1 Metal Dusting Corrosion in SMR plants

Metal Dusting Corrosion in Steam Reforming PlantsJ. Bohle, Dr. C. Beyer, U. Wolf, Dr. D Ulber

Steam Reforming Technology User Conference

Labuan, Malaysia

March 5-7, 2007

2 Metal Dusting Corrosion in SMR plants

Metal Dusting Corrosion (MDC)Metal Dusting Corrosion (MDC)

Disintegration of metals and alloys into a dust of graphite and metal particles after carbon ingress and over-saturation.

3 Metal Dusting Corrosion in SMR plants

OverviewOverview

Phenomena of Metal Dusting Corrosion (MDC)

Mechanism involved / Reactions

Material considerations

Examples of MDC in Steam Reforming Plants

Prevention of MDC

Influence of MDC on process design

Literature

4 Metal Dusting Corrosion in SMR plants

Steps in Metal Dusting CorrosionSteps in Metal Dusting Corrosion

Diffusion of reducing / carburizing gas through oxide protection layers to metal surface

Formation & supersaturation of carbides

Dissociation into metal particles and graphite

Diffusion of catalytically active metal particles

Loss of carbon, metal, metal carbide, metal oxide

5 Metal Dusting Corrosion in SMR plants

Phenomena involved in MDCPhenomena involved in MDC

Gas-phase and gas-metal reactions (T, p, composition fi)

Diffusion of reducing gas, carbon and metals (T, fi)

Flow and temperature distribution (vel, T) – equipment design

Catalytically active components in gas and metal

Thermodynamic & mechanical stability of protective layers

Stresses / fractures imposed on surfaces by gradients

Metal crystallographic structure

Sulfidic components in gas

6 Metal Dusting Corrosion in SMR plants

ReactionsReactions

Carburization reactions

CO + H2 <-> C + H2O aC =K1*pCO*(pH2/pH2O)

2 CO <-> C + CO2 aC =K2*(p2CO/pCO2)

CH4 <-> C + 2 H2 aC =K3*(pCH4/p2H2)

Gas-phase reactions

H2O + CO <-> CO2 + H2

H2O + CH4 <-> CO + 3 H2

aC carbon activity

Ki equilibrium constant

Pi partial pressure

7 Metal Dusting Corrosion in SMR plants

Potential for Metal Dusting CorrosionPotential for Metal Dusting Corrosion

8 Metal Dusting Corrosion in SMR plants

Temperature rangePromoting componentsTemperature rangePromoting components

450°C < MDC temp. range < 800°C / Boudouard temp.

At [Fe/Ni] > ~ 2/3 mass-frac, metal dusting is retarded at the lower regimes of the metal dusting temp. range

MDC promoting gas components (negative impact on metal oxide protection layer)

9 Metal Dusting Corrosion in SMR plants

Material ConsiderationsMaterial Considerations

Surface oxide stability is enhanced by alloying elements such as Cr, Al, Si, Ti, Mo providing a barrier to carbon diffusion

Carbon and alloying elements diffusion is influenced by crystallographic structure and surface condition (e.g. grain size)

Surface coatings or surface finish (grinding) can provide added stability by influencing the carbon diffusion and/or physical resistance to mechanical and thermal effects

10 Metal Dusting Corrosion in SMR plants

Material ConsiderationsMaterial Considerations

Fe-based and Ni-based metals show different behaviour

Empirical equation of alloying material resistance to MDC (Parks & Schillmoller)

Crequiv. = Cr % + 3 x (Si % + Al %)

Inclusion of the effects of other alloying elements such as Ti, Mo, Ni outstanding

Preferred material Nicrofer® 6025 HT – alloy 602 CA

No alloy is MDC resistant under all conditions

11 Metal Dusting Corrosion in SMR plants

Where can Metal Dusting Corrosion occur?Where can Metal Dusting Corrosion occur?

Reducer Sockets

Transfer Line at Reformer Outlet

Process Gas Boiler (PGB) Inlet chamber

PGB tube inlet section (ferrules) and tube sheet

PGB bypass tube, bypass flow control device

PGB outlet chamber

Heat Exchanger d/s of PGB, e.g. Feed Preheater

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SMR Outlet System – Reducer SocketsSMR Outlet System – Reducer Sockets

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Manifold, Transfer LineGas BarriersManifold, Transfer LineGas Barriers

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Process Gas Boiler„Cold“ Bypass DesignProcess Gas Boiler„Cold“ Bypass Design

15 Metal Dusting Corrosion in SMR plants

Process Gas BoilerFlow and temperature distributionProcess Gas BoilerFlow and temperature distribution

16 Metal Dusting Corrosion in SMR plants

Process Gas Boiler Flow and temperature distributionProcess Gas Boiler Flow and temperature distribution

Temperature distribution in outlet chamber mixing zone of a process gas boiler

below 450°C

450 – 1000°C

Gastemperatures:

Bypass open

Bypass closed

17 Metal Dusting Corrosion in SMR plants

Inserts in PGB tubes for temp. controlInserts in PGB tubes for temp. control

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

0 2000 4000 6000 8000 10000

Distance from Inlet (mm)

Tem

pe

ratu

re (

°C)

Feedgas

Wall medium

Steam Cooling

300

310

320

330

340

350

360

370

380

390

400

0 2000 4000 6000 8000 10000

Distance from Inlet (mm)

Tem

pe

ratu

re

(°C

)

Wall inside

Wand outside

Steam Cooling

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Measures against MDC Pro & ConsMeasures against MDC Pro & Cons

Avoid metal wall temperatures in MDC temperature range

Use of non-metallic materials in critical areas

Change gas atmosphere– Introduction of process gas (for purge) in critical areas– Catalytically activated refractory (Lurgi Patent)

Material science, Protection layers

Sulfidic compounds in gas

Design for easy maintenance / replacement

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Influence of MDC on process designInfluence of MDC on process design

Process efficiency / consumption figures

Steam to Carbon Ratio

Steam Superheater for Process Gas Cooling

Export Steam Value

Gas-heated Steam Reformer design

20 Metal Dusting Corrosion in SMR plants

Literature ReferencesLiterature References

R.T. Jones, K.L. Baumert; Metal Dusting – An Overview of Current Literature; Corrosion 2001; No. 01372

H.J. Grabke, E.M. Müller-Lorenz; Occurrence and Prevention of Metal Dusting on Stainless Steel; Corrosion 2001; No. 01373

F. Hohmann; Improve Steam Reformer Performance; Hydrocarbon Processing; 03/1996; p. 71-74