MONS-T-08

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Page 1 of 15Doc No: MONS-T-08 Date 16/03/09Title: Technical Standard for Material Selection for Topside Process and Utility Piping Rev A2

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REVISION RECORD

Current revisions are identified on the relevant page(s) by a vertical line in the right handmargin adjacent to where the revision was made. All previous revision identification isremoved.

REV DATE REVISION DETAILS A1 31/07/08 Approved for Use A2 16/03/09 Re- Approved for Use

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TABLE OF CONTENTS

1. INTRODUCTION.... ............................ ............................ ............................. .................... 3 2. REGULATIONS, CODES AND STANDARDS .............................. ............................... ... 3

2.1. Mandatory Regulations........ .............................. ............................. ......................... 3 2.2. Codes and Standards...... ............................. ............................ ............................ ... 3 2.3. Additional Requirements ......................... ............................. ............................ ....... 4

3. DEFINITIONS AND ABBREVIATIONS ............................ .............................. ................. 4 4. MATERIAL SELECTION ......................... ............................ ............................. ............... 4

4.1. Introduction............ ............................. ............................ ............................ ............. 4 4.2. Corrosivity Assessment .......................... ............................ ............................ ......... 4

4.2.1. Establish the Presence of Water ........................... ........................... ............... 5

4.2.2. Definition of Sour Service Conditions ............................ ............................. ..... 5 4.2.3. Erosion-corrosion.................... ........................... ............................ .................. 5 4.2.4. Prediction of Sweet (CO2) Corrosion ........................ ............................. ......... 6 4.2.5. Corrosion Inhibition............. ........................... ........................... ....................... 6 4.2.6. Corrosion Resistant Alloys.......................... ............................. ........................ 7 4.2.7. Galvanic Corrosion ......................... ............................. ............................ ........ 8

4.3. Material Requirements for Process Piping ............................ ........................... ....... 8 4.3.1. Flow Lines and Manifolds ............................ ............................ ........................ 8 4.3.2. Produced Water System........................... ............................. .......................... 9 4.3.3. Wet Gas System.............................. ............................ ............................ ........ 9 4.3.4. Dry Gas System....................... ............................. ............................ ............. 10 4.3.5. Flare Systems............................... ............................ ............................ ......... 10 4.3.6. Crude Oil/Condensate Systems .......................... ............................ .............. 10

4.4. Material Requirements for Utility Piping................................................... .............. 10 4.4.1. Fresh and Potable Water Systems .......................... ............................. ......... 10 4.4.2. Air Systems......................... .............................. ............................. ................ 10 4.4.3. Sea Water Systems ............................ .............................. ............................. 11 4.4.4. Closed Cooling Water Systems .......................... ............................. .............. 11 4.4.5. Open Drain Systems...................... ............................. .............................. ..... 11 4.4.6. Closed Drain Systems ............................. ............................ .......................... 11 4.4.7. Fire-water Systems............................. ............................. .............................. 11 4.4.8. Instrument and Hydraulic Tubings ........................ ............................ ............. 11 4.4.9. Sewage........ ............................ ............................. ............................ ............. 11

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1. INTRODUCTION

This Technical Standard (MONS-T-08) covers material selection for topside process and utilitypiping. It is concerned with internal degradation. External degradation is not addressed in thisdocument.

Compliance is required with all applicable parts of the Mandatory Regulations and of theCodes and Standards specified below.

MONS-T-08 is one of a whole set of Technical Standards. It contains additional Maersk OilNorth Sea UK Limited (MONS UK) requirements and specifies requirements where theRegulations, Codes and Standards allow alternatives.

2. REGULATIONS, CODES AND STANDARDS

All Regulations, Codes and Standards etc. referred to in this Standard shall apply in latestedition unless otherwise stated.

2.1. Mandatory Regulations

UK Offshore Regulations:Offshore Installations (Safety Case) Regulations (SCR) 2005 SI No. 2005/3117Offshore Installations (Design and Construction) Regulations (DCR), SI 913: 1996.

Offshore Installations (Prevention of Fire and Explosion, and Emergency Response)Regulations (PFEER), SI 743: 1995

2.2. Codes and Standards

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2.3. Additional Requirements

The required design life is 30 years unless otherwise specified.

For carbon steel, piping corrosion allowance of minimum 3 mm shall be used unless otherwise

specified.

In connection with piping modifications to existing installations, the material selectionprocess shall take the existing construction material into account.

