Argo Float Druck Pressure Sensor Micro-Leak Problem and Warranty Replacement

We have been working to understand the details of a problem with the Druck pressure sensors used in SBE 41 and SBE 41CP CTDs on Argo floats. The problem is called Druck micro-leaks because, in 3 cases over the last two years where sensors were recovered, it was determined that oil was leaking out of a sealed inner sensor chamber through micro-cracks in glass-to-metal seals at the back of the sensor. The oil leak rate is very slow, just a few micro-litres per month. As oil leaks, a flexible titanium diaphragm, that transmits ocean pressure to the oil chamber, deflects into the sensor chamber to make up for the oil loss, and as a consequence, the sensor develops a progressive negative offset in measured pressure. This becomes evident in Argo data as a negative surface pressure. With enough oil loss the diaphragm deflects inward far enough to contact and short out the pressure sensing element. There is evidence that the diaphragm bottoms out and does not result in a further leak of oil or ocean water through the sensor.

We welcome your questions and will do our best to answer them completely.

Sea-Bird's warranty policy is dependent on whether the float has been deployed or not:

• Case 1: Floats that are not yet deployed --
  Please return these CTDs/floats. Click here for instructions.

• Case 2: Floats that are deployed --
  Sea-Bird will provide information (in the near future) on how to recognize the micro-leak problem through an analysis of the float's pressure data. If Sea-Bird agrees that the pressure sensor data indicates a micro-leak problem, we will issue a certificate to the user for a free CTD for use on a subsequent float.

• Case 3: Floats that are not yet deployed, but which must be deployed --
  If you must deploy these floats because of substantial commitments, Sea-Bird will treat these in the same manner as floats that have been deployed (Case 2). 

• Sea-Bird Notice 1 (4 May 2009): Problem with SBE CTD Pressure Sensors on Argo Floats, Recommendation to Stop Float Deployments and Return CTDs to Sea-Bird for Repair
• Sea-Bird Notice 2 (2 March 2010): Request for Help from the Argo Data Management Group
• Sea-Bird Notice 3: (coming soon)
• Other links:
  Argo home page on University of California at San Diego website
  International Argo Information Center home page on JCOMMOPS website

Last modified: 26-Apr-2010

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