Overview of characteristics of stainless pipes

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Stain­less steel is a mate­r­i­al that is par­tic­u­lar­ly resis­tant to cor­ro­sion. Pipes made from it can last for decades even when exposed to an aggres­sive envi­ron­ment. In addi­tion, stain­less steel prod­ucts have an attrac­tive appear­ance. But in order to take full advan­tage of these advan­tages, you need to know the types of any stain­less pipes, their main dimen­sions and char­ac­ter­is­tics.

Stain­less steel pro­files

Properties of stainless steel pipes

The main require­ment for all steel grades in this cat­e­go­ry is a high con­tent of chromi­um in it. The min­i­mum con­tent of this met­al is reg­u­lat­ed at 12%. It cre­ates a spe­cial film on the sur­face of the prod­uct that pro­tects the mate­r­i­al from exter­nal influ­ences. It also con­tributes to the fact that the medi­um pumped through the pipeline is also not sub­ject to changes. This is espe­cial­ly impor­tant for drink­ing water and food mains.

Inex­pen­sive steel grades are lim­it­ed only by the pres­ence of chromi­um. They dif­fer in plas­tic­i­ty and resis­tance to defor­ma­tions. To give spe­cial strength and resis­tance to cor­ro­sion, molyb­de­num, nick­el, tita­ni­um and oth­er alloy­ing addi­tives are added to the com­po­si­tion.

In addi­tion to chromi­um, the pres­ence of sul­fur and its com­pounds in steel is also reg­u­lat­ed. It is believed that their max­i­mum con­tent should not exceed 0.02%.

The sur­face of stain­less steel pro­files can be pol­ished on spe­cial machines to a mir­ror state. This not only gives an attrac­tive appear­ance, but also cre­ates addi­tion­al pro­tec­tion against sources of cor­ro­sion. Despite the increased price of pol­ished prod­ucts, they are in demand as a design ele­ment.

Classification of stainless steel pipes

Accord­ing to the shape of the inter­nal sec­tion, they dis­tin­guish:

  • round,
  • ellip­ti­cal,
  • square and rec­tan­gu­lar.
Pos­si­ble forms of stain­less steel pro­files

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Cor­ru­gat­ed options are con­sid­ered a sep­a­rate class. They are char­ac­ter­ized by spe­cial plas­tic­i­ty and the abil­i­ty to under­go repeat­ed cycles of com­pres­sion and ten­sion both in the lon­gi­tu­di­nal and trans­verse direc­tions.

With var­i­ous meth­ods of man­u­fac­tur­ing stain­less steel, they may dif­fer in the pres­ence or absence of a seam on the fin­ished prod­uct. Accord­ing to this para­me­ter, pipes are dis­tin­guished:

  • seam­less,
  • straight seam,
  • spi­ral stitch.

Seamless technology

The pro­duc­tion of sol­id pro­files is car­ried out with­out the use of weld­ing, by rolling on spe­cial blanks. Such prod­ucts have increased ten­sile strength and are able to with­stand sig­nif­i­cant loads. There­fore, they are used in pipelines with high pres­sure or where spe­cial reli­a­bil­i­ty is required.

The method of man­u­fac­tur­ing with­out seam for­ma­tion leads to an increase in the cost of the out­put prod­uct. It is unprof­itable to use these prod­ucts in the domes­tic sphere.

Pro­duc­tion and stan­dard sizes of seam­less stain­less pipes are reg­u­lat­ed by GOST 9940–81 and 9941–81.

Straight seam welding

The blanks for this tech­nol­o­gy are steel sheets. They are bent on spe­cial press­es into a cir­cle of the required diam­e­ter. The edges of the sheets at the junc­tion are weld­ed togeth­er to form a seam run­ning along the entire length.

Stain­less pipes with a straight seam

Weld­ing meth­ods can be dif­fer­ent, but the main one is elec­tric weld­ing.

The para­me­ters and require­ments for the pro­duc­tion of straight-seam stain­less steel pipes are set out in GOST 11068–81.

Spiral stitch technology

The pro­duc­tion is also based on the weld­ing of bent steel sheet. But the join­ing of the edges does not go in a straight line, but in a spi­ral cov­er­ing the entire length.

Spi­ral Weld­ed Pipe

Such a seam is con­sid­ered more durable, since it excludes the for­ma­tion of lon­gi­tu­di­nal cracks. But its total length is greater than in the straight-line ver­sion. This also leads to high­er weld­ing costs.

The pro­duc­tion of spi­ral pipes is reg­u­lat­ed by GOST 8696–74.

