‫בעיות קורוזיה ופתרונות‬
‫בשימוש בגז טבעי‬
‫ד"ר אליק גרויסמן‬
‫יו"ר האגודה למהנדסי כימיה וכימאים‬
‫‪ 8‬ליוני ‪ ,2014‬תל אביב‬
Typical Composition of Natural Gas
Methane
Ethane
Propane
Butane
Carbon dioxide
Oxygen
Nitrogen
Hydrogen
sulphide
Rare gases
CH4
C2H6
C3H8
C4H10
CO2
O2
N2
H2S
He, Ne, Ar, Xe
70-90%
0 - 20%
0-8%
0-0.2%
0-5%
0-5%
trace
Trace Component Recovery or Removal
1. Hydrogen
2. Oxygen
3. Radon (Naturally occurring radioactive material, NORM)
4. Arsenic As(CH3)3 - gas < 1 mg/m3
5. Helium
If ≥ 0.3 vol%
6. Mercury
≤ 0.01 mg/m3
7. Benzene, toluene, ethylbenzene, and xylene (BTEX)
Mercury
an element found in trace amounts in most
hydrocarbon formations.
Hg
Liquid metal embrittlement
(a form of SCC) – Al !
Mercury removal systems are placed
before the aluminum heat exchangers on
offshore processing platforms
Gas Quality Daily Report
(mole %, avg) – 17.01.2012
Methane
Ethane
99.46
0.1893
Propane
0.0270
i - Butane
0.0050
n - Butane
0.0030
i - Pentane
0.0019
n - Pentane
0.0012
C6+
0.0093
Nitrogen
0.1952
Carbon dioxide
0.1083
Corrosiveness of Natural Gas
H2O
CO2
“sweet” corrosion
H2S
“sour” corrosion
[H2S] > 4 ppmV
O2 ?
Corrosion problems start
if [O2] > 50 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.
The effect of dissolved gases on the corrosion of
carbon steel
ppm
Dissolved gas concentration in water phase, ppm
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.
CO2 corrosion :
CO2 is not corrosive provided it stays dry.
pH = 4 – 4.5
Acidic rain
CaCO3 scale may be protective !
CO2(g) + H2O(l) → H2CO3(aq)
Mesa corrosion
Mesa corrosion looks like the United States`
Mesa Mountains, California
Mesa corrosion
Measures against CO2 corrosion :
- Corrosion inhibitors;
This may not work at high T
- Application of hydrate preventer (glycol)
- 9% Cr for downhole tubing;
SCC !
- Martensitic SS ( > 12 %Cr) and other CRA;
- pH control with caustic soda (NaOH).
H2S corrosion
Gas that contains sulphur is termed sour
gas, and the most form of sulphur is H2S gas
H2S is very toxic. Its release can cause
death within seconds !
H2O(l)
H2S(g) → H2S(aq)
pH = 4 – 4.5
MIC – 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
designed for sour conditions even if the
production starts out non-corrosive !
International Standard
NACE MR 0175/ISO 15156 Petroleum and Natural Gas
Industries – Materials for use in H2Scontaining 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
Hardness HRC < 22 !
Austenitic stainless steels (e.g. 304, 316)
are limited to a maximum service
temperature of 60°C
Aluminum can be used without
restrictions to PH2S, Cl-, pH
H2S detection
ASTM D1838 -12, Standard Test Method for Copper
Strip Corrosion by Liquefied Petroleum Gases.
Copper fittings can corrode.
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).
Control of H2S Corrosion and Cracking
- pH control (NaOH use)
- H2S scavengers
- Corrosion inhibitors
- Internal coatings
(organic or cement)
Organic acids
oilfield corrosion
HCOOH, CH3COOH – weak acids
Their presence is most important at high
pressures in gas condensate
SCALE
Solids in oil and gas production:
CaCO3, CaSO4, BaSO4, CaSiO3
Changes in chemistry (Conc., pH), T and P
Scale generally keeps metals dry
and reduces uniform corrosion.
When scale is imperfect – CORROSION !
Scale is abrasive –
EROSION
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 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
‫קרקעיים‬-‫ימיים ותת‬-‫קווים ומבנים תת‬
‫ הגנה קתודית‬+ ‫ציפויים‬
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.
2014
2010