Ultra-High-Polish Stainless Steel Tubing at 18-Inch Length Certificati | EAGLE

While asking about 18-inch sections of ultra-high-polish stainless steel tubing, the client has raised three questions: which material and surface specifications are to be considered, what documents will come together with the order, and how the certification is maintained having in mind the fact that the tubing is cut and delivered. It should be noted that all three questions are crucial but the most difficult one out of these is the last one. The difficulty here is that it is quite possible that the cut product may be certified. This problem exists when there is no connection between the item which is unpacked and the heat number in the certificate. Therefore, in the given paper the author will present some distinctions of the applicable norms which characterize ultra-high-polish stainless steel tubing, surface specifications of the goods, checking the tubing and the paper needed.

ASTM A270 (sanitary tubing) or ASTM A269 (general use) are probably the most commonly used standards, whereas ASME BPE is used for pharmaceuticals and biotechnology, 3-A SSI 33-03 is for milk and food, and EN 10357 and DIN 11850 are mainly European dimensioning standards. Super-polished implies that the tubing is treated with electropolishing to a certain roughness determined by ASME BPE from SF0 to SF6, which means that the tubing has at least SF4 degree (Ra ≤ 0.38µm or around 15µin), although the most expensive electropolishing can even go down to Ra ≤ 0.20µm. In terms of minimum required certification, EN 10204 3.1 material test report, eddy current test result, and weld inspection result must be provided at a minimum. It should be considered that the 18-inch cut length of a piece has standard mill length of 6m or 20ft, which means that there are no requirements regarding certification, but only traceability should be noted.

Which Certification Applies

There is no such thing as an "ultra-high-polish tubing certification." In fact, certification consists of multiple components such as material standards to define the type of steel and tolerance, surface finishes designating the type of polishing, and procedures to show that the two are compatible, along with documents binding everything together.

Most clients will be satisfied with tubing certified according to ASTM A270 as a material standard and ASME BPE as a surface finish specified in the purchasing orders for pharmaceutical-grade or high-purity applications alongside an EN 10204 3.1 test report, if the country of destination of the tubing is located in Europe where EN 10357 replaces or augments ASTM A270. If the application of the tubing is dairy or food rather than pharmaceuticals, 3-A SSI 33-03 will be used as a hygienic standard as it is less stringent than BPE for pharmaceuticals.

However, these standards are not interchangeable as they specify different things: ASTM A270 sets numerous norms and requirements for dimensions, specifications, and surface quality; ASME BPE standards have a greater scope of options for manufacturing high-purity equipment; and 3-A SSI sets hygiene standards for milk and food — surfaces must be smooth, impermeable, non-absorbent and self-draining in order to meet requirements.The wider framework these standards sit within is surveyed in our overview of sanitary pipeline standards.

The Material Standards

Standard	Region	Scope	Typical application
ASTM A270	United States	Seamless and welded austenitic stainless food-grade tubing; dimensions, tolerances, surface finish	The default US standard for sanitary and hygienic tubing
ASTM A269	United States	Seamless and welded austenitic tubing for general service	General instrumentation and process tubing where sanitary criteria do not apply
ASME BPE	United States, international	Bioprocessing equipment; graded surface finishes, weld criteria, documentation, cleanability	Pharmaceutical, biotech, WFI and clean steam systems
3-A SSI 33-03	United States	Metal tubing for dairy and food; hygienic design, Ra ≤ 0.8 µm across the polish direction	Dairy, food and beverage processing
EN 10357	Europe	Current European standard for hygienic stainless steel tube; Series A dimensions harmonised with DIN 11850 Reihe 2	European food, dairy and beverage installations
DIN 11850	Germany	Older German hygienic tube designation, still widely specified by name	Dairy and food OEM equipment, particularly legacy designs
ISO 2037	International	Hygienic tubing dimensions for the food industry	International projects specifying ISO dimensions
BS 4825-1, AS 1528.1, JIS G3447	UK, Australia, Japan	National hygienic tubing standards with their own dimension series	Projects in those markets, and exported equipment built to them

There’s a caution that goes with that table. These specifications aren’t dimensionally interchangeable. ASTM A270 uses inch-based outer diameters, EN 10357 and DIN 11850 use a metric series, there’s ISO 2037 and SMS, and then there’s JIS G3447. It cannot be assumed that pipes bought to one standard would fit a system designed according to another, and users should ensure what standard is to be purchased based on the fabrication drawing of the project rather than on the destination country.The dimensional conventions that cause the most problems are covered in our article on what sizes stainless steel pipe comes in.

