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Localised corrosion of stainlesssteels depending on chlorine dosagein chlorinated water

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

Te European Drinking Water Directive sets a maximumlimit of 250 ppm for chlorides in drinking water but doesnot contain guidelines for chlorine. Te WHO drinking water standard states that 2– 3 ppm chlorine should be addedin order to gain a satisfactory disinfection and adequate residualconcentration. Te residual chlorine has a signicant inuenceon the corrosion behaviour of stainless steels and may havedetrimental consequences in the form of localized corrosionif an inappropriate stainless steel grade is used.

Tis article clearly demonstrates that the novel duplex

grades LDX 2101® and LDX 2404® provide attractivealternatives for handling potable water and cooling water.Tey also have a price less affected by nickel price uctuationsand higher strength compared to the standard austenitic grades4307 and 4404. In 30-day laboratory tests, the lean duplexgrade LDX 2101® performed as well as or better than 4307at both 30°C and 50°C. It is also shown that the presence ofcrevices strongly increases the risk for localized corrosion ina chlorinated environment.

Introduction

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Localised corrosion ofstainless steels depending

on chlorine dosage inchlorinated water

Sukanya Mameng, Rachel Pettersson, Outokumpu Stainless AB,

Avesta Research Centre, Avesta / Sweden

Summary

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

Te European Drinking Water Directive sets a maximum limit of 250 ppm (mg/L) forchlorides in drinking water but does not contain guidelines for chlorine. Drinking wateris 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. Te WHO drinking water standardstates that 2–3 ppm chlorine should be added to water in order to gain a satisfactorydisinfection and adequate residual concentration. For a more effective disinfection theresidual amount of free chlorine should exceed 0.5 ppm after at least 30 minutes ofcontact time at a pH value of 8 or less.

Te residual chlorine has a signicant inuence on the corrosion behavior of stainlesssteels. Te remaining of residual chlorine in drinking water is a major factor leading to theennoblement of the natural potential of stainless steel. Tis oxidizing effect of chlorine mayhave detrimental consequences in that stainless steels may suffer from localized corrosionif an inappropriate grade is used.

Te aim was to understand and determine to what extent residual chlorine levels atvarious chloride contents will affect the localized corrosion behaviour of the standardaustenitic 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. Te specimens wereinvestigated by visual examination and microscopy.

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

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

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

First of all, stainless steels have generally excellent corrosion resistance and require

little maintenance. Tere 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.Terefore 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 levelspermitted by the European Drinking Water Directive (50 and 20 µg/L respectively) [2].Te low leaching levels from the use of stainless steel in the drinking water system areclearly of benet in this situation.

Another point to be considered is the mechanical properties. Te good ductility,strength and weldability enable the use of lightweight structures, for example thin walledtubes. Among the stainless steels, the duplex materials exhibit much higher mechanicalstrength than corresponding austenitic grades as shown in able 1. Compared to othermaterials 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 Elongationsteel 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 forLDX 2404 ® corresponds to the internal standard AM 641.

Fig. 1 Nickel (Ni) and Chromium (Cr) content of water drawn fromstainless 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

M e t a l c o n

t e n t o

f w a t e r

( µ g / l )

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

Cr from 316 - Cold waterCr from 304 + 316 - Hot water

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allow a reduction in wall thickness and consequently reduces investment costs. Alltogether stainless steels give a life cycle cost benet.

Te 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 onthe stainless steel composition and chloride content of water, these materials may beresistant to aqueous corrosion in a wide range of pH at ambient temperature. Stainlesssteels ability to resist pitting corrosion may be estimated by calculation of the PittingResistance Equivalent Number (PREN). Equation (1) gives the most frequentlyemployed 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 austeniticstainless steel grades 4307 and 4404. Te grade selection depends on the chloride levels

of the water and also on the severity of the crevices the materials are exposed to, as shownin able 2 from the Nickel Development Institute. Te chloride content of the water isthe most important parameter because of its inuence on localized corrosion, crevicecorrosion in particular. Te European Drinking Water Directive sets a maximum limitof 250 ppm (mg/L) for chlorides in drinking water but does not contain guidelines forchlorine [2].

2 Water ChlorinationChlorination is a one of many methods that can be used to disinfect water and controlbacteria. 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, itimmediately begins to react with compounds found in the water to give hypochlorous

acid (HOCl) and hypochlorite (OCl-). Te remaining amount is called free residualchlorine.

