Smarter Materials Selection for Corrosion Control

8/3/2019 Smarter Materials Selection for Corrosion Control

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Smarter Materials Selectionfor Corrosion Control


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Uniform Corrosion

Uniform or general corrosionis the most classical form ofcorrosion, but is not always themost important in terms of costor safety.

Te consequences of uniformcorrosion are a decrease in metalthickness per unit time or a more

or less uniform deposit of thesecorrosion products in the surfaceof the metal.

Uniform corrosion can belimited or prevented by anappropriate choice of materialor modication of the mediumamong other solutions.

The ProblemUsing the right materials and processes can help to beat

corrosion problems throughout industry.

Galvanic Corrosion

Galvanic corrosion can bedened simply as being theeect resulting from the contactbetween two dierent materialsin a conducting corrosiveenvironment.

In many cases, galvanic corrosionmay result in quick deterioration

of the least corrosion resistantmaterial, and can lead tofatal failure.

Common methods of minimisingand preventing galvaniccorrosion are choosing materialcombinations in which theconstituents are all made

from the same material ordierent materials as close aspossible in the correspondinggalvanic series, avoiding anunfavourable surface area ratio,using protective coatings, orcontrolling the aggressiveness ofthe environment.

> LESSON: Do not mix tube and fitting or valve alloys wherever possible.

Galvanic reaction created by mixing different body & nut materials.


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Pitting Corrosion

Pitting is characterised by thelocalised attack in the form ofdeep and narrow holes that canpenetrate inwards extremelyrapidly, while the rest of the

surface remains intact. Acomponent can be perforated ina few days with no appreciableloss in weight on the structure asa whole.

Pitting corrosion is mostaggressive in solutionscontaining chloride, bromideor hypochlorite ions. Tepresence of sulphides and H2S

is also detrimental to this typeof attack. Te stainless steelsare particularly sensitive topitting corrosion in seawaterenvironments.

Pitting corrosion can be reducedor prevented by choosing themost appropriate material forthe service conditions, avoidingstagnant zones and deposits,

reducing the aggressiveness ofthe medium or using cathodicprotection.

Crevice Corrosion

Crevice corrosion is anelectrochemical oxidation-

reduction process, which occurswithin localized volumes ofstagnant solution trapped inpockets, corners or beneath ashield (seal, deposit of sand,gasket or fastener, for instance).

Crevice corrosion is highlyaccelerated if chlorine, sulphideor bromide ions are present inthe electrolyte solution. Once

a crevice is initiated, even themost benign atmospheric

environments can becomeextremely aggressive. Crevicecorrosion is considered muchmore dangerous than uniformcorrosion as the corrosion ratecan be up to 100 times higher.

Crevice corrosion isencountered particularlyin alloys which owe theirresistance to the stability of a

passive lm. A classic example isstainless steel in the presence of

moderate to high concentrations ofchlorine ions.

Crevice corrosion can be limitedor prevented by using weldsrather than bolted or riveted

joints, designing installations witha proper draining system andavoiding stagnant areas, using solidand high quality seals or controllingthe severity of the electrolyte.

Crevice corrosion between the

tube/tube trap interface.

The Problem

> LESSON: Every batch of Parker 6Mo steel is tested for Pitting Corrosion as per the ASTMG48 standard.


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Intergranular Corrosion

Intergranular corrosion is aform of attack that progresses

preferentially along the grainboundaries paths and can causethe catastrophic failure of theequipment, especially in thepresence of tensile stress. Undercertain conditions, the grainboundaries can undergo markedlocalized attack while the rest ofthe material remains unaected.Te alloy disintegrates and losesits mechanical properties. Tis

type of corrosion is due either tothe presence of impurities in the

boundaries, or to local enrichmentor depletion of one or morealloying elements.

Many alloys can suer fromintergranular attack, but themost common example is theintergranular corrosion ofaustenitic stainless steels, relatedto chromium carbide depletionin the vicinity of the boundaries,

during a sensitising heattreatment or thermal cycle.

