Rerating: old hydro versus new pneumatic

[robsalv]

Apologies for X-post - it seems a topic to cover the two selected forums...

I'd appreciate your thoughts.

In simplistic terms, if one needed to rerate an existing line that was originally hydro tested [1.5xDP old], but it couldn't be hydrotested today due to water contamination issues... and the original hydrotest pressure was GREATER than the calculated new pneumatic test pressure [1.1xDP new]... and the line condition was sound such that the original hydro test could be considered a valid test all these years later... could the line rerating be treated as a paper excercise and not require any leak testing at all??

With some due considerations, I'm leaning towards yes since the original hydro was greater than the calc'd pneumatic.

References I've been using are B31.3 and API570.

Much appreciate your thoughts.

Thanks.

Rob

 

[ChemFemme]

How can you be sure the pipe is sound? How long has it been in service? Have you conducted UT inspections to ensure there hasn't been any corrosion? How long ago was it hydrotested? Is it welded or threaded pipe? If welded, was there an X-Ray inspection completed??

I would tend to err on the side of safety/conservative and conduct a leak test. It's hard to know what has happened to the integrity of the pipeline over time. A re-rate also has to be signed off by an AI (authorized inspector), who may interpret the code differently, so your best bet would be to find out who the AI would be and get their opinion as well.

BTW, where is the other post? I'd like to see other's comments on this.

 

[metengr]

Forget about the 1.5X hydro design pressure. This only shows that at the time the line was designed and fabricated, it met the hydrotest requirements of the construction Code. Design pressure is what it is design pressure.

What exactly are you asking? Are you re-rating to a lower DP or are you going to increase the DP of the line?

Second question; does the line fall under any Jurisdictional or regulatory requirements?

 

[jamesl]

We had same situation before. We used exactly the same argument (orignal hydrotest pressure higher than the new one required)and convinced the AI to waive the hydrotest.

I agree that such argument has no basis in the code. However, it makes sense in terms of engineering judgement. If UT inspection has not find any defect, what can a new hydrotest with a lower pressure prove?

 

[stanweld]

robsalv,
8.3 d. of API 570 permits elimination of the pneumatic leak test for the rerate as you described when the line had previously been pressure tested at a higher pressure than is required for the rerate. All other requirements listed under 8.3 must also be met.

 

[robsalv]

Thanks folks for all the comments.

ChemFemme, all those questions are being and have been considered, but didn't want to complicate the post, hence the wording in my question i.e., "in simplistic terms". I too would prefer to err on conservative side... I mean, who in the inspection and integrity game doesn't tend to the conservative? But the line's service does not allow a hydro test - so it would require a pneumatic test... and if the integrity of the line is sound (it's not leaking now and there's no visible external corrosion, and the service is not corrosive) what would a pneumatic test LOWER than the original hydro prove???

Metengr, the rerate of DP is to a moderately higher DP. In Victoria Australia, the regulatory regime is a self managed with regulatory audits at any moment, so there's no AI to consult. This is our decision. As we're an American managed petrochem company, we tend to use B31.3, API570 etc as guiding standards. In your view, if all things piping integrity wise were eqaul, can the pneumatic pressure test to 1.1xDPnew be waived given that it would be lower than the original 1.5xDPold hydro?

Jamesl - sounds just like our situation here! Good to hear I'm not inventing the wheel. Any down side so far from waiving the hydro?? What kind of argument did the AI put up against it?

Stanweld - thank you for the hot tip! I will look into it.

Cheers all.
Regards, Rob

 

[metengr]

Rob;
I don't have a copy of API 570 handy. But as stanweld mentions, if you follow the specific requirements in 8.3 d and piping integrity is sound (some type of condition assessment), I would consider waiving the pneumatic leak test. The key is to assure that you had no in-service damage that could result in a lowering of DP.

 

[robsalv]

For the record, API 570 8.3 says:

8.3 RERATING
Rerating piping systems by changing the temperature rating
or the MAWP may be done only after all of the following
requirements have been met:
a. Calculations are performed by the piping engineer or the
inspector.
b. All reratings shall be established in accordance with the
requirements of the code to which the piping system was built or by computation using the appropriate methods in the latest edition of the applicable code.
c. Current inspection records verify that the piping system is satisfactory for the proposed service conditions and that the appropriate corrosion allowance is provided.
d. Rerated piping systems shall be leak tested in accordance
with the code to which the piping system was built or the latest edition of the applicable code for the new service
conditions, unless documented records indicate a previous
leak test was performed at greater than or equal to the test
pressure for the new condition. An increase in the rating temperature that does not affect allowable tensile stress does not require a leak test.
e. The piping system is checked to affirm that the required
pressure relieving devices are present, are set at the appropriate pressure, and have the appropriate capacity at set pressure.
f. The piping system rerating is acceptable to the inspector
or piping engineer.
g. All piping components in the system (such as valves,
flanges, bolts, gaskets, packing, and expansion joints) are
adequate for the new combination of pressure and temperature.
h. Piping flexibility is adequate for design temperature
changes.
i. Appropriate engineering records are updated.
j. A decrease in minimum operating temperature is justified
by impact test results, if required by the applicable code.


It would seem the situation I have is adequately covered by API570. Based on the company internal email traffic on the topic, it's clear its an issue that generates differing technical opinions!

Any other thoughts on the topic??

Cheers

Rob