SURGICAL STAINLESS STEEL:
THE DEFINITIVE STANDARDS, SPECIFICATIONS, AND TESTS.
By Cheyenne Morrison, Proprietor, The Piercing Temple,
Cairns, Australia. cheyennemorrison@hotmail.com
INTRODUCTIONIs Surgical Steel safe for use in body piercing? in my opinion yes!, it has been constantly proven by extensive testing to be one of the safest things to use for the purpose of medical implantation. Professional Body Piercers, and manufacturers of body piercing jewellery have an obligation to their customers, to produce, and use only the highest quality jewellery. At present there is very little mention made in any piercing literature of the specific requirements of the production of Surgical Steel for the use of Body Piercing jewellery, and therefore there hasn't been any standards to use as a benchmark of quality.
As Surgical Steel accounts for the great majority of jewellery used for piercing, I have attempted to find the most comprehensive material related to 316L grade Stainless Steel, which is classified for the use of "Surgical" implantation purposes. Hopefully this article will provide the exact details that responsable jewellery manufacturers and body piercers need to determine the quality of the Surgical Steel jewellery they use, or produce.
The bodies internal environment, is unique in it's rapid degradation of many materials previously thought to be unaffected by highly caustic fluids. The pH and Ionic conditions within the human body cause a relatively hostile corrosion enviroment for metals, The severe corrosive environment of the body is largely caused by the presence of Chloride Ions (0.11N, Interstitial Fluid) these Chloride ions have a highly corrosive effect particularly on Stainless Steels.
for this reason the jewellery used for body piercing must be as inert and hypoallergenic as possible. Most metals are not static, durable materials and have been purified above the form found in nature, their natural tendency is to revert to their original form by corrosion and oxidisation. The exceptions to this rule are called Noble metals, they are Gold, Silver, and the Platinum group of metals.
The metals used for body piercing jewellery must conform to the same standards as for use in surgical implantation. They must exhibit a high degree of corrosion resistance, not only because of the deterioration of the jewellery, but also because of the possible physiological effects of harmful or even cytotoxic corrosion products that may be released into the body. There are 250,000 artificial hip and knee operations performed annually in the United States, and this has led to the study of the biological effects of biomaterials, it's a separate branch of science and is referred to as biocompatability.
There are very few metals which meet the criteria required for surgical implantation, the noble metals i.e Gold, Platinum, Palladium etc. resist corrosion altogether, even when alloyed with base metals they still retain their corrosion resistence properties. Other metals such as Titanium, Niobium, and Chromium resist corrosion because they react with oxygen to form a strongly adherant and passivating surface oxide layer which resists corrosion. The majority of materials used for implantation are chromium, Titanium and Vanadium alloys.
It is also imperative that all jewellery used for body piercing, must be highly polished to remove any surface imperfections. Even minute surface imperfections can retard the healing process, by providing a haven for bacteria, and by tearing the inside of the wound and preventing epethelialisation. There should be no visible sharp edges on the jewellery when examined under a microscope at 300 times magnification. And it also must only possess minute amounts of magnetism, because magnetism can attract negative ions into the wound.
ALLERGIC REACTIONS TO SURGICAL STEEL
Allergic reactions to Surgical Steel are rare, but this led to the adoption of either Titanium, or Titanium Stainless Steel alloys being used for Surgical implants i.e. hip replacements. Surgical steel is still in use for things like bone screws, pins, etc.
There have been some statements that the Nickel content of surgical steel (12%), can lead to allergic reactions, however, repeated tests have shown that surgical steel very rarely causes allergic reactions. This is because the Nickel is bonded to the other elements of the Surgical Steel in such a way that the nickel is held within the crystaline structure of the steel, and the Chromium Di-oxide layer prevents any Nickel leaching into the body to cause allergic reactions. However, there are documented cases of allergic reactions to the nickel and chromum content of Surgical Steel.