Intergranular corrosion canbe prevented by selecting theright material, avoiding low costequipment where the materialis likely to have impurities andpoor heat treatment, using lowcarbon or stabilised grades if

welding or applying post-weldheat treatments correctly.

Stress Corrosion Cracking

Stress corrosion cracking(SCC) is a process involving theinitiation of cracks and theirpropagation, possibly up tocomplete failure of a component,

due to the combined action oftensile mechanical loading anda corrosive medium. Te timenecessary for a part to fail by SCCcan vary from a few minutes toseveral years.

Tis kind of attack normallyoccurs in media that are littleor non-aggressive towards themetal or alloy concerned inthe absence of tensile loading.

Tis form of corrosion is of aparamount importance andrepresents a permanent risk innumerous industrial installations,in terms of both the safety and

economic consequences involved.No commercial alloy is fullyimmune to SCC.

Stress corrosion can be avoidedby selecting materials that arenot susceptible in the speciccorrosion environment andminimised by stress relievingor annealing after fabricationand welding, avoiding surfacemachining stresses and controllingthe corrosive environment.

Intergranular Corrosion HAZ Area Stainless Steel

Weld in Seawater Environment

Stress Corrosion Cracking Stainless Steel in

Seawater Environment

> LESSON: Our stainless steel is capable of passing the intergranular corrosion test as perthe ASTM A262 Practice.

> LESSON: Do not take shortcuts. Select the best material for a safer & more costeffective application.


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Some of the most popular factors that can have a signicant inuence in terms of corrosion are listed below:

The Facts

Materials Selection:

Environment Mechanical Properties Availability of Design & est Data Cost Availability Maintainability Compatibility with other components Reliability Appearance

Some Figures About Corrosion

Te industrial importance oflocalized corrosion problemshas been revealed in manyreports. Te following pie chartsummarizes the ndings of363 corrosion failure casesinvestigated in a major chemicalprocessing company. Teimportance of pitting comessecond, just after generalcorrosion and before stresscorrosion cracking which is oftenalso initiated by pitting.

Sour Gas Service and NACE MR0175Hydrogen sulphide (H2S) isa colourless, ammable, andextremely hazardous gas.It occurs naturally in crudepetroleum, natural gas, and hotsprings. In addition, hydrogensulphide is produced by bacterialbreakdown of organic materials

and human and animal wastes(for instance, sewage systems).Industrial activities that canproduce the gas includepetroleum/natural gas drillingand rening, wastewatertreatment, coke ovens, tanneries,and paper mills. Hydrogensulphide can also exist as a liquidcompressed gas.

When dissolved in water, H2S

forms a weak acid which isextremely corrosive, especiallyin the case of steel where thecorrosion products of iron,

sulphide and atomic hydrogencan penetrate the steel andembrittle it. Under the inuenceof applied stresses, cracking candevelop in a very short time andresult in failure of the equipmentand potential human andenvironmental loss. Tis type

of failure is known as sulphidestress corrosion cracking (SSCC)and there are many cases inhistory that account for this typeof failure.

NACE MR 0175/ISO 15156 isa Materials Standard issuedby the National Association ofCorrosion Engineers. It aimsto assess the suitability ofmaterials for oileld equipment

where sulphide stress corrosioncracking may be a risk inhydrogen sulphide (sour)environments. Tis 3-part

document gives requirementsand recommendations for theselection and qualication ofcarbon and low-alloy steels,corrosion-resistant alloys,and other alloys for servicein equipment used in oil andnatural gas production and

natural gas treatment plants inH2S-containing environments,

whose failure could pose a riskto the health and safety of thepublic and personnel or to theenvironment. It can be appliedto help to avoid costly corrosiondamage to the equipment itself.

Parker Instrumentation canoer all the range of materialscompliant to the metallurgical

requirements of NACE MR0175in selected ranges. For moreinformation, please contact us.

Process Parameters:

Media Chemistry emperature Velocity Pressure

Construction Parameters:

Drainage, Welding, etc.