Degree of heating

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Accord­ing to the meth­ods of heat treat­ment in the man­u­fac­ture of stain­less prod­ucts, there are:

  • cold worked method. Made with­out heat. If nec­es­sary, heat treat­ment of the fin­ished prod­uct is car­ried out.
  • Ther­mal­ly deformed. When form­ing a pro­file, the work­piece is sub­ject­ed to slight heat­ing.
  • Hot-formed. The pipe is formed from steel heat­ed to a red-hot state.

The cold method is more com­pli­cat­ed, but gives the fin­ished prod­ucts greater strength. There­fore, cold-formed pipes are pro­duced with a small­er wall thick­ness than those made using hot tech­nol­o­gy.

The dif­fer­ences between the stan­dards gov­ern­ing the pro­duc­tion of seam­less pipes are pre­cise­ly in the tem­per­a­ture regime dur­ing man­u­fac­ture. GOST 9940–81 is intend­ed for the hot-worked method, and GOST 9941–81 is for cold and heat-worked pro­duc­tion.

Wall thickness

In addi­tion to this val­ue itself, there is an indi­ca­tor show­ing the ratio of diam­e­ter to wall thick­ness. The larg­er it is, the thin­ner the prod­uct is con­sid­ered. This para­me­ter is denot­ed SDR.

There are the fol­low­ing cat­e­gories:

  • espe­cial­ly thin-walled — SDR > 40;
  • thin-walled — SDR = 13 — 40;
  • thick-walled — SDR = 6 — 13;
  • espe­cial­ly thick-walled – SDR 6.
Thin-walled pipes

Appearance

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Depend­ing on the addi­tion­al sur­face treat­ment after man­u­fac­ture, three types of pipes are dis­tin­guished:

  • Mat­te. Only bumps and burrs are removed.
  • Sand­ed. The mate­r­i­al is only sub­ject­ed to ini­tial grind­ing using fine-grained abra­sives.
  • Pol­ished (mir­ror). Fin­ish­ing the sur­face after grind­ing to the final gloss. There are meth­ods of mechan­i­cal, chem­i­cal and elec­trolyt­ic pol­ish­ing.
Pol­ished stain­less sur­faces

Applications of stainless pipes

The cor­ro­sion resis­tance of such prod­ucts deter­mines their use in pump­ing aggres­sive media and in par­tic­u­lar­ly crit­i­cal sec­tions of con­ven­tion­al pipelines. And the lack of con­tact with the pumped sub­stance allows them to be used in the food indus­try.

The beau­ti­ful appear­ance of the pol­ished sur­face is used in the design of res­i­den­tial and indus­tri­al premis­es.

It is pos­si­ble to cre­ate street struc­tures from stain­less pro­files.

Pedes­tri­an rail­ing made of pol­ished stain­less steel

Determining the weight of a running meter

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For large batch­es of pipe prod­ucts, prices are indi­cat­ed by weight — per ton. It is more con­ve­nient, since the assort­ment of pipes is reduced. The price of met­al of the same qual­i­ty does not depend on the diam­e­ter and wall thick­ness. Only in retail trade and for house­hold pur­pos­es, the cost is cal­cu­lat­ed based on the length in meters.

To recal­cu­late prices, you need to know the weight of 1 lin­ear meter of pipe with the required char­ac­ter­is­tics. Required data for cal­cu­la­tions:

  • mate­r­i­al den­si­ty,
  • diam­e­ter (and for rec­tan­gu­lar sec­tions — length and width)
  • wall thick­ness.

For plumb­ing prod­ucts, the diam­e­ter is often indi­cat­ed in inch­es. The cor­re­spon­dence is some­thing like this:

  • 1/2 inch = 15mm
  • 3/4 = 20 mm
  • 1 inch = 25mm

The spe­cif­ic den­si­ties of the most com­mon steel grades are shown in the table in the fig­ure:

Den­si­ty table

It turns out that the dif­fer­ence between the min­i­mum and max­i­mum val­ues ​​does not exceed 3%. There­fore, an accu­rate den­si­ty val­ue is only required when cal­cu­lat­ing large batch­es. For nor­mal cal­cu­la­tions, it is enough to sub­sti­tute the aver­age num­ber — 7850 kg / m3.

The weight of a lin­ear meter of a stain­less pipe of cir­cu­lar cross sec­tion is cal­cu­lat­ed by the for­mu­la Р= S*h*T, where:

  • S — sur­face area u003d 3.142 * out­er diam­e­ter of the pipe;
  • h is the wall thick­ness;
  • T is the spe­cif­ic grav­i­ty.

