Chloride Content Of Condensed Water

[SJones]

1.When undertaking materials selection, particularly for CRAs in H2S service, what concentration of chloride ions would you assume to be present in condensing water (i.e. water forming below the water dew point for the process only, not direct water production)?

2. Is the value empirical or estimated?

3. Does it account for chloride introduced into the system by, for example, maintenance activities?

Grateful to hear your views and experience.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[zdas04]

What is your source of chloride? Water vapor is H2O and nothing else. When it condenses the pH is really close to 7.0 and the TDS is really close to zero.

Distilled water doesn't stay pure very long in the presences of contaminants, but it starts that way and can only acquire those contaminants that are present. If no chloride is present then you can assume zero.

The condensing water will quickly move toward acidic pH by absorbing the H2S, but I don't see a source of chlorides.


David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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[SJones]

EFC 17 assumes that it is 1000 ppm NaCl (about 600 ppm Cl-) in condensing water. Of course, we can all ask where the chlorides come from and you will get as many answers as there are people on the forum - hydrotest water residue, desert sand ingress during maintenance, and so on... I was trying to find out what approach others took if it differs from EFC 17.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[zdas04]

Not to question EFC 17, but I've taken many samples of condensing water and the only rule I can find that stands up to those observations is that the longer the water sits, the higher the TDS will be. But the makeup of the TDS depends on the contaminants that are available.

Most samples I've taken have been in gas that is high in CO2 and the pH has drifted into the acidic region and the primary thing disolved in the water is iron.

Could it be that EFC17 pulled that suspiciously round number from the air and they're just trying to develop a conservative evaluation?

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[SJones]

Highly likely that EFC played it conservative but, for most materials, whether it be 100 or 1000 ppm NaCl, it isn't really going to make much difference. Where it does come into play is when simulated service testing is required to qualify a material as per ISO 15156-3.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[zdas04]

Many of us here in eng-tips.com have participated in writing standards, recommend practices, and industry guidelines--they don't come down from on high graven in stone. The review process is generally designed to keep opinions and wild-ass guesses out of the final documents, but it doesn't always work. Every time I see a number like 1,000, 100, 10, I remember all of the times I've seen engineers substitute 1,000 for "there can be some".

I stand by my contention that condensed water does not have a specific propensity to contain 1000 ppm (0.1%) NaCl. If there is produced water of desert sand in the pipe then my guess is that the result would soar past 1,000 NaCl ppm very quickly.

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem