Stainless steel arrives in several surface conditions, and the specification treats them very differently. A pipe order that does not name the condition you need leaves the decision to the mill’s production route. That is a real commercial exposure, because the clause that governs it explicitly puts the choice with the purchaser.
SA-312/SA-312M Section 6.1.7 is the clause to read first. The pipe shall be free of scale and contaminating exogenous iron particles. Pickling, blasting, or surface finishing is not mandatory when pipe is bright annealed. And then the sentence that matters: the purchaser is permitted to require that a passivating treatment be applied to the finished pipe.
Permitted, not required. Nothing in the standard obliges a producer to deliver pickled, passivated or descaled austenitic pipe unless the purchase order says so. Section 6.1.6 gives the producer the option of furnishing pipe either hot finished or cold finished, which means two different surface outcomes are compliant with the same grade. If the order is silent, you have accepted whichever route the mill ran.
What each specification says
| Specification and clause | What it requires | What the buyer must state |
|---|---|---|
| SA-312/SA-312M §6.1.7 | Pipe free of scale and contaminating exogenous iron particles. Pickling, blasting or surface finishing not mandatory when bright annealed | Whether a passivating treatment is required on the finished pipe |
| SA-312/SA-312M §6.1.6 | Pipe furnished either hot finished or cold finished, at the manufacturer’s option | Delivery condition, if hot or cold finished matters to you |
| SA-999/SA-999M §28.8 | Where scale-free pipe is required for US Government agencies: pipe free from heavy oxide or scale, internal surface of hot finished ferritic steel pipe pickled or blast cleaned to a free-of-scale condition equivalent to the CSa2 visual standard in SSPC-SP6, cleaning per a written procedure shown to be effective and available for audit | Whether the scale-free requirement is invoked, and the visual acceptance standard to be applied |
| SA-999/SA-999M §22.3.4 | All surfaces free of scale, dirt, grease, paint and other foreign material that could interfere with interpretation of test results; cleaning must not be detrimental to base metal or surface finish | Nothing, but the surface condition is a precondition for reading the NDE result |
| SA-961/SA-961M §15.2.2.2 | Stainless steel and nickel alloy fittings need not be coated. Unmachined surfaces of stainless steel fittings shall be passivated by exposure to an acid bath, or electropolished | For forged and machined parts, whether passivation or electropolishing is required on unmachined surfaces |
| SA-182/SA-182M §14.2 | Forgings and finished parts free of scale, machining burrs which might hinder fit-up, and other injurious imperfections. Machined surfaces to have a surface finish not exceeding 250 AA roughness | Roughness requirement if the machined surface is a functional dimension |
Two of those rows carry a qualifier that is worth reading twice. The SA-999 scale-free requirement sits in Section 28, Government Procurement, and Section 28.1 states that these requirements are considered in the inquiry, contract or order for agencies of the US Government where scale-free pipe is required, and that they take precedence over the applicable product specification in case of conflict. It is a conditional clause, invoked by the contract rather than applied automatically. For a private buyer, the reference point is instead the state of the surface as delivered.
The difference between a defect and a mark
The other question a buyer needs answered is where the line falls between an imperfection that must be removed and one that is acceptable. SA-961 Section 15.5 draws it, and it does so in terms of wall thickness rather than appearance, which is the correct basis for a pressure-retaining part.
| Clause | Limit | Action if exceeded |
|---|---|---|
| SA-961 §15.5.1 | Seams, laps, tears or slivers not deeper than 5 % of the actual wall thickness at the point of interest or 1/16 in. [1.6 mm], whichever is less | Removed by machining or grinding |
| SA-961 §15.5.2 | Mechanical marks, abrasions and pits acceptable without grinding or machining provided depth does not exceed 1/16 in. [1.6 mm] | Removed by machining or grinding to sound metal, if they do not encroach on minimum wall |
| SA-961 §15.4 | Depth encroaching on the minimum specified wall thickness of the finished part | Treated as injurious regardless of appearance |
| SA-961 §15.5.3 | Wall thickness at the point of grinding determined by deducting the amount removed from the nominal finished wall thickness, never less than the specified minimum | Grinding cannot be used to recover an undersized wall |
| SA-999 §28.13 | Handling marks, straightening marks, light mandrel and die marks, shallow pits and scale pattern not defects if removable within the wall thickness tolerance or 0.005 in. [0.1 mm], whichever is greater; bottom visible and profile rounded and faired-in | Rejected if the profile is sharp or the bottom cannot be seen |
Section 15.5.3 is the clause that catches people out. It is an allowance to remove an imperfection, not a permission to grind a part down to the minimum acceptable wall. Once you grind, the wall has to still be at or above the specified minimum, and in a thin-wall stainless component the two limits can meet in a very short distance.
SA-961 Section 15.2 also adds two requirements that are easy to miss on a purchase order. The finished parts shall be cleaned to remove all scale and processing compounds prior to the final surface examination, and the cleaning process shall not injure the surface finish, material properties or the metallurgical structure. The cleaned parts shall then be protected to prevent recontamination. On austenitic material, contamination is not a cosmetic issue; it is the mechanism by which free iron turns a stainless surface into a rusting one, and SA-312 Section 6.1.7 addresses exactly this by naming contaminating exogenous iron particles.
Six lines to add to the enquiry
You do not need a long specification to control the outcome. To make the surface condition unambiguous, state the following:
- The delivery condition: solution annealed and pickled, or bright annealed, or solution annealed and passivated.
- Whether a passivating treatment is required on the finished pipe, as permitted by SA-312 Section 6.1.7.
- Whether the material will be cut or welded on site, so that the supplier can confirm which procedure qualification applies to the delivered condition.
- Whether an unpickled or unscaled internal surface is acceptable, and what visual acceptance standard applies if it is not.
- Any functional surface roughness requirement for machined parts, referenced to the 250 AA limit in SA-182 Section 14.2.
- Whether the order is placed under a government procurement contract that invokes the scale-free provisions of SA-999 Section 28.
If the material is austenitic stainless for corrosive service, our Incoloy 825 seamless pipe listing and the Incoloy 800H pipe listing are typical examples where the delivery condition has to be written into the order rather than assumed. For the broader picture of what is available, see the main seamless pipe page. When you have the six lines settled, talk to our sales team and we will quote against them.