The Nickel component of Surgical Steel is important for two reasons, firstly, Nickel resists corrosion far better than iron, thus improving Surgical Steel's ability to remain it's integrity within the bodies internal enviroment. Secondly, Nickel is added to the Steel to increase it's strength and toughness, which is important for such body piercing jewellery as ball closure rings, which depend on the tension of the steel ring to hold the ball.
A recent study was conducted on the nickel release from certain grades of Stainless Steel, 316L Surgical Steel patch tests were conducted on 50 Nickel-sensitive patients. The patches were 1.5 centimetres in diameter, and a nickel plated patch was used as a benchmark. the 316L used in the test contained 11.29% nickel. 96% of the nickel-sensitive patients were intolerant to the nickel-plated steel, while no patients showed intolerance of the 316L Surgical Steel.
The classical allergic symptoms are, itching, redness,an intensely pruritic patch with vesicles and secretion of histamine, a clear fluid. In the rare case of an allergic reaction to Surgical Steel it can be replaced with Titanium or Niobium which are totally inert. Be aware however that these metals require even more care in production and are much harder to produce to the standards required for implantation than Surgical Steel.
STAINLESS STEEL: IT'S HISTORY & MANUFACTURE
Stainless Steel is a generic term commonly used to describe a group of Iron-based alloys which exhibit a phenomenal resistance to rusting or corrosion because of it's Chromium content. Chromium has been added in small amounts to strengthen Steel since the Famous Eads Bridge spanned the Mississippi River at St. Louis, Missouri, in 1872. But it was only discovered in the present century that when Iron was alloyed with Chromium in excess of 10%, and Carbon held suitably low, it was effectively rustproof. The term "Stainless" was first used to describe steel cutlery that was produced in Sheffield England in C.1916. In 1913 316L stainless Steel was first patented, In 1926 a Stainless Steel composed of 18% Chromium and 8% Nickel was developed, however this steel still had problems with corrosion resistance. This problem was solved by the addition of 2-4% Molybdenum.
Stainless Steels can be broken down into three main types:
Ferritic:
Ferritic alloys are obtained when Chromium is added to Iron to develop corrosion resistance without steel-type hardening. ferritic alloys are mainly used for construction, and for use in automobiles.Martensitic:
Martensitic alloys result when Chromium is added to steels with carefully chosen Carbon contents, they range from the least expensive and most widely used 410 grade, to 440-C grade which is used for knives and surgical tools due to it's great hardness.Austenitic:
Nickel is the next most important alloying element, the most famous alloy being "18-8" containing 18% Chromium and 8% Nickel. Unlike the atomic structure of ferritic or Martensitic Steels, Austenic Steel has a face-centred cubic form made stable by the presence of Nickel. This gives the Austenitic Steels unique properties of workability, toughness, and corrosion resistance. The Austenitic grades of Steel are the most highly prised for these properties, and also the most expensive.STANDARDS FOR "SURGICAL" STEEL
Some reports in Body Piercing literature state that there is no such thing as "Surgical" Steel, However, there is a certain grade of steel which is used for implantation into the body, or "Surgical" purposes. So we can therefore use the term "Surgical Steel" even though that's not the exact scientific terminology, it's easier to use that term than to try to get the public used to all the other more complex classifications used for it.
316L is the most useful for body piercing jewellery, as it is fairly strong, easy to work with, and will not lose it's corrosion resistance during manufacture Type 316L (L = Low Carbon at 0.03%) 316LVM (Low carbon Vacuum Manufacture), and 317 are the only steels classified for use for surgical implantation.
MANUFACTURER'S CLASSIFICATIONS:
Because there are so many different alloys of steel available on the market, industry groups i.e. SAE (Society of Automotive Engineers) and AISI (American Iron & Steel Institute) have devised a numbering system, 316L is the old version, the new version is 30316L, and this has been superceded by the Unified Numbering System (UNI) which is S31603. But the old version has become almost a generic term and is still recognised by most manufacturers and body piercers, and I will therefore use it here. There are various standards applying to Stainless Steels throughout the world, and several different classifications are used to designate "Surgical"Steel. The most common are listed here.
