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Localised corrosion of stainless steels depending on chlorine dosage in chlorinated water

acom3 - 2011A corrosion management and applications engineering magazine from Outokumpu

The European Drinking Water Directive sets a maximum limit of 250 ppm for chlorides in drinking water but does not contain guidelines for chlorine. The WHO drinking water standard states that 2–3 ppm chlorine should be added in order to gain a satisfactory disinfection and adequate residual concentration. The residual chlorine has a significant influence on the corrosion behaviour of stainless steels and may have detrimental consequences in the form of localized corrosion if an inappropriate stainless steel grade is used. This article clearly demonstrates that the novel duplex

grades LDX 2101® and LDX 2404® provide attractive alternatives for handling potable water and cooling water. They also have a price less affected by nickel price fluctuations and higher strength compared to the standard austenitic grades 4307 and 4404. In 30-day laboratory tests, the lean duplex grade LDX 2101® performed as well as or better than 4307 at both 30°C and 50°C. It is also shown that the presence of crevices strongly increases the risk for localized corrosion in a chlorinated environment.

Introduction

2acom | 3 - 2011

Localised corrosion of stainless steels depending on chlorine dosage in chlorinated water

Sukanya Mameng, Rachel Pettersson, Outokumpu Stainless AB,

Avesta Research Centre, Avesta / Sweden

SummaryIn drinking water systems the main stainless steel grades used are the standard austenitic stainless steel grades 4307 (304L) and 4404 (316L), with the grade selection depending on the chloride and chlorine levels in the water. The lean duplex grades LDX 2101® and LDX 2404® provides attractive alternatives, with a more stable price and higher strength level, but there is little available data on their use in drinking water systems.

The European Drinking Water Directive sets a maximum limit of 250 ppm (mg/L) for chlorides in drinking water but does not contain guidelines for chlorine. Drinking water is normally treated to give a residual level of 0.2 to 0.5 ppm of chlorine to kill bacteria, but the actual concentrations added are usually higher. The WHO drinking water standard states that 2–3 ppm chlorine should be added to water in order to gain a satisfactory disinfection and adequate residual concentration. For a more effective disinfection the residual amount of free chlorine should exceed 0.5 ppm after at least 30 minutes of contact time at a pH value of 8 or less.

The residual chlorine has a significant influence on the corrosion behavior of stainless steels. The remaining of residual chlorine in drinking water is a major factor leading to the ennoblement of the natural potential of stainless steel. This oxidizing effect of chlorine may have detrimental consequences in that stainless steels may suffer from localized corrosion if an inappropriate grade is used.

The aim was to understand and determine to what extent residual chlorine levels at various chloride contents will affect the localized corrosion behaviour of the standard austenitic stainless steel grades 4307 and 4404, also the duplex grades LDX 2101®, LDX 2404® and 2205. A simulated chlorination system was created in which the specimens were immersed for 30 days at 30°C and 50°C at chloride levels of 200 ppm and 500 ppm, with residual chlorine levels of 0.2, 0.5 and 1 ppm at pH 6.5–7.5. The specimens were investigated by visual examination and microscopy.

The duplex grades LDX 2404® and 2205 perform very well in all the chlorinated environments tested. The lean duplex grade LDX 2101® performed as well as or better than 304L at both 30°C and 50°C. The results also indicated that the presence of a crevice increased the risk for localized corrosion in a chlorinated environment. This study demonstrates that duplex stainless steels are good candidates to use in water pipes or water storage tanks.

Keywords: drinking water, chloride, chlorination, total residual chlorine (TRC), localised corrosion, stainless steel.

3acom | 3 - 2011

1 IntroductionStainless steel use for drinking water applications is increasing in the world. Stainless steels offer several advantages compared to other materials, such as mild steel, cast iron and copper which have been used for decades.

First of all, stainless steels have generally excellent corrosion resistance and require little maintenance. There is no need for any protective coating or any protective system. Correct grade selection and good practice will minimize the risk of any localized corrosion. Therefore there is practically no contamination of water in contact with stainless steel, as has been demonstrated in the investigation [1] shown in Figure 1.

Figure 1 show the leaching values for Cr and Ni were less than 5% of the maximum levels permitted by the European Drinking Water Directive (50 and 20 μg/L respectively) [2]. The low leaching levels from the use of stainless steel in the drinking water system are clearly of benefit in this situation.

