dubey Senior Member Joined: 17 Apr 2014 Posts: 2 Location: PL Expertise: Professional
Posted Thu Apr 17, 2014, 5:15am Subject: La Marzocco Linea MP-2 - water eating through stainless steel!
Hi guys! Fourth year of using La Marzocco Linea MP-2 (mechanical paddle) in cafe. Previous three years with no problem working on basic Faema (copper boiler and tubes). With La Marzocco (stainless steel boiler and some of the tubes) we are experiencing problems with water which led to espresso boiler change - previous was eaten from the inside by water - leaked on seams so much we couldn't fix it. Until begining of the year we were using regular water filtered by dedicated Brita (earlier Water+More) filters. Water was tested at 360 ppm straight from tap and 330 after Brita filtration. pH was 6.5-6.9. No we are runing RO with bypass (bypass consists of three stages: 20 micron filtration/coal/5 micron filtration). It gives ppm of 150-180 (we can go as low as 40 ppm with RO only) and same pH. Since RO introduction in January we had to service espresso machine once again - head groups started to leak, after disassembling parts made of stainless steel were already eaten through a bit (parts made of copper were ok...). In grup head - after removal of top element - there was reddish/rusty mud. Do you have any ideas/recomendations for further investigations into the problem? Iron, chloride and chlorine content testing? Thanks! dubey
billc Senior Member Joined: 15 Jan 2009 Posts: 135 Location: Seattle, Washington Expertise: Professional
Espresso: CC1 - GS - GS3 - GB5 Grinder: Baratza - Mazzer-Marzocco Drip: My own Creation
Posted Sat Apr 19, 2014, 6:44pm Subject: Re: La Marzocco Linea MP-2 - water eating through stainless steel!
When using RO are you adding anything? The material for the boilers is either 304L or 316L depending when it was made. The usual issue is chlorides. While the boilers are made with low carbon stainless (L) there are still some carbon atoms present. chlorides can interact with e carbon (I will let a chemist add the proper words) and disolve the cause the carbon atoms to go into solution. If there is enough concentration of carbon there is a possibility it could lead to a path to the outside. When this happens precipitates can build up and cause additional leakage. This is usually why you might see a drop of water outside of the boiler shell. Additionally there are some problems associated with the weld area (heat affected zone or HAZ) that can cause addional carbon to be present in this area.
The stainless is not really concerned with the pH of the water or to total dissolved solid count. It is the type of solids in the water and if there are anions present (normally in the form of chloride).
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