Manufacturer's Codes
S.A.E. ASSAB SANDVIK 30316L 926L 3R60National Codes
British German Japanese United States new type W.No DIN JIS UNS.No ASTM/AISI type 316S11 1.4404 X2CrNiMo17 13 2 SU316L S31603 316LCOMPOSITION:
There are very specific guidelines for the production of "Surgical" Steel, the one used for the purposes of this article are the American Society for Testing & Materials (ASTM) standards, specifically ASTM F138 (1982) Standard Specification, Stainless Steel Bar and Wire for Surgical Implants (Special Quality).
The term Stainless Steel is a misnomer, these steels are subject to staining and corrosion, although at much lower rates than standard steel. A Chromium content in excess of 10.5% is what makes steel so called "Stainless". The oxidisation of this Chromium content upon exposure to air causes very thin film of Chromium Di-Oxide to form on the surface of the steel. The Film of Chromium Di-Oxide is extremely thin, passive, continuous, tenacious, stable and self-repairable. It renders the surface inert to many chemical reactions and therefore passive, thereby giving stainless steel it's phenomenal built in corrosion resistance, especially in organic enviroments like the internal Human body. The Molybdenum confers a special resistance to pitting corrosion.
The exact Metallic composition of 316L by Heat analysis is:
Chromium 17.00% Nickel 12.00% Molybdenum 2.25% Maximum Manganese 2.00% Maximum Silicon 0.75% Maximum Copper 0.50% Maximum Nitrogen 0.10% Maximum Carbon 0.03% Maximum Phosphorus 0.025% Maximum Sulphur 0.010% Maximum Iron 65.345%* *Approximately the remaining balanceFINISH:
Numerous tests have shown that the corrosion resistance and biocompatability of metals depends greatly on their surface finish. Surgical Steel depends on this because the finer the surface finish the higher the Chromium layer. Electropolishing has been shown to give the most superior finish and highest level of corrosion resistance, this is because it gives a superior surface finish and removes surface contaminants which can cause corrosion. Passivation in HNO3 and conventional sterilisation by Autoclave also improve the surface finish by increasing the Chromium Oxide surface layer on the metal.
It is one of the most important requirements of "Surgical" Steel, that it has the correct type of surface finish. The higher the degree of polish on the surface on the jewellery, the greater is it's ability to resist corrosion, and as the bodies internal enviroment is unique in it's corrosive abilities, it's highly important that proper body piercing jewellery has the ability to resist corrosion. No steel takes a more beautiful polish, and none holds it so well or so long as 316.
The quality of the jewellery's surface finish can signifigently influence it's ability to remain passive within the body, because the jewellery is placed within a wound, the interaction of the body and the metal occur on a cellular level. At this level any small scratch on the surface can damage the very delicate process of scar formation, the jewellery is not static within the wound and this movement excaserbates any imperfections or scratches, tearing away the delicate tissue forming the Fistula around the jewellery.
Because of this the surface of the jewellery should possess no rough edges when examined under a microscope at 300 times magnification, it must be annealed and hand polished three times to a highly reflective lustre, under-polishing will be most evident on the inside of the ring and the tips, where polishing is most difficult. The standards of finish applicable for Surgical Steel are exactly the same for all other forms of body piercing jewellery, regardless of it's shape or metallic composition.
The correct surface finish is achieved be a 3 step process, firstly there is the manufacturing process, followed by polishing, and the final step is passivation. These processes are outlined in more depth below.
THE PRODUCTION PROCESS:
The most common form of Surgical Steel used for body piercing is wire (for use in rings and barbells). Stainless Steel wire comes in a variety of finished forms, the most common finishes being, Cold Drawn, Bright annealed, or Bright Drawn. The term annealed means that the wire has been produced so that it is softer and easier to work with. Ferritic and Martensitic steels are not greatly affected by cold working, but Austenitic grades are greatly strengthened by it.
