Topic

Materials for Demanding Topside

Offshore Application

Presented by

Vikram Pandit

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harm to our people, the environment we work in, our

customers and

our suppliers.

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EMERGENCY

NUMBER

ALARMFIRST AID

KIT

HERITAGE

Founded 1862 in

Sandviken, Sweden

Göran Fredrik Göransson

redesigned the Bessemer

furnace to mass-produce steel

A breakthrough and an innovation

started the company 150 years ago

3

Outline

• Atmospheric corrosion

• The SMT grades

• Field testing

• Material selection

• Summary

Atmospheric corrosion• The atmosphere might look clear and bright, but it hides a lot of

nasty things

• All these chemical species can, especially in combination with water, cause corrosion of metals

Species Chemical name Outdoor / ppbv Indoor / ppbv

O3 Ozone 4-42 3-30

H2O2 Peroxide 10-30 5

SO2 Sulphur dioxide 1-65 0.3-14

H2S Hydrogen sulphide 0.7-24 0.1-0.7

NO2 Nitrogen dioxide 9-78 1-29

HNO3 Nitric acid 1-10 3

NH3 Ammonia 7-16 13-260

HCl Hydrochloric acid 0.2-3 0.05-0.2

HCHO Formaldehyde 4-15 10

HCOOH Formic acid 4-20 20

Atmospheric corrosion

• Many of the mentioned air pollutants are of no great concern to stainless steel

• Some will work as oxidisers and other will lower pH• O2, O3 and H2O2 are oxidising species

• NO2, SO2, HNO3 and HCl will form acids in water

• Detrimental, especially in combination with chlorides

Atmospheric corrosion

• Certain atmospheric environments are especially corrosive• Within or close to industries there can be an increased amount of air

pollutants such as acids or chlorides

• Close to the seacoast salt spray and salt deposits in combination with very humid air can cause localised corrosion and stress corrosion cracking

• Can give effect many kilometres inland

• More severe in tropical regions

• Installations at sea same situation as above• Platforms

• Cargo ships

Atmospheric corrosion

• Atmospheric corrosion is a little bit different compared to wet corrosion

• Usually complicated interactions and mechanisms between the metal and the air pollutants

• Condensation and evaporation can give highly concentrated environments

• Large temperature differences between day and night can give a lot of condensation

• Droplet formation under the tubes

• Plenty of oxidising chemical species

Atmospheric corrosion

Cl-Cl-

Cl-

O2

O2

O2

CO2

Cl-Cl-

Cl-

O2

O2

O2

CO2

SO2

SO2

Evap

ora

tion

Mo

re s

evere

co

nd

itio

ns

Atmospheric corrosion

• If condensation takes place or the tubes are exposed to sea spray the underside of the tubes will be especially vulnerable

• If the tubes are exposed to rain they may get washed clean

• If the tubes are protected from rain, salt accumulation can increase the corrosion rate

The SMT H&I grades

Grade Cr Mo N PRE

316L 17 2.1 - 24

3R60 (316/316L) 17.5 2.6 0.04 26

Sanicro 41 (825) 20 2.6 - 29

2RK65 (904L) 20 4.5 - 35

Sanicro 28 27 3.5 - 39

254 SMO (6Mo) 20 6.1 0.2 43

SAF 2507

(SDSS)

25 4 0.3 43

Material selection• Standard grade for H&I tubing is 3R60 (Dual Grade Certified 316L)

• This grade will work in almost all indoors and inland installations

• Care has to be taken if local conditions are “non-standard” Hydrochloric acid plant

• Sulphuric acid plant, etc

• Is the tube hot?• Good because no condensation

• Bad if exposed to sea spray or similar

• For light weight constructions• Duplex grades (thinner wall thickness)

• Coiled tubing (less couplings)

Material selection• For temperate coastal regions 3R60 can be

a solution indoors or in protected areas

• If the H&I installation is exposed to salt spray etc. 3R60 will stain and possibly experience pitting as well

• If the tubes get warm (>60C) chloride stress corrosion cracking is a real threat to system integrity

