Kealan Allen The answers to these questions are difficult to predict or to give from direct users' experience. However, data information on use of dilute HCL, Methyl Choloride, ammonium chloride and the effect of these chemicals may help you ( i guess) Dil HCL: Effect on S.S 316 L / 317 L is too well known . Pitting and SCC will occur after some years. There is no doubt on this. Methy Chlroide : Long term effect on S.S. 316 L / 317 L will develop / have pitting and SCC. Ammonium Chloride : Transfer to another S.S 316 L vessel : will also develop / get affected with pitting and risks of SCC. For Ammonium Choloride < 10% concetration, the risks may be lower at lower temperatures S.S. 316 L may take longer time to pit. For all three intended and used chemicals in your plant, your potential risks of pitting / SCC are high for continued use of S.S 316 L or S.S 317 L on a long term basis. If you have not experienced any damaging so far, with S.S 316 L or S.S 317 L usage, i suggest that you may restrict further usage (it is worth) instead of continued usage with these corrosive chemicals. Alternatively, you can think / consider some other chemical cleaning approach for this pharmaceutical process . From long term alternative, if cost is not a problem to change metallurgy and if this particular process pharmaceutical operation allows, i think you may go for a better alternative material selection - if the present use of chemicals are the only solution for effective cleaning in this particular pharmaceutical process system. Information given above is based on data input and experience of the materials for specifica corrosive environment . Direct industry users and their experience - if some users can share may help you to understand on the problems faces in similar industry users. Trust this is of some help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India August 09, 2005 E-mail:nishi@vsnl.com >I am working with pharmaceutical cleaning applications - I >have developed a cleaning method for one particularly >difficult process using a 1.4% (weight) solution of HCl in >Methanol. This is currently used in glass lined vessels, >and this solution is the only one which will effect >sufficient cleaning - but due to process changes, this >process will be run in 316 and 316L SS vessels. The >original cleaning operation uses pure methylene chloride. > >The cleaning involves refluxing the solution for a minimum >of an hour, (this is carried out approximately once per >month). I presume we are going to cause stress corrosion >cracking under these conditions. Can you suggest some way >to avoid this - it may be possible to reduce the HCl >concentration to approximately 0.5%. Can you suggest any >laboratory work which your company or similar operators can >carry out to determine the risk of corrosion under these >conditions. > >Is it possible that we are already damaging our vessels with >the methylene chloride we are using? > >Finally, after this operation, the MeOH/HCl mixture is >neutralised with NH3 and sent to a stainless storage vessel >– is there a risk from these low concentrations of ammonium >chloride in stainless vessels? > >Thanks you, >Kealan Allen >kallen13@jacie.jnj.com