CD: Cold Drawn Steel is produced by pulling the wire through a plate with smaller holes, until the required wire guage is achieved, it usually has a dull finish. If soap is used to help the drawing process it is also sometimes called SC finish, or Soap Coated annealed wire.
BA: Bright Annealed wire, has a matt appearance and is softer than Cold Drawn or Bright Drawn wire.
BD: Bright Drawn wire is the most commonly used for the fabrication of Surgical Steel jewellery, as it comes with a highly polished appearance, which comes from the process of drawing the wire using oil as a lubricant.
POLISHING:
Once the Jeweller recieves the Stainless Steel from the Supplier it must be polished to a high degree, to remove any surface imperfections from the manufacturing process, and to minimise corosion. Tests have shown that highly polished, mirror type finish obtained by colour buffing results in the optimum amount of corrosion resistance. This polishing is done by a three step process.
Tumbling: can be used to partially polish the jewellery, prior to the final polishing process. Tumbling works to prepare the surface by the constant rubbing action of small ball bearings in a solution rubbing on the jewellery. However it should not be mistaken for a complete polishing process, as it doesn't remove all the surface imperfections from the manufacturing process.
Buffing: Fine scratches from the production process are removed with a clean buffing pad, to which is applied a cutting compound intermittantly as it rotates. The cutting compounds use very fine artificial abrasives (such as Aluminium Oxide) in the neighbourhood of 300 grit size, using stiff grease as a binder. The cutting compounds adhere to the wheel by impregnating the cloth discs.
Colour Buffing: Is performed in the same manner, except that a colouring compound (usually Rouges) is substituted. A varied assortment of compounds for use on Stainless Steel are available, selection is best made by consulting your suppliers.
Cleaning: When the desired final finish has been achieved, the work should be cleaned with a soft flannel buffing pad, using a product like Whiting (Pulverised Calcium Carbonate) or powdered chalk.
PASSIVATION:
A lot of jewellers leave the Surgical Steel used for body piercing at this stage, the surface has been fully polished so that it has no surface imperfections. But that is not the final step in the production process, the jewellery needs to be passivated. Passivation is a process whereby a chemical (Usually diluted Nitric Acid) is used to remove any iron particles on the surface of the jewellery from handling, production and polishing processes.
Nitric Acid is an oxidising acid, which improves the integrity of the passive Chromium Di-oxide layer needed for body piercing jewellery.Detailed examples for this process are laid out in the sources, but in the brief the process is performed in the following way.
Cleaning: The jewellery should be degreased prior to passivation, by the use of a suitable detergant, and should be vigorously cleaned with hot water and bristle brushes immediately after the acid treatment. Ph of final rinse water should be between 6-8 for most purposes. To minimise staining, surfaces mustn't be permitted to dry between phases of the passivation process. Thorough drying should follow the final water rinse.
Acid cleaning (Passivation): Once the jewellery has been degreased, it should be placed in a 20% by volume solution of Nitric Acid (HNO3) diluted with distilled water, and left at room temperature (21-38 C/ 70-100) for 30-60 minutes. Or alternately it can be left in a heated solution at (49-71 C/ 120-160 F) for 10-30 minutes.
Precautions: Nitric Acid should only be used in a well ventilated area, where it can't be handled by unauthorised staff. Glasses, gloves, and an apron should be worn when handling Nitric acid as it is a caustic acid.
Passivation has been shown in numerous tests to improve the corrosion resistance and biocompatability of Stainless Steels. It does this by removing and surface iron particles which can cause corrosion and because it causes a thicker Chromium Oxide layer to form. Winston Revie and green showed that for type 316L passivation in a 30% HNO3 solution at 55 degrees Centigrade for 30 minutes resulted in the same improvement in surface finish as the more complex ASTM F86-68 method.
