Piping Loads on a Surface Condenser

[Boghi1990]

Hi,

I have run a pipe stress analysis for a piping system which carries condensate to a condenser. Two of the lines (NPS 4 & NPS 6) are piped to a surface condenser. The lines run through the condenser shell(3/4" thickness). They are welded on both sides of the surface condenser and run a few feet inside the condenser. From the piping stress analysis I have got the piping loads(Fx, Fy, Fz, Mx, My, Mz) at the anchor points where the lines are attached to the vessel shell. I have modeled a anchor points the interface where the lines connect to the condenser wall. There are not any allowable loads provided by the manufacturer of the vessel. I have to determine if those piping loads are acceptable from the point of view of the structural integrity of the condenser shell?

Could anyone suggest what I can do in order to evaluate the effect of the piping loads on the wall of the vessel?

Regards,

One Point

 

[austsa]

Two possible options (there may be more) are:
(1) Review existing calc and see what additional safety margin manufacturer has over and above the code. Compare with piping loads and make an engineering judgement (if suitably experienced/competent in this area).
(2) Do a WRC297 calculation.

 

[cloa]

Don't double post.

 

[darshiva]

Conside the maximum forces and moments as follows:

NPS 4

-For in plane forces and momments: F=1334 Lb, M=6667 Lb-ft
-For out of plane force and moment: F=500 Lb, M=2367 Lb-ft

NPS 6

-For in plane forces and moments: F=2000 Lb, M=10000 Lb-ft
-For out of plane force and moment: F=700 Lb, M=3500 Lb-ft

The sum of each actual force and moment divided for the maximum force and moment should be less than or equal to 1.

 

[Boghi1990]

Hi Darshiva,

Thank you for your response. Could you please tell me from where you have got(reference material, bulletin, guideline), those numbers (moments and forces)? How could I translate my piping loads from the stress analysis results, into out of plane and in-plane forces & moments? The output results show Fx, Fy, Fz and Mx, My, Mz, so which of these are out of plane and which of these are in-plane forces and moments?

Best Regards,

One Point

 

[austsa]

OP, Many large companies have their own nozzle load spec. I have seen some that have very high loads and others that are not so high. In almost all cases I have seen, loads are dependent on ANSI flange rating (or design pressure) and nozzle diameter. Thus, I would be a little cautious about using values given by darshiva (as you have not told us your flange rating nor design pressure).
In my opinion, there is no correct or incorrect level of nozzle loads. It depends on your needs - balancing your spend on piping and your spend on vessels.
Suggest you read Norsok R-001 (one standard that specifies nozzle loads).

 

[darshiva]

Bogui1900,

The value are gave are typical ones, but, of course, they have to be checked considering your application.

Usually these chechs are done by the condenser supplier. I suggest you contact them.

If you want, I cand make some more precise numbers, but I would need some additional data.

If you want to do it yourself, I suggest you read WRC-297 fisrt. After that read Roarks 7th edition, Section "Formulas for flat circular plates of constant thickness", Case 21b. Also read papers 22, 85, 86, and 87 referenced in that chapter or section of Roarks.

 

[rmw]

Are these the only nozzles on this wall of the condenser shell? Other nozzles if present can already be imposing loads on the wall in question. Some of those nozzles depending on their source (high temperature drains) can impose tremendous loads on condenser walls. I've seen condenser walls glowing red hot and condenser walls that looked like they had been in an automobile crash. What is the big picture?

rmw

 

[Boghi1990]

Hi rmw,

What do you mean by "big picture"? There are several other nozzles on that condenser shell, each one connected to different lines, carrying different pressures and temperatures. The problem is that I do not have the allowable loads (Forces & Moments) from the manufacturer (Foster Wheeler Limited). This surface condenser has been operating since 1968 at that Coal Fired power plant. The client is upgrading the unit, so some of the lines and equipment will be upgraded, but not this surface condenser..

 

[muld0020]

From a vendor perspective, the allowable loads are calculated per HEI for Surface Condensers Appendix D (simplified WRC107 calculations). You simply look at the max moments (load=0) and max load (moment 0), then you make the linear plot. Then you check where your pipe load lands and it is acceptable under the line and unacceptable over the line.

The inner pipes are designed for flow distribution. If you are increasing the flow and/or temps/pressures this could affect the nozzle velocities as the fluids/steam are entering in the condenser. You should verify your dispersion devices with work properly for a change in flow. You should check to make sure you are not upsetting the original design or going beyond HEI allowables for, enthalpy's, temperatures, and pressures. This would be more of my concern rather than simply the pipe loads at the wall of the condenser (though I have seen many cracked/patch nozzles in older condensers). Bypass / Overload conditions can be very important in the design of these connections.

 

[Boghi1990]

Hi muld0020 (Mechanical),

Thank you for your comments. I do not think that I can use the Appendix D from HEI Steam Surface Condenser. That procedure is valid for cylindrical vessels. In my case I have a flat plate shell. See the attached print screen showing the condenser and the lines attached to the nozzles. The condensate in 6" line has 393 F operating temperature and operating pressure 423.600 psi. The condensate in the 4" line has 361.600 F operating temperature and 290 psi operating pressure.

Regards,

One Point

 

[EdStainless]

Have you taken into account the thermally induced stresses as well from differential thermal expansion?
Is there any effort being made to isolate the wall from the heat and/or load of these penetrations?
What is the current condition? Any signs of distortion or fatigue currently?
Many of us have seen sections of side walls that were torn out of condensers because of ill advised penetrations.


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