The weight of 1 meter of rec­tan­gu­lar and square pro­files is even eas­i­er to deter­mine. The perime­ter of the sec­tion (twice the sum of the width and height) is mul­ti­plied by the wall thick­ness and by the spe­cif­ic grav­i­ty.

Diam­e­ters and walls of stain­less pipes size chart. Part 1.

D, mm Wall thick­ness, mm
1.5 2 2.5 3 3.5 four 5 6 7 eight 9 ten
Weight of 1 lin­ear meter, kg
fif­teen 0.55 0.74 0.92 1.11
twen­ty 0.74 0.99 1.23 1.48 1.73 1.97
25 1.23 1.54 1.85 2.16 2.47 3.08 3.70
32 1.58 1.97 2.37 2.76 3.16 3.95 4.74
38 1.87 2.34 2.81 3.28 3.75 4.69 5.62 6.56 7.50 8.44 9.37
45 2.77 3.33 3.88 4.44 5.55 6.66 7.77 8.88 9.99 11.10
fifty 3.08 3.70 4.32 4.93 6.17 7.40 8.63 9.87 11.10 12.33
57 4.22 4.92 5.62 7.03 8.44 9.84 11.25 12.65 14.06
60 4.44 5.18 5.92 7.40 8.88 10.36 11.84 13.32 14.80
68 5.03 5.87 6.71 8.39 10.06 11.74 13.42 15.09 16.77
76 5.62 6.56 7.50 9.37 11.25 13.12 15.00 16.87 18.75
83 6.14 7.17 8.19 10.24 12.28 14.33 16.38 18.42 20.47
89 6.59 7.68 8.78 10.98 13.17 15.37 17.56 19.76 21.95

Table. Part 2

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6 7 eight 9 ten eleven 12 four­teen 16 eigh­teen twen­ty 22
102 15.09 17.61 20.13 22.64 25.16 27.67 30.19 35.22 40.25 45.28
108 15.98 18.65 21.31 23.97 26.64 29.30 31.97 37.29 42.62 47.95
114 16.87 19.68 22.49 25.31 28.12 30.93 33.74 39.36 44.99 50.61 56.24 61.86
121 17.91 20.89 23.88 26.86 29.84 32.83 35.81 41.78 47.75 53.72 59.69 65.66
133 19.68 22.96 26.24 29.52 32.80 36.08 39.36 45.93 52.49 59.05 65.61 72.17
145 25.03 28.61 32.19 35.76 39.34 42.92 50.07 57.22 64.37 71.53 78.68
159 31.37 35.30 39.22 43.14 47.06 54.90 62.75 70.59 78.43 86.28
168 33.15 37.29 41.44 45.58 49.72 58.01 66.30 74.59 82.87 91.16
180 39.96 44.40 48.84 53.28 62.16 71.03 79.91 88.79 97.67
219 54.02 59.42 64.82 75.62 86.43 97.23 108.03 118.83
245 60.43 66.47 72.51 84.60 96.69 108.77 120.86 132.94
273 67.33 74.07 80.80 94.27 107.74 121.20 134.67 148.14
325 80.16 88.18 96.19 112.22 128.26 144.29 160.32 176.35

Price formation

The cost of a stain­less pipe depends on many para­me­ters: steel grade, the pres­ence or absence of a seam, and the method of man­u­fac­ture. For house­hold pipes of small diam­e­ter, the qual­i­ty of sur­face grind­ing also affects.

There­fore, it is worth con­sid­er­ing only some dif­fer­ences in indi­vid­ual char­ac­ter­is­tics.

Prices per kilo­gram (ton) are weak­ly depen­dent on the diam­e­ters and walls of a par­tic­u­lar pipe. The dif­fer­ence usu­al­ly does not exceed 10–20%.

The grade of steel from which the pipe is made has a much stronger effect on the cost. With oth­er iden­ti­cal char­ac­ter­is­tics, the price varies sig­nif­i­cant­ly. So, steel 12X13 costs 180 — 2 dol­lars / kg, and exact­ly the same pipe, but from the brand 08X18H10T 330 — 3,5 dol­lars / kg.

Com­par­i­son by pro­duc­tion meth­ods:

  • A seam­less pipe made of steel grade 08X18H10T, man­u­fac­tured by the cold-formed method, costs about 330 rubles / kg.
  • The price for hot-formed pro­duc­tion will be 90 — 120 rubles / kg.

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