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Types of Corrosion....Effecting on Natural Gas pipes. 2
- Thread starter myapples
- Start date
For a good general resource, try:
"Forms of Corrosion: Recognition and Prevention", CP Dillon (editor), published by NACE (there are 2 volumes)
The books contain explanations of the 8 forms of corrosion as well as case studies and pictures.
You can find these on the NACE website (as well as other information):
Enjoy!
"Forms of Corrosion: Recognition and Prevention", CP Dillon (editor), published by NACE (there are 2 volumes)
The books contain explanations of the 8 forms of corrosion as well as case studies and pictures.
You can find these on the NACE website (as well as other information):
Enjoy!
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- #3
NiDI has an 11-page booklet 'Selection guidelines for corrosion resistant alloys in the oil and gas industry.'
This is for producers of 'raw' natural gas and oil products and gives the effects of various amounts of CO2, H2S,NaCl and temperature on the corrosion rates of 13Cr, 316, 22Cr,and several more. Comments are made about SCC, SSC (sulfide stress cracking),pitting.
Not as thorough as NACE books, but it's free: download at
NiDI also has 'A guide for petroleum engineers' (10073)
which you can request be mailed to you (free).
This is for producers of 'raw' natural gas and oil products and gives the effects of various amounts of CO2, H2S,NaCl and temperature on the corrosion rates of 13Cr, 316, 22Cr,and several more. Comments are made about SCC, SSC (sulfide stress cracking),pitting.
Not as thorough as NACE books, but it's free: download at
NiDI also has 'A guide for petroleum engineers' (10073)
which you can request be mailed to you (free).
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- #5
- Thread starter
- #6
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1
- #7
1. The depth of the ground bed is determined by the
soil properties. (soil resistivity)
2. Weight of the inert anodes is determined based on
anode type and protection life span. The anodes
are buried over each other for deep ground beds
with connecting cables.
3. Transformer/Rectifier (A/C ---> D/C) has two feeds
with a tapping to control amount of current flow.
The positive feed is connected to the inert anodes
cables via a junction box and the negative feed
is connected to the buried surface which requires
protection.
4. The T/R rating 50/100/200 amps is determined by the
amount of surface area to be protected.
5. At times pipeline corridors are bonded to each other
and bonding stations are in place to measure potential
readings.
There are several NACE RP's in this regard.
Concerns:
a) Bonding between the inert anodes and the cables is
usually inadquate since it corrodes (isolating the
anode) prematurely.
b) Interference is disregarded, along with cable breaks
and the T/R are over-tapped. Anodes fry.
c) A contraversial issue is wether CP systems should be
isolated or emalgamated. Personally my preference is
towards isolation with resistor boxes to control
interface.
Let me know if you need elboration on any specific since this a broad subject. Norsok have nice specifications.
Cheers
soil properties. (soil resistivity)
2. Weight of the inert anodes is determined based on
anode type and protection life span. The anodes
are buried over each other for deep ground beds
with connecting cables.
3. Transformer/Rectifier (A/C ---> D/C) has two feeds
with a tapping to control amount of current flow.
The positive feed is connected to the inert anodes
cables via a junction box and the negative feed
is connected to the buried surface which requires
protection.
4. The T/R rating 50/100/200 amps is determined by the
amount of surface area to be protected.
5. At times pipeline corridors are bonded to each other
and bonding stations are in place to measure potential
readings.
There are several NACE RP's in this regard.
Concerns:
a) Bonding between the inert anodes and the cables is
usually inadquate since it corrodes (isolating the
anode) prematurely.
b) Interference is disregarded, along with cable breaks
and the T/R are over-tapped. Anodes fry.
c) A contraversial issue is wether CP systems should be
isolated or emalgamated. Personally my preference is
towards isolation with resistor boxes to control
interface.
Let me know if you need elboration on any specific since this a broad subject. Norsok have nice specifications.
Cheers
- Thread starter
- #8
- Thread starter
- #9
P.S.P POINTS IN CATHODIC PROTECTION SYSTEM.
May I know that:-
1.what psp point means?
2.After how much interval psp point to be marked on low pressure and high pressure gas pipelines.
3.how to maintain and mark psp points on the drawings of a particular area or vacinity.
Corrosion Engineer.
May I know that:-
1.what psp point means?
2.After how much interval psp point to be marked on low pressure and high pressure gas pipelines.
3.how to maintain and mark psp points on the drawings of a particular area or vacinity.
Corrosion Engineer.
- Thread starter
- #10
P.S.P POINTS IN CATHODIC PROTECTION SYSTEM.
May I know that:-
1.what psp point means?
2.After how much interval psp point to be marked on low pressure and high pressure gas pipelines.
3.how to maintain and mark psp points on the drawings of a particular area or vacinity.
Corrosion Engineer.
May I know that:-
1.what psp point means?
2.After how much interval psp point to be marked on low pressure and high pressure gas pipelines.
3.how to maintain and mark psp points on the drawings of a particular area or vacinity.
Corrosion Engineer.
