Hydro Water Quality 1

[4fletch]

When specifying a fab shop hydro of pressure parts, do you require a minimum level of water quality? request fabricators procedure? or use a water quality standard? Thanx in advance

 

[metengr]

Yes we do. We specify treated water or potable water with a maximum chloride content. Also, after hydrostatic testing we specify drying.

 

[vesselguy]

In addition to metengr's comment, the max chloride content should be limited to 30ppmw max if the steel is high alloy such as austenitic S.S. For run of the mill C.S. you have a choice to specify 100 to 150 ppmw. Some companies specifies 50 ppmw for C.S. I think 50 is too strict for C.S. Frankly, I don't know on what basis those companies can spec it so strict.

Yes, your document deliverables from the vendor should always include the hydrotest proceedure to review. Hope this helped you.

 

[gr2vessels]

Another addition is the correlation between the test water quality and the drying as mentioned above.
The low chloride level is not enough for hydrotesting the Austenitic S/S vessels, particularly the ones with lots of crevices and areas where water can accumulate and stand. The draining only will retain in crevices the water, which in turn will slowly evaporate, thus concentrating the chlorides in the most vulnerable locations, perhaps over days and days time. This will suffice for the start of a local chloride induced cracking.
Another bad practice is the use of hot air to dry the vessel;- the temperature increase will accelerate the evaporation process, but same time increase also the chance of chloride attack, this time at higher temperature, at a faster rate than otherwise would happen. The results are the same..If possible, a rinse or flushing with demin water could reduce the chance of chloride attack considerably.
I am also developing a vacuum drying process at normal temperature. The results so far are excellent, are independent of the day's relative humidity and far better results for long term storage than any other current procedure. Providing a proper sealing of all openings, it eliminates the need for N2 blanketing, monitoring of N2 supply, etc..

Howzat?

Cheers,
gr2vessels