STAINLESS STEEL OVAL PIPE
STAINLESS STEEL OVAL PIPE - industrial steel pipe
Austenitic stainless steel is a type of stainless steel that is widely used in various industrial applications due to its excellent corrosion resistance and versatility.
Austenitic stainless steels are versatile and popular materials, known for their corrosion resistance, high-temperature strength, and suitability for the fabrication process.
A stable austenite structured steel contains about 18% Cr, 8% ~ 10% Ni and about 0.1% C. Chrome-nickel austenitic stainless steel including the most familiar stainless steel 18Cr-8Ni (TP304) and the series of high Cr-Ni steel developed by increase Cr, Ni contents and add Mo, Cu, Si, Nb, Ti and other elements. Austenitic stainless steel is characterized by non-magnetic, high plasticity and ductility but lower strength. It can be only strengthened via cold working (by adding S, Ca, Se, Te and etc, austenitic stainless steel can have excellent machinability).
Grades：304/L/H/LN, 316/L/H/LN/Ti/LMod, 310S/H, 317/L, 321/H, 347H/HFG
Specifications：
Austenitic steels are non-magnetic stainless steels that contain high levels of chromium and nickel and low levels of carbon. Known for their formability and resistance to corrosion, austenitic steels are the most widely used grade of stainless steel.
Features：
There is a fifth specialist type Precipitation Hardening Steels.
Development diagram of common grades of austenitic stainless steel
The fundamental difference between them is their crystaline structure. Steel is an alloy of iron and carbon. At normal temeperatures the atomic structure is that of a cube with an atom of steel at each corner and a single atom in the centre of that cube.
This is known as "ferritic" and, is by the way, magnetic.
When heated to about 900o C the structure changes and each face has an atom at its centre. This is the austenitic structure and is non-magnetic.
When ordinary steel cools down gradually it reverts to a ferritic structure. If you cool it fast, it will adopt another structure with the carbon atoms being arranged in one direction. This is martensitic steel and in its "as quenched" condition is hard but brittle and generally requires further treatment before it can be used.
Strength Graph of 316L Mod at room and elevated temperature
| AISI grade | C max. | Si max. | Mn max. | Cr | Ni | Mo | Ti | Nb | Al | V |
| 301 | 0.15 | 1.00 | 2.00 | 16-18 | 6-8 | |||||
| 302 | 0.15 | 1.00 | 2.00 | 17-19 | 8-10 | |||||
| 304 | 0.08 | 1.00 | 2.00 | 17.5-20 | 8-10.5 | |||||
| 310 | 0.25 | 1.50 | 2.00 | 24-26 | 19-22 | |||||
| 316 | 0.08 | 1.00 | 2.00 | 16-18 | 10-14 | 2.0-3.0 | ||||
| 321 | 0.08 | 1.00 | 2.00 | 17-19 | 9-12 | 5 x %C min. | ||||
| 347 | 0.08 | 1.00 | 2.00 | 17-19 | 9-13 | 10 x %C min. | ||||
| E 1250 | 0.1 | 0.5 | 6.0 | 15.0 | 10.0 | 0.25 | ||||
| 20/25-Nb | 0.05 | 1.0 | 1.0 | 20.0 | 25.0 | 0.7 | ||||
| A 286 | 0.05 | 1.0 | 1.0 | 15.0 | 26.0 | 1.2 | ~1.9 | ~0.18 | ~0.25 | |
| 254SMO | 0.02 | 0.8 | 1.0 | 18.5-20.5 | 17.5-18.5 | 6-6.5 | ~1.9 | ~0.18 | ~0.25 | |
| AL-6XN | 0.03 | 1.0 | 2.0 | 20-22 | 23.5-25.5 | 6-7 |
Annealing
Annealing is a process of heating the steel to a temperature slightly above its recrystallisation temperature and allowing it to cool at an appropriate rate - generally slowly - causing the crystals to reform without the defects caused by "working" the steel.
Annealing can restore the ductility of the steel and its corrosion resistance characteristics.
Carbide Precipitation
When steel contains higher levels of carbon there is a tendency for it to combine with the chromium as it cools - between 900oC and 500oC forming chromium carbide. This reduces the amount of chromium available to form the passive layer and creates intergranular boundaries that are accessible to corrosive chemicals.
This can be overcome by using Low carbon variants of the steel (designated by "L", eg 304L or 316L).
However, the lower carbon levels reduce the steel's performance at elevated temperature. If resistance to carbide precipitation and strength at high temperature are required then the addition of Titanium may be the solution. There are a number of grades available in this form - eg 316Ti.
Creep Strength
Steels perform very differently at elevated temperatures than they do at ambient temperatures. When they are bent at ambient temperatures to below their yield point, they will spring back. At elevated temperatures, they begin to stretch, but very slowly. Some steels have better resistance to this phenomenon than others.
Grain Size
Steel is made up of a lattice of crystals of iron interwoven with atoms of other materials. These crystals are called grains.
The grain size is important because it affects the machining, hardness, strength, and corrosion resistance amongst other things.
Grain size can be determined both by the addition of other alloying elements and by the careful regulation of the heating and cooling processes involved in the production of the steel and by further heat treatment (annealing and quenching) following initial production, welding or "working" on the steel.
Intergranular Corrosion
The atoms in metals are arranged into crystals (or grains) which are aligned closely with each other. In certain conditions, corrosion can attack the grain boundaries rather than the crystals themselves.
When stainless steel containing a higher percentage of carbon is heated it the chromium can react with the carbon to form chromium carbide thereby depleting the passive layer of chromium that protects the surface.
Passive Layer
The passive layer is what makes stainless steel "stainless". It is a microscopically thin layer of chromium oxide that is impenetrable to oxygen, very hard, resists corrosion itself and is virtually transparent. This prevents oxygen and other corrosive materials reaching the iron and reacting with it.
Chromium reacts readily with oxygen with the result that should it become scratched it will repair itself providing there is free oxygen available.