Another point to be considered is the mechanical properties. The good ductility, strength and weldability enable the use of lightweight structures, for example thin walled tubes. Among the stainless steels, the duplex materials exhibit much higher mechanical strength than corresponding austenitic grades as shown in Table 1. Compared to other materials used for applications in the potable water distribution network, duplex grades

Minimum mechanical strengths at 20°C of hot rolled plate/cold rolled strip and sheet according

to EN 10088-4 and EN 10028-7 when applicable [3, 4, 5]. Table 1

Outokumpu EN 0.2% Yield Strength Tensile Strength Elongation steel names Designation MPa MPa %

Austenitic 4301 1.4301 210/230 520/540 45/45

4307 1.4307 200/220 500/520 45/45

4401 1.4401 220/240 520/530 45/40

4404 1.4404 220/241 520/531 45/41

Duplex LDX 2101® 1.4162* 480/530 680/700 30/30

LDX 2404® 1.4662** 550/550 750/750 25/25

2205 1.4462 460/500 700/700 25/20

* LDX 2101® is not yet listed in EN 10028-7. ** LDX 2404® is not yet listed in EN 10088-4 or EN 10028-7. Data for LDX 2404® corresponds to the internal standard AM 641.

Fig. 1 Nickel (Ni) and Chromium (Cr) content of water drawn from stainless steel water systems in a Scottish hospital [1].

20

6

8

10

12

14

16

18

4

2

0125018032253 4 11 18210

Days in use

Met

al c

onte

nt o

f wat

er (µ

g/l)

Ni from 304 - Cold waterNi from 316 - Cold waterNi from 304 + 316 - Hot waterCr from 304 - Cold waterCr from 316 - Cold waterCr from 304 + 316 - Hot water

4acom | 3 - 2011

allow a reduction in wall thickness and consequently reduces investment costs. All together stainless steels give a life cycle cost benefit.

The two main alloying elements of stainless steels are chromium (Cr) and nickel (Ni). From a general point of view, chromium improves the pitting corrosion resistance whereas nickel additions are made for controlling microstructure. Further alloying ele-ments may be added like molybdenum (Mo) for increasing pitting resistance or nitrogen (N) for improving mechanical properties and resistance to pit initiation. Depending on the stainless steel composition and chloride content of water, these materials may be resistant to aqueous corrosion in a wide range of pH at ambient temperature. Stainless steels ability to resist pitting corrosion may be estimated by calculation of the Pitting Resistance Equivalent Number (PREN). Equation (1) gives the most frequently employed formula for PREN calculation.

PREN= Cr (%) + 3.3 Mo (%) + 16 N (%) Equation (1)

In drinking water systems the main stainless steel grades used are the standard austenitic stainless steel grades 4307 and 4404. The grade selection depends on the chloride levels of the water and also on the severity of the crevices the materials are exposed to, as shown in Table 2 from the Nickel Development Institute. The chloride content of the water is the most important parameter because of its influence on localized corrosion, crevice corrosion in particular. The European Drinking Water Directive sets a maximum limit of 250 ppm (mg/L) for chlorides in drinking water but does not contain guidelines for chlorine [2].

2 Water ChlorinationChlorination is a one of many methods that can be used to disinfect water and control bacteria. Sodium hypochlorite (NaOCl) is the form of chlorine normally use for chlori-nation process because it is cheap and easy to dose. When chlorine added to water, it immediately begins to react with compounds found in the water to give hypochlorous acid (HOCl) and hypochlorite (OCl-). The remaining amount is called free residual chlorine.

The free residual chlorine is typically measured in drinking water disinfection systems to find if the water contains enough disinfectant. Typical levels of free chlorine in drinking water are 0.2– 0.5 ppm [7], but the actual concentrations added are usually higher. The WHO drinking water standard states that 2–3 ppm chlorine should be added to water in order to attain a satisfactory disinfection and maintain residual concentration [8]. The maximum amount of chlorine one can use is 5 ppm. For effective disinfection the residual amount of free chlorine should exceed 0.5 ppm after at least 30 minutes of contact time at a pH value of 8 or less.

The residual chlorine has a significant influence on the corrosion behaviour of stainless steels. The remaining residual chlorine in drinking water is thought to be a major factor leading to the ennoblement of the natural potential of stainless steel. This oxidizing effect of chlorine may have detrimental consequences and stainless steels may suffer from localized corrosion if an inappropriate grade is used.

