Hydrotesting Proceedure: tapping pipe welds with a hammer

[curtis2004]

Hi Everyone,

We are working in a project for mining facility located in Russia. I was reviewing local contractor's hydrotest procedure and come a cross to sequence what shall be done tin order to comply with local GOST regulation:

"- reducing the pressure to the operating pressure and final inspection of the pipeline with a light tap of the welds at a distance of 15-20 mm on both sides of the weld: carbon steel pipelines with a hammer with a rounded striker weighing 1-1.5 kg, alloy steel pipelines with a copper mallet (test for tightness)."

Is tapping a pipe undergoing hydro test with hammer safe? I personally wouldn't want to do this work neither want to witness it.

Thanks,
Curtis

 

[LittleInch]

Of course it's safe. It's a welded steel pipe.

You could run over it wuth a tank or get the world's stron gest man to hit it work a sledge hammer and it still wouldn't break.

However it is a Russian welded pipe so maybe watch the first one from a distance....

I love GOST specs sometime. They are stuck in a time warp from the 1950s, a bit like the cars in Cuba from what I hear.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GD2]

One reason could be testing for impact load at the test temperature - brittle fracture at low temperature.
Russia is a cold country and they must have experienced piping failure where workers could have tightening a flanged leak on-stream, hammer accidentally hit the pipe and broke.
Welds/HAZ are more vulnerable areas due to inherent residual stresses and so is the test prescription around the weld joint.
By the way, what's the minimum test temperature they specify? For piping, it should atleast be 9 degrees C above the material MDMT.

GDD
Canada

 

[curtis2004]

GD2,

This is part of regular hydro test with water procedure. The document forbids tapping during pneumatic air pressure test though.

Thanks,
Curtis

 

[curtis2004]

Little Inch,

Russian GOST specifies pre-qualification requirements for welders. If welder doesn't pass the pre-qualification, he/she is not allowed to work.
The standard specifies RT requirements between 20% - 2% for each welder depending hazard category of the line.
Piping materials also have similar to ASTM materials requirements.

Skimming through project specifications I couldn't find anything unusual, except tapping of both sides of each weld. This would be time consuming and have inherent safety hazard though.

Thanks,
Curtis

 

[curtis2004]

Hi everyone,

I have contacted my colleague in Russia. He said, it is kind of insurance from bad workmanship of piping contractor. So, I have apologize to Little Inch, that he was right.

Now, everything make sense: If you did not do good job, during weld tapping you may get results in your face. I have read that in 1850s, Bridge Engineers in Russia supposed to stand under the bridge, as a assurance of confidence, during first run of a railway locomotive on top of the bridge. If you didn't design bridge properly, it will be your last job.

Thanks,
Curtis