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Material Selection and Corrosion Control for Offshore Platform and FPSO


Detailed corrosion prediction evaluations including consideration for CO2 should be performed to establish a materials selection and corrosion control report for all process and utility systems in the offshore environment.

Materials selection should be carried out in accordance with ISO 21457: “Materials Selection and Corrosion Control for Oil and Gas Production Systems”, and any additional standards required and applicable per project.

Materials for all hydrocarbon containing systems should fulfill ISO 15156: “Materials for Use in H2S-containing Environments in Oil and Gas Production”. Carbon and low-alloy steels should fulfill the standards requirements for SSC Region 3, irrespective of the service condition.

The following materials should not be used:

  1. Asbestos
  2. Chlorofluorocarbons and HydroChlorofluorocarbons (CFCs and HCFCs)
  3. Tin or lead-based anti-fouling paint
  4. Lead-based paint
  5. Rockwool or glass wool insulation on process vessels and piping

The following table is the minimum materials requirements for piping systems. All equipment and components should as a minimum be from materials with equivalent corrosion resistance to the piping system in which they are installed.

Materials Selection Table

Area

Service

Titanium

SDSS -

25Cr

DSS -

22Cr

SMO-

254

316L

CuNi

90/10

LTCS

LTCS +

625 Clad

CS

(galv)

GRE

PP

PVDF

PE

Elasto-

Pipe

Process

Hydrocarbon systems, upstream separation


X

X

X




X







Crude / Condensate, downstream separation


X

X

X











Produced water


X

X

X











Produced water, downstream degasser


X

X

X






X



Flare systems > -40°C


X

X

X



X








Flare systems < -40°C


X

X

X











Gas, Wet


X

X

X











Gas, dry







X






Closed drains


X

X

X











Open drains



X







X





Fuel gas, wet





X










Fuel gas, dry





X


X








Cooling & seawater

Cooling water, closed circuit







X








Seawater, service/cooling (serving safety critical equipment)


X


X


X









Seawater, service/cooling (serving non safety critical equipment)


X


X


X




X





Seawater, injection, upstream deaerator


X


X


X




X





Seawater, injection, downstream deaerator







X








Firewater

Firewater, normally wet systems, upstream deluge valve

X

X


X


X









Firewater, normally dry systems, upstream deluge valve

X





X








X

Utilities

Air systems, breathing





X










Air systems, instrument





X




X






Air systems, utility





X




X






Potable water





X






X




Sewage










X





Chemical injection, piping





X





X



X


Chemical injection, tubing

 

X

 

 

 

 

 

 

 

 

 

 

 

 

Ferric Chloride

X











X



Sodium Hypochlorite

X











X



Methanol, MEG, TEG





X


X





X




Piping

Topside process and utility piping materials should be selected in accordance as shown above. All equipment and components should as a minimum be from materials with equivalent corrosion resistance to the piping system in which they are installed.

Piping design should allow for the installation of start-up filters/strainers in front of compressor and pumps.

Glass Reinforced Epoxy Piping

Glass reinforced epoxy (GRE) piping should be subject to dynamic surge analysis and static pipe stress and flexibility analysis, which should be confirmed independently by the GRE material manufacturer. All valves and inline components larger than 2-inch nominal bore should be independently supported.

Qualification of fabrication contractor and staff performing work on GRE piping systems, including work methods and procedures used, should be subject to review and approval by the GRE material manufacturer.

GRE piping fabrication activities as well as the final GRE piping installation should be inspected by the GRE piping manufacturer. Upon completion of the work, the GRE piping manufacturer should issue an unconditional acceptance certificate on a system by system basis.

Calibration Certificate for Pressure Relief Devices

Pressure relief devices that require periodic recalibration should be supplied with calibration certificates that are maximum 6 (six) months old at time of final acceptance by Company of the system in which they are installed.

HP and Clean-Up/Test Separators

HP and clean-up/test separators should be made from solid corrosion resistant alloy (CRA) or alternatively carbon steel internally clad with a minimum 3-mm thick layer of metallurgical bonded Inconel 625. The Inconel overlay should be extended over all gasket surfaces. Gasket surfaces should be re-machined in accordance with ASME B16.5.