Chloride level guidelines for waters at ambient temperatures [6]. Table 2

Chloride level (ppm, mg/L) Suitable grades

< 200 1.4301 (304), 1.4307 (304L), 1.4404 (316L)

200 – 1000 1.4404 (316L), 1.4462 (2205)

1000 – 3600 1.4462 (2205), 6% Mo Super austenitic, Super duplex

>3600 and sea water 6% Mo Super austenitic, Superduplex

5acom | 3 - 2011

This work was conducted to understand and determine to what extent total residual chlorine levels at various chloride contents will affect the pitting and crevice corrosion behaviour of the standard austenitic stainless steel grades 4307 and 4404 , also the duplex grades LDX 2101®, LDX 2404® and 2205. The recently introduced duplex grades LDX 2101® and LDX 2404® provide an attractive alternative, with a more stable price and higher strength level, but there is little available data on their use in drinking water systems.

3 Materials and experimental technique3.1 Materials

The materials used in this study are 4307, 4404, LDX 2101®, LDX 2404® and 2205 which were all tested as plain (sheet), welded and creviced samples. The surface finish, thickness, PREN values and the chemical composition of these materials are reported in Table 3.

3.2 Long-term chlorination experiments

Coupons of duplicate plain (sheet), welded and crevice specimens with size 60x30x3 mm were used with an as-received surface as show in Figure 2A. All cut edges were wet ground to 320 mesh. The crevice samples had a 12 mm hole placed in the centre of the sample. Samples were bolted together with INCO crevice formers on both sides of specimen (Figure 2B). All crevice formers were tightened with a torque of 1.58 Nm. It was verified that there was no electrical contact between the samples and the screw. Plain (sheet) and welded specimens were suspended in the solution on platinum wires to minimize crevice effects when investigating pitting corrosion.

Steel grades, surface finish, thickness, PREN values and the chemical composition for materials

used in long term chlorination. Table 3

Outokumpu EN Product Thickness Typical composition, weight-% steel names EN Conditions (mm) PREN16 C Cr Ni Mo N Others

4307 1.4307 2B 3 18.1 0.02 18.1 8.1 – – –

4404 1.4404 2B 3 24.1 0.02 17.2 10.1 2.1 – –

LDX 2101® 1.4162 2E 3 26.0 0.03 21.5 1.5 0.3 0.22 5Mn

LDX 2404® 1.4662 2E 3 33.6 0.02 24.0 3.6 1.6 0.27 3Mn

2205 1.4462 2E 3 35.0 0.02 22.0 5.7 3.1 0.17 –

2B: Cold rolled, heat treated, pickled, skin passed2D: Cold rolled, heat treated, pickled2E: Cold rolled, heat treated, mech. desc, pickled

Fig. 2 Coupons of plain (sheet), welded and crevice specimens used for long term testing.

Fig. 2A Fig. 2B

Sheet Weld Crevice

6acom | 3 - 2011

The welded samples were obtained by tungsten inert gas welding (TIG). The welding was done with filler material and welding conditions as specified in Table 4 and Table 5 below. This welding process is often used for water applications. All samples have the same thickness of 3 mm. Weld samples were pickled in mixed acid (3M HNO3 and 3M HF).

Chloride (Cl-) containing electrolytes with various total residual chlorine (TRC) levels, at pH 6.5-7.5, were prepared from distilled water. Chloride ions were added to the level of 200 ppm and 500 ppm as sodium chloride (NaCl). The solutions were dosed with a stock solution containing 1000 ppm of sodium hypochlorite to obtain various predetermined total residual chlorine concentrations.

Total residual chlorine (TRC) is defined as the sum of hypochlorous acid (HClO) and hypochlorite ion (ClO-) concentrations.The amount of residual chlorine was measured with a colorimeter using the diethyl-p-phenylene diamine (DPD) method [10]. Three total residual chlorine concentrations were investigated that correspond to the residual concentration typically used for water disinfection treatments: 0.2, 0.5 and 1 ppm.

The open circuit potential (OCP) was monitored for 30 days in the test solutions with the different residual chlorine levels and a temperature of 30°C or 50°C. The chlorine was dosed once every 5–7 days to maintain the residual chlorine level. After testing the specimens were examined and the depth of maximum attack was measured with a light optical microscope. A depth exceeding 0.025 mm was defined as localised corrosion.

