Conquer corrosion with materials selection Offshore Europe 2017 cinema seminar

Clara Moyano, ImechE IEng Beng

Innovation Engineer

• As an innovation engineer and expert metallurgist working across the globe, Clara deals with all sorts of challenges. She is often involved in discussions on materials selection, including advice to oil and gas producers working on new platforms around the world.

• Clara specialises in areas such as tackling corrosion, and materials selection for design specifications. She also advises on quality certifications and regulations around the manufacturing of metals.

Speaker biography

Objectives

• Current market trends & material challenges

• Corrosion mechanisms in Oil & Gas

• Best practices to fight corrosion

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• Choice from 300,000 alloys

• Operations/technology shifts

• Design/performance expectations evolving

• Tight regulations

• Cost increases

• Lack/loss experience

• Unknown territories and failures

• Onshore shale & offshore/deep water

Onshore Shale &

Offshore / deep

water

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Corrosion Challenges

Choice from

300,000 alloys

Operations /

Technology

shifts

Tight

regulations Cost increases

Design /

performance

expectations

evolving

Lack / loss

experience

Unknown

territories and

failures

Cost of Corrosion

Source: NACE

https://www.nace.org/uploadedFiles/Publications/ccsupp.pdf5

• One report relates $276 billion per year

Corrosion in Figures

Source: NACE

https://www.nace.org/Corrosion-Central/Corrosion-101/Testing-for-Localized-Corrosion/6

• Summary of 363 corrosion failures within a major chemical processing company

• Pitting is the second biggest concern for failure

• Pictures of offshore corrosion

Examples of Corrosion

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What is corrosion?

Degradation of the materials’ properties due to interactions with their environments• Inevitable to some extent

• Primarily associated with metallic materials,all material types susceptible

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• Extreme operating temperatures

• Very corrosive media (H2S, C02, Chlorides, Organic Compounds, etc)

• Severe ambient conditions (Hot and humid climates, seawater nearby, etc)

• Improper design

• Low quality equipment & material

• Microbial action

Causes Leading to Corrosion?

Extreme Operating

TemperaturesVery Corrosive Media (H2S, C02,

Chlorides, Organic Compounds, etc)Severe Ambient Conditions

(Hot and Humid Climates,

Seawater Nearby, etc.)

Improper design

Low Quality Equipment

& Material

Microbial Action

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• Pitting Corrosion

• Crevice Corrosion

• Galvanic Corrosion

• Stress Corrosion (Chloride & Sulphide induced)

• Other

Common Types of Corrosion

Pitting Corrosion

Crevice Corrosion

Galvanic Corrosion

Stress CorrosionChloride & Sulphide Induced

Other

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Pitting Corrosion

• Corrosive attack causing rapid penetration of the base material thickness

• One of the most damaging and common causes of failure

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• Large surface areas will become cathodic, pits will become anodic and will corrode.

• This is similar to a small sacrificial anode trying to protect a structure.

Pitting Corrosion Mechanism

e-e- Low pH

High Cl

Stainless Steel

Aqueous Chloride

Solution Cl-

O2

(dissolved)

Passive

Surface

Oxide

++++++++++++++++

- - - -Anode - Active

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Crevice Corrosion

Localised surface attack in the gap or crevice betweentwo joining surfaces

• Can be formed between two metals or a metal andnon-metallic material

• Tubing clamps are a prime example

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• The two metals must be widely separated on the galvanic series

• They must be in electrical contact

• Their surfaces must be bridged by an electrically conducting fluid

Galvanic Corrosion: An Electrochemical Process

The two metals must

be widely separated

on the galvanic series

They must be in

electrical contact

Their surfaces must

be bridged by an

electrically

conducting fluid

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• The best practice is using the same material when different components are coupled together.