Pitting Corrosion
This is a very localised form of corrosion that arises particularly in high chloride conditions such as the marine environment. An initial breach in the passive layer of the steel is not "repaired" by the reformation of chromium oxide. The steel beneath this breach continues to corrode often leaving no obvious signs other than a light surface staining (sometimes called "tea staining) on the surface but continuing to deepen and widen below the surface.
While localised it can result in the penetration of the entire cross section of the steel.
High contents of chromium, molybdenum and nitrogen increase the resistance to pitting corrosion. The degree of resistance can be calculated as %Chromium + 3.5 x %Molybdenum + 16 x %Nitrogen to give a Pitting Resistance Equivalent Number (PREN).
316 has a PERN of between 22.6 – 27.9. Some Duplex steels have PRENs over 40. The span of the numbers given in certain grades is the result of the specification for the quantities of the relevant chemical having max and min figures.
Precipitation hardening
Also known as age hardening, is a process used to increase tensile strength. The alloy is first raised to a temperature that a produces a single phase with all the solute atoms dissolved and evenly distributed. It is then rapidly quenched before reheating to a lower temperature and holding it at that temperature for a predetermined time. At this temperature, the precipitates can clump together in a uniform and distributed manner. It is essential that the right temperature and duration at this stage of the process is correct. If the temperature is held too long it will result in oversize clumps and reduce the strength of the alloy. This is known as "over aging".
Sensitisation
Sensitisation is the process of Carbide Precipitation - See above.
Sigma phase embrittlement.
Is phase change that occurs in some stainless steels when they are heated above about 540C. This results in a dramatic loss of toughness and can lead to brittle fractures.
Stabilisation
Stabilisation is the process of removing or protecting the steel from sensitisation - the danger of carbide precipitation which can lead to stress corrosion cracking (SCC).
There are two approaches commonly used. Low carbon variants can be used; they are inherently more stable but they perform less well at higher temperatures.
Alternatively, steel can be chemically stabilised by alloying it with titanium, niobium (sometimes still called columbium). Both of these readily form carbides thereby preserving the chromium.
However, this may not be sufficient to stabilise the steel should it be held within the carbide forming temperature band 425oC to 850oC. Should this occur during the fabrication process the problem can generally be reversed by annealing at a higher temperature.
Stress Corrosion Cracking (SCC)
Stress corrosion cracking occurs when chemicals attack the intergranular boundaries within an alloy. When the metal is subject to tensile stresses it can result in the sudden failure in generally ductile materials. Because the corrosion only occurs at the grain boundaries it is likely to go unnoticed since the metal will generally maintain an apparently normal surface appearance.
Work Hardening
Work hardening is a term applied to any work done on the steel at a temperature below the metal's recrystallisation temperature.
This work includes any type of squeezing, bending, cutting/shearing or drawing.
These processes cause distortions in the crystalline structure of the metal reducing their ability to move within the metal and makes it more resistant to further deformation.
Hardening can be an advantage or a disadvantage.
The crystalline structure can be restored by annealing.
Austenitic stainless steels are the most common and widely known types of stainless steels. They make up over 70 % of total stainless steel production. These steels contain around 16 % to 25 % chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from cryogenic region to the melting point of the stainless steel. Austenitic stainless steels can also contain nitrogen in solution. Although nickel is the alloying element most commonly used to produce austenitic stainless steels, nitrogen can also be used to produce austenitic stainless steels. The austenitic stainless steels are more easily recognized because of their non magnetic properties. Austenitic steels are non magnetic since the face centered cubic structure of austenite is non magnetic. They are extremely formable and weldable, and they can be successfully used from cryogenic temperatures to the jet engines and red hot temperatures of furnaces.
Austenitic stainless steels are mainly segregated into the following two series
Besides the above two series there are super austenitic stainless steel grades which exhibit great resistance to chloride pitting and crevice corrosion because of high molybdenum content (> 6 %) and nitrogen additions. Higher nickel content ensures better resistance to stress-corrosion cracking than the stainless steels of the 300 series. The higher alloy content of super austenitic steels makes them more expensive.
The straight grades of stainless steel contain a maximum of 0.08 % carbon. In these grades, there is no requirement of minimum carbon in the specification.
The ‘L’ grades are used to provide extra corrosion resistance after welding. The letter ‘L’ after a stainless steel grade indicates low carbon (as in 304L). The carbon is kept to 0.03 % or under to avoid carbide precipitation. Carbon in steel, when heated to temperatures in what is called the critical range (430 deg C to 870 deg C) precipitates out, combines with the chromium and gathers on the grain boundaries. This deprives the steel of the chromium in solution and promotes corrosion adjacent to the grain boundaries. By controlling the amount of carbon, this is minimized. For weldability, the ‘L’ grades are used. However the ‘L’ grades are more expensive. In addition, carbon, at high temperatures imparts great physical strength.
The ‘H’ grades contain a minimum of 0.04 % carbon and a maximum of 0.10 % carbon and are designated by the letter ‘H’ after the steel grade. ‘H’ grades are primarily used at extreme temperatures as the higher carbon helps the material retain strength at extreme temperatures.
Austenitic stainless steels can also be classified into following three groups.
All austenitic stainless steels contain a small amount of ferrite. Conventional austenitic stainless steel grades may contain traces of delta ferrite, for improved weldability. Usually this amount of ferrite is not enough to attract a normal magnet. However, if the balance of elements in the steel favours the ferritic end of the spectrum, it is possible for the amount of ferrite to be sufficient to cause a significant magnetic response. Also, some types of stainless steels are deliberately balanced to have a significant amount of ferrite.
Properties and of stainless steels
Austenitic stainless steels are non magnetic and are not heat treatable. They cannot be hardened by heat treatment. However, they can be cold worked to improve hardness, strength and stress resistance. A solution anneal (heating within the range 1000 deg C to 1200 deg C followed by quenching or rapid cooling) restores the stainless steels original condition, including removal of alloy segregation and re-establishment of ductility after cold working. Stainless steels can be subjected to solution annealing. Due to the solution annealing the carbides, which may have precipitated (or moved) at the grain boundaries, are put back into solution (dispersed) into the matrix of the metal by the annealing process. ‘L’ grades are used where annealing after welding is impractical.