Te free residual chlorine is typically measured in drinking water disinfection systems tond if the water contains enough disinfectant. ypical levels of free chlorine in drinking

water are 0.2– 0.5 ppm [7], but the actual concentrations added are usually higher. Te WHO drinking water standard states that 2– 3 ppm chlorine should be added to waterin order to attain a satisfactory disinfection and maintain residual concentration [8].Te maximum amount of chlorine one can use is 5 ppm. For effective disinfection theresidual amount of free chlorine should exceed 0.5 ppm after at least 30 minutes of contacttime at a pH value of 8 or less.

Te residual chlorine has a signicant inuence on the corrosion behaviour of stainlesssteels. Te remaining residual chlorine in drinking water is thought to be a major factorleading to the ennoblement of the natural potential of stainless steel. Tis oxidizing effectof chlorine may have detrimental consequences and stainless steels may suffer from localizedcorrosion 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

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Tis work was conducted to understand and determine to what extent total residualchlorine levels at various chloride contents will affect the pitting and crevice corrosionbehaviour of the standard austenitic stainless steel grades 4307 and 4404 , also the duplexgrades LDX 2101®, LDX 2404® and 2205. Te recently introduced duplex gradesLDX 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

Te 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. Te surface nish,thickness, PREN values and the chemical composition of these materials are reportedin able 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 groundto 320 mesh. Te 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 veriedthat 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 creviceeffects when investigating pitting corrosion.

Steel grades, surface nish, 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) PREN 16 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

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Te welded samples were obtained by tungsten inert gas welding ( IG). Te welding was done with ller material and welding conditions as specied in able 4 and able 5below. Tis welding process is often used for water applications. All samples have the samethickness of 3 mm. Weld samples were pickled in mixed acid (3M HNO3 and 3M HF).

Chloride (Cl-) containing electrolytes with various total residual chlorine ( RC)

levels, at pH 6.5-7.5, were prepared from distilled water. Chloride ions were added tothe level of 200 ppm and 500 ppm as sodium chloride (NaCl). Te solutions were dosed

with a stock solution containing 1000 ppm of sodium hypochlorite to obtain variouspredetermined total residual chlorine concentrations.

otal residual chlorine ( RC) is dened as the sum of hypochlorous acid (HClO) andhypochlorite ion (ClO-) concentrations.Te amount of residual chlorine was measured

with a colorimeter using the diethyl-p-phenylene diamine (DPD) method [10]. Treetotal residual chlorine concentrations were investigated that correspond to the residualconcentration typically used for water disinfection treatments: 0.2, 0.5 and 1 ppm.

Te open circuit potential (OCP) was monitored for 30 days in the test solutions withthe different residual chlorine levels and a temperature of 30°C or 50°C. Te chlorine

was dosed once every 5– 7 days to maintain the residual chlorine level. After testing thespecimens were examined and the depth of maximum attack was measured with a lightoptical microscope. A depth exceeding 0.025 mm was dened as localised corrosion.

Chemical compositions of GTAW ller (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 inputMaterial 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% N 2 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, N 2: Nitrogen gas

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

Te stainless steel samples were immersed in the test solutions with 200 ppm and 500ppm chloride at 30°C and 50°C for 24 hours before the start of chlorination. Te opencircuit 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. Te values were somewhathigher for the weld and crevice specimens.Te 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. Te result shows that OCPMax increases with

RC level because the oxidising power of the solution increases, able 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)

P o

t e n

t i a l ( m V S

C E

)

OCPMax

720 mVSCE

Average OCP Max of ve different steel grades in water containing chloride

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

Maximum open circuit potential, OCP Max (mV SCE )

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

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Te OCP Max after chlorination compared to the situation before chlorination is shownin Figure 4. Te increase in OCP was about 200 mV SCE for 0.2 ppm RC, about 300mV SCE for 0.5 ppm RC and about 500 mV SCE for 1 ppm RC. Tis indicates that evenat low RC concentrations the open circuit potential increases.

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

Te 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 examinationshowed that pitting had occurred for the welded 4307 and LDX 2101® (Figure 7A).Tese 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)

P o t e n

t i a l i n c r e a s e

( m V )

200 ppm, 30°C500 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 potentialdrop associated with the onset of pitting corrosion.

