Hydrostatic test for a Steel Penstock

[21121956]

Hello everybody:

For a small hydroelectric Project is planned the manufacture of a welded steel penstock, according to ASME Section IX code.

In the Technical Specifications of the Contract it is established that, at the end of the construction of the penstock, the hydrostatic pressure test should be performed in the penstock as a whole unit.

Regarding with the hydrostatic pressure test, I want to comment the following:

1. According to ASCE, “Steel Penstocks. Manuals and Reports on Engineering Practice N° 79”, in the section 13.4.1 can be read that Hydrostatic testing is not a mandatory requirement for penstocks.
In the same section, numeral (3) … The engineer may consider 100% radiographic examination (RT) or ultrasonic examination (UT) and magnetic-particle examination (MT) in lieu of hydrostatic testing.

2. The ANSI/AWWA C200-97, “AWWA STANDARD FOR STEEL WATER PIPE – 6 IN (150 mm) AND LARGER”, in the section 5.2.1 Hydrostatic testing of pipe can be read: NOTE: By agreement between the Purchaser and the manufacturer, other nondestructive test methods may be used in lieu of the hydrostatic test.

I would like to hear your comments regarding to what could be those “circumstances”, “reasons”, “considerations” that can be invoked to reach that agreement and avoid to perform the hydrostatic test.

Any comments will be welcome. Thanks.


El que no puede andar, se sienta.

 

[BigInch]

1) No water in the dam, or the test is somehow otherwise impractical or impossible to conduct.

2) The engineer convinces the client that 100% radiographic testing is sufficient proof of quality and expected performance.

3) The contractor posts a bond in an amount greater than the amount of "liquidated" damages that might be expected if the penstock failed. Bond to be valid for a time to cover the performance testing and some agreed length of extended operational testing period.

I'd go for #1 or #2. I doubt they'll be dumb enough to go for #3, or higher.

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[21121956]

Hello everybody:

Thank you BigInch for your valuable comments.

El que no puede andar, se sienta.

 

[LittleInch]

further to BI reply,

Item 1 seems a little far fetched - no water available for a HE project?

Item 2 - Often this is convince the client / regulator / Insurance company or Third Party inspector for the client. One out of three maybe even two out of three, but three out of three - doesn't happen very often.

Item 3 - cost of the bond >> doing the test

If you search pneumatic test on this forum you'll find much the same debate about the relevance or otherwise of a hydrostatic test.

I'm not clear if this is just of interest or that you're seriously trying to get out of this test.

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Also: There's usually a good reason why everyone does it that way

 

[21121956]

Hello everybody:

I would like to make some observations on the comments given by BigInch and LittleInch:

For Point 1: When finished the construction of the penstock, there will be no facilities to convey water to the pipe (gates at the intake, sand trap or desander, etc. which will be completed 5 months after), so performing the hydrostatic test (when the water is available) lengthen the commencement of commercial operation of the plant.

For point 2: the manufacturer's specifications for the penstock indicate that radiographic inspections shall be made in both the longitudinal welds and the circumferential welds (whether made in the workshop or in the field), So, we do not need "to be convinced" by anyone.

With regards to the pointed out by LittleInch, that I am seriously trying to get out of this test, let me tell you that it is completely the contrary, I am trying to prepare myself (I am in the side of the client or owner of the Project) for an eventual proposal by the Contractor "selling the idea" of avoid the perform of the hydro test in order to start the commercial operation of the power plant as soon as possible.

Once again, thanks to you.

El que no puede andar, se sienta.

 

[rconner]

Just wanted to make sure you have the latest (Second Edition, 2012) of MOP#79, as I believe it now discusses many pros and cons of this issue in same?