Austenitic stainless steels can be made soft enough (i.e. with yield strength of around 200 N/sq mm) to be easily formed by the same tools that work with carbon steel, but they can be made incredibly strong by cold work, up to yield strengths of over 2000 N/sq mm. Their austenitic (fcc, face centered cubic) structure is very tough and ductile down to absolute temperature. They also do not lose their strength at elevated temperatures as rapidly as ferritic (bcc, body centered cubic) iron base alloys.
Austenitic grades of stainless steels are the most common used grades, mainly because they provide very predictable level of corrosion resistance with excellent mechanical properties. The least corrosion resistant versions can withstand the normal corrosive attack of the everyday environment that people experience, while the most corrosion resistant grades can even withstand boiling seawater.
Austenitic stainless steels have good formability and weldability, as well as excellent toughness, particularly at low, or cryogenic, temperatures. Austenitic grades also have a low yield stress and relatively high tensile strength. They have excellent corrosion resistance and excellent high-temperature tensile and creep strength.
Austenitic stainless steels are not very strong materials. Typically their 0.2 % proof stress is about 250 N/sq mm and the tensile strength between 500 and 600 N/sq mm, showing that these steels have substantial capacity for work hardening, which makes working more difficult than in the case of mild steel. However, austenitic stainless steels possess very good ductility with elongations of about 50 % in tensile tests.
Austenitic stainless steels are also highly resistant to high temperature oxidation because of the protective surface film, but the usual grades have low strengths at elevated temperatures. Those steels stabilized with Ti and Nb, grades 321 and 347, can be heat treated to produce a fine dispersion of TiC or NbC which interacts with dislocations generated during creep. One of the most commonly used alloys is 25Cr20Ni with additions of titanium or niobium which possesses good creep strength at temperatures as high as 700 deg C.
Austenitic stainless steels are ductile over a wide temperature range, from cryogenic to creep temperatures. They do not display brittle fracture. Their tensile strength is high at low temperatures. They can be work hardened to high levels of strength by cold forming.
Austenitic stainless steels are less resistant to cyclic oxidation than are ferritic grades because their greater thermal expansion coefficient tends to cause the protective oxide coating to spall. They can experience stress corrosion cracking (SCC) if used in an environment to which they have insufficient corrosion resistance. The fatigue endurance limit is only about 30 % of the tensile strength (vs. 50 % – 60 % for ferritic stainless steels). This, combined with their high thermal expansion co efficient, makes them especially susceptible to thermal fatigue. However, the risks of these limitations can be avoidable by taking special precautions.
The salient feature of austenitic stainless steels is that as chromium and molybdenum contents are increased to increase specific properties, usually corrosion resistance, nickel or other austenitic stabilizers must be added if the austenitic structure is to be preserved.
The tensile properties in the annealed state not surprisingly relate well to composition. The 0.2 % yield strength applies to the austenitic stainless steels.
Austenitic stainless steels have many advantages from a metallurgical point of view. Their properties include good to excellent corrosion resistance. They can be work hardened. They can be easily machined and fabricated to tight tolerances. They have smooth surface finish that can be easily cleaned and sterilized. They are temperature resistant from cryogenic to high heat temperatures.
Austenitic stainless steels are classified in the 200 and 300 series, with 16% to 30% chromium and 2% to 20% nickel for enhanced surface quality, formability, increased corrosion and wear resistance. Austenitic stainless steels are non-hardenable by heat treating. These steels are the most popular grades of stainless produced due to their excellent formability and corrosion resistance. All austenitic steels are nonmagnetic in the annealed condition. Depending on the composition, some austenitics do become somewhat magnetic when cold worked. Austenitics are used for automotive trim, cookware, food and beverage equipment, processing equipment, and a variety of industrial applications.
Corrosion resistance in stainless steels is primarily determined by chromium content. Austenitic stainless steels, as a class, have excellent corrosion resistance and those with molybdenum additions have improved pitting resistance. The nickel content in austenitic stainless steels helps to reduce the rate of corrosion, particularly in acid environments. Austenitic grades, however, are susceptible to chloride stress corrosion cracking (SCC) and are not recommended for service that combines tensile stress and the presence of chlorides, even at moderate temperatures. Higher carbon austenitic grades can be susceptible to intergranular corrosion after certain high temperature exposures, including welding. For applications that require welding, a post-weld heat treatment or selection of a low carbon or stabilized grade such as Type 304L, 316L and 321, is recommended.
304 and 304L (standard grade):
309 and 310 (high chrome and nickel grades):
318 and 316L (high moly content grades):
321 and 316Ti ("stabilized" grades):
200 Series (low nickel grades):
Austenitic steels are non-magnetic stainless steels that contain high levels of chromium and nickel and low levels of carbon. Known for their formability and resistance to corrosion, austenitic steels are the most widely used grade of stainless steel.
Defining Characteristics Ferritic steels have a body-centered cubic (BCC) grain structure, but the austenitic range of stainless steels are defined by their face-centered cubic (FCC) crystal structure, which has one atom at each corner of the cube and one in the middle of each face. This grain structure forms when a sufficient quantity of nickel is added to the alloy—8 to 10 percent in a standard 18 percent chromium alloy.
In addition to being non-magnetic, austenitic stainless steels are not heat treatable. They can be cold worked to improve hardness, strength, and stress resistance, however. A solution anneals heated to 1045° C followed by quenching or rapid cooling will restore the alloy's original condition, including removing alloy segregation and re-establishing ductility after cold working.
Nickel-based austenitic steels are classified as 300 series. The most common of these is grade 304, which typically contains 18 percent chromium and 8 percent nickel.
Eight percent is the minimum amount of nickel that can be added to a stainless steel containing 18 percent chromium in order to completely convert all the ferrite to austenite. Molybdenum can also be added to a level of about 2 percent for grade 316 to improve corrosion resistance.
