I have installed remote seal level transmitter in 33% HCL service (Rest water) with diaphragm material: HASTELLOY"C". But after 6 months, diaphragm was shaped in convex shape. Please tell me what may reason of failure of diaphragm?

Is Hastelloy "C" material is suitable for 33% HCL?

If any guide line to us correct procure diaphragm material in 33% HCL service.

 

you need to investigate the failure in more detail.

you have made no mention of corrosion, only the the diaphragm is bulging outward. That seems to imply that the filled system is intact.

1. was the filled system diaphragm properly evacuated during manufacture?

2. any evidence of leakage

3. convex bulging seems to imply excess pressure from the sensor side not the process.

4. fill liquid?

5. Temperature and pressures involved.

6. ambient conditions

7. is heat tracing used? et., etc.

 

If you had looked up a corrosion chart, of which there are many, you would find that Hastelloy C is not recommended for HCL. You can use Hastelloy C276 (which is a different alloy) or you can use Tantalum. Both are suitable for the service up to 38% aqueous. This advise does not constitute engineering and you should do your own investigation.

Walt Boyes, FInstMC, Chartered Measurement and Control Technologist
Life Fellow, International Society of Automation
Editor in Chief, Control and ControlGlobal.com
[email protected]

 

Changing your transmitter out with a teflon coated chemical seal will solve your problem.

Always look up the chemical charts to see which materials are corrosive resistant against which chemicals. Your supplier can supply your chemical seal in what ever diaphragm material you require so keep him in the loop and get his advice in special applications like these.

 

Thanks for response,
Sorry but We used Hastelloy C276. C276 is suitable or not for 33% HCL.

 

Answers:

1. No type corrosion seemed from outside. Only bulging of diaphragm seemed.

2. No leakage was observed from diaphragm.

3. Filled liquid is silicon

4. Pressure is: close tank height:5 meter
Temp : MAX 50 Degc

5. We are using silica gel on roof of tank to vapor out.

6. Ambient condition: 27 degc Temp

7. Punctured Diaphragm material: HASTELLOY C276

Please advice to me is problem in diaphragm MOC or any problem. We have checked data in engineering books and find Diaphragm HASTELLOY C276 is suitable UP TO 38%HCL. Please advice further.

 

A bulged out diaphragm is the condition that appears from hydrogen ion migration, when hydrogen ions on the process side pass through the diaphragm and recombine into hydrogen gas on the fill fluid side of the diaphragm.

I've read warnings about the high nickel content of Hastalloy C276 and Monel being especially conducive to hydrogen ion migration.

Gold plating the diaphragm has been used to prevent hydrogen ion migration. I don't know if your bulging diaphragm is due to hydrogen ion migration or if gold plating can remedy that in HCL service, but corrosion is pits and cracks and oxides and whatnot, it's not bulging.

 

Pressure is: close tank height: 5m
Temp: MAX 50 DegC
Ambient: 27 DegC
Punctured Diaphragm material:HASTELLOY C276

punctured diaphragm but no leakage, interesting

a. the chemical seal in contact with the process is assumed to be part of a filled capillary installation that pressurizes the transmitter which may have it's own internal diaphragm.

b. assuming that you have a tank at atmospheric pressure and the transmitter is used for level indication.

c. repeating an earlier question, convex bulging implies bulging outward into the process.

If that is the case, then the filled system is being pressurized beyond that when exposed to the liquid level.

Rather that preoccupy yourself with the many mysteries of failure, replace the transmitter Hast. C276 is fine, it could have been damaged in shipment or during installation.

 

Sir,

We are using tantalum, but it works only for 1-1.5 years, and after that diaphragm bulging problem starts. Please suggest?

 

A diaphragm of Tantalum is not very expensive, I spec them all the time for Sulphuric Acid 40%
Gold plating, I haven't seen one but the amount of material is very small.
Is it possible the acid is more concentrated than you think through evaporation?

 

You are correct tantalum although expensive does not cost much for a thin diaphragm. A 33% solution of HCl is normal at STP. Sulfuric Acid will increase concentration when the H2O evaporates.