1 - applications

● immersion in sea water,● heat exchangers and condensertubes in chloride and sea waterenvironments,● chemical and petrochemicalindustries for use in all situationswhere there is risk of stress corro-sion,● sulphuric and phosphoric acidenvironments,● sour oil and gas wells.

2 - main features

The main features of DMV 25.7 Custainless steel tubes are :● a ferritic-austenitic structure,● high tensile properties, doublethose of the classic 316 L type aus-tenitic steels,● a very good resistance to stresscorrosion cracking,● pitting and crevice resistancemaking it suitable for sea waterservice,● ease of fabrication,

● a service temperature range of -50°C to 275°C (-58°F to 527°F).

3 - description

3.1. related speciffications andstandards

● UNS S32550 per ASTM A 789and A 790 and ASME SA 789/SA790.● TUZ2CND 25.07.03 per NF A 49-217.● Z2CNDU25.7 Az per NF A 36-219

With PREn > 38(PREn = Cr +3.3 x Mo + 16 x N )

On request tubes in DMV 25.7 Cucan be delivered with a higher PREn.

3.3. mechanical properties

3.3.1. at 20°C (68°F) annealedcondition :

3.3.4. hardness :28 HRC maximum.

3.3.5 impact resistance KCV :● at room temperature, ruptureenergy is greater than 100J/cm2.● transition temperature less than-20°C (-4°F).

Note :This alloy is susceptible to sigmaphase formation after holding between600-900°C (1100-1650°F) resulting in reduced impact resistance and increase in hardness.

DMV 25.7 CuA super ferritic-austenitic grade with high mechanical properties andsuperior stress corrosion resistance

● Chlorides ● Fresh water● High pressuresSEAMLESS TUBES

Whilst every care has been taken incompiling the technical information inthis brochure, due to the continuingdevelopment and complex nature ofthe various factors used, it is given forinformation only. Our company can-not be held responsible for the infor-mation contained herein and our cus-tomers should carefully check forthemselves where necessary in orderto make the appropriate selection,bearing in mind the conditions gover-ning the fabrication of our alloys aswell as the conditions in service.Informations held in this brochurecan be changed without notice.

3.2. chemical composition

CSiMnSPCrNiMoN

Cu

24.04.52.9

0.151.5

0.0300.751.0

0.0100.03027.06.53.9

0.252.5

% min. % max.

.2 % YS min.

E % min. 2"

MPa Ksi

550 80

750 109

25

min.U.T.S.

1 MPa = 1 N/mm2

3.3.2 at elevated temperatures :

Temperature .2 % Y.S.min. U.T.S. min.

°C °F MPa Ksi MPa Ksi

100

200

300

212

392

572

400

360

320

58

52

46

680

640

630

98

92

91

1 MPa = 1 N/mm2 = .145 Ksi

3.3.3. maximum allowable stresses per ASME Code VIII :

°C °F MPa Ksi

38

93

149

204

260

100

200

300

400

500

190

189

177

170

170

27.5

27.4

25.7

24.7

24.7

Prolonged use beyond 275°C (527°F)can lead to a reduction in impactresistance due to formation ofalpha prime phase.

Density at 20° C (68° F)

Ib/In3Kg/dm3

7.8 0.28

Resistivity 10-6 m

20° C(68° F)

0.80

Coefficient of linear expansion

Temperature

20°C - 100°C(68°F - 212°F)

20°C - 300°C(68°F - 572°F)

12

13.5

6.7

7.5

10-6/°C 10-6/°F

It is always preferable to use a lowheat input, 10-15KJ/cm. MMA canalso be used.In all cases it is imperative that alltraces of surface oxydation beremoved, otherwise there is a riskof initiating localised attack.Post weld heat treatment is notnormally necessary.

6.6. surface treatment

Generally speaking DMV 25.7 Cutubes are treated like classic stain-less steels.Due to DMV 25.7 Cu high resistan-ce to corrosion, pickling time mightbe increased.

7- specifications

Heat exchanger tubes and pipesare delivered in accordance withthe following specifications :● AFNOR, ASTM, DIN,GOST...Our specialists are at your servicefor any guidance on drawing upyour tube specifications.

8 - similar grades

Other versions of this grade existlike DMV 25.7 and DMV 25.7 N.DMV 25.7 has slightly lower corro-sion properties than DMV 25.7 Cuor DMV 25.7 N, however it is lesssusceptible to sigma phase forma-tion . DMV 25.7 Cu can also beproduced with a PREn guaranteedover 40; this would be close toDMV 25.7 N which might be prefe-rable. Other standards exist likeUNS S32750 which is equivalent toDMV 25.7 N.

DM

V 1

03-9

97 -

CR

EA

PR

INT

3.4. physical properties

FRANCETel.: +33 (0) 3 80 89 52 10Fax: +33 (0) 3 80 89 52 26

GERMANYTel.: +49 (0) 21 91 895-06Fax: +49 (0) 21 91 895 540

ITALYTel. : +39 (0) 35 975 611Fax: +39 (0) 35 971 624

U.S.A.Tel. : +1 (0) 713 466 7278Fax :+1 (0) 713 466 3769

HEADQUARTERSTel. : +33 (0) 1 47 96 81 25Fax :+33 (0) 1 47 96 81 26

How to get in touch with your DMV’S sales office :

4 - production range

5 - corrosion resistance

5.1. general corrosion● sulphuric acid

● an acid containing 40% H3PO4,0.26% CI-, at a temperature of80°C (176°F).

● hydrochloric acidDMV 25.7 Cu can be considered foruse in this environment at boiling upto a concentration of 1%.

● other environmentsDue to a high Cr and Mo content,DMV 25.7 Cu tubes have a usefulcorrosion resistance in the mainorganic environments :

● 40% boiling formic acid

● 75% boiling acetic acid

5.2. intergranular corrosion

Due to a high Cr content and a lowcarbon level, DMV 25.7 Cu tubesmeet the requirements of the cop-per-sulphuric acid tests NFA 05159,ASTM A 262 E, and DIN 50914.In the non-sensitized state, theyalso satisfy the standard nitric tests(ASTM A 262 C, NFA 05160, DIN50921).

5.3. stress corrosion

The ferritic-austenitic structuregives this steel an excellent resis-tance to this type of attack.In dilute chloride environments,DMV 25.7 Cu can be considered asvirtually immune from this type ofattack when in the annealed condi-tion and when the stress levels areless than the yield strength.

5.4. pitting and crevice corrosion

Due to its high chromium, molybde-num and Nitrogen content, and to aguaranteed PREn greater than 38, DMV 25.7 Cu has excellent

resistance to localised pitting and cre-vice attack. It is superior to that of theaustenitic alloys such as theZ1NCDU20-25 / UNS N0890 / 1.4539(DMV 904) type.This is substantiatedby values obtained for rupture poten-tials.

DMV 25.7 Cu tubes can be immer-sed in the sea without risk of loca-lised attack , even in crevice situa-tions.They can similarly be used as heatexchangers with sea water coolingas long as the following conditionsare respected :● sea water is inside the tubes,

● the water circulates at greaterthan 1.5 m/s ( 5 ft /sec),

● there is regular cleaning,

● temperature is less than 60°C(140°F).

5.5. galvanic corrosion

The position of DMV 25.7 Cu onthe galvanic scale is very compa-rable to that of other austeniticstainless steels. It can, therefore,safely be used in conjunction withother stainless steels in their areaof passivity.

6 - fabrication

6.1. heat treatment

This is desirable following hot orcold working and is essential afterbeing held in the temperaturerange 450-950°C (842-1740°F ).Heat treatment consists of rapidheating and then quenching from 1040-1150°C (1900-2102°F).The usual cleanliness precautionsrecommended for stainless steelsare, obviously, also valid here.When specifying the heat treat-ment temperature, the possibility ofcreep at high temperature shouldbe taken into account .

Hot working operations must becarried out in temperature range1150-980°C (2100-1795°F) follo-wed by rapid cooling to below980°C (1725°F).

6.2. tube expanding

DMV 25.7 Cu tubes can be expan-ded similarly to classic austeniticstainless steels, taking intoaccount their appreciably highermechanical properties. The TEMAcode “close fit” drilling tolerancesare preferred.

6.3. tube bending

●cold

DMV 25.7 Cu tubes can be bentsimilary to austenitic stainlesssteels, taking into account theirhigher mechanical properties.

6.4. cutting and machining

Conditions are similar to those foraustenitic stainless steels.

6.5. welding

Tube butt welding or welding totube sheets in austenitic stainlesssteels is carried out using the TIGprocess, using a similar grade offiller metal with Ni and Nitrogenenrichment in order to maintain aferrite level of 30-70% after wel-ding. Maximum interpass tempera-ture of 150°C. If heterogeneouswelding is used, choose a fillermetal corresponding to alloy 625(ENi CrMo-3) (WN 2.4831 ).

DMV 25.7 CuSEAMLESS TUBES

● Chlorides● Fresh water● High pressures

Thermal conductivity

Temperature

100° C (212° F)

W/(m.°C) BTU/ft.h. °F

18 10.4

True specific thermal capacity

Temperature

20° C (68° F)

J/(kg. °C) BTU/lb. °F

450 0.11

Modulus of elasticity

Temp.

°C

20

280

°F

68

536

tensile

MPa Ksi

200.000

170.000

29.000

24.600

75.000 10.850

torsion

Ksi Ksi

1 W/m°C = 1 W/(m.K) = 0.860 kcal/h.m°C.

250

200

150

100

50

05 10 15 20 25 30 35 40

thickness (mm)

figure 1O.D. (mm)

300

Generally speaking, the corrosionresistance of DMV 25.7 Cu issuperior to that of 316 L and 317 Lstainless steel in a phosphoricenvironment. It can, therefore, beconsidered for service in the follo-wing typical contaminated condi-tions :● an acid containing 70% H3PO4,0.05% Cl-,1.2% F- ,4% H2SO4, 0.09%Fe at a temperature of 60°C (140°F),

●phosphoric acid

The depassivation pH has beencalculated to be of the order of 0.3in 2 M NaCl at 25 °C (77 °F).

figure 2Isocorrosion chart for 0.1 mm/year

(4 mpy) in H SO2 4

H SO2 4

DMV 25.7 Cu

316L100%0 50

30

40

60

80

100

°Cboiling

316L

316L

Isocorrosion chart for 0.1 mm/year(4 mpy) in H PO

figure 3

3 4

DMV 25.7 Cu

100%0 5040

60

80

100

120

°C

boiling

H PO3 4

figure 5

0

0.5

1

1.5

DMV 954DMV 25.7 Cu

DMV 22.5

DMV 904

DMV 316L

Depassivation pH

figure 4Comparative rupture potentials as

a function of temperature in NaCI 0.5 M solution

(polarisation speed of 250 mV/h)

1000

500

100

20 50 80 °C

mV/ECS

DMV 25.7 CuDMV 904

316L

Ferromagnetic