Sourcing steel tubing for aerospace or defense applications is not like buying commodity material. The specifications are tighter, the documentation requirements are strict, and a wrong call on material compliance can hold up a production line or, worse, create a safety concern downstream. AMS 6349 is one of those specs that buyers encounter and sometimes underestimate. It looks like a standard line item on a purchase order. It is not.
Here is what the spec actually covers, and what you need to check before placing an order.
What AMS 6349 Covers
AMS 6349 is an SAE Aerospace Material Specification covering seamless steel tubing in the chromium-molybdenum family, commonly associated with 4130-type alloy steel. This specification provides standards for tubing employed in aerospace applications pertaining to structure and machinery, where strength and consistency are absolutely essential.
Chemical Composition
The chemical composition standards as per the AMS 6349 specification provide standards on carbon, manganese, phosphorus, sulfur, silicon, chromium, and molybdenum content.These are not suggestions. They are hard limits that the mill must meet and document.
Chromium-molybdenum steels in this family typically carry chromium in the range of 0.80 to 1.10% and molybdenum around 0.15 to 0.25%, though you should verify the exact ranges against the current revision of the specification directly from SAE.
Why does chemistry matter so much? Because small deviations affect hardenability, weldability, and fatigue performance. A tube that looks right dimensionally can still fail in service if the chemistry drifts outside spec.
Heat Treatment Condition
AMS 6349 specifies the heat treatment condition of the tubing. This matters because the same alloy in a different temper condition will have different mechanical properties.
Tubing supplied to this spec is typically in the normalized or normalized and tempered condition. The heat treatment directly affects tensile strength, yield strength, and ductility. If you receive material in the wrong condition, the mechanical properties may not meet your design requirements even if the chemistry is correct.
Mechanical Property Requirements
Here is where procurement teams sometimes get caught. AMS 6349 sets minimum mechanical property requirements that the material must meet. These include:
- Minimum tensile strength
- Minimum yield strength (0.2% offset)
- Minimum elongation in a specified gauge length
- Reduction of area
These values must be supported by actual test data from the heat of material you are buying, not generic grade data from a catalog. If a supplier cannot provide test results specific to your heat lot, that is a red flag worth acting on.
Dimensional Tolerances
The specification sets tolerances on outside diameter, wall thickness, and straightness. Aerospace tubing applications often involve tight fits and precise load paths, so dimensional compliance is not a minor detail.
Outside diameter tolerances under AMS specs are typically tighter than standard commercial tubing. Wall thickness variation is also controlled. If you are working with a fabricator who needs to machine or form the tubing, dimensional consistency directly affects their process.
Ask for dimensional inspection records, particularly if you are sourcing larger quantities or tighter tolerance requirements.
Testing and Inspection Requirements
AMS 6349 requires specific non-destructive testing of the tubing. This typically includes hydrostatic testing or non-destructive electric testing (NDET) to check for seams, laps, or other discontinuities in the tube wall.
The spec may also require eddy current testing depending on the application and revision. If your end-use application is flight-critical, it is worth confirming which NDT methods were applied and requesting the inspection records.
Some buyers assume NDT is standard and skip asking for documentation. That assumption has caused problems.
Certification and Traceability
Every order to AMS 6349 should come with a certificate of conformance and a full mill test report. The MTR needs to show:
- The heat number
- Chemical composition by heat
- Mechanical test results
- Heat treatment applied
- Applicable specification and revision level
Traceability back to the original heat is non-negotiable in aerospace supply chains. If the documentation does not include a heat number that ties to actual test data, you cannot verify conformance. Period.
Some distributors supply material with generic or incomplete documentation. In a commercial context, perhaps that is acceptable. In an aerospace context, it is not.
Revision Levels Matter
AMS specifications get revised. The current revision of AMS 6349 may differ from a previous version that your supplier is referencing. If your purchase order calls out a specific revision, confirm that the material and documentation match that exact revision.
This seems like a minor point. But it’s a major issue when inspecting the source or conducting an audit from your customer’s perspective.
See also: Professional Commercial Plumbing Solutions for Businesses and Large Facilities
Questions You Should Be Asking Your Supplier
Prior to placing an order for AMS 6349, you should ask:
- Is the alloy manufactured per the latest revision?
- Are you able to provide an MTR complete with specific heat chemistry and mechanical property information?
- Which non-destructive testing techniques were used? Can you provide documentation of this testing?
- Was the temper condition recorded on the MTR?
- How does the lead time differ between certified and stock materials?
The answers will tell you quickly whether you are dealing with a supplier who understands the specification or one who is treating it like a standard commodity order.