3. DEFINITIONS AND ABBREVIATIONS

CCT Critical Crevice TemperatureCPT Critical Pitting TemperatureCRA Corrosion Resistant AlloysCSCC Chloride Stress Corrosion CrackingFBE Fusion Bonded EpoxyGRP Glass Fibre Reinforced Plastic

SSCC Sulphide Stress Corrosion Cracking

4. MATERIAL SELECTION

The Technical Standard specifies material selection based on Mærsk Olie requirements to the

safety, reliability, lifetime economics and standardisation of the material selection.

4.1. Introduction

The following description shows how the corrosivity of the process environment is assessed

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temperature, pressure, flow rate and flow regime throughout the lifetime of the facility. Aprocess simulation is accordingly an important parameter in the corrosivity assessment.The required input for the corrosivity assessment is listed in Annexe 1.

4.2.1. Establish the Presence of Water

For gas lines, the internal environment is considered “dry” when the water dew point at theactual pressure is at least 10 oC lower than the actual operation temperature of the system.

For oil systems, it has been found that most oils can safely entrain a water cut of up to 20%as long as the flow velocity is above the critical level of normally about 1 m/s. Operationalexperience has shown that stagnant regions, where water may accumulate, are at risk evenat water cuts below 5%. Accordingly, such regions shall be avoided in the design.

4.2.2. Definition of Sour Service Conditions

The ISO standard ISO15156 defines sour service and presents metallic materialrequirements to provide resistance to the various degradation threats arising from the

presence of hydrogen sulphide, including sulphide stress cracking (SSC), stress corrosioncracking (SCC) and hydrogen induced cracking (HIC). The standard is valid for carbon steelas well as Corrosion Resistant Alloys (CRA). Drying, coating or use of corrosion inhibitorsshall not relax the requirement to use sour service resistant materials if the conditions areotherwise categorised as sour by the above document.

All hydrocarbon-containing systems shall be designed for sour service unless otherwise

specified by MONS UK.

4.2.3. Erosion-corrosion

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flow related phenomena need to be considered, e.g. noise and vibration. Maximum C-valuesfor stainless steel, see section 3.2.6.

4.2.4. Prediction of Sweet (CO2) Corrosion

A number of methods have been developed to predict the expected maximum corrosion ratein a given oil, gas and water environment. The NORSOK standard M-506 is the preferredprogramme for evaluation of CO 2 corrosion; but the results shall always be compared withresults from either the BP Cassandra or the De Waard and Milliams model.

This comparison is important to understand the variability in the predicted corrosion rates,the sensitivity to the input parameters and the particular nuances of each model. The

conditions over the operating life, such as a low water cut during the initial stages of production may justify the use of a lower corrosion rate during the early life compared to thatfor the later stages of production with a resulting decrease in total corrosion allowancerequired.

The corrosion allowance should be sufficient for the predicted corrosion rate(s) over the designlife of the facilities. With an uninhibited rate of 0.2 mm/year, a 6 mm corrosion allowance willgive 30 years life without the need for corrosion inhibitor. For a given corrosion allowance,higher corrosion rates may be tolerated for items with a shorter design life than for those withthe default design life of 30 years stated in the present document.

For predicted uninhibited corrosion rates up to 2.0 mm/y, carbon steel with a corrosionallowance may still be used in conjunction with an effective and reliable inhibition system.For example, a 30 year life can be achieved with an uninhibited corrosion rate of 2mm/y andan assumed inhibitor efficiency of 90% as follows: 2.0 mm/y * 10% * 30 years.

Practical and economic considerations will normally dictate the maximum corrosionallowance above which corrosion resistant alloys are required instead of carbon steel.Typically, 6mm is used as the limit, which could, for example, equate to a corrosion rate of

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Furthermore, the predicted corrosion rate tends to vary during the lifetime of the processpiping and worst case predicted corrosion rate of 2 mm/y is judged as the limitation for corrosion inhibition of carbon steel.

For pipelines, a maximum inhibition efficiency of 95% may be realistic, dependent on the

nature of the fluids, flow rates, etc. The corrosion rate in the inhibited fluid shall bedetermined by corrosion tests unless relevant field data are available. Corrosion inhibitorsshall in general not be applied to process systems with wall shear stresses ( τ ) above 2000Pa and at temperatures above 120 oC. For CO 2 containing condensed water systems, pHadjusted glycol can be applied to reduce the corrosion rate. A corrosion rate of 0.1 mm/y canbe used for design purposes on condition that it is based on meaningful, documented test or field data.