Although nickel is the alloying element most commonly used to produce austenitic steels, nitrogen offers another possibility. Stainless steels with a low nickel and high nitrogen content are classified as 200 series. Because it is a gas, however, only limited amounts of nitrogen can be added before deleterious effects arise, including the formation of nitrides and gas porosity that weaken the alloy.
The addition of manganese, also an austenite former, combined with the inclusion of nitrogen allows for greater amounts of the gas to be added. As a result, these two elements, along with copper—which also has austenite-forming properties—are often used to replace nickel in 200 series stainless steels.
The 200 series—also referred to as chromium-manganese (CrMn) stainless steels—were developed in the 1940s and 1950s when nickel was in short supply and prices were high. It is now considered a cost-effective substitute for 300 series stainless steels that can provide an additional benefit of improved yield strength.
Straight grades of austenitic stainless steels have a maximum carbon content of 0.08 percent. Low carbon grades or "L" grades contain a maximum carbon content of 0.03 percent in order to avoid carbide precipitation.
Austenitic steels are non-magnetic in the annealed condition, although they can become slightly magnetic when cold worked. They have good formability and weldability, as well as excellent toughness, particularly at low or cryogenic temperatures. Austenitic grades also have a low yield stress and relatively high tensile strength.
While austenitic steels are more expensive than ferritic stainless steels, they are generally more durable and corrosion resistant.
Nickel which stabilizes the austenitic structure of these steels restricts their widespread usage since nickel increases the costs of these stainless steels.
Other steels can offer similar performance at lower cost and are preferred in certain applications, for example ASTM A387 is used in pressure vessels but is a low-alloy carbon steel with a chromium content of 0.5 % to 9 %. Low-carbon versions, for example 316L or 304L, are used to avoid corrosion problems caused by welding. Grade 316LVM is preferred where biocompatibility is required (such as body implants and piercings).
Austenitic grades of stainless steels are the most commonly used grades, mainly because they provide very predictable level of corrosion resistance with excellent mechanical properties. Using them wisely can save the designer of a product significant cost. These steels are user friendly metal alloy with life cycle cost of fully manufactured products lower than many other materials.
Austenitic stainless steels are those steels which are commonly used for stainless application. Some of the applications for austenitic stainless steel include the following.
Super austenitic stainless steels contain high levels of chromium and higher levels of nickel together with additions of molybdenum and nitrogen. The result is a series of austenites, stronger than conventional 300 series stainless and with superior resistance to pitting, crevice corrosion, and stress corrosion cracking.
Super austenitic stainless steel is defined as Cr-Ni stainless steel with a Pitting Resistance Equivalent Number （PREN=[Cr]+3.3[Mo]+16[N]）≥40%. It has better resistance to chloride pitting and crevice corrosion than Cr-Ni austenitic stainless steel with Mo ＞4% in highly corrosive media containing Cl-
Grades：
Features：
Specifications：
Machinability
Work hardening produces hard surfaces and hard chips , which in turn lead to notch wear. It also creates adhesion and produces built-up edge (BUE). It has a relative machinability of 60%. The hardening condition can tear coating and substrate material from the edge, resulting in chipping and bad surface finish. Austenite produces tough, long, continuous chips, which are difficult to break. Adding S improves machinability, but results in lowered resistance to corrosion.
Rupture Strength Curve of S30432 Ultra-Supercritical Boiler Tube
Use sharp edges with a positive geometry.
Cut under the work hardened layer.
Keep cutting depth constant. Generates a lot of heat when machined.
The application fields are very wide, mainly nuclear power, oil refining industry, atmospheric and vacuum equipment, catalytic cracking equipment, hydrocracking, hydrotreating equipment; Vinyl chloride production units, formaldehyde synthesis reactors, acetic acid and other organic acid production units in the petrochemical and chemical industry; The oil and gas industry; Pulp and paper industry; Urea industry and phosphate fertilizer industry in fertilizer industry; Seawater environment; Energy and environmental protection industry; Salt and chemical equipment for light industry and food industry, equipment for food and pharmaceutical industry, etc.
To simplify grade identification and align with international designations, China adopted the “Universal Code System for Steel and Alloy Grades” (e.g. 06Cr19Ni10 corresponds to 304). While chemical compositions vary slightly between standards, each grade is governed by its national standard.
