Standard NORSOK M-CR-505 Corrosion Monitoring Design

NORSOK STANDARD

COMMON REQUIREMENTS

CORROSION MONITORING DESIGN

M-CR-505Rev. 1, December 1994

Corrosion Monitoring Design M-CR-505Rev. 1, December 1994

_______________________________________________________________________________NORSOK Standard 1 of 6

CONTENTS

1 FOREWORD .......................................................................................................................2

2 SCOPE..................................................................................................................................2

3 NORMATIVE REFERENCES..........................................................................................2

4 DEFINITIONS AND ABBREVIATIONS.........................................................................2

5 CATHODIC PROTECTION MONITORING - SUBMERGED PARTS......................25.1 General ..........................................................................................................................25.2 Reference electrodes .....................................................................................................35.3 Monitored anodes..........................................................................................................3

6 INTERNAL CORROSION MONITORING - PIPING SYSTEMS...............................36.1 General ..........................................................................................................................36.2 Types of monitoring......................................................................................................36.3 Number, location and accessibility of access fittings/sensors ......................................4

7 DATA AQUISITION AND PROCESSING......................................................................67.1 Monitoring control systems ..........................................................................................67.2 Functional requirements................................................................................................6



1 FOREWORD

This standard has been developed by the NORSOK Standardisation Work Group for thewidest possible national and international application.

2 SCOPE

This Standard is applicable to design and installation of monitoring systems for externaland internal corrosion on offshore structures and production systems in carbon steelmaterial. This document does not cover inspection or erosion monitoring.

Type of monitoring equipment, extent and frequency for monitoring shall be dependent onstructure/ system criticality, corrosivity and lifetime.

3 NORMATIVE REFERENCES

None

4 DEFINITIONS AND ABBREVIATIONS

LPR Linear polarization resistanceER Electrical resistance

5 CATHODIC PROTECTION MONITORING - SUBMERGED PARTS

5.1 General

The objective of a corrosion monitoring system for submerged steel is to monitor theefficiency of the cathodic protection system.

Permanently mounted sensors for cathodic protection monitoring of critical componentsexposed to sea water shall be installed in areas which are not accessible for inspection or ifinspection is not planned for in such areas.

The cathodic protection monitoring of critical components exposed to sea water shall bebased on measurement of the electrochemical potential of the steel surface at differentlocations.



As a supplement, other parameters may be measured, such as :

• Current output from selected anodes.• Current density.

5.2 Reference electrodes

The reference electrodes should either be one of either, or a combination of:

• High purity zinc reference electrodes and• Ag/AgCl reference electrodes.

The lifetime and the stability of the reference electrodes shall be documented.

5.3 Monitored anodes

The monitored anode shall have the same shape as other anodes in the area and be designedto allow recording of current output.

The attachment of the monitored anode support to the structure shall be by welding.

6 INTERNAL CORROSION MONITORING - PIPING SYSTEMS

6.1 General

The objective of internal corrosion monitoring is to monitor corrosivity trends in carbonsteel systems and to verify or adjust means for preventing corrosion.

6.2 Types of monitoring

At least two of the following methods shall be specified:

• Weight loss measurements• Linear polarization resistance measurements (LPR)• Electrical resistance measurements (ER)• Galvanic measurements (injection water)

Additional monitoring methods which shall be considered are:

• Bacterial probes• Water analysis• Chemical analysis



The selection of monitoring method and location of monitoring points shall take intoconsideration system criticality, expected corrosivity, water content and salinity, piggingfacilities, maintenance and shall be in accordance with requirements described below.

If weld corrosion is anticipated as an internal corrosion mechanism, welded weight losscoupons and spot checks using weld probe measurements should be used.

For subsea wellstream flowlines, local monitoring shall be used if reliable signals can beprovided and an overall cost efficiency is gained considering material selection andinspection requirements.

