Stainless Steel Electrical Conduit & Fittings FAQ

Selection of a stainless steel alloy for a job is dependent on optimizing cost vs. performance based on the service environment and available products. Gibson Stainless supplies products for use in many different industries. Here are some examples of preferential alloys based on general service environments in the given industry. Contact the factory if you have specific questions on the preferable grade for your application and for pricing and availability.

• Food & Beverage Processing Facilities – dairy and vegetable processing environments are generally milder and 304 stainless is often sufficient; breweries and facilities processing meats, sauces, pickle liquors, etc. are often better served by the use of 316 stainless;
• Pharmaceutical Industry – generally 316 stainless is the best choice in these uses;
• Oil & Gas – 304 may be sufficient for use in oil and gas drilling and processing, but if the facility is located in a coastal or marine environment, 316 stainless is recommended;
• Pulp & Paper Mills – 316 stainless is recommended for these severe environments;
• Water & Sewage Treatment – 304 stainless if often sufficient for these environments;
• Marine & Coastal Applications – 316 stainless would be preferred for use in or near salt water;
• Heavy Industrial & Chemical Processing – 304 or 316 stainless could be used depending on the chemicals present in the environment; please contact the factory for assistance specifying an alloy, if necessary.

Gibson Stainless provides electrical conduit and some fittings in two different stainless alloys; these alloys are most commonly referred to by their American Iron & Steel Institute (AISI) designations, which are 304 and 316.

AISI 316 stainless steel has a higher nickel content and benefits from the addition of molybdenum as an allowing element. These tweaks to the material chemistry give 316 stainless enhanced corrosion resistance with better protection against the initiation of pits/pitting and crevice corrosion, especially in environments where chloride levels are elevated. These chemistry changes, however, also increase the cost of 316 stainless as compared to 304. Therefore, end users need to balance the need for enhanced corrosion performance with project cost.

For more information about molybdenum and its uses in stainless steel, you can visit the International Molybdenum Association website.

304L and 316L are enhanced chemistries of 304 and 316 stainless that contain lower levels of carbon. When stainless steels are subjected to very high temperatures and/or localized hot work, such as welding, chemical reactions can occur that reduce the metal’s resistance to corrosion. During these reactions, carbon “consumes” chromium, forming chromium carbides. This sensitization, or carbide precipitation, causes the level of chromium remaining in the alloy to drop below the 11% needed to sustain the spontaneously-forming passive oxide layer on the surface. Consequently, for applications where stainless steel is intended to be welded or where it may be subjected to very high temperatures (e.g., 800°F - 1650°F), designers and end users should employ a low carbon version of 304 and/or 316 to provide the best corrosion resistance.

For additional information about 304 stainless, you can visit this product data sheet from ATI.

For additional information about 316 stainless, you can visit this product data sheet from ATI.

CF8M is the cast equivalent of wrought AISI 316 stainless.

Stainless steels are generally non-magnetic in the annealed, fully austenitic condition. Both 304 and 316 stainless alloys offered by Gibson are austenitic and therefore exhibit little to no magnetism. However, heavily cold-worked material and stainless steel castings can exhibit slight magnetism. This slight magnetism alone is not an indication of a material defect.

Note: Ferritic and martensitic stainless steels are generally magnetic.

Many trade organizations and societies provide additional resources that explain how stainless can help with your project and provide technical data to help address questions you may have. Some resources you may want to explore include:

• The Nickel Institute provides resources regarding architecture, building and construction using stainless steel. You can also visit their Knowledge Base to search for technical literature.
• The Specialty Steel Industry of North America has many resources regarding stainless steel production, application, performance and cost.
• The International Stainless Steel Forum

All of Gibson Stainless’ products are designed to meet and exceed industry and UL standards. Gibson Stainless is constantly working to improve its product line. The following product lines are UL Listed and others may be pending UL approval.

• Conduit
• Elbows
• Couplings
• Conduit Bodies
• Device Boxes
• Device Box Covers
• GUA Series Hazardous-Location Conduit Bodies
• Ground Rod Clamps
• Type 304 SS Ground Rods

For more information on UL Certifications, click here.

Currently, our GUA series hazardous-location conduit bodies carry a Type 4X rating.

NEMA Type ratings are applied to electrical enclosures, as summarized in this NEMA document. The purpose of the Type ratings is to provide a characterization of an enclosure’s ability to protect personnel from the contents of the enclosure and to protect the equipment in the enclosure from the environment outside, as well as to ensure overall quality of the part. Fittings intended to be installed with an enclosure may also carry a NEMA Type rating to indicate that the assembly will provide at least an equivalent level of protection as the standalone enclosure. The fitting rating is required to be equal to or greater than the rating applied to the enclosure to maintain an overall rating equal to the enclosure rating.