4.2.6. Corrosion Resistant Alloys

When inhibition cannot give sufficient reduction of corrosion rate, or reliance on filmformation to prevent corrosion of carbon steel is not acceptable, higher alloyed materialshave to be chosen to give sufficient resistance to corrosion. About a handful of differentalloys are used in the oil and gas process systems, although the variety of corrosionresistant alloys is enormous. These alloys have different characteristics such as criticalpitting temperature (CPT), critical crevice temperature (CCT), chloride stress corrosioncracking (CSCC) temperature and maximum velocities (C-value).

CPT * CCT CSCC C-value

Stainless Steel type 316 15 5 60 300

Stainless Steel type 904L 30 20 100Stainless Steel type 22Cr duplex 30 20 100 350Stainless Steel type 25Cr super duplex 80 50 110 350Stainless Steel type 6Mo 80 50 120 350

* ll d l

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Stainless steel type 316 is not normally recommended for use in sea water systems sincestagnant or low flow conditions (< 1.5 m/s) and the presence of deposits can lead to pittingor crevice corrosion.

In atmospheric marine conditions, the maximum acceptable surface temperatures for the

above-mentioned stainless steel types are 40o

C for type 316, 60o

C for type 904L, 100o

C for type 22Cr duplex and 120 oC for type 25 Cr duplex and 6 Mo.

According to ISO 15156, the maximum H 2S partial pressure for stainless steel is dependenton the chloride concentration, temperature and the pH. In general, the maximum H 2S partialpressure is less for the 316 type and the duplex type stainless steel than the 6 Mo typestainless steel.

The use of corrosion resistant alloys requires a higher-level quality assurance on thefabrication, installation and start-up of new facilities than the use of carbon steel (MONS-T-03). In case that the corrosion resistant alloys are not treated correctly, then failures mightoccur after a very short service life.

4.2.7. Galvanic Corrosion

Corrosion resistant alloys in connection with carbon steel may cause galvanic corrosiondependent on the potential difference between the metals and the anode/cathode ratio. Apotential difference above 0.1-0.2 V should be avoided. Ideally the dissimilar metals shall beisolated with a non-conducting spool, but total isolation might be difficult to achieve. Another possibility is to reduce the anode/cathode ratio by coating of the cathode (the noblestmaterial). Length of internal coating to minimum 5 x the internal diameter for the piping.

4.3. Material Requirements for Process Piping

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For systems with a theoretical corrosion rate above 2.0 mm/y in carbon steel, 6 Mo typestainless steel is required for H 2S partial pressures higher than 0.2 bara. For H 2S partialpressures lower than or equal to 0.2 bara, either 6 Mo or super duplex shall be used.

In addition, due consideration should be given to the limits on temperature, chloride and pHspecified in ISO 15156.

For systems specified by MONS UK with potential for high solids, bacterial activity and lowflow rates, FBE coated carbon steel is required.

4.3.2. Produced Water System

For produced water systems with theoretical CO 2 corrosion rate equal to or below 0.2 mm/y,carbon steel can be used without corrosion inhibitor injection facilities.

For a theoretical corrosion rate up and equal to 2.0 mm/y, carbon steel can be used inconjunction with an effective corrosion inhibitor injection system.

For systems with theoretical corrosion rates above 2.0mm/y in carbon steel super duplex or 6Mo type stainless steel is required.

For systems with potential for high solids, bacterial activity and low flow rates, FBE coatedcarbon steel is required.

GRP can be used downstream the degasser.

4.3.3. Wet Gas System

For wet gas systems with theoretical CO 2 corrosion rate equal to or below 0.2 mm/y, carbonsteel with adequate corrosion allowance can be used without corrosion inhibitor injection

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4.3.4. Dry Gas System

For gas systems that are normally water dry, the material shall be carbon steel with acorrosion allowance of either 1.5 or 3 mm depending on the anticipated upset, water wetconditions.

4.3.5. Flare Systems

The required material is either low temperature carbon steel (> -40 oC) with, typically 3 mmcorrosion allowance or stainless steel 316L (< -40 oC), subject to the operating temperature.

4.3.6. Crude Oil/Condensate Systems

The required material is carbon steel for systems with a water cut < 20%. For higher water cuts and a theoretical corrosion rate up and equal to 2.0 mm/y, carbon steel with adequatecorrosion allowance and an effective corrosion inhibitor system are required. For water cuts> 20% and a theoretical corrosion rate above 2.0 mm/y in carbon steel, 6 Mo type stainlesssteel is required for H 2S partial pressures higher than 0.2 bara. For H 2S partial pressures

lower than or equal to 0.2 bara, either 6 Mo or super duplex shall be used.