Chemical compositions of GTAW filler (typical values, %) [9]. Table 4

Welding wire TIG Base Nominal composition, weight-% (EN ISO designation) Material C Cr Mo Ni N Si Mn

Avesta 308L-Si/MVR-Si (W 19 9 L Si) 4307 0.02 20.0 - 10.5 - 0.85 1.8

Avesta 316L-Si/SKR-Si (W 19 12 3 L Si) 4432 0.02 18.5 2.6 12.0 - 0.85 1.7

Avesta LDX 2101 (W 23 7 L) LDX 2101® 0.02 23.0 <0.5 7.0 0.14 0.40 0.5

Avesta 2205 (W 22 9 3 N L) LDX 2404® 0.02 23.0 3.1 8.5 0.17 0.50 1.6

Avesta 2205 (W 22 9 3 N L) 2205 0.02 23.0 3.1 8.5 0.17 0.50 1.6

Welding condition of welded specimens. Table 5

Base Shielding Welding speed Heat input Material gas (cm/min) (kJ/cm) Joint design

4307 Ar 21.72 0.64 Butt joint

4404 Ar 24.66 0.60 Butt joint

LDX 2101® Ar+2% N2 20.17 0.64 Butt joint

LDX 2404® Ar 19.29 0.69 Bead on plate

2205 Ar 20.38 0.50 Bead on plate

Ar: Argon gas, N2: Nitrogen gas

7acom | 3 - 2011

4 Results and discussion4.1 Open circuit potentials (OCP).

The stainless steel samples were immersed in the test solutions with 200 ppm and 500 ppm chloride at 30°C and 50°C for 24 hours before the start of chlorination. The open circuit potential (OCP) usually stabilised after ~4 hours and was typically found to lie in the range 190–220 mV for the sheet specimens after 24 hours. The values were somewhat higher for the weld and crevice specimens.

The addition of sodium hypochlorite gave a strong increase in the open circuit poten-tial. After a certain time, typically 10–24 hours the potential stabilised and the OCPMax could be measured as shown in Figure 3. The result shows that OCPMax increases with TRC level because the oxidising power of the solution increases, Table 6.

Fig. 3 Evaluation of maximum open circuit potential in chlorinated water.

800

200

300

400

500

600

700

100

0302510 15 2050

Time (days)

Pote

ntia

l (m

V SC

E)

OCPMax 720 mVSCE

Average OCPMax of five different steel grades in water containing chloride

and total residual chlorine at 30°C and 50°C. Table 6

Maximum open circuit potential, OCPMax (mVSCE)

Chloride level 0.2 ppm 0.5 ppm 1 ppm TRC, 0.2 ppm TRC, 0.5 ppm TRC, 1 ppm TRC, (ppm) Material TRC, 30°C TRC, 30°C 30°C 50°C 50°C 50°C

200 4307 425 544 722 429 454 723

4404 460 556 794 393 445 683

LDX 2101® 493 619 819 363 444 679

LDX 2404® NT NT 770 NT NT 682

2205 480 589 747 362 535 671

500 4307 345 594 652 349 347 736

4404 375 588 679 356 399 730

LDX 2101® 370 549 722 427 367 712

LDX 2404® NT NT 771 NT NT 720

2205 397 625 673 379 486 683

NT = Not tested, TRC = Total residual chlorine

8acom | 3 - 2011

The OCPMax after chlorination compared to the situation before chlorination is shown in Figure 4. The increase in OCP was about 200 mVSCE for 0.2 ppm TRC, about 300 mVSCE for 0.5 ppm TRC and about 500 mVSCE for 1 ppm TRC. This indicates that even at low TRC concentrations the open circuit potential increases.

4.2. Influence of localised corrosion on OCP for chlorinated water.

The occurrence of localised corrosion is frequently seen as a drop in the open circuit potential, as illustrated in Figure 5. After 30 days, visual and microscopy examination showed that pitting had occurred for the welded 4307 and LDX 2101® (Figure 7A). These both showed a rapid drop in OCP during testing. No corrosion was seen for the welded 2205 which maintained a high OCP throughout the test.

Fig. 4 The potential increase (OCPMax-OCP) versus total residual chlorine (TRC) after chlorine dosage for all steel grades.