• Sanicro 41(Alloy 825) has poor resistance to chloride induced corrosion and will behave only slightly better than 3R60

• Chloride induced stress corrosion cracking is not an issue with Sanicro 41

• 2RK65 (904L) has sufficient resistance towards chloride induced corrosion for this environment and should be the material of choice

Field exposure Swedish West Coast

Alloy 825 (Sanicro 41)316L

904L (2RK65) Super Duplex (SAF 2507)

Material selection• In tropical coastal regions 3R60 is not recommended

• Field exposure and experience from platforms in Brazil shows that 316L tubes will stain and pit extensively under these conditions

• High risk for chloride induced stress corrosion cracking if the tubes are hot

• 2RK65 is at its limits under these conditions

• Staining and some pitting

• No risk for SCC

• SAF 2507 shows no corrosion after field testing in tropical climates

• Specified by Petrobras for platforms

• An alternative is 254 SMO

• Easier to bend

• Specified by Statoil for all their platforms in the North Sea

Field exposure Florida, US

Alloy 825 (Sanicro 41)316L

904L (2RK65) Super Duplex (SAF 2507)

Lower deck installation test (18 months)

316L Super Duplex (SAF 2507)

STRESS CORROSION CRACKING

316L

•Austenitic stainless steels (300

series)

•Temp > 60 °C

•Tensile stress

•Corrosive media like Chlorides,

H2S etc

• Sudden Failure

STRESS CORROSION CRACKING resistance

aa

Temperature,°C (°F)

  0  (32)

 50(120)

100(210)

150(300)

200(390)

250(480)

300(570)

0.0001 0.001 0.01 0.1 1 10Cl–, weight-%

SCC

No SCC

N08028/Sanicro 28SAF 2205

AISI 304/304L

AISI 316/316L

904L

SAF 2507No cracking

SAF 2304

Results of SCC tests with constant load in 40% CaCl2, pH = 1.5 at 100°C, aerated solution

aa

1.00.2 0.4 0.6 0.8Stress/Tensile strength

SAF 2507

100

200

300

400

500

600Time to failure, h

AISI 316L

SAF 2205

The SMT gradesGrade Cr Mo N PRE Environment

316L 17 2,1 - 24 Inland

3R60 (316/316L) 17,5 2,6 - 26 Coastal temperate, protected

Sanicro 41 (825) 20 2,6 - 29 Coastal temperate, protected

2RK65 (904L) 20 4,5 - 35 Coastal temperate

Sanicro 28 27 3,5 - 39 Coastal tropical?

254 SMO (6Mo) 20 6,1 0,2 43 Coastal tropical

SAF 2507

(SDSS)

25 4 0,3 43 Coastal tropical

Material selection– Minimum weight• Large installation

• 20 km tubes

• Max working pressure 350 bar

• Other diameter 12.7 mm

• Solution 1• 3R60 12.7 x 1.63 mm

• Max pressure 351 bar

• Weight = 0.453 kg/m

• Weight installation = 9070 kg

• Solution 2• SAF 2507 12.7 x 0.89 mm

• Max pressure 354 bar

• Weight = 0.261 kg/m

• Weight installation = 5220 kg

Material selection– Coiled tube• Installation 5 km

• Solution 1• Normal length tubes, 6 m

• Fittings ~ 1000

• Fittings ~ 20 € / piece

• Cost of fittings 20000 €

• Solution 2• Coiled tube

• Number of fittings drastically reduced

• Much less scrap

• Save a lot of money!

Summary• 316L has limitation when it comes to

offshore and marine/ sea water application

• Pitting and Stress Corrosion Cracking is the main problem with this grade esp. in Chloride environment

• In coastal areas higher alloyed grades are recommended

• Temperate climates: 2RK65 (904L)

• Tropical climates: SAF 2507 or 254 SMO (6Mo)

• Low weight installations calls for high strength tubes

• Super Duplex

THANK YOUPlease feel free to contact me for any further information-

Vikram Pandit

Vikram.pandit@sandvik.com

+91 9372342108