Experiences with Ti installed offshore Norway

By

Torfinn Havn

Ztrong, Norway

Experiences with Ti installed offshore Norway

• Experiences – services

– Problems

• Fabrication – welding

– forming

• Cost

• Availability

• Conclusions

The Snorre B platform

Experiences with Ti installed offshore

Norway

The motivation for use of Ti:

Considerable corrosion problems

experienced in sea water systems

with carbon steel, copper alloys and

stainless steels

Corrosion problems

Impact on environment by corrosion

• The world steel production is 1.3x109 tonnes (2006)

• About 30% of the steel production is to replace corroded steel

• Production of one tonn of steel leads to production of 3.5 tonnes CO2

• To replace corroded steel implies production of 1.4x109 tonnes CO2

• This is about the same mass of CO2 produced by all the cars in the world

Experiences

• Services where Ti is used

– Fire water systems (piping, valves, deluge, sprinkler)

– Fire water ring main

– Sea water systems

– Heat exchangers

– Hypochlorite systems

– Ballast water systems

– Sea water pumps

– Desalination packages

– Drilling risers

Experiences

• Material is TiGr2 for piping

• TiGr1 is used for plate heat exchangers

• Higher grades for special cases

• Gr2 is excellent for piping

– Sea water, oil & gas with CO2 / H2S

– No corrosion even at high velocities (20m/s)

Experiences

• After 20 years of service the experiences are excellent – Ti replaced cement lined carbon steel for ballast water

– Ti replaced CuNi sea water lines

– Ti replaced carbon steel fire water deluge system

– Ti replaced 6Mo sea water cooling lines

• Now standard for all fire water systems and sea water systems with temperatures > 20°C

In general no corrosion problems experienced.

TiGr2 is regarded safe up to 130 °C

Cold forming of Ti

The Sleipner Gas field

Due to Titans hexagonal

structure, Ti can be easily cold

formed.

Cold formed Ti of up to 8” ND

saves welding and fitting costs

and make the Ti system cheaper

than GRP (Glass Fibre

Reinforced Plastic).

The GRPs are very good for

long runs, but for systems with a

lot of branches and turns, the

GRP can not compete with Ti.

A few problems

• Fatigue – Tubing in heat exchanger due to bad design

• Baffle plates in Cu alloy

• Sea water on shell side

• The tube supports were designed based on the E module of steel (Ti has half the E modulus strength of steel)

– Disc in check valve due to bad design • Design based on CuNi concept

• Certificates due to problems with traceability – Caused big concern among operators

– Many stockists and mix-up of certificates

A few problems (continuation)

• Fabrication

– Cold bending

• The benefit is to avoid costs of fittings, welding and

NDT

– Flaring

• Welding

– Lack of gas protection

Fabrication

• Fabrication Gr.2 – Cold bending is ok if

• Added requirements

• Tubes heat treated after welding

– Flaring is not ok • Not recommended due to cracking

(cracked at -2°C)

• Elongation properties revealed to be 5% after flaring

% ASTM Norsok

O 0.25 0.17

N 0.03 0.02

E 20 25

Welding

High focus 10-15 years ago on

– Cleanliness

– Use of glooves

– Ar 4.6 (99.996%)

– No rubber hoses for gas (shall be impermeable to O2 and H2O)

– Gas Protection down to 250°C (trailer shoe)

– Problems experienced today with cracking and porosity (& discoloration)

– Acceptable colours: Silvery finish, pale straw, light blue

– Not acceptable colours: Dark blue, purple, grey and white (flakey)

Costs of metals

Price comparison USD/kg

0

10

20

30

40

50

60

70

CS CuNi SD Ti2

US

D/k

g

Example of calculated costs of a 5000 m

deluge system

USD/kg As Pipe Installed NPV 15 years

Ti versus carbon steel for a 5000m deluge

pipe systems

Initial cost difference cs vs Ti

600 USD /m

5000m x 600 USD = 3mill USD

Plugging of the sprinkler system

by corrosion products has forced

a platform (not the shown) to

shut down by Norwegian

authorities. Production loss 10

mill USD /day.

Time of shut down: 21 days

Availability

• Few manufacturers

• Availability is sensitive to market

fluctuations (aerospace industry)

• Unacceptable long delivery time has been

experienced for Ti heat exchanger

materials

• Industry is therefore looking for

alternatives

Compatibility to other materials

• Ti is very noble and cathodic to most other

metals and can cause galvanic corrosion

on other metals

• Coupled to less noble metals, hydrogen

can develop on the Ti surface, enter and

diffuse into the Ti causing embrittlement of

Ti by hydride formation

Compatibility to other materials

• Ti is very noble and cathodic to most other

metals

• Reacts quikly with chlorine and chlorite

while stainless steels need some time

• Problem can be solved by installing an

isolation pipe spool (a distance pipe spool)

Compatibility to other materials

• Ti is exposed to hydrogen pick-up when coupled to less noble materials

• A potential of -0.6 to -0.7 V SCE is often used as a limit

• Ti hydrid is formed at H > 50 ppm

• Temperatures >80°C and potentials < -0.7V SCE shall be avoided

• Ti subsea design need care; warm inside and connected to cs under cp on the outside

• Painting will reduce the problem

Absorption of H by unalloyed Ti

From ASM Handbook

Need of ”distance spool piece”

Use isolation pipe spools if necessary

Ti Carbon steel Isolation pipe

U = R I (V)

R = ρ x L / A (Ω) ρ = resistivity

L = length of spool piece

A = cross section

R = resistance

= paint film

Use of isolation pipe spools when replacing parts of ballast

water piping system

Original cement lined ballast water piping was found

corroded, and was to be partly replaced by TiGr2

Ti

Cement lined

Carbon steel Ti

U = R I (V)

R = ρ x L / A (Ω)

ρ = resistivity

L = length of spool piece

A = cross section

R = resistance

= paint film

= cement

Use of Ti in accordance with Norsok

standard M-001

The Grane platform

All new platforms being built

follow the Norsok standards.

Ti is used for fire water

systems and sea water

systems with operating

temperature in excess of

20°C plus a lot of other

systems including

hypochlorite system.

Conclusions

1 By experience it is found that Ti gives

the best material solution in

fire water and sea water

systems above 20°C

2 Ti need special focus on design and

welding

3 The availability of the material is

limited and engineering has to

be aware of the situation

4 Care is to be taken when Ti is to be

coupled to other materials

The end - Thank you