In the spirit of the rating, our conduit and our fittings do prevent ingress of large, solid foreign objects into the raceway and will perform, undamaged, should ice form externally on the raceway. Our conduit and some of our fittings, like other standard, rigid conduit systems, are not designed to be completely watertight and may or may not prevent the ingress of water.

NEMA establishes ratings for enclosures in NEMA 250; these ratings can be self-deducted by the manufacturer. All of Gibson Stainless’ products are designed to meet and exceed industry standards, and Gibson Stainless is constantly working to improve its product line. At any given time, other product lines may be undergoing testing to determine NEMA type rating. Contact the manufacturer for additional information.

For more information on NEMA ratings, click here.

Enclosures are assigned an IP (International Protection) Code to signify the degree of protection they provide against ingress of solid foreign objects and water and against access to dangerous parts inside the enclosure. International Electrotechnical Commission (IEC) standard 60529 contains the guidance for assigning an IP Code to an enclosure, which consists of the letters “IP” followed by two numerals: The first numeral indicates the degree of protection provided to persons against access to hazardous parts inside the enclosure and the degree of protection against ingress of solid foreign objects, while the second numeral indicates the degree of protection against harmful ingress of water. IP ratings, and IEC standards in general, are typically applied to products with a significant presence in the European market; as such, Gibson Stainless products do not carry IP ratings.

For more information on IP ratings, click here.

Gibson Stainless' conduit is manufactured in accordance with and certified to ANSI/UL 6A-2014, which is the Standard for Safety for Electrical Rigid Metal Conduit - Aluminum, Red Brass, and Stainless Steel. Based on the scope of ANSI C80.1-2015, this standard is intended for use with conduit employing a metallic zinc coating or alternate corrosion protection coating; therefore, it does not apply to Gibson Stainless’ conduit. ANSI/UL 6A-2014 would be the parallel standard for stainless steel conduit that does not need to employ any type of corrosion protection coating.

Stainless steel: -50 °F (-45 °C) to 1700 °F (925 °C)
- For optimum corrosion resistance, limit temperatures to 800°F (425°C)
- For intermittent service, limit temperatures to 1600°F (870°C); despite the reduced time at temperature inherent in intermittent service, the upper end of the range is suppressed as a result of the thermal cycling and resultant fatigue in an environment where service temperatures are changing.

Low Temperature Performance:
Austenitic stainless steels (e.g., 304SS and 316SS) have a face-centered cubic crystalline structure, which prevents them from undergoing a ductile-to-brittle transition like metals with a body-centered cubic crystalline structure. This means that austenitic stainless steels have good low temperature properties, even permitting use at cryogenic temperatures.

High Temperature Performance:
Austenitic stainless steels (e.g., 304SS and 316SS) maintain their atomic structure at high temperatures giving them great value as structural materials. Ordinary carbon steel undergoes a phase change around 1400 °F (760 °C) that results in rapid shrinkage, which can cause catastrophic structural failure in structural elements already weakened by heat. Testing on fiberglass, aluminum, galvanized steel and stainless steel structural members under load and exposed to temperatures from 430°F (220°C) to in excess of 1050°F (565°C) demonstrate significant degradation to complete failure of the alternate structural materials while stainless steel remains intact.

At temperatures above 800°F (425°C), sensitization, or carbide precipitation, can occur reducing the overall corrosion resistance of the product. If service temperatures in this range are anticipated, low-carbon variants of the stainless steel alloy should be specified by the purchaser. The manufacturer should be contacted for additional information.

Rubber and Plastic:
Products containing chloroprene/neoprene gaskets, BUNA-N/nitrile O-ring, and polypropylene seals (liquidtight fittings):
-20 °F (-29 °C) to 190 °F (88 °C)
Products containing Polyetherimide (PEI) Thermoplastic (insulated, grounding bushings):
-40 °F (-40 °C) to 302 °F (150 °C)

Liquidtight fittings are intended for use in an environment where they could be exposed to machine coolant and/or shop oils. These fittings are subjected to an oil spray test when they are listed by UL.