700

200

300

400

500

600

100

01.21.00.4 0.6 0.80.20

Total residual chlorine, TRC (ppm)

Pote

ntia

l inc

reas

e (m

V)

200 ppm, 30°C 500 ppm, 30°C200 ppm, 50°C500 ppm, 50°C

Fig. 5 Corrosion potential change of TIG welded specimens of 4307, LDX 2101® and 2205 in 500 ppm chloride and 1 ppm TRC at 50°C showing the potential drop associated with the onset of pitting corrosion.

900

100

200

300

400

600

800

0

-100700600200 300 5004001000

Time (hours)

Pote

ntia

l (m

VS

CE)

500

700

50°C, 500 PPM CI-, 1 PPM TRC No Pitting corrosion

Pitting corrosion

Pitting corrosion

4307-weld 2205-weldLDX 2101®-weld

9acom | 3 - 2011

Figure 6 shows the OCP change of TIG welded and creviced samples of 4307 and 2205 in 200 ppm chloride and 1 ppm TRC at 30°C. Visual examination showed that localized corrosion had occurred for 4307 (Figure 7B) but not for 2205.

Fig. 7 Appearance of localized corrosion after tested in 500 ppm chloride and 1 ppm TRC at 50°C.

4.3 Visual examination after 30 days.

Samples were examined after exposure in the 200 ppm and 500 ppm chloride solutions with different total residual chlorine levels at 30°C and 50°C for 30 days. A summary of the results from this investigation is shown in Table 7. Where corrosion occurred, the cells are filled dark blue and where no corrosion occurred the cells are light blue.

Table 7 show that the lean duplex LDX 2101® was found to be at least as resistant as 4307. In all experimental conditions tested, the duplex grades LDX 2404® and 2205 perform very well with no significant localised attack. Both these grades have a high PREN (>30), whereas for the grades with PREN<30 some localised attack was observed.

The results show that the alloying elements influence the localised corrosion resistance of stainless steel. For the austenitic steels, the corrosion resistance for molybdenum (Mo) containing grade (4404) is higher than for the molybdenum (Mo) free grade (4307). A higher chromium (Cr) level in combination with nitrogen (N) addition has the same positive influence for duplex grades.

Fig. 6 Corrosion potential change of TIG welded and crevice specimen for 4307 and 2205 in 200 ppm chloride and 1 ppm TRC at 30°C.

900

200

300

400

500

700

100

0700600200 300 5004001000

Time (hours)

Pote

ntia

l (m

VS

CE)

600

80030°C, 200 ppm CI-, 1 ppm TRC

No crevice corrosion

Crevice corrosion

Pitting corrosion

4307-weld4307-crevice

2205-weld2205-crevice

No Pitting corrosion

Fig. 7B Crevice corrosion for 4307Fig. 7A TIG welded-LDX2101®

Pitting corrosion on the weld Crevice corrosion

10acom | 3 - 2011

100

90

80

70

60

50

40

30

2010

°C

100Chloride, ppm

1000

100

90

80

70

60

50

40

30

2010

°C

100Chloride, ppm

1000

Green: No corrosion Red: Pitting corrosion 0.5 ppm TRC 1.0 ppm TRC

4307 (304L)Pitting

4404 (316L)Pitting

The results also indicated that the presence of a crevice increases the risk for localized corrosion in chlorinated environments. Special attention should be taken, to avoid crevices in construction, since residual chlorine solution can remain in crevice areas and cause corrosion.

4.4 Comparison with engineering diagrams.

Engineering diagrams for a given steel grade as a function of temperature and chloride content are a useful illustration of the risk areas for localized corrosion in drinking water applications [11].

These diagrams are based on a combination of laboratory testing and extensive practical experience and provide a useful reference base for the present investigation. As can be seen in Figure 8 there is excellent agreement between the diagram and the present data

Summary of visible pitting and crevice corrosion in this investigation. Table 7

Fig. 8 Engineering diagram indicating the maximum temperatures and chloride concentration allowed in slightly chlorinated (<1 mg/L) drinking water for 4307 and 4404 [11].

