PROCEDURE For most vessel polishing, the plate and heads should be pre-polished prior to fabrication. The exceptions to this will usually be related to either the size of the vessel, the thickness of the plate or a weld overlay application. With small vessels (6'D and smaller) that are not ordered in large quantities, it usually has little or no financial benefit to pre-polish. With clad vessels, the backing is sometimes so thick that the companies who perform pre-polishing won't have a machine capable of doing work. With weld overlay vessels, the metal removal with mechanical polishing almost becomes a visual task that has to be determined as the grinding is taking place. Some areas will require more metal removal than others. Besides this, the plate backing is usually fairly thick in these applications. Pre-polishing will usually be bought to a #3 or #4 finish. These are architectural finish terms used to describe an 80 to 120 grit or 150 to 180 grit finish. Sometimes a plate manufacturer may only polish as high as a #3 finish. It would probably be best in this case to work with your mechanical polishing or electropolishing vendor to determine if the plate should be sent for additional pre-polishing prior to fabrication. On 95% of the vessel job performed by Fin-Tech, the plate is pre-polished to a 180 grit finish. Polishing to the customers final specification is not wise because the surfaces will be damaged during fabrication and will ultimately require more polishing. when hiring a vendor to polish a vessel, whether it be mechanical polish or electropolish, the bottom line is that you are handing the vendor total surface finish responsibility. In other words, you can't allow the vendor to have any reason to blame you're pre-polished finish for his poor workmanship. This is much more likely in an electropolish application but could happen in either case.