- Thread starter
- #11
P.S.P POINTS IN CATHODIC PROTECTION SYSTEM.
May I know that:-
1.what psp point means?
2.After how much interval psp point to be marked on low pressure and high pressure gas pipelines.
3.how to maintain and mark psp points on the drawings of a particular area or vacinity.
Corrosion Engineer.
May I know that:-
1.what psp point means?
2.After how much interval psp point to be marked on low pressure and high pressure gas pipelines.
3.how to maintain and mark psp points on the drawings of a particular area or vacinity.
Corrosion Engineer.
Sir,As a finishing doc candidate in the field of Cp applications on pipelines:
I have been having the major problem of knowing the factors governing the placement of an anode greoundbed (horizontal, vertical) with respect to the protected line.
I think your expertise will help me overcome these worries I have been having these years.
Thanks very much.
I have been having the major problem of knowing the factors governing the placement of an anode greoundbed (horizontal, vertical) with respect to the protected line.
I think your expertise will help me overcome these worries I have been having these years.
Thanks very much.
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- #13
Can anyone tell me the possible and full content requirement of a Corrosion(Carbon Dioxide) Survey(Scope of Work) in a proposed new offshore gas injection project? Using reciprocating compressors and water cooling ect.
To INCLUDE?
a)Pipe & Fitting & Bulk Material, b)Cathodic Protection, c)Gas Composition (Dew Points, d)Spread Sheet for all Applications etc.
e) Chemical Injection?, f)Major Equipments
g) Specifications & Codes?
Can anyone please furnish a sample survey or tell me where to download a case study?
To INCLUDE?
a)Pipe & Fitting & Bulk Material, b)Cathodic Protection, c)Gas Composition (Dew Points, d)Spread Sheet for all Applications etc.
e) Chemical Injection?, f)Major Equipments
g) Specifications & Codes?
Can anyone please furnish a sample survey or tell me where to download a case study?
Myapples
You have the title: “Corrosion Engineer” but you are asking about the very basics of Corrosion Engineering. My personal advice would be to go through the book on Corrosion Engineering by P. Body.
Now normally natural gas pipelines are laid under ground and they have asphalt or some other coating on them. Ideally this coating should be enough to prevet corrosion of the pipe surface but under normal circumstances this is not possible because all coatings are pours to some extent.
Why does a metal corrode when it’s in the soil?
Basically it is an established fact that the soil has its own potential, normally around – 0.6 volts and if we place a metal in the soil its potential is normally around – 0.4 volts. We can measure this potential with a half-cell. (The honorable members of the forum may correct me if I am wrong because I am not an expert in the field of corrosion). Now if we leave the metal in this soil the Fe++ ions from the metal would start to come out of the metal and move to the soil and electrons from the soil will move to the metal. It’s like a battery; you have positive and negative plates and also an electrolyte. In order to stop this chemical reaction the best thing to do is to take the potential of the metal below the soil by applying a forced external voltage through a transformer rectifier unit (also called a CP Station). So you have a transformer which steps down the phase voltage to the desirable level and then it is converted to dc with the help of a rectifier. The output can further be adjusted by a variac or a variable transformer connected before the rectifier unit.
The negative lead of the rectifier is connected to the pipeline and the positive to anode bed. The anode bed has a certain number of anodes depending on the conditions of application. The anodes are normally of Magnesium (I think). Once we have this forced CP in place....... What happens is that if the current finds a path in the coating of the pipe to come out it will travel to the anode but now this current will be actually due to electrons flowing to the anode and not Fe++ ions. This means that no metal is lost from the pipeline. The minimum recommended protection level for a pipeline is –0.85 volts, which ensures that Fe++ ions won’t leave the pipeline. On the other hand Positive ions (Mg++) will move from the anode bed towards the pipeline and if it can find its way through the coating it will deposit on the pipe surface and will not allow corrosion to occur. It can be seen that there is a closed loop for the current to flow.
Why apply coating on the pipeline along with CP?
Because if the pipe is bare then a very large amount of current would flow through the transformer which would require huge transformer and rectifier and anode bed. So the better the coating the lesser the CP current.
PSP?
Its pipe to soil potential recorded with a half-cell. Basically voltage readings are taken between the pipe (through a PSP post…(normally 1 km apart) which has a direct metallic connection to the pipe) and the soil. This is to ensure that the potential of the pipe at this point is above –0.85 (i.e. above the minimum protection level) and also that it is not over protected.
Over protection is a detailed topic and cannot be addressed here.
You have the title: “Corrosion Engineer” but you are asking about the very basics of Corrosion Engineering. My personal advice would be to go through the book on Corrosion Engineering by P. Body.
Now normally natural gas pipelines are laid under ground and they have asphalt or some other coating on them. Ideally this coating should be enough to prevet corrosion of the pipe surface but under normal circumstances this is not possible because all coatings are pours to some extent.
Why does a metal corrode when it’s in the soil?