Test condition Type of specimen

Temp. Chloride TRC* 4307 4404 LDX 2101® LDX 2404® 2205 (°C) (ppm) (ppm) P W C P W C P W C P W C P W C

30 200 0.2

0.5

1.0

30 500 0.2

0.5

1.0

50 200 0.2

0.5

1.0

50 500 0.2

0.5

1.0

No corrosion

*TRC = Total residual chlorine, P = Plain (sheet) sample, W = Welded sample, C = Creviced sample

Corrosion Not tested in this studyCrevice corrosion not observed; possibly due to loosening of the screw, but expected based on 30°C results.

11acom | 3 - 2011

for 4404 tested with 1 ppm TRC: pitting corrosion occurred only at 500 ppm chloride and 1ppm TRC at 50°C for the sheet specimen, and this point is above the line. For 4307 all four of condition tested showed pitting with 1ppm TRC, and should thus lie above the boundary line. If, however the comparison is made to the 0.5 ppm data, the curve seems instead slightly too conservative. The overall agreement is thus very good, and underlines the point that the chloride tolerance of different stainless steel grades is very sensitive to the chlorination level.

A summary of chlorination limits for different grades from this investigation are shown in Table 8.

It is important that a material is not exposed to excessive levels of residual chlorine. For effective disinfection the residual chlorine should exceed 0.5 ppm after at least 30 minutes of contact time [8]. During practical operation, the chloride content will most probably be lower than during this test. Thus, there is a good chance that the 4307, LDX 2101® and 4404 can be used successfully for normal service in water piping systems as long as problematic crevices can be avoided. In doubtful cases upgrading to LDX 2404® or 2205 may be advisable.

Chlorination limits which did not cause corrosion in the 30 days immersion tests for different

grades depending on chloride content. Table 8

Test condition TRC limits (ppm) for different grades depending on chloride content

Temp. Chloride 4307 4404 LDX 2101® LDX 2404® 2205 (°C) (ppm) P W C P W C P W C P W C P W C

30 200 0.5 0.5 <0.2 1.0 1.0 1.0 1.0 1.0 <0.2 1.0 1.0 1.0 1.0 1.0 1.0

30 500 0.5 0.5 NT 1.0 1.0 0.2 0.5 0.5 <0.2 1.0 1.0 1.0 1.0 1.0 1.0

50 200 0.5 0.5 0.2 1.0 1.0 0.5 0.5 0.5 0.2 1.0 1.0 1.0 1.0 1.0 1.0

50 500 0.5 0.2 NT 0.5 0.5 0.2 0.5 0.2 <0.2 1.0 1.0 1.0 1.0 1.0 1.0

P = plain (sheet) sample; W = welded sample; C = creviced sample; TRC = total residual chlorine; NT= not tested

12acom | 3 - 2011

Summarised results of 30 day tests in chlorinated solutions

containing 200 ppm chloride at 30°C or 50°C. Table 9

BM Weld Crevice

304L 316L 304L 316L (304L) 316L

LDX 2101® LDX 2404® LDX 2101® LDX 2404® (LDX 2101®) LDX 2404®

2205 2205 2205

304L 316L 304L 316L 304L 316L

LDX 2101® LDX 2404® LDX 2101® (LDX 2404®) LDX 2101® (LDX 2404®)

2205 2205 (2205)

304L 316L 304L 316L 304L 316L

LDX 2101® LDX 2404® LDX 2101® (LDX 2404®) LDX 2101® (LDX 2404®)

2205 2205 (2205)

304L 316L 304L 316L 304L 316L

LDX 2101® LDX 2404® LDX 2101® LDX 2404® LDX 2101® LDX 2404®

2205 2205 2205

304L 316L 304L (316L) 304L (316L)

LDX 2101® (LDX 2404®) (LDX 2101®) (LDX 2404®) LDX 2101® (LDX 2404®)

2205 (2205) (2205)

304L 316L (304L) (316L) 304L (316L)

LDX 2101® (LDX 2404®) (LDX 2101®) (LDX 2404®) LDX 2101® (LDX 2404®)

2205 (2205) (2205)

Ch

lori

ne

(pp

m)

10.

50.

21

Tem

per

atu

re 5

0°C

Tem

per

atu

re 3

0°C

200 ppm Chloride

0.5

0.2

Red-corrosion, (Red)-possibly corrosion, not tested in this studyGreen-no corrosion, (Green)-possibly no corrosion, not tested in this study

5 CONCLUSION• Inlong-term(30days)immersiontests,thehighestalloyedduplexgrades2205and

LDX 2404® performed very well in the chlorinated environments tested (200 or 500 ppm chloride, 30°C or 50°C). No pitting, crevice corrosion or weld attack was seen in any of the environments for these grades.

