·t;hat any surface film
on the samples will be rem9ved. 'l'herefore, ·the rat,e
of attack will no·t be hindered.
5. Constant agitation. should be applied to
the pickling baths at all times so that ·the rate of
pickling will be more uniform because the
.... 53-
concentration of the pickling ba.th will be more
uniform.
6. A better method of' drying the sample should
be employed beer,.use o.f the amoun;t of time lost in
drying the sample.
Lin.ti t&tions
'l'his investigation was carried out under the
following conditions:
1. The steel being pickled w·a.s black stov·epipe
steel conta:i.n.in.g 0.095 per cent carbon.
2. The pickling solutions used were lf5.J per
cent sulfuric acid solution, 3. 9E3 per cen·t sulfuric
acid and 6.S? per cent ferric sulfate s6lution,
17 .6 5 per cent sulfuric acid and .3. Tl p,ar cent
hydrochloric acid solution, 8. ?7 pHr cent ci.t,ric
acid and 2.17 per cent ammonia solut;ion, 18. 75 per
cent phosphoric acid solution, and 20. 5 per· cent
hydrochloric acid solution ..
3o The temperatures at which the 18.3 per cent
sulfuric acid solution wa.s t.es·ced were 73, 77, 79,
106, 126, 140, and 144 °F. 4. The te1np1~ratures at which the 3.98 per cent
sulfuric acid and 6.87 per cent ferric sulfate
solution was 'tested were 82 and 160 °F.
5. 'rhe temperature at which the 17.65 per cent
sulfuric acid and 3.77 per cent hydrochloric acid
solu·tion was tested we.s 80 °F.
-55-
6. The tempera tu.re at ·which the 8 .?7 per cent
citric acid and 2.17 per cent e.mmonia solution was
tested was 210 °F (boiling).
7. Jrhe temperature a-c ·which the 18.75 per
cent phosphoric acid was tested were 165 and 177 °F ..
8. The temperature at which the 20.5 per cent
hydrochloric acid was tested was 79 °F.
9. 'l'he time of each immersion for the samples
ranged from one minute to 32 minutes.
10. The total time of immersion for each samplG
ranged from 48 minutes to 95':minutes.
11. ''fhe volume of the pickling media used in
the ·tests to determine the mosti efficient pickling
solution was 250 milliliters.
12. 'l1he volume of the pickling media used in the
study of the effect of the inhibi·tor Rodine 82-A was
200 millilit~rs.
1.3. The inhibitor studied was Rodine 82-Ao
V. CONCLUSIONS
'l'he following paragraphs contain the conclusions
drawn from 'this in:v·estigation.
1. The rate of a:t·tack on the bare metal increases
with increasing temperature; particularly in the
pickling of black s·tovepips steel in 18. 3 per cent
sulfuric acid solution where the rate of attack on the
bare metal at 75 °Fis 0.097 milligrams per square
inch per minute, while at ll~2 °ft' the rate of attack
is o. 51 milligrams per square inch per minut,e •
2. 1'he tirne required to remove t,he surface oxide
from the samplo decreases with increasing ·temperature.
3. The 18. 75 per cent phosphoric a.cid solut;ion
removed the most surface o.x.ide in thG least amount of
time at 165 and 177 °F.
4. The effect of Rodine 50 inhibitor on 20.5 per
cent hydrochloric acid pickling solution cannot be
studied because the rate of attack on the bare metal
of uninhibited pickling solution was too small, at 80 °F.
The addition of Rodine $2-A inhibitor to a
pickling bath containing 1g.5 per cent sulfuric acid
decreased th(~ rate of attack on the bare metal
from 0.0858 milligrams per square inch per minute
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to 0.0286, without appreciabl;l affecting the time
required to remove this scale, at 78 °Fo
6 .. No valid conclusions can be made concerning
the life of the· Rodine 82-A inhibitor because of 'the
errat:f,,c nature of the results.