Ultra-High Polish and Ra Values

“The term 'ultra-high polish' is a marketing gimmick; the actual meaning of the term is a roughness number. Surface roughness is indicated as Ra, which is the arithmetic average of the surface profile and the line average; it is presented in microns or micrometres.”

Finish level	Typical Ra	Process	Where specified
Mill / as-welded bright annealed	Around 0.8-1.0 µm	Inline bright anneal, no mechanical polish	General hygienic service where cleanability demands are moderate
3-A hygienic finish	Ra ≤ 0.8 µm (32 µin)	Mechanical polish	Dairy and food processing — the baseline hygienic standard
ASME BPE SF1-SF3	Approximately 0.51-0.76 µm (20-30 µin)	Mechanical polish only	Product contact in less critical bioprocess duties
ASME BPE SF4	Ra ≤ 0.38 µm (15 µin)	Mechanical polish plus electropolish	The most commonly specified tier for direct product contact in bioreactors, WFI and media systems
ASME BPE SF5-SF6	Ra ≤ 0.25 to 0.20 µm	Electropolish to a higher standard	Critical high-purity duties
Premium electropolished	Ra ≤ 0.20 µm (8 µin)	Electropolish on selected sizes	Pharmaceutical, biotech and semiconductor systems

There are three misconceptions with Ra that lead to conflicts during the goods in process.

Geometries must be accounted for. The roughness measured across the polishing direction will yield different results than when measuring the roughness along the polishing direction, which is identified by certain standardized definitions such as 3-A. States that the order only specifies the Ra number without giving the requisite measurement direction is incomplete.

Technique can make a difference. Devices and their settings will give different results, so the technique for the measurement has to be agreed before beginning production to avoid differences later.

Luster is not equal to roughness. A shiny finish does not imply that the correct Ra has been achieved; shiny surfaces can be rough and dull surfaces can be smooth. Thus, it is prudent to put the exact Ra number in the purchasing order that gives rise to a measurement report, rather than describing the desired finish as "shiny", since the difference is important in the pharmaceutical and semiconductor business, where the surface properties are paramount.

What Electropolishing Does

The process of electropolishing is different from mechanical polishing as it uses electrochemical action to remove a thin layer of metal from the surface instead of grinding and stressing it. The reasons that electropolishing is preferable to mechanical polishing in terms of finishing quality in the dairy industry can be summarized as follows.

It eliminates the damaged layer left by mechanical polishing. Due to the way that mechanical polishing works, the surface of the metal can be damaged and thus form a contaminated layer which can be destroyed only by electropolishing.
The process leaves a layer rich in chromium. The reason for this is that iron is removed leaving a surface that is now covered with chromium which is better resistant to corrosion. This is the reason why a tube treated with electropolishing will be less prone to corrosion compared to a tube polished mechanically.
The process makes the tube cleaner and more suitable for the inspection. Electropolishing gives an opportunity to remove the contaminants more easily also giving better results in terms of quality inspection due to its particular properties.

However, this process doesn't make a poor tube??? Any tube subjected to electropolishing process but crafted from a low-quality base material will still fail a Ra. It means the process doesn't guarantee the end results thereby making it crucial to set detailed specifications in the purchase order regarding the finish used for manufacturing rather than assuming that the technology will solve all possible issues.

The Documents That Matter

Certification is issued as a set of documents, and every document has its own purpose.

Document	What it proves	Why it is needed
EN 10204 3.1 material test report (MTR)	Chemical composition and mechanical properties of the actual heat used	The core traceability document; issued by the manufacturer's own inspection department
Heat number	Links the delivered piece to the MTR	Without it the certificate proves nothing about your tube
Surface roughness report	The measured Ra against the specified value and method	The evidence that "ultra-high polish" was achieved
Eddy current test record	Freedom from surface and subsurface defects	Typically performed on 100% of hygienic tube
Weld inspection record	Weld quality on welded tube, often by automated laser inspection	Critical on welded product where the weld is the likely failure path
Dimensional inspection record	Outside diameter, wall thickness, length, squareness of cut ends	Confirms the piece matches the drawing
ISO 9001 certificate	A controlled quality management system	The baseline evidence that processes are documented and auditable
PED 2014/68/EU conformity	Compliance with European pressure equipment requirements	Required where the tube forms part of pressure equipment placed on the EU market
Internal cleanliness reports	Absence of residue, particulates and contamination	Often required in pharmaceutical and semiconductor service, sometimes with borescope evidence
Packing specification compliance	Protection during transit	Hygienic tube is normally sleeved in plastic film with capped ends and supplied in closed cases

Among all types of certification, MTR should be particularly emphasized, as it is the one that is usually wrongly provided. EN 10204 3.1 report is a document issued by an independent inspection department of the manufacturer and is related to concrete heat; the report 2.2 is a general statement of compliance that does not have the same significance as 3.2 that is acknowledged by a third party. Those who query "mill certificate" but omit to specify the type will usually receive 2.2 and learn of the issue during an evaluation rather than during receiving.

