Peter D. Clark

Director of Research, Alberta Sulphur Research Ltd. and Professor Emeritus of Chemistry, University of Calgary

and

N. I. Dowling

Senior Research Scientist, Alberta Sulphur Research Ltd. Contact: pdclark@ucalgary.ca

Corrosion Due to Elemental Sulfur in Sour Gas Production and Claus Sulfur Recovery Systems

MESPON 2016 Abu Dhabi, United Arab Emirates, October 9 – 11, 2016

Wet Sulfur Contact Corrosion of Carbon Steel

The Safety Moment: Iron Sulfide and Fire

Fe + S8 FeS H2O

FeS

O2 (Air)

Fe2O3 + SO2 + Energy (∆H = -1,226 kJ)

The Fe2O3 becomes red hot igniting any flammable material (sulfur)

Result: Fires inside the Claus plant (catalyst beds), sulfur pits, tanks, sulfur forming plants and more

Electrochemical Mechanism of Sulfur Corrosion

steel sulfur iron sulfide ‘mackinawite’

S-deficient FeS(1-x) “non-stoichiometric” FeS is pyrophoric when

dry and finely divided

steel sulfur iron sulfide ‘mackinawite’

Mechanistic Overview of Steel / Sulphur Corrosion

non-stoichiometric e- conducting FeS

layer

2e-

Effect of Moisture and Steel / Sulfur Contact

- Contact and moisture are essential for corrosion -

(free-standing H2O) (2-3 wt% moisture)

Effect of Temperature on The Rate of Wet Sulfur Contact Corrosion

> 20oC most of the time

PANAMA CANAL TRANS-ATLANTIC

TRANS-PACIFIC

Partial Oxidation of FeS and Formation of Sulfuric Acid

FeS + O2 (Air) Fe2 (SO4)3 Fe2 (SO4)3 + H2O 2 Fe3+ [6 H2O] + 3 SO4

2- [6 H2O]

Partial oxidation

Solvolysis

Fe3+ (H2O)6 Fe2+ (H2O)5 OH + [H+]

• Iron sulfate forms acidic solutions (pH ≈ 1-2) which corrode steel

S8 Deposition within a Sour Gas Flow Line+

Two Examples of Sulfur Deposition in Sour Gas Production Facilities

S8 Deposition in a Gas Plant Inlet Separator*

+ Photograph courtesy of John Morgan, John M. Campbell & Company * Photograph courtesy of Mark Townsend, Burlington Resources

Sulfur Deposition Arising from Oxidation of ppm Level H2S

Sources: 1. Chesnoy, A.-B., and Pack, D.J., S8 Threatens Natural Gas Operations, Environment, OGJ, V.95, No.17, pp.74-79, Apr. 28, 1997. 2. Courtesy of PG&E, Technological and Ecological Services (TES), San Ramon, California

Natural Gas Distribution Regulator Cage 2 200-mm ANSI 600 Turbine Meter 1

Magnified Image of Elemental Sulfur on Restrictor Valve

Surface 2

Elemental sulfur confirmed by SEM/EDX analysis

In Situ Formation of Sulfur in Sour Gas Equipment

FeS Protective Coating

H2S S8

O2 (Air) (ppmv)

High P Sour Gas

CH4 / H2S / CO2 (S8 / H2O)

2 Fe2+ (S) + ½ O2 2 Fe3+ + O2-

2 Fe3+ + H2S 2 Fe2+ + 2 H+ + 1/8 S8 2 H+ + O2- H2O

• The protective FeS coating becomes a catalytic layer

• The reaction is fast at high P; the amount of sulfur (H2O) formed depends on amount of O2 ingress

Sulfur Formation and Corrosion in Amine Plants

Steam Condensate

• Sulfur is formed at FeS layer in the contactor and then transported around the amine loop • Degradation occurs in the regenerator; ionic species enhance corrosion

~130°C

CH4 H2S – CO2

~40°C FeS

CH4/H2S- CO2

O2 (ppmv)