When determining the applicable water cut, consideration shall be given to operatingconditions throughout the life of the asset

4.4. Material Requirements for Utility Piping

For utility systems, the corrosivity assessment and material selection are much simpler as theconditions are generally well defined and will remain unchanged during the lifetime of thesystems.

4 4 1 Fresh and Potable Water Systems

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4.4.3. Sea Water Systems

For untreated sea water systems, the required materials are 6 Mo type stainless steel or GRP.If elevated temperatures will be encountered, for example, where untreated seawater is usedfor cooling, then due consideration shall be given to the effects thereof on the materials. For 6Mo type stainless steel materials, the maximum operating temperature shall be 50°C. Amaximum design temperature of 75°C shall be applied to GRP in accordance with Norsok M-001.

Carbon steel is acceptable for deaerated sea water (< 5ppb) or produced water re-injection. A6 mm corrosion allowance is recommended, unless realistic assessments of corrosivitythroughout the anticipated design life justify the use of 3 mm.

4.4.4. Closed Cooling Water Systems

Carbon steel is the required material. A 3 mm corrosion allowance is recommended unlessthe operation of the system will be such that reliable inhibition and the exclusion of oxygen canbe guaranteed, thereby justifying a reduced 1.5 mm corrosion allowance.

4.4.5. Open Drain Systems

Both the hazardous and non-hazardous open drain shall be constructed in GRP.

4.4.6. Closed Drain Systems

Stainless steel 316L is required

4.4.7. Fire-water Systems

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4.4.10. Fuel Gas

For the fuel gas system, carbon steel with a 3 mm corrosion allowance is required unlessDry gas is used, in which case Section 3.3.4 applies. From the KO-drum upstream the filter

and the heater to the fuel gas users, stainless steel 316L is required.

4.5. Material Requirements for Chemical Injection Systems

The required material for the majority of the chemical injection systems is stainless steel316L. The chemical injection system is defined as the piping from chemical storage tank tothe chemical injection quill (including house for quill). All chemical systems requireinstallation of chemical injection quills pointing in the flow direction.

The following chemicals are known exceptions and require other materials of construction.

4.5.1. Ferric Chloride and Sodium Hypochloride

The required material is titanium or PVDF

4.5.2. Methanol, MEG and TEG

The required material is carbon steel.

4.5.3. Use of Polymers

Polymer piping and hoses for chemicals are only acceptable upon Mærsk Olie approval .

5 DOCUMENTATION OF SELECTED MATERIALS

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Title: Technical Standard for Material Selection for Topside Process and Utility Piping Rev A2 __________________________________________________________________________________________

ANNEXE 1 REQUIRED INPUT FOR CORROSIVITY ASSESSMENT OF PRODUCTIONSYSTEMS

Production forecast (oil/gas/water)Well fluid PVT-analysisProcess simulationTemperature + pressure

Process simulationPipe dimensions

CO 2 contentH2S contentpHBicarbonate (mg/l)Ionic strength (salts) (g/l)Content of organic acidsContent of solids (sand)

Inhibition detailsLaboratory tests, field or test data for inhibitor performance

Information about unstable process conditions, e.g. condensation during process shutdown.Definition of upper and lower process limits such as flow velocities, temperatures etc.

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Title: Technical Standard for Material Selection for Topside Process and Utility Piping Rev A2 __________________________________________________________________________________________

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ANNEXE 2 MATERIAL SELECTION FOR TOPSIDE PROCESS AND UTILITY PIPING

Titanium Super Duplex 254 SMO SS 904L SS 316L LTCS CS* CS (inh.) CS (galv.) GRP CS (coated) PP PVDF PE

Flowlines/manifolds

Gas fields X X X X

Oil fields X X X X X

Produced Water X X X XSolids/bacteria X X

Wet gas X X X X

Dry gas X X

Flare systems

> -40C X

< -40C X

Crude/condensate X X X X

Open drain X X

Closed drain X X

Fuel gas

wet X

dry X

Seawater X X

Water injection

< 5 ppb oxygen X

Closed cooling water X

Air s yst ems

Breathing X

Combustion X

Instrument X

Utility X

Fresh/potable water X X X

Firewater X

Instrument tubing X

Sewage

Chemical Injection X X X

Ferric Chloride X X

Sodium Hypochloride X X

Methanol, MEG and TEG X

* For new buildings requiring CE-marking according to PED 97/231EC only LTCS is acceptable.

MATERIAL SELECTION FOR TOPSIDE PROCESS AND UTILITY PIPING

MONS-T-08

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