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Supercritical Steam Piping Design and Analysis 3
- Thread starter JGard1985
- Start date
In the US the code requirements are found in asme B31.1 Power Piping .
The sizing of the piping is based on the allowable pressure drop at MCR load, typically 1% of the pipes inlet pressure.
The use of modern creep strength enhanced ferritic steels ( P92, P91,P122 etc) has enabled the use of lighter, thinner walled piping with the need for fewer flexibility bends, but the B31.1 requirements must be met nonetheless. If the unit is load cycling or 2 shift cycling then a fatigue analysis would then be required, and I would recommend the fabrication details and fatigue analysis procedure of EN 12952-3 be followed. Specifically the weld geometry details needed to extend the life of the thick walled welds ( pipe to valve welds, tees, wyes, etc) .
The modern alloys are less likely to stress relieve the fabrication stresses upon initial unit shakedown, so the older techniques used on P22 piping will not work with the newer alloys.
Sent from the crypt.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
The sizing of the piping is based on the allowable pressure drop at MCR load, typically 1% of the pipes inlet pressure.
The use of modern creep strength enhanced ferritic steels ( P92, P91,P122 etc) has enabled the use of lighter, thinner walled piping with the need for fewer flexibility bends, but the B31.1 requirements must be met nonetheless. If the unit is load cycling or 2 shift cycling then a fatigue analysis would then be required, and I would recommend the fabrication details and fatigue analysis procedure of EN 12952-3 be followed. Specifically the weld geometry details needed to extend the life of the thick walled welds ( pipe to valve welds, tees, wyes, etc) .
The modern alloys are less likely to stress relieve the fabrication stresses upon initial unit shakedown, so the older techniques used on P22 piping will not work with the newer alloys.
Sent from the crypt.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
as always, DaveFitz gives good advice ...
I also have some suggestions regarding design and stress analysis of High Energy piping systems and pipe support selection
What is your MAXIMUM OPERATING pressures/temperatures and design massflow rate ?
Is this your first involvement with a High Energy Piping system ?
Who is it that will select materials ?.... Is it you or your boss or your client ????
MJCronin
Sr. Process Engineer
I also have some suggestions regarding design and stress analysis of High Energy piping systems and pipe support selection
What is your MAXIMUM OPERATING pressures/temperatures and design massflow rate ?
Is this your first involvement with a High Energy Piping system ?
Who is it that will select materials ?.... Is it you or your boss or your client ????
MJCronin
Sr. Process Engineer
- Thread starter
- #5
Thanks, I've done alot with B31.1 high energy systems at saturated steam conditions at powerplants. This would be a process line with super critical steam. The client/consultant has already selected materials, I'd verify the stresses are within code allowable limits.
Some of the newer alloys have "weld creep strength reduction factors" to be applied to the butt welds if the continuous pipeline axial stress plus the axial primary pressure stress exceeds some fraction of the code allowable stress. This was not required of older P22 pipelines.This means the location of each butt weld should be programmed as a discrete point in the flexibility program and the butt weld stress must be determined to be less than that fraction defined by code.
Also, much better QA/QC of the field welds can be had with the robotic orbital welders or TIP/TIG welders , so the piping designer should consciously plan the location of the field welds so these welding machines can be used in the field.
Advanced supercritical units that are designed for over 1150F desing temp may be using costly nickel alloy piping, or possibly even HEA high entropy alloy piping, and in both instances plant desingers have postulated that to reduce the cost of these pipe half of the steam turbine may need to be located at the same elevation as the boiler penthouse. If the overall site objective is to lower specific CO2 emisiions, then the advanced supercritical plant would be a double reheat configured as the Elsam "master cycle" , with most regenerative feedwater heaters supplied with etraction steam from the BFP drive turbine and not from the power turbine.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
Also, much better QA/QC of the field welds can be had with the robotic orbital welders or TIP/TIG welders , so the piping designer should consciously plan the location of the field welds so these welding machines can be used in the field.
Advanced supercritical units that are designed for over 1150F desing temp may be using costly nickel alloy piping, or possibly even HEA high entropy alloy piping, and in both instances plant desingers have postulated that to reduce the cost of these pipe half of the steam turbine may need to be located at the same elevation as the boiler penthouse. If the overall site objective is to lower specific CO2 emisiions, then the advanced supercritical plant would be a double reheat configured as the Elsam "master cycle" , with most regenerative feedwater heaters supplied with etraction steam from the BFP drive turbine and not from the power turbine.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
- Thread starter
- #8
Maybe I got off on the wrong foot...I didn't realize that eng-tips forum posts were time sensitive. I had some other commitments this week that took priorities
To answer previously asked questions:
So you will not tell us temperatures, pressures materials or massflow rates ?....all Top Secret ? No, at this time, not supplied by potential client for RFP. I posted looking for reference material to read.
