Mistake 1 — Ordering "Stainless Steel" Without Specifying a Grade
What happens: Buyer places an order for "25mm round bar, stainless steel, 500kg." Supplier ships SS202. Buyer expected SS304.
Why it happens: The buyer assumes "stainless steel" implies a specific grade. It does not. Stainless steel covers over 200 standard grades — from SS202 to SS904L. Without specifying a grade, the supplier will typically supply whatever is most economical for them.
How to avoid it: Always specify the grade explicitly in your purchase order. Write: "25mm round bar, SS304 (AISI 304 / UNS S30400 / IS 6911 Grade 04Cr18Ni10), HRAP finish, 6-metre random lengths, ASTM A276 compliance, with MTC."
Mistake 2 — Specifying SS316 When SS316L Is Needed for Welding
What happens: Fabricator orders SS316 round bar, welds it into a chemical vessel, and finds corrosion at the weld zones within 12 months.
Why it happens: Standard SS316 has up to 0.08% carbon. During welding, heat causes carbon to migrate to grain boundaries and form chromium carbides — sensitisation — which strips the chromium passive layer from those zones and creates corrosion initiation points.
How to avoid it: Any SS316 component that will be welded must be SS316L (carbon max 0.030%). If the bars will only be machined and not welded, standard SS316 is fine. The rule is simple: welding requires the L grade.
Mistake 3 — Using SS202 in Coastal or Marine Environments
What happens: Fabricator uses SS202 for a coastal project to save cost. Within 6–18 months, the material shows rust staining and pitting.
Why it happens: SS202 has lower nickel content (4–6%) than SS304 (8–10.5%), which reduces its resistance to chloride attack. Coastal atmospheric chloride concentrations are high enough to pit SS202 within months.
How to avoid it: Never use SS202 within 5–10km of a coastline or in environments with chloride exposure. Use SS304 minimum for outdoor coastal use, SS316 for marine or direct seawater contact.
Mistake 4 — Accepting an MTC Without Verifying the Chemistry
What happens: Buyer receives material with MTC. MTC claims SS316 but molybdenum (Mo) shows 0% or is absent from the certificate.
Why it happens: Some suppliers provide generic or copied MTCs that do not reflect the actual heat chemistry. Buyers who do not read MTCs accept these documents without checking.
How to avoid it: Always check the MTC for the elements that define the grade:
- SS316: Mo must show 2.00–3.00%
- SS316L: C must show 0.030% maximum
- SS304: Cr must show 18.00–20.00%, Ni 8.00–10.50%
Real SPECTRO results show decimal precision (e.g., Mo: 2.14%) — not round numbers. If Mo is absent on a "SS316" MTC, the material is not SS316. Reject it.
Mistake 5 — Confusing Surface Rust for Grade Failure
What happens: Buyer notices orange-brown staining on new stainless steel bars and assumes the material is substandard or wrong grade.
Why it happens: Stainless steel can show surface rust in two situations that are NOT grade failures:
- Iron contamination: Small particles of carbon steel (from cutting tools, grinding, storage on carbon steel racks) deposit on the SS surface and rust. The SS itself is fine — the iron contamination rusts.
- Water staining: Chloride-containing water (even tap water in hard water areas) left to evaporate on the surface can leave staining.
How to avoid it: Clean new SS bars with dilute nitric acid or proprietary SS cleaner before inspection. True grade-related pitting corrosion is different — it creates small pits in the base metal, not surface staining. If staining wipes off or responds to cleaning, it is contamination, not grade failure.
Mistake 6 — Ordering by Diameter Without Specifying Dimensional Standard
What happens: Buyer orders "25mm hex bar." Supplier ships material where 25mm refers to the corner-to-corner dimension rather than the across-flats dimension. The bar does not fit the spanner or tooling.
Why it happens: Hex bars have two possible measurements — across flats (AF, flat-to-flat, the spanner size) and across corners (AC, corner-to-corner). Industry standard is to specify and bill on AF. But without explicitly stating AF, confusion arises.
How to avoid it: Always specify hex bar by Across Flats (AF). Write: "19mm AF hex bar" — not just "19mm hex bar." The AF dimension equals the spanner or socket size that fits the finished component. Navkardeep supplies and quotes all hex bars by AF as standard.
Mistake 7 — Buying from a Trader When You Need Mill-Certified Material
What happens: Buyer purchases from a trader for a quality-critical application. Trader provides an MTC but cannot confirm the source mill, heat number traceability, or current certificate status.
Why it happens: Traders often buy from multiple sources and may not have full traceability to the originating mill. For applications where MTC authenticity matters — pharma, chemical, pressure vessel, export — this creates quality risk.
How to avoid it: For applications where material traceability is critical, buy direct from the manufacturer. The MTC issued by the manufacturer is primary-source documentation, traceable to the specific heat, the specific furnace batch, and the specific SPECTRO analysis. At Navkardeep, every MTC is issued by us for material produced in our own melt shop — full traceability from raw material to finished bar.
Have a grade selection question for your specific application? Our technical team answers without obligation.