| No | China (GB) | Japan (JIS) |
USA | Korea (KS) |
Europe (EN Werkstoff) |
India (IS) |
Australia | Taiwan (CNS) |
||
|---|---|---|---|---|---|---|---|---|---|---|
| Old | New (2007) | SUS | ASTM | UNS | STS | W.-Nr. | IS | Approx. | CNS | |
| Austenitic stainless steel | ||||||||||
| 1 | 1Cr17Mn6Ni5N | 12Cr17Mn6Ni5N | SUS201 | 201 | S20100 | STS201 | 1.4372 | 10Cr17Mn6Ni4N20 | 201-2 | 201 |
| 2 | 1Cr18Mn8Ni5N | 12Cr18Mn9Ni5N | SUS202 | 202 | S20200 | STS202 | 1.4373 | – | – | 202 |
| 3 | 1Cr17Ni7 | 12Cr17Ni7 | SUS301 | 301 | S30100 | STS301 | 1.4319 | 10Cr17Ni7 | 301 | 301 |
| 4 | 0Cr18Ni9 | 06Cr19Ni10 | SUS304 | 304 | S30400 | STS304 | 1.4301 | 07Cr18Ni9 | 304 | 304 |
| 5 | 00Cr19Ni10 | 022Cr19Ni10 | SUS304L | 304L | S30403 | STS304L | 1.4306 | 02Cr18Ni11 | 304L | 304L |
| 6 | 0Cr19Ni9N | 06Cr19Ni10N | SUS304N1 | 304N | S30451 | STS304N1 | 1.4315 | – | 304N1 | 304N1 |
| 7 | 0Cr19Ni10NbN | 06Cr19Ni9NbN | SUS304N2 | XM21 | S30452 | STS304N2 | – | – | 304N2 | 304N2 |
| 8 | 00Cr18Ni10N | 022Cr19Ni10N | SUS304LN | 304LN | S30453 | STS304LN | – | – | 304LN | 304LN |
| 9 | 1Cr18Ni12 | 10Cr18Ni12 | SUS305 | 305 | S30500 | STS305 | 1.4303 | – | 305 | 305 |
| 10 | 0Cr23Ni13 | 06Cr23Ni13 | SUS309S | 309S | S30908 | STS309S | 1.4833 | – | 309S | 309S |
| 11 | 0Cr25Ni20 | 06Cr25Ni20 | SUS310S | 310S | S31008 | STS310S | 1.4845 | – | 310S | 310S |
| 12 | 0Cr17Ni12Mo2 | 06Cr17Ni12Mo2 | SUS316 | 316 | S31600 | STS316 | 1.4401 | 04Cr17Ni12Mo2 | 316 | 316 |
| 13 | 0Cr18Ni12Mo3Ti | 06Cr17Ni12Mo2Ti | SUS316Ti | 316Ti | S31635 | – | 1.4571 | 04Cr17Ni12MoTi20 | 316Ti | 316Ti |
| 14 | 00Cr17Ni14Mo2 | 022Cr17Ni12Mo2 | SUS316L | 316L | S31603 | STS316L | 1.4404 | 02Cr17Ni12Mo2 | 316L | 316L |
| 15 | 0Cr17Ni12Mo2N | 06Cr17Ni12Mo2N | SUS316N | 316N | S31651 | STS316N | – | – | 316N | 316N |
| 16 | 00Cr17Ni13Mo2N | 022Cr17Ni13Mo2N | SUS316LN | 316LN | S31653 | STS316LN | 1.4429 | – | 316LN | 316LN |
| 17 | 0Cr18Ni12Mo2Cu2 | 06Cr18Ni12Mo2Cu2 | SUS316J1 | – | – | STS316J1 | – | – | 316J1 | 316J1 |
| 18 | 00Cr18Ni14Mo2Cu2 | 022Cr18Ni14Mo2Cu2 | SUS316J1L | – | – | STS316J1L | – | – | – | 316J1L |
| 19 | 0Cr19Ni13Mo3 | 06Cr19Ni13Mo3 | SUS317 | 317 | S31700 | STS317 | – | – | 317 | 317 |
| 20 | 00Cr19Ni13Mo3 | 022Cr19Ni13Mo3 | SUS317L | 317L | S31703 | STS317L | 1.4438 | – | 317L | 317L |
| 21 | 0Cr18Ni10Ti | 06Cr18Ni11Ti | SUS321 | 321 | S32100 | STS321 | 1.4541 | 04Cr18Ni10Ti20 | 321 | 321 |
| 22 | 0Cr18Ni11Nb | 06Cr18Ni11Nb | SUS347 | 347 | S34700 | STS347 | 1.4550 | 04Cr18Ni10Nb40 | 347 | 347 |
| Austenitic-ferritic (Duplex) stainless steel | ||||||||||
| 23 | 0Cr26Ni5Mo2 | – | SUS329J1 | 329 | S32900 | STS329J1 | 1.4477 | – | 329J1 | 329J1 |
| 24 | 00Cr18Ni5Mo3Si2 | 022Cr19Ni5Mo3Si2N | SUS329J3L | – | S31803 | STS329J3L | 1.4462 | – | 329J3L | 329J3L |
| Ferritic stainless steel | ||||||||||
| 25 | 0Cr13Al | 06Cr13Al | SUS405 | 405 | S40500 | STS405 | 1.4002 | 04Cr13 | 405 | 405 |
| 26 | – | 022Cr11Ti | SUH409 | 409 | S40900 | STS409 | 1.4512 | – | 409L | 409L |
| 27 | 00Cr12 | 022Cr12 | SUS410L | – | – | STS410L | – | – | 410L | 410L |
| 28 | 1Cr17 | 10Cr17 | SUS430 | 430 | S43000 | STS430 | 1.4016 | 05Cr17 | 430 | 430 |
| 29 | 1Cr17Mo | 10Cr17Mo | SUS434 | 434 | S43400 | STS434 | 1.4113 | – | 434 | 434 |
| 30 | – | 022Cr18NbTi | – | – | S43940 | – | 1.4509 | – | 439 | 439 |
| 31 | 00Cr18Mo2 | 019Cr19Mo2NbTi | SUS444 | 444 | S44400 | STS444 | 1.4521 | – | 444 | 444 |
| Martensitic stainless steel | ||||||||||
| 32 | 1Cr12 | 12Cr12 | SUS403 | 403 | S40300 | STS403 | – | – | 403 | 403 |
| 33 | 1Cr13 | 12Cr13 | SUS410 | 410 | S41000 | STS410 | 1.4006 | 12Cr13 | 410 | 410 |
| 34 | 2Cr13 | 20Cr13 | SUS420J1 | 420 | S42000 | STS420J1 | 1.4021 | 20Cr13 | 420 | 420J1 |
| 35 | 3Cr13 | 30Cr13 | SUS420J2 | – | – | STS420J2 | 1.4028 | 30Cr13 | 420J2 | 420J2 |
| 36 | 7Cr17 | 68Cr17 | SUS440A | 440A | S44002 | STS440A | – | – | 440A | 440A |
During manufacturing, the actual dimensions of stainless steel tubes and pipes often deviate from the nominal sizes. Such deviations are defined as tolerances and have been strictly standardized.
A positive deviation is called positive tolerance, and a negative deviation is called negative tolerance.
Outside diameter (OD), wall thickness and length are the three fundamental parameters in stainless steel tube & pipe manufacturing and distribution. Among them, OD and wall thickness are critical to structural design, fluid conveyance and downstream processing.
A. Nominal Pipe Size: The idealized dimension specified in standards such as ASME B36.10M and ASME B36.19M. It is the ordered size stated in contracts.