Source: ASTM F86-68, Recommended practice for surface requirements of metallic surgical implants, Annual book of ASTM standards, part 7, American Society for Testing and Materials, Philadelphia, 1972, 1050.
MAGNETISM:
Surgical Steel should have a very small level of magnetism. The magnetic permeability of 316L in the annealed condition should be approximately 1.02. The degree of magnetism of Surgical Steel can be affected by the type of manufacturing process that is used, inform your supplier that the magnetism must be minimal.
CORROSION RESISTANCE TESTING
The second most important factor in determining Surgical grade steel after the finish, is it's ability to resist corrosion. As stated earlier, the surface finish of the jewellery determines it's ability to resist corrosion, the finer the finish, the greater degree of corrosion resistance. 316L was chosen as the metal for surgical implantation purposes because of it's high degree of corrosion resistance.
What if you are a piercer, and you are buying finished jewellery for piercing? how can you be sure that what you are being sold is truly "Surgical" Steel, and not something of inferior quality? There are two different tests for the corrosion resistance, the Boil Test, and the Copper Sulphate Test. Both these tests should be performed by the responsable Piercer to determine if the jewellery they are using is truly "Surgical" Steel, they can easily be performed by any person without a degree in Chemistry. Alternately, you could look in the Yellow Pages for a Metallurgist, and ask them to run the test for you.
These tests are described in detail in US Military Specification No. GG-I-526b, and The International Standards Organisation (ISO) draft No. DIS-7151. But in brief, they can be conducted as follows.
THE BOIL TEST
The Boil Test requires that the jewellery should be scrubbed using soap and warm water, rinsed thoroughly in hot water, then dipped in 95% Ethyl Alcohol. It should then be in boiling distilled water, in a glass or ceramic beaker for at least 30 minutes, and subsequently allowed to cool in the distilled water.The Military Specification requires that it be cooled in the distilled water for 24 hours, at which time it should be examined. ISO requires that the metal be removed from the distilled water after boiling for thirty minutes, then remain in air 2 hours prior to examination.
In the interpretation of the test, the ISO draft states "The instrument shall be wiped with a dry cloth, and inspected for visible signs of corrosion. Any blemish not removed by vigorous hand rubbing with a cloth, shall be considered evidence of corrosion.
THE COPPER SULPHATE TEST
This requires the immersion of the jewellery in a chemical solution consisting of Copper Sulphate (CuSO4-5H20) 4g, Sulfuric Acid (H2SO4) 10g, and distilled water 90ml. The jewellery should be thoroughly scrubbed with soap and water, followed by immersion in 95% Ethyl Alcohol. It should then be immersed in the Copper Sulphate solution for 6 minutes at room temperature. The Copper Sulphate solution will react with any free iron on the surface of the jewellery, and plate out copper on them, any reddish discolouration of the surface indicates that the composition of the metal is not of a surgical grade.
A HOME MADE TEST:
For piercers who don't have the means necessary to use the above mentioned tests, or for members of the public who are uncertain of their jewellery quality; there is a cheap and quite reliable method of comparing the quality of different types of jewellery.
Wrap one end of the jewellery with a small piece of Scotch tape, making sure that it adheres tightly. Leave the jewellery for 24 hrs in a glass of room temperature tap water. Remove after 24 hrs and allow to stand on a piece of paper towel, don't dry it just allow it to dry naturally. After another 24 hrs remove the scotch tape and examine the jewellery, any blemishes or discoloration should be able to be removed by lightly rubbing with a polishing cloth. If there is any difference between the two areas, pitting, discoloration or blemishes that can't be removed by a ligt polish then it's fairly certain that it's not proper Surgical Steel. This method is only a rough guide, if your uncertain about your jewellery then you owe it to yourself and your customers to get it checked out using a metallurgist or use the other methods I've described above.