Dissimilar Metals

Crevices

Corrosion Allowance

Operating Lifetime

Maintenance & Inspection

Requirements

Fatigue

Embrittlement

Intergranular

Erosion

Crevice

SCC

Pitting

General


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The Solution

As the worldwide search for oiland gas, power generation orchemical production is turningto more challenging applicationsan increasing number ofsituations are being encountered

where corrosive productionenvironments and products arepresent. Many of these cases

often involve signicant amountsof hydrogen sulphide, carbondioxide, brine or hazardouschemicals among others, wheretheir high corrosivity along withthe wrong decisions made duringthe design stage have often leadto fatal failure and invaluable

Corrosion control does not just happen. It must be planned.

We can help you nd the best solution for your application.

human, environmental andeconomic loss. In most cases,these situations could have beenavoided by properly analysingthe specic operating parametersand designing the most suitableequipment.

In addition, other factors such

high pressures and temperaturesor severe environments areon demand. Requirementsfor higher production rates ormore complex processes along

with climate change and newenvironmental regulations cancomplicate the material selection

process and ultimately theperformance and integrity ofthe application. Under thesecircumstances materials canoer a valid and cost eectivealternative to conventionalmethods of corrosion control.

Te material selection process

can sometimes becomecomplex, usually involvingmultiple factors like highstrength requirements,operating temperature, highcorrosion resistance, availabilityand cost.

Our Materials Statement

Our primary philosophy is to build

reliable, ecient, cost-eectiveequipment for the intendedservice. We always strive for thebest quality in the designs weproduce, the materials we selectand manufacturing processes

we apply. All our materials comefrom the most prestigious millsin Europe and North America,and are fully traceable to thesource of origin and mercuryand radioactive free. We want toadd value to every component

we create and make all theapplications we servesmarter, faster, cleaner and safer.

Due to their versatility, reliability

and excellent corrosion resistance,the set of alloys and equipmentthat we oer usually meet all thedemands in markets, includingthe oil and gas, chemical andpetrochemical processing,pollution control, marineengineering, power generation, orpulp and paper among others.

However, the uniquerequirements of some ofthe projects often demandspecial approaches. ParkerInstrumentation understandthose needs and has the technical

knowledge and experience

to help our customers to ndthe better solutions for theirapplications and meet even themost challenging demands.

Together, we can createinnovative solutions thatensure your success


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Materials Range for Corrosion ControlOur experienced credentials in materials selection are the results

of years of expertise in successful applications worldwide.

Materials Range

Parker oers the most extensive range of alloys in the market. Te range varies from conventional steels tohigh nickel alloys and titanium for the most demanding applications. Te table below depicts the standardrange of materials per product family. Other alloys might be oered on request.

Operating conditions, including temperature,pressure and media contained

Environment

Legislation and Internal Regulations Cost

Availability

Lead time

Expected life time of the equipment

Safety

Mechanical properties

Corrosion resistance to media and environment

emperature operating range

Cost

Availability on request

Although the mechanism of corrosion is highly complex the actual control of the majority of corrosionreactions can be eected by the application of relatively simple concepts. Indeed, the Committee on

Corrosion and Protection concluded that better dissemination of existing knowledge was the mostimportant single factor that would be fundamental in decreasing the enormous cost of corrosion in the UK. *

* Report of the Committee on Corrosion and Protection, Department of rade and Industry, H.M.S.O. (1971)

Parameters o Be Considered in the Materials Selection Process

Te main parameters to be considered when selecting any equipment are:

In terms of materials, the selection criteria normally translate into some of the following parameters:

A-LOKFittings

Phastite

FittingsValves Manifolds

FlangedProducts

Brass Yes No Yes No No

Carbon Steel No No Yes No Yes

Stainless Steel 316/316L Yes Yes Yes Yes Yes

Duplex Steel No Yes Yes Yes Yes

Superduplex Steel No Yes No Yes Yes

Super austenitic 6Mo Yes Yes Yes Yes Yes

Monel 400 Yes Yes Yes Yes Yes

Alloy 825 Yes Yes Yes Yes Yes

Alloy 625 Yes Yes Yes Yes Yes

Alloy C-276 Yes Yes Yes Yes Yes

Titanium Yes No Yes Yes Yes


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Materials Quick Selection Guide forGeneral Industrial ApplicationsTe following table classies our materials range in terms of mechanical strength and general corrosion

resistance, and aims to be a generic tool and guidance at an early stage of the design. Te values given tothe specic parameters are not absolute and should be used as a reference only. Each application needsto be evaluated carefully and individually as the rules below might not apply at all times.

ImprovedCorrosionRe

sistance

AvailabilityBar/For

ging/Tube*

Average Price

Increasing Strength - UTS

Titanium Gr.2

Titanium

Titanium Gr.5

SuperduplexSteel

SuperduplexSteel

Brass

Brass

Monel 400

Monel 400

Stainless 316

Stainless 316

Carbon Steel

Carbon Steel

Duplex Steel

Duplex Steel

6Mo Steel

6Mo Steel

Alloy 825

Alloy 825

Alloy C276

Alloy C276

Alloy 625

Alloy 625

* For instrumentation applications

Low

Low

Medium

Medium

High

High


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Tink of the equipmentreplacement cost, depreciation,re-qualication of the newsystems, downtime or low

production rates, nes or humanand environmental loss. Avoidlow cost equipment. Investing ina more expensive material todaycould be a cheaper and trouble-free solution in the medium andlong term.

Parker Hannin carried out StressCorrosion Cracking esting asper ASM G48 conducted by anindependent party and its aim

was to determine the time tofailure of the 6Mo super austeniticsteel (UNS S31254) and theconventional 316/L stainless steel(UNS S31600/03) in exactly thesame conditions. Results showedthat the 6Mo grade took over 3

times more to fail than the316 grade.

In service applications, those

results translate into a lifeexpectancy of 6Mo threetimes longer than that of 316in the same given conditions,reducing leakage and

downtime and increasing

safety by over 60%.

Cost Considerations

Example of a typical installation and associated life cycle cost:

** Figures exclude material cost increase 40% cheaper

Materials Selection A:Stainless Steel 316

Materials Selection B:Superaustenitic 6Mo

8,000 meters of 1/2"x 0.065" tubing

$7/m $23/m

1,500 Fittings 1/2"x straight shapes

$15/unit $40/unit

Design Parameter 5 Years Life 15 Years Life

Tubing & FittingReplacement**

Tube: $7/mFitting: $15/unit $0

MHR Labour Cost

40 MHR per 300 meters $0

$80 labour/hour $0

Tubing & FittingReplacement**

Tube: $7/ftFitting: $15/unit

$0

MHR Labour Cost

40 MHR per 300 meters $0

$80 labour/hour $0

TOTAL $406,380 $244,000

After10Years

After5Years

InitialInstallation


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Some of Our ExperienceHere are some basic guidelines based on our extensive

knowledge and experience in applications worldwide:

Tink about cost eectiveness,safety and reliability

A cheap option today usuallytranslates into high cost ofownership tomorrow

Do not mix tube and tting/valve alloys whenever possible

Use 6Mo for high pitting/crevice corrosion performance

Use Super Duplex for its tensile

strength

Do not use win Ferrule onSuper Duplex rather usePhastite

Use our range of exoticmaterials for demandingapplications and NACEcompliance

Let us help you select the best solution for your application.Start thinking smarter, faster, cleaner and safer.

For a successful and prolonged corrosion-free service, make sure the following parametersare checked during the design stage:

Operating conditions, including temperature, pressure and media contained

Environment

Legislation and Internal Regulations

Cost

Availability

Lead time

Expected life time of the equipment

Safety


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Instrumentation Products

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Catalogue CORROSION-PROMO

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Smarter Materials Selection for Corrosion Control