B. Actual Pipe Size: The real dimension obtained after production. Deviation occurs when the actual size is larger or smaller than the nominal size.
European standards define four tolerance classes for OD and wall thickness based on the nominal dimension, expressed either as percentages or absolute values. Larger diameters or heavier walls typically use percentage tolerances, while small-diameter or thin-wall tubes use absolute values.
| Standard | Process & Type | OD Tolerance | Wall Thickness Tolerance | Remarks | |
|---|---|---|---|---|---|
| OD (mm) | Class | ||||
| EN 10216-5 | Hot Finished Seamless | 219.1–610 | D1 | +22.5%T, –15%T | T/D ≤ 0.05 |
| T1 | T/D ≤ 0.09 | ||||
| T2 | T/D > 0.09 | ||||
| 30–219.1 | D2 | T1 | |||
| T2 | |||||
| Cold Finished Seamless | ≤219.1 | D3 | T3 | ||
| D4 | T4 | By agreement | |||
| EN 10297-2 | Hot Finished Seamless | – | D1 | T1 | |
| D2 | T2 | By agreement | |||
| Cold Finished Seamless | – | D3 | T3 | ||
| D4 | T4 | By agreement | |||
| EN 10217-7 | Welded | >168.3 | D2 | T3 | |
| ≤168.3 | D3 | T3 | |||
| D4 | T3 | By agreement | |||
| EN 10296-2 | Welded | >168.3 | D2 | T3 | |
| ≤168.3 | D3 | T3 | |||
| ≤114.3 | D4 | T3 | By agreement | ||
| EN 10312 | Welded | Series 1 | D4 | T3 | T = 0.6–2 mm |
| Series 2 | D3–D4 | T3–T4 | T = 1–3 mm | ||
OD classes D1–D4 and wall thickness classes T1–T4 follow DIN EN ISO 1127: Dimensions, tolerances and conventional masses per unit length.
| Outside Diameter | Wall Thickness | ||
|---|---|---|---|
| Class | Tolerance | Class | Tolerance |
| D1 | ±1.5% or ±0.75 mm min. | T1 | ±15% or ±0.6 mm min. |
| D2 | ±1.0% or ±0.5 mm min. | T2 | ±12.5% or ±0.4 mm min. |
| D3 | ±0.75% or ±0.3 mm min. | T3 | ±10% or ±0.2 mm min. |
| D4 | ±0.50% or ±0.1 mm min. | T4 | ±7.5% or ±0.15 mm min. |
| T5 | ±5.0% or ±0.10 mm min. | ||
Where both percentage and absolute values apply, the greater value shall be used.
ASTM specifications are primarily governed by ASTM A999/A999M and A1016/A1016M.
| ASTM A999 | ASTM A1016 |
|
|
A511 (seamless mechanical tubing) and A554 (welded mechanical tubing) are exceptions and have independent tolerance tables.
| Standard | Process / Condition | OD (mm) | OD Tolerance (mm) | Wall Thickness T (mm) | Wall Thickness Tolerance | |
|---|---|---|---|---|---|---|
| Minimum | Average | |||||
| ASTM A1016/A1016M | Hot Drawn Seamless | ≤100 | +0.4 / –0.8 | ≤2.4 | +0.4t / 0 | |
| 100–200 | +0.4 / –1.2 | 2.4–3.8 | +0.35t / 0 | |||
| 200–225 | +0.4 / –1.6 | 3.8–4.6 | +0.33t / 0 | |||
| ≥4.6 | +0.28t / 0 | |||||
| Cold Drawn Seamless | <25 | ±0.1 | +0.20t / 0 | ±0.10t | ||
| 25–40 | ±0.1 | +0.20t / 0 | ±0.10t | |||
| 40–50 | ±0.2 | +0.22t / 0 | ±0.10t | |||
| 50–65 | ±0.25 | +0.22t / 0 | ±0.10t | |||
| 65–75 | ±0.3 | +0.22t / 0 | ±0.10t | |||
| 75–100 | ±0.38 | +0.22t / 0 | ±0.10t | |||
| 100–200 | +0.38 / –0.04 | +0.22t / 0 | ±0.10t | |||
| 200–250 | +0.38 / –1.14 | +0.22t / 0 | ±0.10t | |||
| Welded | 40–50 | ±0.2 | +0.18t / 0 | ±0.10t | ||
| 50–65 | ±0.25 | +0.18t / 0 | ±0.10t | |||
| 65–75 | ±0.3 | +0.18t / 0 | ±0.10t | |||
| 75–100 | ±0.38 | +0.18t / 0 | ±0.10t | |||
| 100–200 | +0.38 / –0.04 | +0.18t / 0 | ±0.10t | |||
| 200–250 | +0.38 / –1.14 | +0.18t / 0 | ±0.10t | |||
| ASTM A999 | Seamless & Welded | <48.3 | +0.4 / –0.8 | –0.125t | ||
| ASTM A312 | Seamless & Welded | 48.3–114.3 | ±0.8 | OD=10.3–73 | +0.20t / –0.125t | |
| 168.3–219.1 | +1.6 / –0.8 | t/OD≤5%, OD=88.9–457.2 | +0.225t / –0.125t | |||
| 219.1–457.2 | +2.4 / –0.8 | t/OD>5%, OD=88.9–457.2 | +0.15t / –0.125t | |||
| Welded | 508–660 | +3.2 / –0.8 | OD≥508 | +0.175t / –0.125t | ||
| 711–864 | +4.0 / –0.8 | t/OD≤5%, OD≥508 | +0.225t / –0.125t | |||
| Seamless | 914–1209 | +4.8 / –0.8 | t/OD>5%, OD≥508 | +0.15t / –0.125t | ||
| ASTM A409 | Welded | ±0.2% (t<4.8) ±0.4% (t≥4.8) |
||||
| ASTM A358 | Welded | ±0.50% | ||||
| ASTM A511 | Seamless Mechanical | ≤12.7 | ±0.1 | ±0.15t | ||
| 12.7–38.1 | ±0.2 | ±0.10t | ||||
| 38.1–88.9 | ±0.3 | ±0.10t | ||||
| 88.9–139.7 | ±0.4 | ±0.10t | ||||
| 139.7–203.1 | ±0.8 | ±0.10t | ||||
| 203.1–220 | ±1.1 | ±0.10t | ||||
| 220–325 | ±1.6 | ±0.10t | ||||
U.S. standards predominantly use absolute OD tolerances, often asymmetrical. In many cases, average OD accuracy exceeds D4 class per EN ISO 1127.