Gibson Stainless offers rigid (heavywall) conduit. Proper wiring methods cited by NEC Article 501.10(A) permit all threaded rigid metal conduit (RMC) for use in hazardous locations. NEC Section 500.8(E) requires installing RMC with five threads fully engaged and wrench tight allowing gases within the raceway to cool before discharging into the atmosphere. RMC must meet the wrench-tight requirement for all locations, including hazardous. This wiring method also prevents arcing or sparking at threaded joints if a fault current passes over the conduit during a ground-fault event. Although full explosion prevention is not possible, the threaded connection confines any explosion to the inside of the conduit, thereby mitigating the possibility of an explosion in the larger area.

NFPA, UL, and OSHA agree on the importance of installing only approved wiring methods for all locations to ensure the electrical continuity of raceways. RMC is known for its ease of installation, durability, and is NEC-approved for all locations, including hazardous.

Gibson Stainless products are provided with a machined and/or a polished finish. In general, smooth, polished surfaces have greater resistance to corrosion.

Gibson Stainless’ conduit is welded. These welds are automatic and autogenous (e.g., performed without the addition of filler metal), ensuring a high degree of consistency in the weld and the material chemistry.

All Gibson Stainless conduit bodies and device boxes (when paired with a blank device box cover and gasket) are concrete tight. Any UL-listed, wet-locations fitting or UL-listed threaded fitting is also concrete tight.

Gibson Stainless’ conduit is not completely watertight and may or may not prevent the ingress of water as specified in a NEMA/UL-Type 4X rating.

1. Groundwater or other water from the environment can enter at the joints in the raceway, or
2. Condensation can occur inside the raceway as a result of environmental temperature changes.

It is not possible to guarantee a watertight raceway, even with the use of thread compounds, as the mating joint between a stick of conduit and a coupling is not designed to be watertight. Rigid conduit has tapered threads which mate with a straight thread in the coupling (as opposed to mating joints in plumbing pipe or some other electrical fittings where the tapered pipe thread on the conduit/pipe mates with a tapered thread on the fitting). This design (i.e., tapered-to-straight mating thread) actually allows condensation that accumulates in the system to drain out. Furthermore, rigid conduit is designed to carry current. Should a breach in the insulation of a conductor inside rigid conduit occur, the raceway must act as a path to ground for the current. This means that any thread sealant that would electrically insulate the joint cannot be used.

Our conduit bodies are Form 8.

Each conduit body is supplied complete with a cover, gasket, and Type 316 SS screws. Cover and gasket sets can also be purchased separately.

Gibson Stainless products are threaded which eliminates extensive installation procedures. Our products can be installed using ordinary hand tools and require very little maintenance or repair. For requirements and guidelines regarding the installation of a rigid conduit system, please consult NFPA 70: National Electric Code (NEC) and your local AHJ (Authority Having Jurisdiction).

Yes, there is a risk of corrosion of the less noble metal (e.g., aluminum, galvanized steel, copper) if coupled with stainless products in a raceway in an electrically conductive environment (e.g., saltwater). Gibson Stainless always recommends a full stainless raceway and support system if the end use environment presents an elevated risk of corrosion. If coupling a dissimilar metal with the stainless raceway is unavoidable, see the description of galvanic corrosion below and the linked technical bulletin from Atlas Steels for design advice and steps that can be taken to mitigate the risk of galvanic corrosion. You can also contact Gibson Stainless for additional assistance.

Galvanic corrosion is the degradation of one metal near a joint or juncture that occurs when two electrochemically dissimilar metals are in electrical contact in an electrolytic environment, for example, when copper is in contact with steel in a saltwater environment. However, even when these three conditions are satisfied, there are many other factors that affect the potential for, and amount of, corrosion, namely the and surface areas of the metals in contact. In order to reduce the risk of galvanic corrosion, 1) choose metals that are as close together as practicable on the galvanic series; 2) electrically insulate the joint, if possible;3) design the joint so that the anodic area is large relative to the cathodic area, which will reduce the noticeable effects of corrosion. Temperature and surface finish of the metals will also affect corrosion. For more information on galvanic corrosion as well as a representation of the galvanic series, see this technical bulletin from Atlas Steels.

Standard threaders can be used on stainless steel; it is normal to experience faster wear of the dies, especially in the larger sizes (2-1/2”, 3” and 4”).

For more information on threading, please see our guide: Cutting, Threading, and Bending Instructions for Stainless Rigid Conduit

Standard benders can be used on stainless steel; it is normal to experience greater spring back in the larger sizes (2-1/2”, 3” and 4”).

For more information on bending, please see our guide: Cutting, Threading, and Bending Instructions for Stainless Rigid Conduit