6.3 Number, location and accessibility of access fittings/sensors

The monitoring probes/coupons shall be installed in 2" access fittings at preselectedlocations with an individual distance of minimum 0.5 m in each pipe to be monitored.Number of access fittings at each location shall be selected as listed in table 6.1.

The probes/coupons shall be located at representative locations where there is a highprobability of corrosion taking place e.g. bottom of line location in stratified flow wherewater is likely to accumulate.

A retriever tool is required to install and to retrieve the coupons/probes from equipmentunder pressure. Sufficient space for the tool shall be allowed for in the piping layout andwhen selecting the sensor locations. Adequate working space and safe access to the fittingby service personnel shall be established.

Based on process parameters and selected material, an evaluation of process lines to bemonitored shall be done. Guidelines are given below (for carbon steel only). This shall as aminimum include:

• All ingoing and outgoing riser lines on the platform, downstream the injection pointfor corrosion inhibitor (if any).

• Each oil flowline downstream the injection point for corrosion inhibitor (if any).• The inlet of 1st stage oil separator and test separator.• The water outlet pipe from each oil separator.• In gas outlets from each oil separator.• In gas lines downstream gas coolers with direct seawater cooling (also applicable

when corrosion resistant materials are used).• In a selected number of produced water lines from gas scrubbers.• In fuel gas downstream gas scrubber.• Downstream deaerator in water injection systems.• Downstream injection pumps in water injection systems close to the injection

manifold.• In main closed water systems with corrosion inhibitors, e.g. cooling water system.



A piping system which is designed in corrosion resistant materials will not need corrosionmonitoring equipment. However, 2" access fittings (with blind flanges) should beconsidered installed in flowlines upstream manifolds and in piping for outgoing riser lines.

Table 6.1 - Corrosion monitoring methods in different systems and number of accessfittings at each location.

CORROSION MONITORING

SYSTEM

METHODS

NUMBER OF ACCESSFITTINGS PR.

LOCATION

Oil producing flowlines

Gas lines

Produced water lines

Water injection lines

Closed water lines, incl.cooling systems

Weight Loss Coupons, Weld Probemeasurements (spot checks), ER-probes

Weight Loss Coupons, ER-probes

Weight Loss Coupons, Weld Probemeasurements (spot checks), ER-probes/LPR

Weight Loss Coupons, ER Probes, LPRProbes, Weld Probe measurements (spotchecks), Galvanic Probes, BacterialProbes, Chemical analysis.

Weight Loss Coupons, LPR Probes

3

2

2

3

2

NOTES

• All probes/coupons shall be retrievable using standard retriever tools. • The weight loss coupons and ER probes shall be made of a similar material as the wall

material being monitored. This also includes filler material and weld procedure for weldedprobes. Coupons shall also be used for bacteria- and scale control.

• The linear polarization resistance (LPR) technique shall only be used where water forms themajor constituent of the fluid (at least 35 %) and the salinity is above 0.1 %.

• Probes in oil flowlines and produced water lines have a high risk of being filmed and thereforethe readings may not be representative. This shall be considered when selecting monitoringpoint location.



7 DATA AQUISITION AND PROCESSING

7.1 Monitoring control systems

Monitoring Control Systems shall be based on one of the two alternatives:

• Central Corrosion Monitoring Computer System, based on on-line data acquisition• Portable Data Acquisition

A portable data acquisition system shall be based on field readings using one of the belowalternatives:

• System units set out in the field which are logging relevant data. The units shall betapped at regular intervals.

• Portable instruments for logging of data.

A PC-based program shall be included for evaluation of relevant corrosion data.

7.2 Functional requirements

The PC-based database shall include data of the following categories:

• Cathodic protection monitoring• Corrosion rate measurements from different types of corrosion sensors (weight loss

coupons, ER and LPR probes).

Recommendation:For production systems a cost evaluation should be performed assessing the option forincluding relevant process data into the database.

Statistical techniques for evaluating the data and the data quality shall be supplied with thedata processing unit.

Standard NORSOK M-CR-505 Corrosion Monitoring Design

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