Typical wall thickness tolerance: ±10%t or tighter. Pipeline products allow larger tolerances, with hot-finished seamless pipe being the most permissive.
China’s stainless steel tube & pipe standards are broadly aligned with European practice, while incorporating select provisions from U.S. specifications.
| Specification | Process | OD (mm) | OD Tolerance | Wall (mm) | Wall Tolerance | |
|---|---|---|---|---|---|---|
| GB 13296 | Cold Rolled Seamless | 6–30 | ±0.15 / –0.2 | 1–3 | +20% | 0% |
| >30–50 | ±0.3 | >3 | +22% | 0% | ||
| >50 | ±0.75% | Average wall thickness applies | ||||
| GB/T 14976 | Cold Rolled Seamless | 6–10 | ±0.15 | 1–3 | +12.5% | –12.5% |
| 10–30 | ±0.2 | >3 | +12.5% | –10% | ||
| 30–50 | ±0.3 | Average wall: +22% | ||||
| >50 | ±0.8% | |||||
Wall thickness tolerances in Chinese standards are generally comparable to mainstream U.S. and European specifications, though slightly less stringent than the highest EU accuracy classes.
OD tolerances in Chinese standards are typically tighter than U.S. requirements and approach EU levels. U.S. standards place stronger emphasis on tight OD control relative to wall thickness.
Neither Chinese nor European standards prescribe weight tolerances. Seamless tubes may be delivered by actual or theoretical weight; welded tubes are typically delivered by theoretical weight, optionally by actual weight.
Ovality is the difference between the maximum and minimum OD measured on the same cross-section. It is determined by measuring the high and low points of the tube or pipe.
Eccentricity describes variation in wall thickness around the circumference. High-precision applications require tight concentricity.
EN standards incorporate concentricity within wall thickness tolerances. ASTM A1016/A1016M specifies concentricity for OD ≥ 50 mm and t ≥ 5.6 mm.
Seamless tubes:
WTmax – WTmin ≤ ±10% × (WTmax + WTmin) / 2Welded tubes:
WTmax – WTmin ≤ 5% × (WTmax + WTmin) / 2Standard tubes are supplied straightened to the eye. For special applications, permissible deviation from straightness may be agreed upon. It is expressed per unit length, e.g. 1 mm per 1000 mm.
| OD (mm) ≤ | OD (inches) ≤ | Wall | Commercial Straightness | Achievable (mm/m) |
|---|---|---|---|---|
| 15.9 | 0.625 | All sizes | 1 in 600 | 1 in 2000 |
| 25.4 | 1.00 | ≥2% of OD | 1 in 600 | 1 in 1500 |
| 25.4 | 1.00 | <2% of OD | 1 in 400 | 1 in 1000 |
Delivery length is the length requested by the purchaser and specified in the contract. Standards define several types:
A. Normal / Random Length: Within the standard range, without fixed length requirement. Example: hot-finished pipe 3000–12000 mm; cold-drawn pipe 2000–10500 mm.
B. Fixed Length: A specific length within the normal range. An allowable positive deviation applies.
Fixed-length production yields significantly lower than random length. Price premiums of approximately 10% are common.
C. Multiple Length: Total length is a multiple of a single length, with an additional cutting allowance. Example: 3000 mm × 3 = 9000 mm total.
Cutting allowances: 5–10 mm for OD ≤ 159 mm; 10–15 mm for OD > 159 mm.
D. Range Length: A defined length interval within the normal range. Example: 6000–8000 mm or 8000–10000 mm. Premiums of ~4% are typical.
Density is defined as mass per unit volume. For stainless steels, typical densities range from 7600 kg/m³ to 8000 kg/m³, depending on alloy composition.
Stainless steels contain a minimum of 10.5% chromium, along with alloying elements such as nickel, molybdenum, titanium and copper. These elements enhance strength and corrosion resistance but also influence density.
Even within the same grade, exact density may vary slightly due to compositional tolerances. The values below are theoretical references for engineering calculations.
| Grade Family | Typical Grades | Density (g/cm³) | Density (kg/m³) |
|---|---|---|---|
| Austenitic (Cr-Ni) |
201, 202, 301, 302, 303, 304, 304L, 304LN, 305, 321 |
7.93 | 7930 |
| Austenitic (Mo-bearing) |
309S, 310S, 316, 316L, 316Ti, 316LN, 317, 317L, 347 |
7.98 | 7980 |
| Super Austenitic | 904L | 7.98 | 7980 |
| Duplex | 2205 / S31803 | 7.80 | 7800 |
| Super Duplex | S32750 | 7.85 | 7850 |
| Martensitic | 403, 410, 410S, 416, 431 | 7.75 | 7750 |
| Martensitic (High C) | 440A / 440C | 7.74 / 7.62 | 7740 / 7620 |
| Martensitic | 420 | 7.73 | 7730 |
| Ferritic | 439, 430, 430F | 7.70 | 7700 |
| Ferritic (Mo-bearing) | 434 / 444 | 7.74 / 7.75 | 7740 / 7750 |
| Ferritic | 405 | 7.72 | 7720 |
* Values are given at standard temperature and pressure (STP).
304 and 316 are the most widely used austenitic grades. 304 has a density of 7930 kg/m³, while 316 measures 7980 kg/m³. This difference must be accounted for when calculating theoretical weights for procurement or design.
