בעיות קורוזיה ופתרונות בשימוש בגז טבעי ד"ר אליק גרויסמן יו"ר האגודה למהנדסי כימיה וכימאים 8 ליוני 2014, תל אביב

Typical Composition of Natural Gas 70-90% CH 4 Methane % C2H6C2H6C2H6C2H6Ethane C3H8C3H8C3H8C3H8Propane C 4 H 10 Butane 0-8% CO 2 Carbon dioxide 0-0.2% O2O2O2O2Oxygen 0-5% N2N2N2N2Nitrogen 0-5% H2SH2SH2SH2S Hydrogen sulphide trace He, Ne, Ar, Xe Rare gases

Trace Component Recovery or Removal 1.Hydrogen 3. Radon ( Naturally occurring radioactive material, NORM ) 4. Arsenic 2. Oxygen 5. Helium 6. Mercury 7. Benzene, toluene, ethylbenzene, and xylene (BTEX ) ≤ 0.01  g/m 3 If ≥ 0.3 vol% As(CH 3 ) 3 - gas < 1  g/m 3

Liquid metal embrittlement (a form of SCC) – Al ! Mercury removal systems are placed before the aluminum heat exchangers on offshore processing platforms an element found in trace amounts in most hydrocarbon formations. Mercury Hg

Gas Quality Daily Report (mole %, avg) – Methane Ethane Propane i - Butane n - Butane i - Pentane n - Pentane C6+C6+C6+C Nitrogen Carbon dioxide

Corrosiveness of Natural Gas H2OH2OH2OH2O CO 2 H2SH2SH2SH2S “sweet” corrosion “sour” corrosion O 2 ? Corrosion problems start if [O 2 ] > 50 ppmv [H 2 S] > 4 ppmV

Gas Treating

Some pipelines have specifications < 10 ppmv O 2 Oxygen causes problems in gas processing: Enhancing pipeline corrosion if liquid water is present. Reacting with amines in gas treating – corrosive compound formation. Reacting with glycols – corrosive acidic compounds.

Dissolved gas concentration in water phase, ppm Dissolved gas concentration in water phase, ppm ppm The effect of dissolved gases on the corrosion of carbon steel The effect of dissolved gases on the corrosion of carbon steel

Measures against oxygen corrosion : - Inert gas blankets over storage tanks; - Oxygen scavengers; - Corrosion inhibitors; - Protective coatings; - Cathodic protection of water-wetted interior surfaces of process vessels and storage tanks.

CO 2 corrosion : CO 2 is not corrosive provided it stays dry. CO 2(g) + H 2 O (l) → H 2 CO 3(aq) CaCO 3 scale may be protective ! pH = 4 – 4.5 Mesa corrosion Acidic rain

Mesa corrosion looks like the United States` Mesa Mountains, California Mesa corrosion

Measures against CO 2 corrosion : - 9% Cr for downhole tubing; - Martensitic SS ( > 12 %Cr) and other CRA; - Corrosion inhibitors; This may not work at high T SCC ! - pH control with caustic soda (NaOH). - Application of hydrate preventer (glycol)

H 2 S corrosion Gas that contains sulphur is termed sour gas, and the most form of sulphur is H 2 S gas H 2 S is very toxic. Its release can cause death within seconds ! H 2 S (g) → H 2 S (aq) pH = 4 – 4.5 H 2 O (l) MIC – Microbiologically Induced Corrosion

Fe (s) + H 2 S (aq) FeS (s) + H 2(g) Black fine powder – can be pyrophoric in pipelines and metering FeS Cu Ni

H 2 S can lead to metal cracking: - Sulphide Stress Cracking (SSC) - Hydrogen Stress Cracking (HSC) - Hydrogen Induced Cracking (HIC) - Stress-oriented hydrogen Induced Cracking (SOHIC)

Long-life oilfield equipment should be designed for sour conditions even if the production starts out non-corrosive ! International Standard NACE MR 0175/ISO Petroleum and Natural Gas Industries – Materials for use in H 2 S- containing Environments in Oil and Gas Production

NACE MR0175/ISO consists of 3 parts: · Part 1 - General Principles for Selection of Cracking - Resistant Materials; · Part 2 - Cracking - Resistant Carbon and Low Alloy Steels; · Part 3 - Cracking-Resistant CRAs (Corrosion-Resistant Alloys) and Other Alloys

Aluminum can be used without restrictions to P H S, Cl -, pH Austenitic stainless steels (e.g. 304, 316) are limited to a maximum service temperature of 60°C Hardness HRC < 22 ! 2

ASTM D , Standard Test Method for Copper Strip Corrosion by Liquefied Petroleum Gases. Copper fittings can corrode. H 2 S detection ASTM D (2012), Standard Test Method for Analysis of H 2 S in Gaseous Fuels (Lead Acetate Reaction Rate Method). A lead acetate-coated tape darkens in the presence of H 2 S (0.1 ppmv).

- pH control (NaOH use) Control of H 2 S Corrosion and Cracking - H 2 S scavengers - Corrosion inhibitors - Internal coatings (organic or cement)

HCOOH, CH 3 COOH – weak acids Organic acids oilfield corrosion Their presence is most important at high pressures in gas condensate

CaCO 3, CaSO 4, BaSO 4, CaSiO 3 SCALE Solids in oil and gas production: Changes in chemistry (Conc., pH), T and P

Scale is abrasive – EROSION Scale generally keeps metals dry and reduces uniform corrosion. When scale is imperfect – CORROSION !

Tubing, Casing and Capillary Tubing Most corrosion problems in oil and gas production are associated with tubing and casing. The reason for this is the large volume of these components used per well. While it is common to use CRAs for wellhead equipment, pumps, packers, economic incentives and availability drive the trends for continued use of CS and low-alloy tubing and casing.

Tubing Corrosion The cost of tubing replacement can be upward of $1 million per well, and many operators have adopted the policy of starting oil well production with 13Cr tubing in the hopes that they can avoid tubing replacement at some time in the future. NORSOK standard M Material Selection recommendations for various well components to include tubing and liners.

Casing Corrosion Casing is the structural retainer for the walls in oil and gas wells. About 75% by weight of oil country tubular good (OCTG) shipments are for casing, which is intended to last for the life of the wells and not be pulled, inspected, or replaced. Corrosion of casing can be from either the interior, in the annular spaces shared with tubing exteriors, or on the exterior.

Most corrosion control of casing interiors is by appropriate alloy selection and by packer fluid inhibitor use, either filming inhibitors at lower T, or O 2, CO 2 and H 2 S scavengers at elevated T. Exterior corrosion protection is usually provided by cementing, which provides a high-pH noncorrosive environment for the casing exterior, and by electrical separation at the wellhead with insulated flange assemblies that are intended to isolate the well from flowlines that could produce stray current corrosion.

Corrosion control: - Material choice (including corrosion allowance) - Protective coatings - Cathodic protection - Treatment of environment (inhibition, etc.) - Corrosion monitoring: on-line, periodical, scheduled maintenance, and inspection

Cathodic Protection קווים ומבנים תת-ימיים ותת-קרקעיים ציפויים + הגנה קתודית The metallic structures in the atmosphere, in fuels and demineralized water (or other media of high electrical resistance) will not be protected by cathodic protection.