• TheleanduplexgradeLDX2101®performedaswellasorbetterthan4307(304L) at all conditions tested. In the pitting test it performed as well as 4404 (316L) in 200 ppm chloride at 30°C.

• Chlorinesolutionwithsignificantresidualchlorineconcentrationscanremainin crevice areas and cause corrosion, and therefore special attention should be taken in construction.

• TheleanduplexsteelLDX2101®isagoodcandidateforwaterpipingsystemsandtanks, when the water is mildly chlorinated. In more severe condition the higher alloyed LDX 2404® or 2205 are more suitable.

• Materialselectionguidelinesdependingonchloridecontent,chlorinedosage and temperature are shown in Table 9 and Table 10 below. In order to ensure good performance deposits and surface contamination should be avoided.

13acom | 3 - 2011

6 REFERENCES[1] C.A. Powell and W.Strassburg, Stainless Steel for Potable Water Service,

2nd European Stainless Steel Congress, Düsseldorf, 1996.[2] European Drinking Water Council Directive 98/83/EC, Nov, 1998.[3] Outokumpu data sheet, Standard Cr-Ni stainless steel.[4] Outokumpu data sheet, Standard Cr-Ni-Mo stainless steel.[5] Outokumpu data sheet, Duplex stainless steel[6] Peter Cutler, Stainless steel and drinking water around the world,

Nickel Development institute (NiDi).[7] The chlorine institute.INC, Chlorine effect on health and the environment,

3th Edition-Nov.1999.[8] Guidelines for Drinking Water Quality, 3rd Edition, 2008.[9] Avesta Welding handbook, 3rd Edition-Dec, 2007.[10] Pradyot Patnaik, (1995), Dean’s Analytical Chemistry Handbook,

McGraw Hill, New York.[11] Outokumpu, Corrosion Handbook, 10th Edition-Nov, 2009.

BM Weld Crevice

304L 316L 304L 316L (304L) 316L

LDX 2101® LDX 2404® LDX 2101® LDX 2404® (LDX 2101®) LDX 2404®

2205 2205 2205

304L 316L 304L 316L (304L) 316L

LDX 2101® LDX 2404® LDX 2101® (LDX 2404®) (LDX 2101®) (LDX 2404®)

2205 (2205) (2205)

304L 316L 304L 316L 304L 316L

LDX 2101® LDX 2404® LDX 2101® (LDX 2404®) LDX 2101® (LDX 2404®)

2205 (2205) (2205)

304L 316L 304L 316L (304L) 316L

LDX 2101® LDX 2404® LDX 2101® LDX 2404® (LDX 2101®) LDX 2404®

2205 2205 2205

304L 316L 304L (316L) (304L) 316L

LDX 2101® (LDX 2404®) LDX 2101® (LDX 2404®) LDX 2101® (LDX 2404®)

2205 (2205) 2205

304L 316L 304L (316L) 304L (316L)

LDX 2101® (LDX 2404®) LDX 2101® (LDX 2404®) LDX 2101® (LDX 2404®)

2205 (2205) 2205

Ch

lori

ne

(pp

m)

10.

50.

21

Tem

per

atu

re 5

0°C

Tem

per

atu

re 3

0°C

500 ppm Chloride

0.5

0.2

Red-corrosion, (Red)-possibly corrosion, not tested in this studyGreen-no corrosion, (Green)-possibly no corrosion, not tested in this study

Summarised results of 30 day tests in chlorinated solutions

containing 500 ppm chloride at 30°C or 50°C. Table 10

Presented at Eurocorr 2011 in Stockholm, Sweden

www.outokumpu.com

1491EN

-GB

Art 58. S

eptember 2011

Outokumpu Stainless AB, Avesta Research Centre

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Activating Your IdeasOutokumpu is a global leader in stainless steel with the vision to be the undisputed number one. Customers in a wide range of industries use our stainless steel and services worldwide. Being fully recyclable, maintenance-free, as well as very strong and durable material, stainless steel is one of the key building blocks for a sustainable future.

What makes Outokumpu special is total customer focus – all the way, from R&D to delivery. You have the idea.We offer world-class stainless steel, technical know-how and support. We activate your ideas