Basically it is an established fact that the soil has its own potential, normally around – 0.6 volts and if we place a metal in the soil its potential is normally around – 0.4 volts. We can measure this potential with a half-cell. (The honorable members of the forum may correct me if I am wrong because I am not an expert in the field of corrosion). Now if we leave the metal in this soil the Fe++ ions from the metal would start to come out of the metal and move to the soil and electrons from the soil will move to the metal. It’s like a battery; you have positive and negative plates and also an electrolyte. In order to stop this chemical reaction the best thing to do is to take the potential of the metal below the soil by applying a forced external voltage through a transformer rectifier unit (also called a CP Station). So you have a transformer which steps down the phase voltage to the desirable level and then it is converted to dc with the help of a rectifier. The output can further be adjusted by a variac or a variable transformer connected before the rectifier unit.
The negative lead of the rectifier is connected to the pipeline and the positive to anode bed. The anode bed has a certain number of anodes depending on the conditions of application. The anodes are normally of Magnesium (I think). Once we have this forced CP in place....... What happens is that if the current finds a path in the coating of the pipe to come out it will travel to the anode but now this current will be actually due to electrons flowing to the anode and not Fe++ ions. This means that no metal is lost from the pipeline. The minimum recommended protection level for a pipeline is –0.85 volts, which ensures that Fe++ ions won’t leave the pipeline. On the other hand Positive ions (Mg++) will move from the anode bed towards the pipeline and if it can find its way through the coating it will deposit on the pipe surface and will not allow corrosion to occur. It can be seen that there is a closed loop for the current to flow.
Why apply coating on the pipeline along with CP?
Because if the pipe is bare then a very large amount of current would flow through the transformer which would require huge transformer and rectifier and anode bed. So the better the coating the lesser the CP current.
PSP?
Its pipe to soil potential recorded with a half-cell. Basically voltage readings are taken between the pipe (through a PSP post…(normally 1 km apart) which has a direct metallic connection to the pipe) and the soil. This is to ensure that the potential of the pipe at this point is above –0.85 (i.e. above the minimum protection level) and also that it is not over protected.
Over protection is a detailed topic and cannot be addressed here.
Sngpl,
Pretty good post, IMO. Couple of corrections-hope I get these right-it's 1AM here.
The electrons come from the metal itself, not the soil. They are "liberated" on the surface at cathode sites. The iron ions leave the surface at the anode sites.
The -.85v is referenced to a Cu/CuSO4 cell electrode.
In impressed CP, the anodes aren't Mg; they're a Pt alloy, usually. Mg, Zn and Al are used in sacrificial anode CP.
That's enuf for now.
Pretty good post, IMO. Couple of corrections-hope I get these right-it's 1AM here.
The electrons come from the metal itself, not the soil. They are "liberated" on the surface at cathode sites. The iron ions leave the surface at the anode sites.
The -.85v is referenced to a Cu/CuSO4 cell electrode.
In impressed CP, the anodes aren't Mg; they're a Pt alloy, usually. Mg, Zn and Al are used in sacrificial anode CP.
That's enuf for now.
- Thread starter
- #17
JimMetalsCeramics
Materials
You should check various publications from
Here is a list of some relevant papers from their journal.
Here is another related link:
If you haven't already, you might post this question in one of the chemical engineering forums.
Here is a list of some relevant papers from their journal.
Here is another related link:
If you haven't already, you might post this question in one of the chemical engineering forums.
- Thread starter
- #19
Metalguy,
Kindly do not hold us in suspence
please indulge
us by addressing the following in your customary manner that has always gained my recognition:
1. Half cells (Cu/CuSO4 versus Ag/AgCl)
2. Data sheet on coating system (CP Disbondment)
3. NACE-RP-0XXX, (protection level, -1.5 ?)
4. Coupling of the anodes.
5. Current dispersion
6. Soil Characteristics (Sink Anodes (Mg), shallow
ground bed, deep ground bed)
7. Service temperature (anode type)
8. Polarizing effects on (anodes)
9. OPtimization (Decay Rate, Mass)
10. Over tapping
Am sure Sngpl would appreciate your feedbback in this matter; and perhaps we can all appreciate the fact that the more we learn the more we aknowledge how little we really know; as myapples has so elegantly shown us.
With Appreciation,
Kindly do not hold us in suspence
please indulgeus by addressing the following in your customary manner that has always gained my recognition:
1. Half cells (Cu/CuSO4 versus Ag/AgCl)
2. Data sheet on coating system (CP Disbondment)
3. NACE-RP-0XXX, (protection level, -1.5 ?)
4. Coupling of the anodes.
5. Current dispersion
6. Soil Characteristics (Sink Anodes (Mg), shallow
ground bed, deep ground bed)
7. Service temperature (anode type)
8. Polarizing effects on (anodes)
9. OPtimization (Decay Rate, Mass)
10. Over tapping
Am sure Sngpl would appreciate your feedbback in this matter; and perhaps we can all appreciate the fact that the more we learn the more we aknowledge how little we really know; as myapples has so elegantly shown us.
With Appreciation,
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