R3 NH HS / HSx

+

- -

Contactor: H2S + ½ O2 H2O + 1/8 S8 R3 NH HSX

Regenerator: R3 NH HSX R CO2 H + HS2O3 / HSO4 + - pH >10 - -

Amine R3N, H2S

-

+

“Combustion” of Steel with Sulfur in the Claus Furnace

S8

Process gas

Acid gas

Air

Ceramic brick

• O2 is very rapidly consumed by H2S in the flame

• Steel is oxidized by sulfur forming a mixture of FeS and FeS2

Fe + S2 FeS2 H2S H2 + ½ S2 Fe + H2S H2 + FeS FeS2

½ S2

Brick failure

The Chemical Function of the WHB Ferrule

Ceramic ferrule

H2O T < 400°C

Steam

T < 400°C H2S, S8, H2

H2O, N2

Furnace gases

(T > 1,000°C)

• The alumina ferrule is chemically inert to all species

• Steel (Fe) is relatively inert to sulfur and other species < 400°C.

S8

S8

Steam

H2O Hot Purge (CH4 combustion)

The Importance of Purging Sulfur From a Claus Unit During Shutdowns

• Ceramic brick and catalyst retains sulfur after unit shut down

• Conditions must be maintained to prevent condensation of sulfur in places other than the condensers

Corrosion in Off-Gas Line Below Water Dew Point

• Inadequate heating at line support allows water condensation

• Rapid Fe/S corrosion: Fe + 1/8 S8 FeS

• Aqua Claus reaction: 2 H2S + SO2 [H2SxOy] 3/8 S8 + 2 H2O

• Highly acidic aqueous solution is formed

H2O(l)

H2O(l)

Tail Gas Insulation

TGU Incinerator

Line Support (“heat” sink) S8 + H2O(l)

FeS Corrosion Products

Field Pictures of Corroded Claus Tail Gas Line

Pictures provided to ASRL by:

Mechanisms for Deterioration of Concrete in Sulfur Pits

Liquid S8 130ºC

Concrete

• Migration of H2S, SO2, O2, H2O and S (vap) into internal pore structure of the concrete followed by chemical reactions.

H2S + S8 H2Sx Solid/ liquid S8

T ºC = 90→130

AIR

Liq S8

H2S S8 SO2

O2 O2 N2

(H2O)

Formation of Sulfur Inside the Concrete

Detailed Chemistry

H2S + O2 SO2 + H2O 1/8 S8(vap) + ½ O2 SO2 2 H2S + SO2 3/8 S8 + H2O “CaO” CaSO4, CaS2O3

Lower density, higher volume unconsolidated products.

Concrete pore

structure

“H2 SO4” “H2 S2O3”

Concrete

Claus chemistry intermediates [strong acids]

Secondary Corrosion Processes at Concrete Pit Reinforcing Steel

Fe

Fe CaO

CaO

Fe2 (SO4)3 Fe2O3, H2SO4

Fe H2O,

S8

Fe FeS

O2, H2O

Secondary Corrosion Enhanced Sulfur Formation at Steel Fe + H2SO4 FeSO4 + H2 CaO + H2SO4 CaSO4 + H2O

2 H2S + SO2 3/8 S8 + 2 H2O H2S + ½ O2 1/8 S8 + H2O

Fe2O3

Fe2O3

Primary Corrosion in Sulfur Tanks – Air Drafted Systems

Air / SO2 / S8(vap) To scrubbers Air (H2O)

Insulation

• Poor roof insulation (or poor heating) may result in inner roof temperature of < 100°C • S8 solid deposition and water / H2SXOY condensation (from SO2 / H2O) • Fe / S8 corrosion Fe + 1/8 S8 FeS • Acid corrosion

2 Fe + H2SXOY 2 Fe SXOY + H2

Steam coil

Steam ~ 140°C

Liquid S8 SO2

SO2

N2

S8(vap) O2

H2O or H2SXOY

Consequences

Secondary Corrosion on Sulfur Tank Roofs – Air Drafted Tanks

Air (H2O) < 100°C

Insulation

T = 140°C

S8(liq)

SO2

SO2

N2

O2

Air / SO2 / S8(vap) To scrubbers

O2

[H2O]

FeS corrosion layer

Oxidation of FeS 2 FeS + 3/2 O2 Fe2O3 + 2/8 S8 2 FeS + SO2 2 FeO + 3/8 S8 Continued Sulfur Corrosion Fe + 1/8 S8 FeS (H2O)

• Without roof heating, T may fall to < 100°C, allowing H2O or H2SXOY condensation. • Partial oxidation of FeS may reform S8 at surface. • Corrosion at “cool” roof surface may result from condensed acids (H2SXOY), sulfur deposited or formed by chemical reaction.