Pressure Vessels and Heat Exchangers

Materials for hydrocarbon and produced water containing pressure vessels and heat exchangers should be selected in accordance with above materials selection guidance.

The following materials should be considered as minimum requirements:

  • Solid corrosion resistant alloy (CRA)
  • Carbon steel internally clad with a minimum 3 mm-thick layer of metallurgical bonded Inconel 625. The Inconel overlay should extend over all gasket surfaces. Gasket surfaces should be re-machined in accordance with ASME B16.5
  • For equipment with a design temperature lower than 93°C, carbon steel internally coated with 1000 micron hand applied Belzona 1391 or alternative coating system approved by project team. The internal coating system should be applied, tested and inspected. Only application procedures and personnel that have been qualified and approved by the coating manufacturer should be used. Upon completion of application, cleaning, testing and conservation for shipping/storage, the coating manufacturer should issue an unconditional acceptance certificate for each piece of equipment

Seawater Treatment Vessels

Deaerators and coarse and fine filter vessels should be carbon steel internally coated with 1000 micron hand applied Belzona 1391 or alternative coating system approved by project team. The internal coating system should be applied, tested and inspected. Only application procedures and personnel that have been qualified and approved by the coating manufacturer should be used. Upon completion of application, cleaning, testing and conservation for shipping/storage, the coating manufacturer should issue an unconditional acceptance certificate for each piece of equipment.

Shell and Tube Heat Exchangers

Strength of tube to tubesheet joints, whether welded or not welded, should be demonstrated through qualification testing in accordance with EEMUA Publication No. 143 “Recommendations for Tube End Welding.”

Seawater and Firewater Lift Pumps

Seawater and firewater lift pumps materials should be solid 25% Super Duplex Stainless Steel with PREN >40.

Water Injection Pumps

Water injection pump materials should be solid 25% Super Duplex Stainless Steel with PREN >40.

Instrument Tubing Systems

All instrument tubing systems, including pneumatic and impulse-tubing, tube fittings, valves, manifolds, instruments and bolting should be from 25% Super Duplex Stainless Steel with PREN >40.

Bolting

Austenitic stainless steel bolting should not be used for any exterior applications.

Qualification of Manufacturers of Special Materials

All raw material manufacturers of Class I special materials components as well as the product itself should be qualified in accordance with Norsok M650, Rev. 3, 2004, or a similar qualification process approved by project team. Special materials in this context are defined as follows:

  1. Duplex stainless steel (all grades, product forms and dimensions)
  2. High alloyed austenitic stainless steel (all product forms and dimensions)
  3. Nickel base alloys (castings)
  4. Titanium and its alloys (castings)

Duplex SS should also comply with the requirements of EEMUA 218, “Quality requirements for the manufacture and supply of duplex stainless steels - Edition 1”

Corrosion Allowance

The requirements for corrosion allowance or minimum additional thickness to be added to exposed surfaces of structural components (for instance, plates, stiffeners and girders) above the thickness required for strength, buckling and fatigue design are provided in the following table.

The corrosion allowances in the following table should be used instead of the requirements of the Classification Society unless the Classification Society corrosion allowance values are higher. The corrosion allowances in the table should form part of the overall corrosion protection philosophy.

Required Corrosion Allowances for Service Life

Hull Area

Corrosion Allowance (mm)

Continuously ventilated spaces

0.8

Void spaces and permanently empty tanks

0.8

Void bottom plating

1.5

Ballast tank internal horizontal plates, webs, stiffeners and girders

3.25

Ballast tank internal vertical plates, webs, stiffeners and girders

2.5

Drain well for submerged pumps or ejectors

3.0

Outer shell except splash zone exterior

2.0

Structures exposed to marine atmosphere (for each exposed side)

1.25

Outer shell external surface in splash zone

6.0


All carbon steel caissons should have at least 6mm of corrosion margin.

Chain blocks and trolleys should be provided for each monorail. Trolleys should be non-sparking and corrosion resistant, and should be geared and supplied with parking brakes to accommodate offshore motions.

The corrosion protection of the platform should be achieved through a combination of protective coatings and cathodic protection with sacrificial anodes.



Tags: platform FPSO corrosion material selection