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Hydraulic test problem for main steam pipe of thermal power plant

Hydraulic test problem for main steam pipe of thermal power plant

Hydraulic test problem for main steam pipe of thermal power plant

(OP)


 I find the main steam pipe section of thermal power plant contract require the follows:
 
The test pressure for Hydraulic test at shop of pipe
= 1.5*allowable stress at room temperature*design pressure/allowable stress at design temp

 Ratio of allowable stress at room temperature and allowable stress at design temperature is always more than 1. It means that if the design pressure is 30Mpa , I need to do more than 45 Mpa Hydraulic test at workshop! Or at site.(if it is at site , that may be reasonable )
It is unbelievable. Who knows where can do hydraulic test more than 30Mpa?
   I find in ASTM A 335 the max pressure for hydraulic test is 19Mpa .  En 10216-2 only specifies 7Mpa for hydraulic test. Therefore more, EN and ASTM specifies electromagnetic test can instead hydraulic test. But Indian do not accept it.
   I want to know what is the main purpose of hydraulic test for high pressure pipe ?
 

RE: Hydraulic test problem for main steam pipe of thermal power plant

I can't speak to the specific standard/application you are referring to, and do not sit on the standards committees, yet I strongly believe that the purpose of the properly run filling and hydrostatic testing procedure of an installed pipeline is to protect all parties (whether they realize it or not, in many arguable fashions) to the construction contract, and ultimately the public (to much extent) from then on.  "Stuff" can happen, at all stages of the process.      

RE: Hydraulic test problem for main steam pipe of thermal power plant

To verify the strength of the installation is actually equal to or greater than the strength that was assumed possible during the design (not only design pressure, it includes design conditions plus necessary safety factors).  Once hydrotested, the "assumed" is "verified".

 

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Hydraulic test problem for main steam pipe of thermal power plant

The test pressure for Hydraulic test at shop of pipe
= 1.5*allowable stress at room temperature*design pressure/allowable stress at design temp

----

Check your pressures:  

Assume 1100 psig steam at 1000 degrees = operating conditions.
Strength of material (at 1000 degrees) = 0.80
Strength of material (at 70 degrees)   = 1.00

Your initial (First time ever hydro) test = 1.5 x 1100 psig x (1.0/.8) = 2062 psig.  Not impossibly high.

Subsequent hydro tests - after repairs or pipes are rewelded - is normally only 110% or 125% operating pressure. If eqpt or pipe flanges are merely unbolted and reinstalled, only a NOP (100 % pressure) test is required.  

Check your contract carefully, I usually don't see the material hot/cold strength ratio in the spec.  The 1.5 ratio is also higher than what I've seen vefore: I remeber my first-time plant steam hydro's were usually 1.35 operating pressure, with no multiplier for hot strength.

RE: Hydraulic test problem for main steam pipe of thermal power plant

(OP)
because it is not test pressure of the installation piping . it specifies hydraulic test pressure of pipe during the manufacture of piping . So at the workshop , i need to do high pressure hydraulic test.

RE: Hydraulic test problem for main steam pipe of thermal power plant

You know, if your facility claims that it is capable of manufacturing piping spools for the main steam pipe of a power plant, your facility most certainly ought to be capable of doing a proper pressure test.  That's something I would have expected to have been covered during a shop inspection prior to award.

30MPa is already 4350psig, which is some might high pressure.  45MPa takes that to 6530psig so you are working with some highly energized pipe there.  I'm not familiar with the EN code you specify.  

As for A335 - those testing requirements apply to the mill producing the pipe.  I may be reading incorrectly, but I gather you are taking A335 pipe from a supplier and welding it to flanges and fittings to make pipe spools.  So, A335 does not address your testing requirements.  Those would fall under the piping code the facility is being built to (like B31.1, but maybe B31.3 since you have the Sac/Sah requirement)

As I look through B31.1, it appears to limit the test pressure to 1.5*design pressure

B31.3, which I'm more familiar with, imposes the design pressure*1.5*Sac/Sah requirement with a limit to the ratio of Sac/Sah being less than 6.5 which gives a maximum multiplier of 9.75.  However, the codes also make it clear that the test pressure cannot create a stress in the pipe that exceeds the yield strength of the pipe - so that is the ultimate limit.  Whoever is setting up the hydrotest better have made that calculation check.  

If the contract test pressure creates a case of stressing the pipe beyond yield, that is something you'd better talk to the customer about before you kill/maim a bunch of people in the test area.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

RE: Hydraulic test problem for main steam pipe of thermal power plant

(OP)
thanks for StressGuy's explanation. But ASME B31.3 is process piping guidebook which is used in petrochemical piping.  I think ASME B31.1 may be suitable which is used as power piping guidebook.

 my contract belong to thermal power plant.

RE: Hydraulic test problem for main steam pipe of thermal power plant

Ed Klein is well experienced in piping design and analysis.

He gives good advice.... and I too do not have a good feeling about these exteme high pressures.

You state "I need to do more than 45 Mpa Hydraulic test at workshop"..???? What exactly did you have in mind ??

What is the diameter of the piping system ?

-MJC

   

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