בעיות קורוזיה ופתרונות בשימוש בגז

ד"ר אליק גרויסמןטבעי יו"ר האגודה למהנדסי כימיה

וכימאים

, תל 2014 ליוני 8אביב

Typical Composition of Natural GasTypical Composition of Natural Gas

MethaneMethaneCHCH4470-90%70-90%

EthaneEthaneCC22HH66

0 - 20%0 - 20% PropanePropaneCC33HH88

ButaneButaneCC44HH1010

Carbon dioxideCarbon dioxideCOCO220-8%0-8%

OxygenOxygenOO220-0.2%0-0.2%

NitrogenNitrogenNN220-5%0-5%

Hydrogen Hydrogen sulphidesulphide

HH22SS0-5%0-5%

Rare gasesRare gasesHe, Ne, Ar, XeHe, Ne, Ar, Xetracetrace

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/m3

If ≥ 0.3 vol%

As(CH3)3 - gas < 1 g/m3

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 Gas Quality Daily Report (mole %, avg) – 17.01.2012(mole %, avg) – 17.01.2012

MethaneMethane99.4699.46

EthaneEthane0.18930.1893

PropanePropane0.02700.0270

i - Butanei - Butane0.00500.0050

n - Butanen - Butane0.00300.0030

i - Pentanei - Pentane0.00190.0019

n - Pentanen - Pentane0.00120.0012

CC66++0.00930.0093

NitrogenNitrogen0.19520.1952

Carbon dioxideCarbon dioxide0.10830.1083

Corrosiveness of Natural Gas Corrosiveness of Natural Gas

HH22OO

COCO22

HH22SS

““sweet” corrosionsweet” corrosion

““sour” corrosionsour” corrosion

OO22? ? Corrosion problems start Corrosion problems start if [Oif [O22] > 50 ppmv] > 50 ppmv

[H[H22S] > 4 ppmVS] > 4 ppmV

Gas Treating

Some pipelines have specifications < 10 ppmv O2

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, ppmDissolved gas concentration in water phase, ppm

ppmppm

The effect of dissolved gases on the corrosion of The effect of dissolved gases on the corrosion of carbon steelcarbon steel

Measures against oxygen corrosion Measures against oxygen corrosion : : - Inert gas blankets over storage tanks;- Inert gas blankets over storage tanks;

- Oxygen scavengers;- Oxygen scavengers;

- Corrosion inhibitors;- Corrosion inhibitors;

- Protective coatings;- Protective coatings;

- Cathodic protection of water-wetted - Cathodic protection of water-wetted interior surfaces of process vessels interior surfaces of process vessels

and storage tanks.and storage tanks.

COCO22 corrosion corrosion : :

COCO22 is not corrosive provided it stays dry. is not corrosive provided it stays dry.

COCO2(g)2(g) + H + H22OO(l)(l) → H → H22COCO3(aq)3(aq)

CaCOCaCO33 scale may be protective ! scale may be protective !

pH = 4 – 4.5pH = 4 – 4.5

Mesa corrosionMesa corrosion

Acidic rainAcidic rain

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

Mesa corrosionMesa corrosion

Measures against COMeasures against CO22 corrosion corrosion : :

- 9% Cr for downhole tubing;- 9% Cr for downhole tubing;

- Martensitic SS ( > 12 %Cr) and other CRA;- Martensitic SS ( > 12 %Cr) and other CRA;

- Corrosion inhibitors;- Corrosion inhibitors; This may not work at high TThis may not work at high T

SCC !SCC !

- pH control with caustic soda (NaOH).- pH control with caustic soda (NaOH).

- Application of hydrate preventer (glycol)- Application of hydrate preventer (glycol)

H2S corrosion

Gas that contains sulphur is termed Gas that contains sulphur is termed sour sour gasgas, and the most form of sulphur is H, and the most form of sulphur is H22S gasS gas

HH22S is very toxic. Its release can cause S is very toxic. Its release can cause

death within seconds ! death within seconds !

HH22SS(g)(g) → H → H22SS(aq)(aq) pH = 4 – 4.5pH = 4 – 4.5HH22OO(l)(l)

MIC – Microbiologically Induced CorrosionMIC – Microbiologically Induced Corrosion

Fe(s) + H2S(aq) FeS(s) + H2(g)

Black fine powder – can be pyrophoric in pipelines and metering

FeS Cu Ni

H2S 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 Long-life oilfield equipment should be designed for designed for sour conditionssour conditions even if the even if the production starts out non-corrosive ! production starts out non-corrosive !

International Standard NACE MR 0175/ISO 15156 -Petroleum and Natural Gas

Industries – Materials for use in H2S-containing Environments in Oil and

Gas Production

NACE MR0175/ISO 15156 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 PH 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 D1838 -12, Standard Test Method for Copper Strip Corrosion by Liquefied Petroleum Gases.

Copper fittings can corrode.

H2S detection

ASTM D4084 - 07 (2012), Standard Test Method for Analysis of H2S in Gaseous Fuels

(Lead Acetate Reaction Rate Method). A lead acetate-coated tape darkens in the

presence of H2S (0.1 ppmv).

- pH control (NaOH use)

Control of H2S Corrosion and Cracking

- H2S scavengers

- Corrosion inhibitors

- Internal coatings (organic or cement)

HCOOH, CH3COOH – weak acids

Organic acids

oilfield corrosion

Their presence is most important at high pressures in gas condensate

CaCO3, CaSO4, BaSO4, CaSiO3

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-001 2004 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 O2, CO2 and H2S

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 controlCorrosion control : :

- Material choice - Material choice (including corrosion (including corrosion allowance)allowance)

- Protective coatings- Protective coatings

- Cathodic protection- Cathodic protection

- Treatment of environment - Treatment of environment (inhibition, etc.)(inhibition, etc.)

- Corrosion monitoring: on-line, - Corrosion monitoring: on-line, periodical, scheduled maintenance, periodical, scheduled maintenance, and inspection 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.

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