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Line stop support in High pressure high temperature steam pipe

pepeuy (Mechanical) (OP)
28 Apr 10 8:12
Hi everybody,

I've asked some questions regarding steam turbine nozzle strengths and your replies were very useful.

I now have to design a line stop for a SA335-P22 8" NPS that runs 65 barg steam at 530ºC.

Some engineers around say that a we can't use a guide (IPN type welded to the pipe) due to stress concentration. I however believe that if we can build an IPN type guide with maximum displacements stops (in the appropriate material for high T) the line stop can be used.

What do you think?

Thanks in advance
BigInch (Petroleum)
28 Apr 10 9:25
Listen to the people that can see the piping configuration.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/

pepeuy (Mechanical) (OP)
28 Apr 10 9:59
BigInch, i don't really get your reply.

BTW there must be, perhaps a couple of engineers that have worked with this steam conditions in Uruguay and for sure they never used FEA to work them out.

And they aren't the ones around me.

In Vino Veritas

unclesyd (Materials)
28 Apr 10 12:14
Piping Technology is just one of many that can supply a bolted line stop or guide for your line.
You also may want to look at the Cryo guides and stops as they use a lot of bolted on products.

http://www.pipingtech.com/index.htm
BigInch (Petroleum)
28 Apr 10 12:26
I mean its hard to say exactly what you can or can't use for a stop when you supply no configuration, no forces, no wall thickness, no nothing, except material, pressure and temperature.  If you were asking if the material was OK, that would have been a more or less valid question.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/

MJCronin (Mechanical)
29 Apr 10 19:33
I am more than a little concerned...

"SA335-P22 8" NPS that runs 65 barg steam at 530ºC."

Not the kind of system for a novice to be learning & discovering piping design.

Hope that you have Schedule 80 or thicker piping....

What wall thickness do you have ?

-MJC



 

   

pepeuy (Mechanical) (OP)
30 Apr 10 7:39
MJCronin, as you well say i'm a novice learning with this pipe :S

I have selected a Sch. 120 and the many (more than 1000) runs with autopipe confirm that the pipe complies with B31.1, if the supports are well fabricated.

The only messy point is that the stresses on the turbine nozzle are over (less than 50%) the ones that the manufacturer has informed.

I had accomplished the stresses before, but due to civil construction i had to modify the layout and the stresses went up again. At this point i don't really care anymore since this pipe has been around well over 12 months.

I know it's unethical to do this, but nobody else cares about the pipe flexibility and turbine nozzle stresses rather than me. It's like if i'm surrounded by insane people. And i'm really tired of looking for solutions running in circles, with no good ideas coming from anyone else.  

In Vino Veritas

BigInch (Petroleum)
30 Apr 10 9:50
Hummm.  How long do you think it (and you for that matter) will survive?

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/

Kentech394 (Mechanical)
4 May 10 7:38
Why you are not using the expansion joint to reduce the stresses as i belive most of the stresses are due to expansion at high temperature.

thanks  
pepeuy (Mechanical) (OP)
4 May 10 16:53
@Kentech394: If you know any company that manufactures expansion joints for that operating point please let me know, I couldn't find any.

 

In Vino Veritas

saplanti (Mechanical)
4 May 10 20:30
I guess you can weld shear keys (which thermal gradients can be kept as low as possible through keeping the height of the keys) on to the pipe (horizontal or vertical) and take the load by a riser clamp. Keys, depending on the load direction(s), can be on both side of the riser clamp and welded with complete penetration. Key face against the clamp should be kept flat. Key numbers can be determined by the allowable bearing pressure at the design temperature, and the lengths can be determined by the allowable shear stress with some margin in accordance with the applicable code. Firs you need to select the riser clamp from a reputable supplier.

This is very common application, however increasing the height of the key will increase the thermal gradient, and thermal stresses. So you need to use the required height (check the thickness of the riser clamp plate) only to keep it minimum. I have not seen anyone doing any FEA and fatigue analysis on this application, it is well proven common application. But I would like to hear if there is an available proof analysis for this application.

Hope it helps.

Ibrahim Demir
unclesyd (Materials)
4 May 10 20:41
Just for curosity did you consider the application of any cold spring in the steam supply line?




 
saplanti (Mechanical)
4 May 10 21:22
My comment above was for the line stop in axial direction of the pipe.

In case you want to stop lateral movement of the pipe you still can use plate welded onto the pipe, facing a structural member, but you need to reduce the thermal gradient and thermal stresses by introducing thermal barriers . If you do not know what you are doing it can be very risky application.

If the loads are very large, I guess you should not stop the pipe moving sideway. Common approach is not to use weld integral supports onto the pipe to eliminate/reduce all the local thermal/mechanical stresses.

Ibrahim Demir
Kentech394 (Mechanical)
5 May 10 1:58
please use the following link to get an expansion joint for you temperature and pressure ranges.

http://www.pipingtech.com/products/expjtcat/expansion_joint-design.htm

thanks

Sameer
pepeuy (Mechanical) (OP)
5 May 10 7:57
@unclesyd: I have consider cold spring, but the forces that are over the limits are the ones perpendicular to the flange and not in axial direction.

In Vino Veritas

DSB123 (Mechanical)
5 May 10 8:21
pepeuy,
       Surely all of your pipework does not run axially to the flange - you must have legs perpendicular to the nozzle orientation where you can apply cold-pull to lower loads!!!
StevenHPerry (Mechanical)
5 May 10 8:26
@kentech: we're talking bar, not psi.

- Steve Perry

saplanti (Mechanical)
5 May 10 8:36
I understand from your description that your piping system needs more flexibility to eliminate this kind of problems. Restraining piping under thermal loads will transfer supports excessive loads, and this will increase secondary stresses in the piping.

I suggest you to review the pipe route and supports all together.

Ibrahim Demir

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