Dear Sir
As CII5.0 allow user to choose Eh(hot elastic modulus) over load case option. for some China Power users are thinking that Eh should be used always while caculating restraint force over nozzle load rather than Ec(cold elastic modulus). the China Power in-house software GLIFF and 2010 are based upon Eh rather than Ec. As CII's OPE nozzle load is much higher than using Eh for caculation. so the user has to get more expansion loop to increase the flexibility, the the main steam pipeline is very expensive. by the user's experience, their steam turbine nozzles load could be satisfied via Eh caculation. so they insist on using Eh for restraint force caculation. certainly Ec is used for the stress caculation.
so I want to get some comments on this, I want to know the opinions of peoples who is working over Power industries engineering.

Hello Richard,

Always the first question: What Piping Code is to be applied?

Assuming ASME B31 Pressure piping Code, if the purpose of the calculation is to evaluate stresses, the modulus of elasticity of the material at the ambient temperature must be used. This will result in an analysis of a less flexible (than it will actually be at operating temperature) system. So, the loadings on the terminal equipment will greater.

It has always been my opinion that if the purpose of the calculation is to evaluate the loadings transferred from the piping to potentially strain sensitive terminal equipment, the modulus of elasticity of the material at the operating temperature should be used. This will result in an analysis of the system that will be cloaser to its actual flexibility at operating temperature.

Regards, John.

richwang... regardless of piping code physics denies the use of Eh by itself alone... Think about what happens as the system is brought up to operating temperature, true while E drops once the maximum temperature is reached, by far the vast majority of thermal strain is imposed on the system prior to the decrease in E.

Yes, once the system is fully soaked the end reactions drop, but not until a larger end reaction is achieved along the way to the operating temperature.

B31.1 para 119.1.10 contains a method for using a portion of the decrease but frankly I believe prevalent practice here in the U.S. and Europe does not take advantage of this affect.

I suggest you graph Mod E, and thermal growth coefficients vs Temperature to look at what I refer to.

The turbine should remain within load limits from the cold start to the operating temperature.

As for Chinese customs, codes, and software I defer to your local knowledge but physics are universal.

Thanks a lot for all John's great answers, it's getting clear already!

Dear,

As the steam turbine nozzle allowable load is provided by the steam turbine vendor, they should be informed before using Eh in computing the load. Many a vendor accept it.

Even if the load returns in reverse direction after completion of self-springing, the load will be in installation temperature when turbine vendor may allow higher load allowable.

regards,

sam

Dear John C. Luf,

I have read your post, As you have mensioned "graph Mod E, and thermal growth coefficients vs Temperature"

I made a simplelist for low carbon steel:
temperature/modules/Exp.coeff/multiply
C GPa
21 /203
93 /199 /11.48 /(93-21)*199*11.48= 164485.44
149 /195 /11.14 /278054.4
204 /191 /11.41 /398813.73
260 /188 /11.7 /525704.4
316 /184 /11.99 /650817.2
371 /176 /12.24 /753984
427 /167 /12.53 /849559.06
482 /154 /12.78 /907303.32
538 /141 /13 /947661
593 /124 /13.18 /934831.04
first,suppose the low carbon steal can be used in 593C,
noticed that in temperature 538C,the multiply results is 947661 which is biger than the results in 482C (907303.32)and 593C(934831.04).

So,if the calculate temperature is 593C,the terminal points loads are not the biggest one, because the biggest terminal points loads may occur in the process of heating-in temperature 538C,not in 593C.

Is it what you really mean?

ps,if your answer is yes, does it mean that in 21C-482C We
can use hot modules if the purpose is to calculate equipments nozzle(terminal points)loads?

Thank you sir!

"We can use hot modules if the purpose is to calculate equipments nozzle restraint loads?"

My answer is an absolute yes!

sir,

I want to hear your answer to my first question:"

if the calculate temperature is 593C,the terminal points loads are not the biggest one, because the biggest terminal points loads may occur in the process of heating-in temperature 538C,not in 593C.

Is it what you really mean?"

Thank you very much, sir!

The loads that occur to restraints and equipment during startup must ALL be accounted for. The Mod E at the specific temperature in question may be used for these Reaction numbers (exclusively not piping stresses!)

Now this is soley my opinon... the B31.1 code is silent to the specifcs of equipment loads.... other than to use good practice and judgement, which hopefully I have in these and other remarks made by myself in the past.

John C. Luf, Thank you very much for your prompt reply!