Duan C.G., Karelin V.Y. Abrasive Erosion and Corrosion of Hydraulic machinery

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264

Abrasive Erosion and Corrosion of Hydraulic Machinery

Table 5.10 Typical molding conditions and mechanical properties

of thermosetting polyurethane and RTV elastomer

Moulding condition

Prepolymer

Viscosity (cps)

Curing agent

Viscosity (cps)

Mixing ratio (parts by wt.)

Prepolymer

Curing agent

Mixing temperature (°C)

Prepolymer

Curing agent

Pot life (min.)

Curing temperature (°C)

Curing time(hour)

Post cure temperature (°C)

Post cure time (week)

Mechanical property

Hardness (Shore A)

100%

modules (kg/cm

)

300%

modules (kg/cm

)

Tensile strength (kg/cm

)

Elongation at break (%)

Tear strength (kg/cm)

Tabor abrasion loss

(mm/1000 cycle) (H-18 wheel, 1kg)

Water absorption (%)

(40°Cx7 days)

Thermosetting

polyurethane

TDL-PIMG

2000 (80°C)

MOCA®

500~600(120°C)

120

100-110

3-4

R.T.

1-2

306

503

1.4

RTV

RTP

3000 (25°C)

RTC

1000 (25°C)

R.T. (Room-temp.)

R.T.

5.5

R.T.

1-2

R.T.

1-2

83 (ASTM D2240)

43 (ASTM D412)

85 (ASTM D412)

387 (ASTM D412)

519 (ASTM D470)

69 (ASTM D470)

40 (ASTM D1242)

1.6 (ASTM D690)

2> The size of product is limited because the scale of equipment for heating

is limited.

Erosion - Resistant Materials

265

3> Casting and curing at 100° to 110°C make it impossible to repair the

polyurethane lining in the field.

Typical

Thermosetting

Polyurethane

Lined Pipe

Prepolynen

Curina Aoent

melting

degassing

melting

degassing

10-30 mmHg

120'C

10-30 mmHg "

^nxing

[—

100-120'C

Steel Pipe;

blasting -j-

degreasing

primer

application

drying

baking

pre-heating

eveling ->

centrigugal casting

(mold)

(1 layer) 100-110T 100-110'C

-^-pouring

-^-curing >

100-110'C

30-60 min

100-110T

3-4 hours

post cure

(aging)

■>

product

R. T.

1-2 weeks

R T V

Lined Pipe

R T P

melting

degassing

R T C

melting

degassing

R. T.

10-30 rinHg

R, T,

10-30 mmHg '

^•jnxing

|—

R. T.

Steel Pipe;

blasting

degreasing

primer

application

drying

baking

^pouring

eveling -5>

centrigugal casting

(mold)

(2 layer) R. T.

-?»

curing

R. T,

£0-30 min

R. T.

1-2 hours

post cure

(aging)

■>

product

R. T.

1-2 weeks

Figure 5.15. Manufacturing processes of typical thermosetting

Polyurethane lined pipe and RTV lined pipe

5.3.2 Room-Temperature Curing Polyurethane (RTV)

(1) Improving polyurethane curing reaction characteristics:

To control the polyurethane curing reaction, it is necessary to modify the

composition of functional groups. RTV chemistry is basically similar to

conventional thermosetting polyurethane but special polymeric compo-

nents are added to both prepolymer (RTP) and curing agent (RTC) in

order to improve molecular cross-linking reactivity at room temperature.

Modified points include the composition ratios of active-NCO, -OH, and -

groups in the prepolymer and curing agent, and the molecular weight

266 Abrasive Erosion and Corrosion of Hydraulic Machinery

distribution of the polymer components. These changes create a new

polyurethane system that can be cured at room temperature, RTV molding

conditions and the initial properties of RTV are shown in Table 5.10.

Physical properties of RTV bear some comparison with those of

thermosetting polyurethane.

(2) Erosion resistance:

Erosion resistance is the most important characteristic for a lining

material used in slurry transportation pipes. Slurry erosion tests were

performed to compare the erosion resistance of RTV to other materials.