Why 18-Inch Length Changes the Question

A length of 457mm is equivalent to 18”. First, it is essential to understand that this length does not correspond to the standard mill length. A hygienic stainless tube is manufactured and offered in 20 ft lengths, which means short segments are cut from this initial length. This fact carries four implications.

Existing traceability could be transferred but should not be assumed. The MTR refers to that specific heat from which the involved mill length has originated. This means that once a segment is cut from the remaining mill length, the only relation that connects that particular 457 mm length to the MTR is its marking or labelling. Any respected supplier will either mark every piece or label it properly so that its heat number, grade, and standard, are indicated. If this is not the case, it means that the tube is coming from the original MTR but is no longer recognizable.
The end of the tube is new. A cut end is not the same as a bore because it is not polished or passivated in the manner bore is. In many cases, there are burrs present, and thus to be used in hygienic service this end of the tube should be cut square, deburred, and if needed, passed again. Whether this degree of finishing qualifies for certification or not depends on the particular application of the tube.
Packaging is naturally discussed as the packaging assumes that there is a full-length piece available. The packaging of mill-length tubes usually includes sleeves and caps that preserve the bore in the process of transportation. In case of shorter segments, the pieces might be touched more frequently, thus there is a need to specify packaging types in the order.
Documents for every cut piece may be required. In the cases when there are several different pieces of length 18-inches produced from different heats, there is no way to use one MTR for the order. The order should clarify whether all pieces should have been produced from one heat or not because it would affect the delivery.

None of this makes an 18-inch length harder to certify. It makes it necessary to specify how the certification follows the piece, which is a different and easily overlooked requirement. Where tube is being ordered for spares, prototypes, sampling or small-batch pharmaceutical work — the applications where short lengths are most common — the same rigour applies as for a full-length order, and the components it will connect to are covered in our primer on what a sanitary fitting is.

What Each Industry Requires

Industry	Material standard	Finish requirement	Key documentation
Dairy and food processing	ASTM A270 or EN 10357	3-A hygienic, Ra ≤ 0.8 µm	MTR, eddy current records, 3-A compliance evidence
Beverage, brewery, winery	ASTM A270 or EN 10357	Mechanically polished, sometimes electropolished	MTR, surface finish report, weld records
Pharmaceutical and biotech	ASME BPE, ASTM A270	Electropolished, typically SF4 (Ra ≤ 0.38 µm) or finer	MTR, Ra report, weld acceptance records, internal cleanliness, sometimes borescope
Water for injection and clean steam	ASME BPE	Electropolished, SF4 to SF6	Full BPE documentation set with weld maps
Semiconductor and high purity	ASME BPE or customer specification	Electropolished to Ra ≤ 0.20 µm in some sizes	Particle and residue testing, internal surface certification
Chemical and general process	ASTM A269 or A270	As required by the process fluid	MTR, pressure test records where applicable
Pressure equipment (EU market)	EN 10357 with PED compliance	Per application	PED 2014/68/EU conformity, 3.1 MTR

The trend shows that as pollution increases, demands get stricter. The brewing industry may accept the surface to be machine finished because its product is filtered and its cleaning practices are effective, while the bioprocess industry cannot because the surface is crucial for pollution control and is treated accordingly by the legislators. Thus, matching certification with the industry is not about buying the best product possible but rather purchasing the one that would pass compliance inspection.

Grades and Selection

The certification selection process rests upon a choice of materials, and the issue should be approached in an integrated manner. The principal grades used in the manufacture of sanitary tubes are 304/304L and 316/316L, with 321 being appropriate wherever higher temperature service is required. The low-carbon grades — the L grades — possess a greater degree of resistance to sensitization at the weld points, which is important due to the existence of the heat affected zone in welded tubes, which can be susceptible to intergranular stressing if made from standard carbon grades.

The choice of one family over the other depends on selecting a material rather than on the specification of certain properties, as the 316L formulation has significantly superior performance in cases where exposure to chloride ions or a variety of processing chemicals is expected, while 304 is sufficient for cases of less aggressive applications.Cleaning chemicals, product acidity, chloride exposure and temperature all drive the decision, and the differences that matter in practice are set out in our guide to 304 versus 316 stainless steel selection. In the case of a Purchase Order, the grade should be shown next to the standards as "ASTM A270" does not clarify the alloy.

