Hydro test for dissimilar weld

[kissjxp]

How to determine the hydro test pressure of a dissimilar welded pipe system (carbon steel to 2.25Cr-1Mo).

According to ASME B31.3, the test preussre can be determined by Pt=1.5*P*St/S. Now we have two values for the hydro test. Which one we should use, the lower one or the higher one?

Thanks.

 

[XELR8]

Hi Kissjxp,

What is your design pressure and temperature? What is the pipe diameter and schedule? What is the yield strength of the carbon steel and the 2.25Cr-1Mo steel?
What is the flange ratings on the pipe line? What is the atmospheric temperature? Why did you use a different pipe material and what if any problems did you have with when consdiering replacement material? Sorry for the questions, just trying to make sense of things. Just answer the best you can.

 

[Apakrat]

What authority specifies Your hydrostatic testing requirements?


At 74th year working on IR-One2 PhD from UHK - - -

 

[kissjxp]

Carbon steel pipe: ASTM, A106-B; 18" SCH80;Maximum Design Temperature: 427 DegC

2.25Cr-1Mo:ASTM A335 P22, 18" SCH60;Maximum design Temperature 515 degC

Flange rating: 1500#

Service condition: High pressure steam: 427 DegC.

 

[BigInch]

Obviously you cannot test the lower pressure pipe to the test pressure of the higher pressure pipe, as that would place the low pressure pipe over yield.

Option 1:
Pick the lowest calculated pipe pressure (or lowest pressure of all components) and multiply by 1.5 and test the whole system at that test pressure value.

Option 2:
If you do not need to operate above the lower pressure, you could simply do the minimum required test pressure, which must be greater than your maximum expected operating pressure x 1.5

In any case, your MAXIMUM OPERATING PRESSURE for the entire system MUST BE LESS THEN the lowest actual measured test pressure divided by 1.5

**********************
"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/

 

[metengr]

kissjxp;
You really need to review 345.4 in B31.3. I just reviewed it and it is really self explanatory. Review subparagraphs b) and c).

 

[XELR8]

Kissjxp,

I have some good news and I have some bad news.

The good news first:
A106B Gr B St = 10.8 ksi, Sa = 15.0 ksi, Sy = 35.0 ksi
A335 P22 St = 11.0 ksi, Sa = 15.0 ksi, Sy = 30.0 ksi

Ptest = 1.5 * Pdesign (St/Sa)

For A106 St/Sa = 0.72
For A335 St/Sa = 0.733

So your test pressure for each material is approximatley the same any way you calculate it.

The bad news is:
1) I am concnered about thermal expansion from disimilar materials. Your temperatures are really high and the allowables are derated accordingly. Check this out by a consultant. You can use the formula for your pipe stress = M/S where M is the wl^2/8 and S is the section modulus for the pipe. This number needs to be less then 0.66 Sy. Remember to include the weight of water and steel (about 260 lbs/ft) plus insulation. w is weight per unit foot and l is your pipe span. Remember to reduce the A106 pipe thickness for corrosion. The 335 P22 will not corrode.

2) If these pipes are welded together their ID's don't match up and you will have weld concerns. The ID's are 16.126 and 16.5 inch.

3) Include any static head pressure from pipe that is not at the same elevation. This pressure must be backed out from the bottom head pressure.

Good luck.

 

[BigInch]

Dracula,

I have bad news.

Have you forgotten that even if the allowable stress is the exact same value, the different wall thicknesses will give DIFFERENT TEST PRESSURES?

**********************
"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/

 

[XELR8]

Kissjxp,

BigInch is correct.

There are two reasons why I did not orignally follow the above logic:
1) If you calculate the design pressure from the allowable steel stress at hydrotest pressure 0.90*Sy, you will get an enormous amount of pressure. You would not possibly operate steam at this pressure nor would you have steam.

2) You can have the same design pressure for superheated steam at your temperatures of 427C and 515C.

Yes, I am aware that the pipe inside radius, pipe wall thickness, weld joint efficiency and material allowable stress will produce different design pressures based on their conditions.

So this is a much easier problem by design pressure:
Calculate the required design pressure for the pipe;

P = 2tSE/(D-2tY) A335 P22 P = 1037 psi, A106 Gr B P = 1317 psi. A335 P22 governs the design at 1037 psi.

Pt = 1.5*Pd*St/Sa = 1.5*1037*.73 = 1136 psi Test Pressure.

I do not have a code book in front of me so I suggest a brief check of my values.

 

[kissjxp]

all,

Thanks for your advise.