Pipe Decontamination 3

[SgtMurt]

Hi,
I am currently an intern in a pharmaceutical plant and was asked my expertise on a situation. Unfortunately I didn't have a clue.
The problem is that HCl was being pumped through a large pipe but now the pipe is to be inspected it needs to be completely decontaminated. We tried pumping water through it and measured the pH using a probe but the highest the pH would go was around 3.5. After that the change was so slow we decided to forfeit the idea. Was just wondering why this happens and is there a better measurement than pH to take in the pipe to show when it is clean?

 

[ash9144]

The best way to decon an acid pipe is to blow it clear using nitrogen. Then using full ppe break the line away from the rest of the process and if necessary flush only the section necessary with excess water, at least 12 hours. Then when going back in service you need to dry it out with nitrogen.
By adding water first you have created weak acid which is highly corrosive. I'd recommend you get the line blown clear with N2 asap.

 

[MJCronin]

Sarge..

How big and of what schedule was your "large pipe" ?

What is the material of construction ?

(We all hope that it's not 304 SS sched 10...)

-MJC

 

[moltenmetal]

You're flushing with deionized water which probably already has a pH on the acidic side of neutral. It has zero buffering capacity, hence no ability to neutralize acid. So a little bit of acid trapped in a few stagnant or low spots (hopefully you don't have too many of these in pharma piping) can keep the pH low for a long time.

Is the concern personnel protection, or contamination of the process? Or is there a risk of material damage to the piping itself? (ie. is this piping ordinary austenitic stainless steel, or is it glass- or teflon-lined?). pH 3 isn't all that low from a personnel protection risk perspective.

 

[HEC]

Moltenmetal has hit on a good point, I have personally hit that one too. Flushing a line with DI Water and waiting for pH to come up. We checked the pH of the DI water going in and found it to be the same as pH comming out. Consequently modified the flushing protocol to a minimum number of pipe volumes and to look for change in pH of the flush water not the outlet pH value.

Mark Hutton

 

[SgtMurt]

Thanks a million lads! The problem was to set up a proper SOP for decontaminating the pipe for personnel protection during inspection periods so I suggested the fixed number of volumes idea to the guys and also the possible reasons for the continuous low pH (deionised water) and they seemed well impressed! A few of them may be off to join eng-tips right now!! Cheers for the help!
Martin.

 

[quark]

The better way, and often used in formulation process, (I don't know about API) is to measure conductivity (since water is a polar solvent). The CIP systems use acid/alkali cleaning and measuring conductivity to decide upon the final rinsing stage.