Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

FDA Stainless processing

FDA Stainless processing

FDA Stainless processing

We are making parts for others, this will be used in food service (dispensing.) This piece is AISI 304, but what after processing must be done? We grind/lap to finish size so do we must passivate afterwards? Anything else to do?

RE: FDA Stainless processing

Thorough cleaning and passivation is all that is normally required.
The most common stainless use in food contact is AISI 316 SS due to it better resistance to organic acids and somewhat better tolerance of Chlorine containing cleaners.

RE: FDA Stainless processing



YOU WILL ALSO FIND ADDITIONAL INFO EG; Carbon and stainless steels coated with the AgION™ antimicrobial compound from AK Coatings, a subsidiary of AK Steel, suppress the growth of bacteria, molds, fungi and other microbes.

RE: FDA Stainless processing

Probably the most important standard legalwise for US food equipment is NSF/ANSI No. 2 Food Equipment which you can purchase via SUPSHIP's link above.

ASTM has some standards on Food Service Equipment in Annual Book of Standards vol. 15.08; see  Table of Contents at http://www.astm.org/cgi-bin/SoftCart.exe/BOOKSTORE/BOS/TOCS_2005/15.08.html?L+mystore+wkpo1039+1132124306
Enter a standard number, e.g., F1604 (for ice cream makers & dispensers), at www.astm.org for an abstract of the standard. Note that it references 2 standard sfor SS material:
ASTM A167 Specification for Stainless and Heat-Resisting Chromium-Nickel Steel Plate, Sheet, and Strip
ASTM A176 Specification for Stainless and Heat-Resisting Chromium Steel Plate, Sheet, and Strip

I'm not sure whether these ASTM standards have been legally adopted or incorporated into the NSF/ANSI document.  I do know that SS food handling equipment is sometimes electropolished and always passivated, and that the large pharmaceuticals Amgen & Baxter International, with even higher standards, have literally acres of electropolished and passivated 316 & 316L within their plants.

Other publications of general and/or international interest on selection, fabrication and surface finishing of SS for food and drinking water:

The Nickel Institute has many useful, free publications on stainless steels.  www.nidi.org
They also have a Hygienic Stainless in Food & Beverage website at www.hygienicstainless.org

A discussion of the European guidelines (see EHEDG below) on materials and construction of equipment for food use of general interest at http://www.nickelinstitute.org/index.cfm/ci_id/10818.htm  
Some relevant passages [note agreement with unclesyd's comments above]:

Re Surface Finish:

“According to EC Directive 98/37/EC, machinery can only be regarded as having been hygienically designed and constructed if those components which are to come into contact with the product can be cleaned before initial use and then, by applying an appropriate cleaning and disinfection programme after each use, restored to an acceptable level of cleanliness, economically and in a reasonable time...
Essential to cleanability is a superior surface finish...

Moreover, whilst some proprietary polishing techniques produce a clean-cut surface others produce a damaged surface containing micro-cavities, tears and laps which can be difficult to clean.  So the current European steel supply standard EN 10088-2: 1995 calls for "transverse Ra < 0.5 μm with a clean-cut surface". However, the Ra value alone can be misleading.

For some years, an Ra value of 0.8 μm or less has been seen as acceptable for food processing plant, but cleaning efficiency is strongly influenced by the way it is performed and EHEDG Document No. 17 "Hygienic design of pumps, homogenisers and dampening devices" recognises that higher washing liquid velocities may allow surfaces with a roughness of up to Ra = 3.2 μm to be cleaned acceptably.

Electro-polishing can typically reduce the roughness by half by reducing peaks and rounding them off, and a similar effect can be achieved on stainless steels by new post-rolling brushing processes which leave a super-smooth surface that can often be cleaned without physically- or chemically-aggressive detergents.”

[Re materials of construction]
“stainless steels of the austenitic 18%Cr-10%Ni AISI 304 type as these will, in the majority of environments meet all these requirements very well.

But chloride levels may be high in supply waters, in heating, cooling, or process fluids, in detergents and sanitising agents (some of which are based on sodium hypochlorite or organic chlorine donors) and in the brines widely used as refrigerants.  And, of course, the food product itself very often also contains sodium chloride.  In this case, one of the 17%Cr-12%Ni-2.5%Mo AISI 316 types (see Table 1 below) may be specified.  Given tensile stresses and chlorides and a processing temperature above about 60° C, there may be a risk of stress corrosion cracking, to which the solution may be a duplex or high alloy grade such as 23%Cr-4%Ni or 22%Cr-5%Ni, or super-stainless steels such as those containing 6% Mo, or even special alloys with nickel contents of up to 33%.

...For their greater hardness and therefore wear-resistance the 1.4021-grade martensitic steels, whilst less corrosion-resistant, are commonly employed for knife blades or cutters.  But for fish preparation knives, where both hardness and better corrosion resistance are required, grade 1.4122 may be appropriate.”

The European Hygienic Engineering and Design Group (EHEDG) has 31 guideline documents covering matters such as the welding and passivating of stainless steels, the hygienic design of equipment, and methods for testing whether equipment complies with these criteria.
The English versions of the EHDG Guidelines can be purchased (£30 apiece) at http://www.campden.co.uk/publ/PUBFILES/ehedg.htm  

A few that seen most relevant:
No.8  Hygienic equipment design criteria (second edition) (13 pages)
No. 9  Welding stainless steel to meet hygienic requirements (19 pages)
No.18  Passivation of Stainless Steel
(11 pages).[/b]

Other language versions can be reached here: http://www.ehedg.org/  

A British standard OPERATIONAL GUIDELINES AND CODE OF PRACTICE (OGCP) FOR STAINLESS STEEL PRODUCTS IN DRINKING WATER SUPPLY – DWI Application 56.4.47 is free at http://www.euro-inox.org/pdf/map/GuidelinesDrinkingWater_EN.pdf

It gives selection of SS grade according to the chloride concentration in potable water systems:

“Subject to the requirements for good design and standards of workmanship, type 1.4301 (304) grades may be used in most flowing water systems where chloride levels are less than 200 ppm (at temperatures normally encountered in drinking water supply and treatment)....

The molybdenum-containing type 1.4401/4436 (316) grades, with their higher resistance to pitting and crevice corrosion, may be used for waters with chloride levels of up to 1000 ppm...

For chloride levels up to 3,600ppm, alloy 1.4462 (2205), super austenitic and super duplex grades can be used. For 3,600-26,000ppm (sea water) then super duplex and super austenitic grades are more appropriate.”

Surface finish is covered rather briefly; it refers to ASTM A 380-99 for cleaning and passivation of stainless steels.  Also,
“For certain, principally hygienic, requirements, a finer mechanical polish followed by electro-polishing is appropriate.”

RE: FDA Stainless processing

Thanks, we order standards from NSF today. Maybe get EHEDG too for comparison.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close