Figure 5.16 shows test conditions and relative erosion resistance obtained

in a rotary erosion testing apparatus (Figure 5.17). The erosion resistance

of RTV to coarse silica stone was 10 to 12 times greater, and to fine silica

stone 40 to 50 times greater than that of mild steel. Thermosetting

polyurethane also showed good erosion resistance; to coarse silica stone 7

to 10 times greater, and to fine silica stone 30 to 40 times greater than

mild steel.

Test

Condition

Material

Relative Wear Resistance '

No 1

Coarse

Silica

Stone

ok,

10mm

dnax 20mr

■■

657

V ■ 2n/sec

150 hours

RTV

Thermosetting PU"

Polyester PU*

High Density PE"»

Low Density

PE**

Polybwtylene

Polyamde

Natural Rubber

1,57. Cr Steel

Mild Steel

. XX \ \ 1

No Z

Fine

Silica

Stone

1.5mm

3.5mm

357.

V : 2m/sec

280 hours

RTV

Thermosetting PU"

Polyester PU*

High Density PE*"

Low Density PE"

Polybutylene

Polyamiole

Natural Rubber

1.57 Cr Steel

Mild Steel

\\\\\\X\\\M

PU*: Polyurethane; PE**: Polyethylene

*** Wear resistance of mild steel is expressed as 1.

Figure 5.16 Chart of relative erosion resistance to mild steel

by means of rotary erosion test

Erosion - Resistant Materials

267

rotating direction

slurry

Figure 5.17 Schematic drawing of rotary erosion tester

(3) Effects of mechanical properties ofRTVon erosion resistance:

Relationships between erosion resistance and mechanical properties are

shown in Figs 5.18 (a) to (f) for RTV and other materials. These figures

show the relative erosion resistance of materials as compared with mild

steel, the figures being obtained from the rotary erosion tests using coarse

silica stone. It can be seen that the erosion resistance of polyurethane

elastomers increases with the increase in tensile strength, tensile

elongation and tear strength. It also increases with the decrease in

hardness and Tabor abrasion loss

These results may imply that the erosion process of these materials can be

regarded as a mechanical fracture phenomenon, because the most erosion

resistant polyurethane has the largest tensile strength multiplied by elongation

among the materials tested (see Figure 5.18 (e)), and the mechanical fracture

energy, which is an index of resistance to the mechanical fracture energy,

which is an index of resistance to the mechanical fracture, is proportional to

the tensile strength multiplied by elongation.

Lower hardness and larger tear strength are desirable for increasing the

erosion resistance of RTV as shown in Figures 5.18 (a) and (b). But these

properties are closely correlated with other properties. For example, lower

hardness relates itself to reduced tensile strength,, and increased tear strength

leads to decrease in elongation. Therefore, we may conclude that a balance of

properties is needed for the best results.

268

Abrasive Erosion and Corrosion of Hydraulic Machinery

Tabor abrasion resistance showed a good correlation with slurry erosion

resistance, as is shown in Figure 5.18 (f). This test may be usable for

selecting materials.

) 20 40 60 80 100

Hardness (Shore A)

915

Crf10

4> 5

•(b)

-•

•

o --

,ff-°

»V-'

••

O * A A

50 100 150 200

200 400 600 800

Tear Strength (kg/cm) Tensile Strength (kg/cm

)

1000

a 15

Prf 10

<L>

(u 5

* 0

Ke)

-o-.

-»'•

* A A O

1 2

■

3 4

"15

Crf 10

_C3

Crf

Elongation at Break (%) Tesile Strength (kg/cm

)

x Elongation at

Break (%)xl0

■(f)

»" a

■

) 50 150 250

Taber Abrasion Loss

(H-18 wheels,

kg)

(mg/1000 cycle)

Wear test condition: Coarse silica stone; No.l in Figure 4.2

Symbols: o-RTV, • -Thermosetting polyurethane, A-Polyethylene

A-Polybutylene, -Natural rubber,

■-Poly

amide

Figure 5.18 Relation between erosion resistance and mechanical property

(4) Hydrolytic stability:

The hydrolytic stability of polyure-thane is a major factor in ensuring the

long-term durability of polyurethane lined pipe in slurry service. It is

greatly affected by the composition of the prepolymer. Generally

Erosion - Resistant Materials

269

speaking, polyether-polyurethane has a better hydrolytic stability than

polyester-polyurethane does. The susceptibility to hydrolysis of ester

linkage in polyurethane structure is far larger than that of ether, urethane,

urea, biuret, or allophanate linkages. Cross-links of polyester-

polyurethane are destroyed in a shorter time than polyether-polyurethane.