VI • SUMr4ARt,
The purposes of this irrvestiga:tion are to
determine which pickling solution ·will remove the
greatest amount of scale in the least amount of time,
to determino the life of Ik>dine 82-A inhibitor in a
pickling bath containing 18.3 per cent sulfuric·acid
solution, · to determine the effect of the a.ddi tion of
Rodine 82-A inhibito-.r to the pickling bath con·taining
18.J per cent sulfuric acid soluti'on, and to determine
the frequency factor and activation energy for the
pickling of black stovepipe steel in 18.3 per cent
sulf'uric acid solution.
ifhe temperatures at which the pickling baths were
tested, and the pickling baths used were:· 18.3 par
cent, sulfuric acid solution a:t 73, 77, 79", 100·, 126;
140, and 144 ·0 1'"'; 3. 98 per cent sulfuric acid and 6 .$?
per cerrt ferric sulfate solution at 82 and 160 °F;
17.65 per cent sulfuric acid and 3.77 per cent
hydx·ochloric acid solution at 80 °F; s·. 77 per cent
citric•acid and 2.17 per cent ammonia solution at
210 °t (boiling), 18.75 per cent phosphoric acid
solution at, 165 °F {air agitat;ed) and 177 °F; and
20.5 per cent hydrochloric acid solution at 79 °F.
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The steel being pickled was-black stovep~pe steel
containing 0.095 per _cent carbon. The p:i.ckling
solution which removed the greatest am<:>unt of' scale
in · the lea.st amount of time was determined from plots
of the loss in weight of ·the sample per unit area
versus time for each of the t;ests run. The effect, and
life, of Rodine 82-A inhibi·hor upon a pickling bath
containing 18.3 per cent sulfuric acid solution was
studied.
'rhe samples were immersed in the pickling baths
for one to 32 minutes. l'he samples were removed from
the baths, cleaned, dried, and Weighed. · This sl:une
procedure was utilized 'in the study of the inhibitor
except th.at:; t~he inhibited pickling bath was first
utilized before the tests began.
It was found ·that 18. 75 per cent phos'phoric aci'd
rernoved 38. 5 milligrams of scale per square inch of
sample in three minut,es. It was concluded thi;1t
increased temuerat,ure increased the' rate of attack .,
on the bare metal, decreased ·the length' of time
req_uired to remove the scale from ·the sample. 'f.he
addition of Hodine $2.;.A inhibit;or to a pickling bath
containing 18~5 per cent sulfuric acid solution
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decreased the rate of attack on the bare metal without,
appreciably affecting the amount of scale removed, or
the time required to remove t,hit1 scale. No valid
conclusions concerning the l:i.fe of t,he Rodine 82--A
inhibitor in ·the 18. 5 per cent. sulfuric acid pickling
bath could be made because of the erratic nature of the
results. Due to the slow rate of attack, or 0.0210
milligrams per square inch, on the bare me·lial in a
20. 5 per cent hydrochlo;r·ic acid pickling bath the
effec·t of the addition of an i:nhib:i.-tor to this bath
was f!-Ot studied. The frequency factor was fov.nd to
be 1. 2 x 106 sec -l, and th(~ energy of aeti va tion to
6000 calories p~:;r gram mol.
It is recommended that the effects of temperature,
air agi·tati.on, and an inhibitor cm a pickling bath
Gonta.ir1ing 18. 75 per c~nt phosphoric acid be studied
in future investigations.
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VII. BIBLIOGRAPHY
1. Hall, Nathan: . Pickling and Acid Dipping, Metal
Finishing Guide Book .. Directory, p,. 243.
Metals and Plastics Publica:tion.s, Inc.,
Westwood, N'ew Jersey,· 1961. 29 edo
2. McCollum, G. H. and D. L. Warwick: The Pickling
of Iron and t;teel Products, 11Metals Handbook' 1
('11 • Lyman, gditor), PP• 725-729. Arn. Soc.
for I,Ieta.ls, Cleveland, Ohio, 1948 ..
VIII.. ACKNOWLEDGl'vHmTs
The author wishes t(, express .his sincere
appreci::rtion to Dr. N. F s £.ifurphy, Research Professor,
Department of Chemical Engineering, Virginia
Polytechnic Institute, .Blacksburg, Virginia.-, thesis
advisor for the many helpful" suggestions given t,o
the author during the course of this investigation.
The author would also likf~ · to thank· the American
Chemical Company, Ambler, Pennsylvania, for the free
samples of Rodine.
Special thanks are extended to the author's wife
for inspiration during this investigation.
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