Hydrotesting Of Reduced Port Ball valves. 2

[steepo1]

thread408-189144

Hello,
i work in oil and Gas industry as testing engineer.
i have some Class 300 piping lines to be Hydrotested up to 70 Bars.

in those lines,there are Reduced Port ball valves ,wich are bolted,and have the Tag " Maximum Operating Pressure: 50 Bars"

My boss told me that we could leave them in the line,half opened,and he is sur that the valves could hold this pressure...

Myself i"m not confident with this,for safety reasons.

could anyone help me with this please?

 

[zdas04]

Verify what the tag says. Sometimes the tag shows MAWP and sometimes it shows max dP. If it is max dP then your boss is right. If it is MAWP (which is consistent with ANSI 300 flanges) then a 70 bar hydrotest is 140% of MAWP and still no problem.

I don't think you have any problem either way.

David

 

[steepo1]

Thanks david!
we will ask our client to have final approval of valve statut.

one last question:could we flush the piping with the valve fully open?

we could damage the valve with debris and scale....

 

[gerhardl]

Why half opened?

Check the reason for this, normal for BFL-valves the recommended position is 100% open by tests larger than MAWP, thus only the body is exposed, and flanges and shell have to be, and are normally, tested to piping class and equal to piping tests.

Why should this be different for ballvalves? I can not see the reason for half opened valves, this would load sealings askew and expose sealings more. Is venting of 'hidden volumes' the reason?

And please also verify through producer that the test with fully opened (or partly opened) valves is OK. After all, a test that the producer cannot accept, will give you valves without guarantee.

Flushing: likewise.

 

[brubakerj]

My advice.

#1 What was the design code of the valve, and by connection the hydro test requirement for the valve in that code. Is it 1.5 x the Cold working pressure? What is this test pressure

When you hydro test the pipeline, are you testing it to 1.5 x the cold working pressure?

Depending upon the answer to #1, you may be retesting the valve to its hydro test pressure.

 

[zdas04]

gerhardl,
The "half open" condition is pretty common in tests. For a floating ball valve, this condition is zero load on the seals (since the ball only acts against the seal when the ball "floats" into it). For a trunnion ball valve the springs will unevenly load the seat, but the amount of loading is based on spring tension not on pressure applied so it should be accounted for in the valve design.

The reason that people do this is to make sure that the valve body is evenly loaded. With a floating ball valve, full open may not allow test pressure into the body cavity (it generally will, but you just don't know. With a trunnion ball valve fully open will not allow test pressure into the body cavity. For a floating ball valve, fully shut will test the body cavity. For a trunnion ball valve fully shut will probably not test the body cavity (but again you just don't know).

In the half-open position you can be confident that the entire body cavity will be tested.

David

 

[bcd]

Maybe I'll beat gerhardl in this reply, but floating ball vavles do indeed have a load between the ball and seats when they are first assembled. There are several reasons why the load can dissipate voer time, such as creep, large temperature cycles, high pressure loading, etc., but more than liely, a new valve is going to have a preload of the seats. There is a chance that a floating ball left in the half open position is going to result in an indentation on the seat sealing edge as it distorts around the ball edge. May not happen to all brands as it depends upon the seat shape, material, and how much preloading there is.

Check with the manufacturer as many have a stem slot hole that goes through to the waterway, or put a hole through the bottom of the stem slot into the waterway so that pressure does not get trapped between the seats when the valve is fully open. If the valve has this feature, then test with the valve full open. Pressure will get between the seats. Leaving the vavle half open is a risk. May be a small risk or a large one. Depends on the brand. If you have done it before with no problems, then you know from experience its OK. If it is OK if the valves leak after testing half open, then no problem again.

It is dangerous to generalize what should happen most of the time. The potential cost from fixing the damage can be pretty expensive. Best to find out for sure what will happen.

 

[zdas04]

Really? Once I had a 12-inch floating ball valve sitting on the ground and I wanted to test that exact question. I reached into the valve (it was shut) and pushed on the ball. It moved a bit (maybe 1/8 inch). I went to the other side and pushed and it moved a bit farther (I didn't have a dial indicator on it, but it felt like it moved farther). For something that heavy to move that far, there really couldn't have been much of a preload on the ball. Maybe that was just a bum valve (I hate to think that, it was a major-name valve and cost a bunch of money). Looking at the design drawings that I have from several manufacturers I can't see a preload mechanism on any of their floating ball valves, but maybe I'm just not understanding the drawings.

I am really curious about what would cause a partially open floating ball valve to have any [additional] load on the seats. No dP across the ball seems to say that the fluid isn't putting any force on it. What am I missing here?

David

 

[stiffler]

Subject completely deviated here but in my view, a quality, well designed floating ball valve does not need any preload. Cheaper manufacturers will squash the seats onto the ball to make up for irregular shaped balls and / or a lack of understanding.

In response to the original query, the valves tested @ 1.4 times MAWP are ok when the valves are in new condition but it is advisable to test at 1.1 x MAWP on older equipment. Testing pipelines with valves 1/2 open ensures that the valve shell integrity is proved as well as the rest of the pipeline so they should be tested like that. Best efforts should be made to remove scale beforehand with flushing, pigging etc.

 

[steepo1]

guys,

i just got test report from supplier of valves and he had test them to 1.5 The MOP in half opened position...so there is no safety issue with this!

two new decks will be coming up next few months but the client specifies that all the ball valves shall be left full open during flushing and hydrotesting,so i think that every project has his own specifications ,own material and therefore conditions...

Is anyone has courses or informations regarding valves components:seat,seal,preload,flotting ball?

im a little bit lost with those words.

thanks guys for ur help!