Galvanic series: mixing dissimilar materials

A properly designed cathodic protection system can protect

offshore structures from the onset of galvanic corrosion15

Stress Corrosion Cracking (SCC)Under the combined effects of stress and certain corrosive environments

materials can be subject to this very rapid and severe form of corrosion

The stresses must be tensile and can result from loads applied in service,

or stresses set up by the type of assembly

Corrosive media

Tensile Tensile

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Stress Corrosion Cracking (SCC)• Most damaging environment is a solution of chlorides in water, such

as sea water, particularly at elevated temperatures

• As a consequence, stainless steels are limited in their application

for holding hot waters (above about 50°C) containing even trace

amounts of chlorides (more than a few parts per million).

Series 300 stainless

steels are especially

vulnerable to

chloride-induced SCC

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Other Types of Corrosion

General

MIC

Intergranular

Anaerobic Bacteria

H2S GAS

Thiobacillus

Bacteria creates

Sulphuric Acid

MIC Intergranular

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• Zone 1 – Topsides

• Zone 2 – Splash Zone

• Zone 3 – Tidal

• Zone 4 - Seawater

Corrosive Challenges in an Offshore Rig

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• Corrosion rate trend +/- >1mm a year

Corrosive Challenges in an Offshore Rig

• Selecting materials and controlling corrosion for a given application is one of the main design steps towards a safe and cost efficient system, yet a commonly overlooked stage.

• Benefits

• Asset safety and integrity

• Optimum performance with minimal maintenance and shutdown time

• Longer life expectancy

• COST SAVINGS

Implications of Corrosion Control

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Benchmarking Alloys

• Factors Limiting Pitting in Stainless Steel

• PREN - Pitting Resistance Equivalent Number

• Developed to reflect and predict the pitting resistance of an alloy.

• Note – there are several variations of the formula for PREN in the nitrogen value.

• The following definition is from NACE MR0175 / ISO 15156-2003, part 3, para 6.3.

• PREN = % Cr + 3.3 x (% Mo + 0.5 x % W) + 16 x % N

• Cr = chromium

• Mo = Molybdenum

• W = Tungsten

• N = Nitrogen

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• Table showing least to most resistant alloys

Corrosion Resistance: Pitting & Crevice

Most

Resistant

Least

Resistant

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• Table showing elevated temperature rating factors

Operating Pressure & Temperature

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• Diagram showing corrosion resistance vs strength

Strength vs Corrosion Resistance

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• Diagram showing average price vs. availability

Cost vs. Availability

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• Operating conditions, including temperature, pressure and media contained

• Environment

• Legislation and internal regulations

• Cost

• Availability

• Lead time

• Expected life time of the equipment

• Safety

Materials Selection Criteria

KNOW YOUR PROCESS AND CONTROL IT

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According to industry standards such as NORSOK M-001, Materials Selection standard:

“At galvanic connections between dissimilar materials without isolation/distance spool, it can be assumed that the local corrosion rate between the interface is approximately 3 times higher than the average corrosion rate’’.

Does Size Matter?

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Suparcase™ Principle

• Good Tube Grip = Harder Rear Ferrule

• Suparcase™ process perfected by Parker gives the Differential Hardness & Improved Corrosion Resistance

• Some competitor hardening process corrode i.e. Nitride Hardening

• 30+ years in service

Over 100 million

pieces in service

without failure due to

corrosion or cracking

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• 40% cheaper

• Not counting downtime or safety

Tubing installation life cycle costs:example

** Figures exclude material cost increase

40%

cheaper

Not counting

downtime or

safety

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Summary

1. Know your process

2. Correct material selection

3. Corrosion control strategy

4. Avoid complexity

5. Use high quality equipment

6. Think long term

7. Question low cost supplies

8. Do not intermix materials if alternatives are available

9. Use NACE & NORSOK equipment as required

10. Do not be afraid to ask…It’s all about control and cost effectiveness

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Contact for further information

Clara Moyano, ImechE IEng Beng

Innovation Engineer

T: +44 (0)1271 313151E: CMoyano@parker.com

Questions and discussion

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