(5) Corrosion resistance:

Corrosion resistance of lining materials in the principal consideration in

severely corrosive slurry environments. RTV is generally resistant to the

mild conditions of common acids, bases, and organic reagents encountered

in slurry environments.

5.3.3 Durability of RTV Lined Pipe

(1) Loop test:

The loop test was carried out using closed loop equipment totaling 35 m long.

This loop is composed if 89 mm or 114 mm (O.D.) pipes, a slurry tank, a

slurry pump, an electromagnetic flowmeter and a thermometer. The flow rate

and the temperature of slurry were automatically monitored.

Table 5.11 shows the shape of specimens and materials tested. All pipe

specimens had the same inside diameter and carefully joined using flange

joints to avoid discrepancy in level.

Table 5.11 Specimens and materials used in closed loop test (mm)

Specimen

Straight pipe:

dimater (O.D.)

thiness

length

90° Bend pipe

dimater (O.D.)

thiness

bending radius

89,

114

500

89,

114

450

Material

RTV lined pipe:

lining thickness 4

hardness (shore A) 80

Thermosetting:

lining thickness 4

hardness (shore A) 80

Lined pipe

Steel pipe: ASTM A53-71a

thickness 8

270

Abrasive Erosion and Corrosion of Hydraulic Machinery

Coarse silica stone, medium and fine silica stones, coarse and fine coals,

and fine iron ore were used as abrasive particles to simulate dredging slurry,

dam deposit slurry, coal slurry and iron ore slurry respectively. Table 5.12

shows, the testing conditions.

Table 5.12 Testing conditions of loop test

Specimen

size

(mm)

.114

114

Slurry

silica

stone

silica

stone

silica

coal

iron ore

concentrate

Particle

size

(mm)

dmax 6

1.5

Umax

*■■•>

0.5

max

2.4

dmax 15

Concentration

(wt%)

Velocity

(m/sec)

Tempe-

rature

(°C)

20-36

5-19

15-35

6-34

25-50

25-45

8.1-8.3

8.1-8.2

7.8-8.2

7.7-8.1

8.3-8.5

7.3-7.6

Period

(day)

120

Average erosion loss and maximum erosion loss were obtained

respectively from the weight loss and the thickness loss of a specimen.

Correction for water absorption was made by using a dummy specimen

immersed in water at the same temperature during the same period as the loop

erosion test. Table 5.13 shows the loop test results. The erosion loss of a

straight pipe is the average erosion loss, and that of a bend pipe the maximum

thickness loss. It also shows the relative erosion resistance of polyurethane

lined pipe taking the erosion resistance of

steel

pipe as 1.

The test results in Table 5.13 are summarized as follows. The coarse

silica stone slurry caused larger erosion than the medium one independent of

the material tested and of the specimen shape. The fine silica stone (condition

No.

3), fine coal (condition No. 5) and iron ore (condition No. 6) caused so

little damage to lined pipes that their erosion resistance relative to the steel

pipe could not be estimated. The bend specimens suffered larger erosion than

the straight specimens, even though it was taken into account that the erosion

Erosion-ResistantMaterials

111

loss of the bend pipe was the maximum loss in thickness and, that of the

straight pipe was the averaged

loss.

In every test condition, PTV polyurethane

lining pipe exhibited better erosion resistance than thermosetting polyurethane

lining pipe.

The adhesion strength of the RTV elastomer after the loop test was more

than 20 kgf/cm at 90°

peel-off.

Thus, any deterioration in adhesion was not

detected.

