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Frequently Asked Questions

In order to provide the most accurate quotation we would need the following information at a minimum:

  • Print/Drawing with dimensions listed.
  • Part weight
  • Standard being requested – If you are looking for a specific standard please let us know, otherwise parts will be quoted to standard commercial specifications such as ASTM A380 for pickling, ASTM A967 for passivation or ASTM B912 for electropolishing.
  • Material Alloy – It is important to know the material prior to the process as small details of the process may change based on the stainless steel alloy (i.e. 17-4, 304, 440C)
  • Packaging requirements - EMI offers special packaging but this must be communicated otherwise all parts are packaged as received. Please see our Specialty Packaging page for more details.
  • Dimensional Requirements - We can control the removal of material through the electropolishing process down to .0001" but there are standard total removals of .0005”-.001” through our typical processing parameters. Items such as springs can lose load strength if too much material is removed so we can control this and take as little as possible while still achieving a fully polished and passive piece.

Electropolishing typically removes .0005”-.001” total material from the part after electropolishing but can be controlled down to most minimal of removals. However, electropolishing is not a milling procedure capable of removing .005” of material. For removal of excessive material we recommend a different process.

Passivation and pickling do not typically remove any recordable material from the surface through the process.

Although the processes will remove some discoloration they are not meant to remove heavy rust and corrosion. The pickling process is a descaling bath designed to remove free iron, heat tint, weld scale, etc. Items with heavy rust concentration can actually contaminate our baths so it is recommended to perform a preclean process such as deoxidizing or blasting to remove heavy rusts prior to the processes listed above.

No. We must have ample space to perform polishing on the interior surface of vessels and tanks. In order to achieve a polish on the inside surface we must add auxiliary cathodes to the space in order to get the proper throwing power for the EP process to take place. In some instances, such as with closed end vessels or tanks with only small openings we do not have the space to apply the proper racking or let the part outgas as the process requires which results in a less than optimal finish. Generally you can expect the electropolishing to reach into interior surfaces as far as the opening is wide. If you have a 1” fitting, without adding cathodes to the interior space, you will get an EP finish 1” down into the cavity.

We can electropolish just the inside or just the outside of your parts depending on what your needs are. If you are looking for an interior surface polish only on a tank or vessel we can provide that.

We cannot pinpoint a feature and electropolish only that feature unless the part is maskable everywhere else. A better candidate for this would be electrochemical machining.

Electropolishing is a process utilizing a DC current to dissolve the material slowly and evenly off the part attacking the peaks first creating a smooth passive surface. This process leaves a chromium rich oxide layer on the outside of the part creating an aesthetically pleasing piece as well as a passive piece.

Passivation is an immersion process that attacks the free iron on the piece leaving you with a clean oxide rich layer that will resist corrosion by protecting the parent material.

Electropolishing has been dubbed the superior form of passivation but more and more engineers are calling out for an electropolish process followed by a passivate process to remove any additional free iron still remaining after the electropolish process.

We utilize several different methods of testing to confirm the passivity of the part after processing.

  • Copper Sulfate - spot test seeking out any free iron in the testing area. If the part has any free iron remaining the copper will plate out. If the part is passive and clean there will be no reaction.
  • Salt Spray – Salt spray per ASTM B117 subjects the parts to corrosion inducing stresses for a specified amount of time. Any corrosion after the salt spray process constitutes a failure. No corrosion after the test represents a fully passive piece with no free iron present.
  • High Humidity – Similar salt spray the parts are subjected to a certain humidity at a specified amount of time.
  • Water Immersion - This test mimics a corrosive environment and promotes corrosion at an accelerated rate. The parts are subjected to immersion in water for one hour followed by one hour drying for a period of 24 hours. Any corrosion or spotting constitutes a failure. No corrosion after this test represents a clean passive piece.

Stainless steel is called stainless because of the oxide layer that protects it from environmental stimuli. This is a naturally occurring oxide layer that is formed once the stainless surface reacts with oxygen. The goal of our processes is to take this oxide layer to its maximum potential. With that being said, the parts are not protected forever as some would believe. Environmental stimuli such as high humidity, temperature fluctuations, corrosive material or air can deplete the passive layer resulting in corrosion if the parts are not maintained and cleaned properly. Cleaning stainless steel with bleach or other strong chemicals can attack the passive layer and render it useless over time as well so it is important to make sure and rinse any corrosive materials from the piece once in service.

EMI offers industry leading turnaround times for all processes offered.

Pickling/passivation – 5-7 days

Electropolishing – 7-10 days

Media blast, oxygen clean – 7-10 days

We also offer expedited services such as same day, next day or 2nd day line interruptions. Typically, we are the last stop of the manufacturing journey and by the time the parts get to us they are already behind due to previous steps so we can keep you out of trouble with your customers and get them the parts they need when they need it. We pride ourselves on our lead times and quick turnarounds. If you need something in a pinch, EMI is the place to call for your finishing.

We do offer pickup and delivery in the Chicagoland area for a fee of $75.00.

Here at Electro-Max, Inc. we run hundreds of different specifications from standard commercial ASTM specs to customer specific specs with special requirements. In the quoting phase we will review the spec to see if we can provide the service as the spec calls out. If we are able, this spec will be added to our approved spec list and a process master will be developed and loaded into the system for any future work that calls out that specification. If we cannot meet the requirements of the specification we will not quote the job or request a deviation approval. Please check our standards page for more information.

Passivation alone will not affect the overall surface finish and will not remove heat tint or any other strong scales. This will require a preclean such as pickling or blasting. Pickle will get you a soft, satiny matte finish. Electropolish will remove some light weld scale or heat tint.

Do you have questions?
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