Water quality

[ghoshtathagata2000]

Hi,

There is a requirement in API 610 for Centrifugal Pumps (Cl. no. 7.3.2.3) that the water quality to be used for Hydrostatic testing pumps with austenitic stainless steel materials shall not exceed 50 ppm w. Can anybody please clarify why this water quality requirement is not applicable for water to be used during the performance testing of the pumps?

In one of of the projects we are executing the hydro test is to be performed for 4 hrs and the combined performance and mechanical run test is scheduled for 6 hrs total. This way I suppose the performance test is to be regarded as more severe?

Thanks,
Tathagata Ghosh

 

[bimr]

"Hydrostatic testing of austenitic stainless steel vessels shall be done with potable quality water having a chloride content less than 50 ppm shall be used for hydro testing." is the way it is normally written.

Austenitic stainless steels are subject to stress cracking corrosion typically when the chloride concentration is over 200 mg/l for the entire service life. The service life is in terms of year.

Specifying the chloride content for a 4-hour test period is very conservative because the austenitic stainless steel will not be attacked in such a short time period.

Use of "potable water" is more appropriate as a standard for testing water. Most potable waters actually have a chloride content less than 200 mg/l.

Probably the reason that this is specified is that the pump manufacturers are probably not that familiar with the details of water quality.

 

[GPRnD]

There are probably 2 reasons why they don't call out a specific limit for the performance test.

1. API 610 has things that are inconsistant and not well thought out. This may be one instance where it has simply been overlooked.

2. Water used on hydrotest tends to be drawn from a city water system, used once in the pump then dumped down the drain. As such it is freshly treated water where the chlorine has not had a chance to decompose.

Water in test loops is typically reused with a relatively small amount of makeup water added. Perhaps the experience of the API committee was that such water typically has a very low chloride level ?