When writing the specification from scratch rather than looking at the existing drawings, it is advisable to find out what the suppliers have to offer and what is actually documented.Our survey of leading stainless steel fittings and tube manufacturers sets out how the suppliers compare on standards coverage and documentation, which is the comparison that matters most when audit evidence is the deciding factor.

FAQ

What are the different grades of stainless steel tubing?

Stainless steel grades commonly utilized in hygienic and high-purity tubing are 304, 304L, 316, 316L and 321. The L grades are low carbon grades which minimize the susceptibility of the welded connections to sensitization, hence their use for hygienic welding tubes. The 316 and 316L grades have superior resistance to chlorides and harsh chemicals, which is why they are used for the pharmaceutical, marine and chemical industries whereas the 304 and 304L grades may be utilized in other applications such as food and beverage manufacturing because of reasonable corrosion resistance and lower cost. The 321 grade is utilized for high temperature applications requiring intergranular corrosion resistance.

What is the HS code for stainless steel tubes?

The classification of stainless steel pipes and tubes falls under two main headings depending on the way the tube is manufactured. Seamless stainless steel tubes are classified under HS 7304, with cold drawn and cold rolled seamless stainless steel tubes classified under 7304.41 while the other seamless tubes are classified under headings 7304.49. On the other hand, welded circular seamless stainless steel tubes are classified under 7306.40. It should be noted that sanitary and hygienic tubes can either be made of seamless or welded tubes, hence either of the headings may apply. Because of the varying duties and regulations of various places countries e. g. customs broker and tariff schedule of the country importing.

What is the thickness of 18 gauge stainless steel tubing?

The eighteen-gauge stainless steel is considered to be equivalent to approximately 0.049-0.050-inch or about 1.24-1.27 mm. However, it is typical for sanitary and hygienic tubing to be specified in terms of the actual thickness in inches or millimeters rather than by gauges since the gauge designations are not the same across the different materials. Thus, according to the ASTM A270 standard of sanitary tubular products, the common specification for the outside diameters ranging from inches to 11/2 inches is a thickness of 0.049 inch (1.24 mm) whereas for larger diameters heavier thicknesses are used such as 0.065 inch. The exact thickness is the measurement given in the standard and confirmed by the mill certificate, instead of the gauge number.

What is the PSI rating for stainless steel tubing?

There cannot be a standard rating for the pressure because the permissible pressure will depend on outside diameter, thickness of the wall, type of material, temperature, and the code of design applied. For example, let us assume a tube that is 1 inch (OD) and 0.049 inch thick, made of 316L material, is rated for pressure at ambient temperature using a design code which is ASME B31.3 and a stress level (S) that is around 20,000 psi. Based on the thin-wall relationship P = 2St/(D-2t), the internal pressure that can be anticipated in case of such a tube would be around 2,000 psi. However, that value keeps decreasing with higher temperature, as well as when weld joint efficiency factor related to welded tubing is accounted for, and must be recalculated for tubes with different diameters and thicknesses.

Does cutting tube to 18 inches invalidate its certification?

No, but the certification requirements are different. The material certification refers to the heat which produced the tube, so as long as the link to this heat is maintained, for instance, by marking the end or providing the certification with the heat number, grade and standard information written on it together with the piece or using a packing that contains such information, everything will be all right. Problems arise when loose cut pieces with a generic certificate are delivered, as this way the document covered material of indeterminate provenance. If there are several cut pieces required under one order, it is best to specify whether all pieces can be sourced from different heats or must come from the same heat and provide information on finish.

References

Conclusion

The ultra-polished stainless steel pipe certification documents are referred to as stack documents rather than a single one. A pipe of 18 inches long does not result in any changes of what’s needed in the paper but does change the way the evidence travels together with the product. Let’s start with the materials standards in the USA: ASTM A270 for sanitary piping, ASME BPE for pharma and biotechnological purposes, 3-A SSI 33-03 for dairy industry, EN 10357 for European pipe dimensions. The required finish should be stated along with actual Ra parameter indicated and the name of the used measuring method, accordingly, one also should indicate the applicable BPE classification during the mill test for Ra ≤ 0.38 µm in relation to product specifications. Verification has to include the provision of EN 10204 3.1 document confirming conformity issuing instead of standard conformity declaration. One also should check that all necessary testing results are available including those for magnetic testing, checks of the welding process, and measuring surface roughness. Finally, the cutting length has to be dealt with as per format, so that all pipes get labelled in accordance with their heat numbers.