Hydrotesting to warranty limits

[konman]

I have some potentially defective 10" pipe that I need to use and need to develop the hydrotest criteria for. I say it is potentially defective because some 12" pipe that we bought from the same mill had some long seam defects that were discovered while hydrotesting. The mill has given us extended warranty on all the pipes, so I want to throw out the following question:

Should we test this pipe to 100% SMYS (using a yield plot) to ensure that this pipe meets the warranty criteria, or test to 95% SMYS which is the maximum test pressure (at low point) required to achieve the required MAOP.

This pipe is 273.1 mm OD x 4.8 mm WT, Gr. 359, ERW, Cat II - CSA Z245.1M and we are working under the CSA Z662-07 code. MAOP = 8619 kPa

 

[BigInch]

Sorry, I don't know the CSA code, but isn't that test pressure at the high point. Otherwise you couldn't have your MAOP pipeline operation pressure at the high point and your MAOP would be variable depending on elevation. That would make entering the MAOP on the GIS database pretty complicated. Just curious about that point.

If the mill is giving extended warranty coverage to 100%, I'd do a 100%, but that's just my idea. They didn't do you any favors. Provided you don't have a new Merceds in the driveway this morning , why should you do one for them at this point.

**********************
"Being GREEN isn't easy"
.... Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com/

 

[SNORGY]

I think what konman is saying is that if they hydrostatically test all of the pipe to 95% SMYS, they will have proven the MAWP at the high point in the proposed system because, accounting for hydrostatic head, the calculated pressure at the low point would be the 0.95 x SMYS and, simultaneously, at the high point, (0.95 x SMYS - [rho*g*h*D]/[2*t]) would still correspond to a pressure for which the MAWP is proven.

Or something like that...if I did it right...

I would try 100% NDE on all long seams without pressure testing if the pipe hasn't shipped yet. If the pipe has shipped you could say that you were, in essence, going to proof test it at 100% or 95% SMYS in the field and that they would be on the hook for any ensuing warranty claims, but I doubt the Seller would agree to that. Further, you would likely be faced with a non-routine application with the Regulatory Authority for any such test (above 80% x SMYS), who would ask what the technical justification for it would be. If the justification is that you have doubts about the integrity of the long seams, be careful how you word that.



Regards,

SNORGY.

 

[BigInch]

Snorgy, that's why I said I didn't know CSA.

In ASME B31.8 ss 845.214 states,

(2) The test pressure to be used in the maximum
allowable operating pressure calculation shall be the
test pressure obtained at the high elevation point of the minimum strength test section and shall not be higher
than the pressure required to produce a stress equal to
the yield strength as determined by testing. Only the
first test to yield can be used to determine maximum
allowable operating pressure.
......
(5) While the maximum pressure of a test used to
establish the maximum allowable working pressure is
not limited by this paragraph except by (a)(2) above,
due caution should be exercised in selecting the maximum
test pressure.

So, for a US gas pipeline B31.8 is saying to use the pressure registered at the high elevation as the value to divide by the location factor to arrive at the MAOP. Low point pressure is irrelevant to determining MAOP. It additionally states that that pressure shall not be higher (at the high point) than yield pressure, which would also allow that a pressure at a low point actually be higher than yield pressure, as so provided for in (5).

Does CSA limit the test pressure as you have said?
He didn't mention any elevation head .. specifically.

**********************
"Being GREEN isn't easy"
.... Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com/

 

[CanucklePipe]

In CSA, the pipeline MAOP is limited to the minimum strength test pressure at the high point of the pipeline. Given konman's specs, his minimum test pressure at the high point would be 125% of MAOP (1562.5 psig) assuming Class Locations of 1 or 2. This is roughly 84% SMYS for the pipe. He said that it would be 95% at the low point so this would indicate elevation changes.

In CSA Z662, yield plots are required for test pressures that would stress the pipe to 100% SMYS or greater.

 

[konman]

To do 100% NDE on the long seam would be a bit impractical. We have 85 km stockpiled at the coating mill and 15 km is already coated. The coating mill is in a different city from the pipe mill. The pipe mill does 100% NDE on the long seam in the plant and we had third party mill inspectors during the running of this pipe.

The 12" pipe that had the long seam defects was purchased at "discount rates" and we did not have mill inspectors. The mill did foot the bill for the cost of repairs and the UT tool run after repairs were made. We are doing digs on the 12" pipe this year to confirm the UT tool data.

Doing the test to 100% SMYS does require a yield plot, but I am reluctant to take the test up to yield. I figure there is not much point stretching the pipe if I don't have to. The test to 100% would prove the pipe meets the specifications, but only at the low points in each test section.