Density is commonly expressed in g/cm³, kg/m³ or lb/in³. The following conversion applies:
1 kg/m³ = 0.001 g/cm³ = 0.000036127 lb/in³
Stainless steel density varies with environmental conditions. Increasing temperature generally reduces density, while increasing pressure raises density. For precision engineering, these effects should be considered in high-temperature or high-pressure service.
Seamless and welded tubes and pipes are the two primary product forms for stainless steel. For decades, there has been ongoing discussion regarding which type offers superior performance.
With advances in metallurgy and welding technology, the debate now centers on structural integrity and corrosion resistance—particularly within the weld zone of welded products. Fundamentally, the key distinction lies in the manufacturing process.
In certain highly corrosive or high-pressure applications, selecting a higher-performance alloy—rather than simply choosing seamless over welded—may be the most effective solution.
Strip-welded tubes are produced from stainless steel coils or strips. The strip passes through grooved rollers, gradually forming a circular profile. As the edges converge, they are joined by automatic welding.
The most common welding process is TIG (GTAW), which provides excellent protection of the weld seam and consistent metallurgical quality.
After welding, the seam is typically ground flush, followed by solution annealing or stress-relief heat treatment, depending on application requirements. Modern production lines often integrate inline induction annealing, straightening, dimensional calibration, cutting to length, deburring and non-destructive testing.
TIG welding of stainless steel tubing
For large-diameter or heavy-wall pipes, the manufacturing route differs. Production begins with stainless steel plates rather than strips. Plates are plasma-cut to size, edge-prepared, and formed using roller bending machines or hydraulic presses.
Welding methods such as EFW (Electric Fusion Welding) or ERW (Electric Resistance Welding) are commonly applied. For critical services, double-sided welding may be employed to ensure full penetration and structural integrity.
For large-diameter welded pipes, radiographic examination (RT) and hydrostatic testing (HT) are typically mandatory. Double-sided welding is commonly accepted and specified for high-integrity applications.
Chemical composition inspection, mechanical properties test(tensile strength,yield strength, elongation, flaring, flattening, bending, hardness, impact test), surface and dimension test,no-destructive test, hydrostatic test.
identification of the chemical composition of the metal used to manufacture the fitting. Uses PMI sensors, including X-ray fluorescence or optical emission spectrometry.
Common delivery conditions for stainless steel tubes and pipes: cold-hard (BK), cold-soft (BKW), stress-relieved (BKS), annealed (GBK), and normalized (NBK).
| Term | Symbol | Explanation |
|---|---|---|
| Cold-finished / Hard | BK | No heat treatment after final cold-forming. Low deformability. |
| Cold-finished / Soft | BKW | Light finishing pass after heat treatment. Limited cold-formability (bending, expanding). |
| Annealed | GBK | Annealed after final cold-forming in controlled atmosphere or vacuum. |
| Normalized | NBK | Annealed above upper transformation point in controlled atmosphere or vacuum. |
Bare packing / bundle packing / crate packing with wooden protection at both ends, suitable for seaworthy delivery or as requested.
While hundreds of packing methods exist, two principles are mandatory: corrosion prevention and secure sea transport.
Sunny Steel packing can be fully customized to meet customer requirements.
Stainless steel tubes can be beveled at one or both ends to match complementary joints. Beveling simplifies welding preparation, reduces on-site cutting time and lowers installation costs.
Sunny Steel provides heat treatment for selected 400-series stainless steels. Processes include stress relieving, tempering, quenching, normalizing and solution annealing to achieve required mechanical properties and microstructure.
Honing and turning refine the internal surface of tubes and pipes to precise diameters and geometric tolerances. This secondary operation relieves residual stress and improves surface finish after drilling, reaming and heat treatment.
Internal and external polishing is available to meet sanitary, pharmaceutical and high-purity process requirements.
PMI testing verifies alloy composition to ensure compliance with specifications. Sunny Steel performs in-house PMI or coordinates with independent laboratories for critical applications.
UT uses high-frequency sound waves to detect internal flaws, measure wall thickness and verify material integrity. This non-destructive test is routinely applied to seamless and welded stainless steel tubes.
All products are supplied with EN 10204 3.1 Mill Test Certificates. Third-party inspection (SGS, BV, TÜV) is available upon request.
Commonly used alloying elements and their effects are listed in the table given below.
| Alloying Elements | Effect on the Properties |
|---|---|
| Chromium | Increases Resistance to corrosion and oxidation. Increases hardenability and wear resistance. Increases high temperature strength. |
| Nickel | Increases hardenability. Improves toughness. Increases impact strength at low temperatures. |
| Molybdenum | Increases hardenability, high temperature hardness, and wear resistance. Enhances the effects of other alloying elements. Eliminate temper brittleness in steels. Increases high temperature strength. |
| Manganese | Increases hardenability. Combines with sulfur to reduce its adverse effects. |
| Vanadium | Increases hardenability, high temperature hardness, and wear resistance. Improves fatigue resistance. |
| Titanium | Strongest carbide former. Added to stainless steel to prevent precipitation of chromium carbide. |
| Silicon | Removes oxygen in steel making. Improves toughness. Increases hardness ability |
| Boron | Increases hardenability. Produces fine grain size. |
| Aluminum | Forms nitride in nitriding steels. Produces fine grain size in casting. Removes oxygen in steel melting. |
| Cobalt | Increases heat and wear resistance. |
| Tungsten | Increases hardness at elevated temperatures. Refines grain size. |
Ceramic lined pipe is made through self-propagating high-temperature synthesis (SHS) technique.
Cast basalt lined steel pipe is composed by lined with cast basalt pipe, outside steel pipe and cement mortar filling between the two layers.
Ceramic tile lined pipes have very uniform coating of specially formulated ceramic material that is affixed to the inner of the pipe.
The material of the rare earth alloy wear-resistant pipe is ZG40CrMnMoNiSiRe, which is also the grade of rare earth alloy steel.
Tubes Erosion Shields are used to protect boiler tubing from the highly erosive effects of high temperatures and pressures thereby greatly extending tube life.
The ASTM A213 T91 seamless tubes are primarily used for boiler, superheater, and heat-exchanger.
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