SOURCES:
The American Society for Testing and Materials provides standards for the production of Surgical Steel. The main standard which should be examined is: ASTM F138 (1982) Standard Specification Stainless Steel Bar and Wire for Surgical Implants (Special Quality). It describes the complete specifications for the manufacture of Surgical Steel, and the other standards applicable to Surgical Steel, which are:
A 262 : Recommended Practices for Detecting Susceptability to Intergranular Attack in Stainless Steels 2.
A 484 : Specification for General Requirements for Stainless and Heat-resisting Wrought Steel Products (Except Wire) 3.
A 555 : Specification For General requirements for Stainless and Heat-resisting Wire 2.
A 751 : Methods, Practices, and Definitions for Chemical Analysis of Steel Products 2.
A 45 : Recommended Practice for Determining the Inclusion Content of Steel 4.
E 112 : Methods for Determining Average Grain Size 4.
F 361 : Practice for Assessment of Compatability of Metallic Materials for Surgical Implants with Respect to Effect of Materials on Tissue 5.
2.2 American Society for Quality Control (ASQC) Standard C1- 1968 : Specification for General Requirements For a Quality Control Program 6.
2. Annual Book of ASTM Standards, Vol 01.03.3.
Annual Book of ASTM Standards, Vol 01.05.4.
Annual Book of ASTM Standards, Vol 03.03.5.
Annual Book of ASTM Standards, Vol 03.056.Available from American Society for Quality Control, 161 W. Wisconsan Ave. Milwaukee, WI 53203
ASTM Standards are available from The American Society for Testing and Materials, 1916 Race St., Philadelphia, Pa. 19103.
American Society for Metals, "Metals Handbook, Properties & Selection: Irons and High Performance Alloys" 10th Edition, Vol 1, 1990
A Submission on Body Piercing, For the Sub-Commitee on Body piercing, of the Skin Penetration Act Review Committee, Queensland Health Department, Australia. Cheyenne Morrison, Proprietor of The Piercing Temple Cairns Australia. 1995.
ASTM A 380. Recommendations and Precautons for Acid Cleaning of Stainless Steel.
ASTM F 138. (1982) Standard Specifications for Stainless Steel Bar and Wire for Surgical Implants (special Quality)Australian Stainless Referance Manual 1996. Edited & Published by The Australian Stainless Steel Development Association, Level 12, GWA House, 10 Market St, Brisbane, Qld, Australia
Atlas Steels Melbourne, Australia). Technical Note #5, September 1995
British Standards Institution. Hospital Equipment Guide to British Standards. (Current)
Byrd, D.H. (1973) Preventing Spotting of Surgical Instruments. AORN Journal April 1987
Corrosion Resistance of Surgical Instruments, Gary Hamman, Metal Progress, May 1985
Defence Personnel Support Centre. Index of Federal Specifications & Standards (Current).
Available from The Superintendant of Documents, US Government Printing Office,Washington DC 20402Defence Personnel Support Centre.
Current Federal Specifications for various surgical instruments.
Newsletter of Biomedical Safety & Standards (monthly). Quest Publishing Company, 1351 Titan Way, Brea, CA 92621. USA
Nickel release from 304 & 316 Stainless Steels in synthetic sweat. Comparison with nickel and nickel-plated metals. Consequences on Allergic Contact Dermatitis. by P.Haudrechy, J. Foussereau, B. Mantout, and B. Baroux, Corrosion Science, Vol 35, nos 1-4, pages 329-336.
Selection & care of Surgical Instruments, in Clinical Science for Surgeons, 1981 EditedBurnett, Butterworth.Technology for Surgery.
Monthly Technical Report. ECRI, 5200 Butler Pike, Plymouth Meeting, PA 19462, USA.
"Stainless Steel" R. A. Lula 1985.
Diem, K & Lentner, C Eds. "Documenta Giegy-Scientific Tables" 7th Ed, CIBA-GEIGY, Switzerland 1973, 523.