[/b]
...and you have worked on "systems at saturated steam conditions ... process line with super critical steam." Yes I've completed multiple B31.1 piping analyses for small bore piping up to 30" critical steam headers, so I'm far from new to piping. Again looking for refernce material for the design/fabrication of supercritical steam piping
In short I haven't lost interest, I appreciate the comments and codes stated in the above postings. While codes and provide guidance for stresses, I'm still wondering if anyone can suggest reference material (textbook, design guide, etc) to expand my knowledge of best practices for super-critical pipe routing.
Thank you
To answer previously asked questions:
So you will not tell us temperatures, pressures materials or massflow rates ?....all Top Secret ? No, at this time, not supplied by potential client for RFP. I posted looking for reference material to read.
[/b]
...and you have worked on "systems at saturated steam conditions ... process line with super critical steam." Yes I've completed multiple B31.1 piping analyses for small bore piping up to 30" critical steam headers, so I'm far from new to piping. Again looking for refernce material for the design/fabrication of supercritical steam piping
In short I haven't lost interest, I appreciate the comments and codes stated in the above postings. While codes and provide guidance for stresses, I'm still wondering if anyone can suggest reference material (textbook, design guide, etc) to expand my knowledge of best practices for super-critical pipe routing.
Thank you
The design/fabrication of supercritical steam piping for modern units will be using modern materials at advanced steam temperatures, so much of the design guidelines used for the 1970 era plants is outdated. The modern alloys are not fault tolerant in regards to fabrication processes , and the plant designer will need to refer to metallurgists familiar with the new alloys in order to ensure the fabrication procedures do not destroy the assumed strength properties of the new alloys.
Examples of the new alloys are P91, P92, P93 ( SAVE12AD) and nickel based alloys. The ferritic alloys obtain their high temperature creep strength by virtue of a tempered martensitic crystal structure with small amounts of finely dispersed trace elements , and these particular properties are lost if the fabrication processes are not perfect. For example:
a) the martensitic structure of optimum grain size implies the N+T treatment be held at 1950 F for a defined time range ( for crystal size) and cooled faster than -10F/minute to ensure ferrite or pealite are not formed. The spec for the fabrication of any such alloy piece ( pipe, pipe bend , forging , casting) must require individual thermocouples be applied on each piece and the temperature history of each piece be reviewed before the piece is accepted for use . This departs from the default practice of monitoring only 1 piece per batch in the furnace. If you witnessed how the N+T furnace is operated you would see why this is an issue.
b) hot bending of bends must be followed by a full N+T of the bent piece
c) weld repair of large castings must be followed by a full N+T of the piece
d)PWHT procedures are strict , regarding both time vs temperature but also placement of the PWHT thermocouples and the rate at which the piece is heated to the weld preheat temp and to the PWHT temp. Local overheat above the 1st critical temp during these operations could occur if the monitoring T/C's are spaced too far from the heating coils.
e) Reducing the assumed fabrication stresses by the practice of initial shakedown creep relief is not available for these newer alloys as they dont creep relief in the same manner as P22 did.
f) some steam turbine vendors are now requiring zero end raction at the turbine nozzles for both the hot and cold case- not easy to accomplish.
g) modern automated orbital welding machines are better able to meet the qa/qc needs of these alloys, in particualr the very high weld preheat temperatures that tend to cause a manual welder to turn down the preheat to avoid personal injury or stress.
h) as mentioned earlier , the ASME code now identifies a creep strength weld reducion factor for some of these alloys. This may only be ingored for a pure butt weld not subjected to constant axial loads. However, fabricated wyes and els and pipelines eposed to constant axial loads need to consider this weld strength reduction factor.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
Examples of the new alloys are P91, P92, P93 ( SAVE12AD) and nickel based alloys. The ferritic alloys obtain their high temperature creep strength by virtue of a tempered martensitic crystal structure with small amounts of finely dispersed trace elements , and these particular properties are lost if the fabrication processes are not perfect. For example:
a) the martensitic structure of optimum grain size implies the N+T treatment be held at 1950 F for a defined time range ( for crystal size) and cooled faster than -10F/minute to ensure ferrite or pealite are not formed. The spec for the fabrication of any such alloy piece ( pipe, pipe bend , forging , casting) must require individual thermocouples be applied on each piece and the temperature history of each piece be reviewed before the piece is accepted for use . This departs from the default practice of monitoring only 1 piece per batch in the furnace. If you witnessed how the N+T furnace is operated you would see why this is an issue.
b) hot bending of bends must be followed by a full N+T of the bent piece
c) weld repair of large castings must be followed by a full N+T of the piece
d)PWHT procedures are strict , regarding both time vs temperature but also placement of the PWHT thermocouples and the rate at which the piece is heated to the weld preheat temp and to the PWHT temp. Local overheat above the 1st critical temp during these operations could occur if the monitoring T/C's are spaced too far from the heating coils.
e) Reducing the assumed fabrication stresses by the practice of initial shakedown creep relief is not available for these newer alloys as they dont creep relief in the same manner as P22 did.
f) some steam turbine vendors are now requiring zero end raction at the turbine nozzles for both the hot and cold case- not easy to accomplish.
g) modern automated orbital welding machines are better able to meet the qa/qc needs of these alloys, in particualr the very high weld preheat temperatures that tend to cause a manual welder to turn down the preheat to avoid personal injury or stress.