Air

Steam coil Steam

~ 140°C S8(liq)

Rupture of Steam Coils in Sulfur Tanks

Air / SO2 (H2S)

(H2S)

Condensate / Steam

• Mechanical erosion of FeS layer leads to thinning of carbon steel coils and eventual rupture

Steam Coil Corrosion

Fe + H2S FeS + H2

S8 (H2S) FeS

Fe

Mechanical erosion

Fe "Clean surface"

H2S (S8(liq))

Fe

New FeS

S8(l) inlet

FeS

Shipping Sulfur By Rail

S8 S8

Steel Box Aluminum Box [Don’t do it!]

• Polymer coating to prevent iron-sulfur corrosion

OR

• Keep sulfur dry by adding a cover or roof

• Aluminum will melt if S8 catches fire

• Al/S8 react explosively at T of burning sulfur to form Al2S3

• Al2S3 reacts with water producing H2S Al2S3 + 3 H2O Al2O3 + 3 H2S

Aluminium (mp=660°C)

Thiobacilli H2SO4

S8 S8

H2SO4

H2O H2O

Corrosion: FeS / Sulfur layer may become H2S saturated > 1000 ppmv.

FeS + H2SO4 FeSO4 + H2S

denser than air — remains in the bottom of the hold.

Corrosion and Acidity Generation in a Ship Hold - a Potentially Deadly Combination -

Sulfur Loading to Limewashed Hold

Development of Zinc-modified Limewash

Chemistry:

Advantage:

• SUCCESSFULLY FIELD TESTED IN SHIP TRIAL

COMBINE LIMEWASH AND Zn2+

Improved barrier plus additional benefit from release of Zn2+ in event of acidity build-up

Mitigation of Corrosion by Zn2+: Fe + 1/8 S8 FeS Zn (OH)2 + FeS ZnS + Fe (OH)2

• ZnS is a perfect insulator stopping e-transfer at iron surface

Effect of Soluble Zn2+ on Wet Sulfur Corrosion

solution phase addition of Zn2+

soluble Zn2+ inhibits S corrosion at concentrations even as low as 1 x 10-2 M

Inhibition works by in-situ formation of insoluble ZnS barrier at steel / S contact area

Zn2+ + S2- ZnS ( stoichiometric )

ASRL Member Companies 2016 - 2017

Aecom Technology Corporation Air Liquide Global E&C Solutions / Lurgi Ametek Process & Analytical Instruments/Controls Southeast AXENS BASF Catalysts LLC Bechtel Corporation Black & Veatch Corporation BP Brimstone STS Ltd. Canadian Energy Services/PureChem Services ConocoPhillips Company CB&I Chevron Energy Technology Company Denbury Resources Inc. Devco Duiker CE E.I. du Pont Canada Company / MECS Inc. Enersul Inc. Euro Support BV ExxonMobil Upstream Research Company Flint Hills Resources Fluor Corporation / GAA HEC Technologies Hexion Inc. Husky Energy Inc. Industrial Ceramics Limited IPAC Chemicals Limited

Jacobs Canada lnc. / Jacobs Nederland B.V. KT – Kinetics Technology S.p.A. Linde Gas and Engineering (BOC) Lubrizol Canada Ltd. Nova Chemicals OMV Exploration and Production GmbH Optimized Gas Treating, Inc. Ortloff Engineers, Ltd. Oxbow Sulphur Canada ULC. (former ICEC) Petro China Southwest Oil and Gas Field Company/RINGT Phillips 66 Company Porocel Industries, LLC Porter McGuffie, Inc. Prosernat Riverland Industries Ltd. Secure Energy Services Shell Canada Energy SiiRTEC Nigi S.p.A. Sulfur Recovery Engineering (SRE) Sulphur Experts Inc. TECHNIP The Petroleum Institute / Abu Dhabi National Oil Company (ADNOC) Total S.A. UniverSUL Consulting WorleyParsons