900

100

200

300

400

600

800

0

-100 700600200 300 5004001000

Time (hours)

P o

t e n

t i a l ( m V

S C E

)

500

700

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

Pitting corrosion

Pitting corrosion

4307-weld2205-weldLDX 2101®-weld

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

Fig. 7 Appearance of localized corrosion after tested in 500 ppm chlorideand 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 summaryof the results from this investigation is shown in able 7. Where corrosion occurred, thecells are lled dark blue and where no corrosion occurred the cells are light blue.

able 7 show that the lean duplex LDX 2101® was found to be at least as resistantas 4307. In all experimental conditions tested, the duplex grades LDX 2404® and 2205perform very well with no signicant localised attack. Both these grades have a high

PREN (>30), whereas for the grades with PREN<30 some localised attack was observed.Te results show that the alloying elements inuence the localised corrosion resistanceof 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 samepositive inuence for duplex grades.

Fig. 6 Corrosion potential change of TIG welded and crevice specimenfor 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)

P o

t e n t i a l ( m V

S C E

) 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

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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

Te results also indicated that the presence of a crevice increases the risk for localizedcorrosion in chlorinated environments. Special attention should be taken, to avoid crevicesin construction, since residual chlorine solution can remain in crevice areas and causecorrosion.

4.4 Comparison with engineering diagrams.

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

Tese diagrams are based on a combination of laboratory testing and extensive practicalexperience and provide a useful reference base for the present investigation. As can beseen 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 slightlychlorinated (<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.

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for 4404 tested with 1 ppm RC: pitting corrosion occurred only at 500 ppm chlorideand 1ppm RC 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 RC, and should thuslie above the boundary line. If, however the comparison is made to the 0.5 ppm data,the curve seems instead slightly too conservative. Te overall agreement is thus very good,

and underlines the point that the chloride tolerance of different stainless steel grades isvery sensitive to the chlorination level. A summary of chlorination limits for different grades from this investigation are

shown in able 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 willmost probably be lower than during this test. Tus, there is a good chance that the4307, LDX 2101® and 4404 can be used successfully for normal service in water pipingsystems as long as problematic crevices can be avoided. In doubtful cases upgrading toLDX 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

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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


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)

C h l o r i n e

( p p m

)

1

0 . 5

0 . 2

1

T e m p e r a t u r e

5 0 ° C


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• In long-term (30 days) immersion tests, the highest alloyed duplex grades 2205 and

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

• Te lean duplex grade LDX 2101® performed as well as or better than 4307 (304L)at all conditions tested. In the pitting test it performed as well as 4404 (316L) in200 ppm chloride at 30°C.

• Chlorine solution with signi cant residual chlorine concentrations can remain increvice areas and cause corrosion, and therefore special attention should be takenin construction.

• Te lean duplex steel LDX 2101® is a good candidate for water piping systems andtanks, when the water is mildly chlorinated. In more severe condition the higheralloyed LDX 2404® or 2205 are more suitable.

• Material selection guidelines depending on chloride content, chlorine dosageand temperature are shown in able 9 and able 10 below. In order to ensuregood performance deposits and surface contamination should be avoided.

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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] Te 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, 10 th Edition-Nov, 2009.

BM Weld Crevice

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


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


2205 (2205) (2205)

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


2205 2205 2205

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

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

C h l o r i n e

( p p m

)

1

0 . 5

0 . 2

1


5 0 ° C


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 2011in Stockholm, Sweden

7/25/2019 OUTO KUMPU (3)


www.outokumpu.com

1 4 9 1 E N- G B A r t

5 8 .

S e p t em

b er 2

0 1 1

Outokumpu Stainless AB, Avesta Research Centre

Box 74, SE-774 22 Avesta, Sweden

Tel. +46 (0) 226 - 810 00, Fax +46 (0) 226 - 810 77

Comments on acom and its articles or suggestions on future articles are appreciated and should besent to the editor Andreas Persson at [email protected]

Tis document is for information only and seeks to provide professionals with the best possibleinformation to enable them to make appropriate choices. Although every effort has been made to ensurethe accuracy of the information provided in this document, Outokumpu can not accept any responsibility for any loss, damage or other consequence resulting from the use of this publication.Te information provided herein may be subject to alterations without notice.

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