h) as mentioned earlier , the ASME code now identifies a creep strength weld reducion factor for some of these alloys. This may only be ingored for a pure butt weld not subjected to constant axial loads. However, fabricated wyes and els and pipelines eposed to constant axial loads need to consider this weld strength reduction factor.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
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2
- #10
2 other items i forgot to mention:
- thick walled valves welded to thin walled pipes need to have a pipe transition piece installed between the two items , with a gradient in wall thickness not greater than 18 degrees ( 3:1 slope) . Likewise the valve weld geometry should also be optimized to minimze the thermal stress that occurs during each startup /shutdown at the weld line. The default weld geometry defines in some valve codes does not adequately address this issue.A time depenent 3D finite element model of the valve+ weld end + transition piece should be used to confirm the startup /shutdown stresses at the weld interfaces are appropriate.
-chromizing of the ferritic pipe ID might be revisited to reduce oxide scale damage to the steam turbine blading. Modern methods of treating the wastewater from the chromizing process may adequately address the hexavalent chrome hazards.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
- thick walled valves welded to thin walled pipes need to have a pipe transition piece installed between the two items , with a gradient in wall thickness not greater than 18 degrees ( 3:1 slope) . Likewise the valve weld geometry should also be optimized to minimze the thermal stress that occurs during each startup /shutdown at the weld line. The default weld geometry defines in some valve codes does not adequately address this issue.A time depenent 3D finite element model of the valve+ weld end + transition piece should be used to confirm the startup /shutdown stresses at the weld interfaces are appropriate.
-chromizing of the ferritic pipe ID might be revisited to reduce oxide scale damage to the steam turbine blading. Modern methods of treating the wastewater from the chromizing process may adequately address the hexavalent chrome hazards.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
Davefitz has provided some terrific information regarding high temperature piping materials and their selection ...
With all respect to davefitz, I believe that the OP is looking for something more along these lines:
High temperture steam piping design and analysis involves a complex balance among 1) calculated stress levels 2) developed anchor and pipe support loadings 3)selection of proper pipe supports and their locations and 4) possible evaluation of relief valve reaction loads.
I have more to say .... but I have some other commitments this week that took priorities ....
MJCronin
Sr. Process Engineer
With all respect to davefitz, I believe that the OP is looking for something more along these lines:
High temperture steam piping design and analysis involves a complex balance among 1) calculated stress levels 2) developed anchor and pipe support loadings 3)selection of proper pipe supports and their locations and 4) possible evaluation of relief valve reaction loads.
I have more to say .... but I have some other commitments this week that took priorities ....
MJCronin
Sr. Process Engineer
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1
- #12
The reference books that I have found most helpful in my design of steam piping systems are:
Reference Books regarding Steam Systems:
"Piping Handbook"; Mohinder L. Nayyar
ASME B31.1; latest edition
"Power Piping", Complete Guide to ASME B31.1,Charles Becht IV
NORSOK STANDARD; L-002 "Piping system layout, Design and Structural Analysis
"Piping and Pipe Support Systems"; PR Smith, TJ Van Laan
"Pipe hanger Design and Engineering"; Anvil International
Spriax Sarco Reference book
There are also many informal rules and guidelines contained within company standards
MJCronin
Sr. Process Engineer
Reference Books regarding Steam Systems:
"Piping Handbook"; Mohinder L. Nayyar
ASME B31.1; latest edition
"Power Piping", Complete Guide to ASME B31.1,Charles Becht IV
NORSOK STANDARD; L-002 "Piping system layout, Design and Structural Analysis
"Piping and Pipe Support Systems"; PR Smith, TJ Van Laan
"Pipe hanger Design and Engineering"; Anvil International
Spriax Sarco Reference book
There are also many informal rules and guidelines contained within company standards
MJCronin
Sr. Process Engineer
- Thread starter
- #13
MJCrobin has given some excellent references, however when it comes to pipe stress analysis, there’s only 1 ultimate reference: Peng & Peng’s book on Pipe Stress Engineering, followed by Sam Kannappan’s book Pipe Stress Engineering.
B31.1, Becht and Nayyar don’t come anywhere close to them (B31.1 has actually very little to say about how pipe stress analysis needs be done, etc.)
B31.1, Becht and Nayyar don’t come anywhere close to them (B31.1 has actually very little to say about how pipe stress analysis needs be done, etc.)
I agree with XL83NL .... these are excellent books on Piping Stress Analysis ... For all types of piping systems
However, I hoped to include references on the layout, design, selection of materials and pipe support design for Steam Systems only.
I also would like to add some "general rules of thumb" for Steam system design that I have collected from various consulting companies over the years ...
But I will do that in another post ....later
MJCronin
Sr. Process Engineer
However, I hoped to include references on the layout, design, selection of materials and pipe support design for Steam Systems only.
I also would like to add some "general rules of thumb" for Steam system design that I have collected from various consulting companies over the years ...
But I will do that in another post ....later
MJCronin
Sr. Process Engineer
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