Table 5.13 Results of loop test

Testing

condi-

tion

Specimen

Straight

Bend

Straight

Bend

Straight

Bend

Straight

Erosion loss (mm/year)

RTV

Thermosetting Steel

polyurethane pipe

2.12 2.35 30.20

23.60 30.70 201.40

1.64 1.64 18.70

19.80 37.40 132.50

0.00 0.00 2.53

0.29 0.31 7.60

1.50 1.50 21.30

0.00 0.00 1.46

0.00 0.00 1.66

Relative erosion resistance

jy Thermosetting Steel

polyurethane pipe

14 13 1

9 7 1

11 11 1

7 4 1

* * i

26 25 1

14 14 1

* * i

*: Impossible to estimate the relative wear resistance.

(2)

Field

test:

Table 5.14 shows the field test results with RTV lined pipe installed in three

slurry pipelines in practical use. In every environment, RTV lined pipe

showed good erosion resistance and enough adhesion strength. Use of RTV

lined pipe in the blastfurnace slag pipeline and the blastfurnace dust

concentrate pipeline are continuing successfully.

272 Abrasive Erosion and Corrosion of Hydraulic Machinery

Table 5.14 Results of field test

Slurry condition

Slurry

Dredging

sand

Blast

furnace

slag

Blast

furnace dust

concentrate

Particle size

(mm)

: 0.15

dma*: 25

: 0.2 ~

0.3

(wt%)

Velocity

(m/sec)

5.0

4.2

5.0

Specimen

(Pipe)

(mm)

750 mm (I.D)

1000 mm long

Steel thickness

12 mm

RTV lining

7 mm

300 mm (I.D)

Steel 10 mm

Natural rubber

lining 20 mm

RTV lining 10

100 mm (I.D)

Steel 8.6 mm

RTV lining 5

Erosion rate

Steel:

4.7 mm/year;

RTV:

0.7 mm/year;

Steel:

> 30 mm/year,

life - 3 months;

Rubber:

10 mm/year,

life - 2 years

RTV:

1.5 mm/year,

predicted life -

5 years;

Steel:

2.3 mm/year,

life - 3 years;

RTV:

no failure after

4 years;

5.3.4 Cost Estimation

In the cost estimation of polyurethane lined pipeline, we have to consider not

only the initial cost but also maintenance and replacement costs, and service

life as well. Because RTV lined pipe is manufactured by an energy-saving

process the manufacturing cost is more than 20% lower than that of

Erosion - Resistant Materials

273

thermosetting polyurethane lined pipe. Table 5.15 shows the relative cost and

life expectancy in two slurry environments. The life/cost ratio may be a

comprehensive measure to demonstrate the advantage of RTV lined pipe over

other materials, even though it leaves the installation and maintenance costs

out of account. It may be concluded that RTV lined pipe is the most

economical material for pipelines which handle the abrasive and corrosive

slurries of dam deposits, dredging sands and coarse coal. Considering

maintenance and replacement costs, its advantages become even greater.

Table 5.15 Relative cost and life expectancy

Installation

environment

Coarse silica stone

Coarse coal

Material

(Pipe)

Steel pipe

RTV lined pipe

Th.PU* lined pipe

Steel pipe

RTV lined pipe

Th.PU* lined pipe

Relative

cost

Relative Life/Cost

life

ratio

1.0

3.5

2.6

1.0

6.5

5.0

Th.PU*: Thermosetting Polyurethane;

All relations based on 300 mm (O. D.), 6-m long flanged pipe.

Thickness: Steel pipe, 14 mm;

Polyurethane lined pipe, steel 8 mm + lining 6mm.

5.4 Ceramics

M. Matsumura

The important components in coal liquefaction plants are known to suffer

severe damage due to the erosive nature of coal slurries as well as to the

corrosive agents contained in them. Very short service lifetime (weeks) is

experienced by the letdown valves trims and seats used to throttle high-

temperature (350 ~ 450°C), high-pressure (30-140 kgf/cm

) slurries. Block

valves lose their tightness owing to the galling on their surface caused by coal