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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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Parker Hannifn Ltd.
Instrumentation Products
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Catalogue CORROSION-PROMO
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