How to choose galvanized pipes for heating and water supply

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Despite the sat­u­ra­tion of the mar­ket with many vari­eties of high-tech poly­mer pipes, met­al for the instal­la­tion of heat­ing sys­tems, hot and cold water sup­ply is wide­ly used today. Met­al pipes for these pur­pos­es are main­ly made from steel and cop­per, less often from alu­minum. Each type of such pipes, depend­ing on the mate­r­i­al of man­u­fac­ture, has a set of indi­vid­ual char­ac­ter­is­tics that pro­vide the con­sumer with enough room for maneu­ver when choos­ing.

One of the most com­mon types of pipes are zinc-coat­ed steel prod­ucts — a mate­r­i­al that has many pos­i­tive char­ac­ter­is­tics, but is spe­cif­ic in appli­ca­tion. Con­sid­er what kind of mate­r­i­al it is, and how to prop­er­ly use gal­va­nized pipes for heat­ing.

Production methods and varieties of galvanized pipes

The main ene­my of steel pipes is cor­ro­sion. One of the ways to pro­tect against it is to apply a pro­tec­tive lay­er of zinc to the sur­face of the steel pipe, after which the mate­r­i­al is clas­si­fied as a sep­a­rate sub­group — a gal­va­nized pipe for water sup­ply and heat­ing sys­tems.

The method is mod­er­ate­ly expen­sive, so the cost of a steel pipe after gal­va­niz­ing remains afford­able — an approx­i­mate price ratio can be found accord­ing to the table:

GWP pipe size

(gas pipeline)

Price (rub/m)
black steel gal­va­nized
15x2.8 st1-3sp/ps 33 fifty
20x2.8 st1-3sp/ps 42 66
25x2.8 st1-3sp/ps 59 95
32x2.8 st1-3sp/ps 81 127
40x2.8 st1-3sp/ps 90 155
50x2.8 st1-3sp/ps 117 194

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Zinc coat­ing can be applied to a steel pipe made by any tech­nol­o­gy — straight-seam, with a spi­ral seam, seam­less, there­fore, gal­va­nized pipes are clas­si­fied in the same way as ordi­nary pipes by the fac­tor of the pres­ence of a seam.

There is no inde­pen­dent stan­dard for gal­va­nized prod­ucts. Steel pipes with zinc pro­tec­tion are pro­duced in accor­dance with the reg­u­la­to­ry doc­u­ments for elec­tric weld­ed prod­ucts with a straight seam (GOST 10704) and mate­r­i­al for gas pipelines (GOST 3262–75).

Zinc Coating Methods

Zinc coat­ing, depend­ing on the oper­at­ing con­di­tions of the pipe, can be car­ried out both on its out­er sur­face and on its inner one.

There are 4 meth­ods of gal­va­niz­ing pipes, each of which is used depend­ing on the size of the prod­ucts and the require­ments for the thick­ness and strength of the zinc coat­ing:

  • hot — the pre­pared part is immersed in molten zinc, which ensures high qual­i­ty and dura­bil­i­ty of the coat­ing, but the ener­gy con­sump­tion of the process is high;
  • cold — prod­ucts are paint­ed with zinc-con­tain­ing sub­stances by one of the paint­ing meth­ods, which does not pro­vide high strength of the zinc lay­er (it is used to pro­tect already assem­bled struc­tures from cor­ro­sion);
  • elec­tro-gal­van­ic — coat­ing is car­ried out by elec­trol­y­sis, that is, depo­si­tion of zinc dis­solved in the elec­trolyte (cath­ode) on the part (anode), when an elec­tric cur­rent pass­es;
  • gas-ther­mal — the device of a pro­tec­tive coat­ing by flame spray­ing on the sur­face of the zinc pow­der part, the dis­ad­van­tage is poros­i­ty and low strength of the lay­er;
  • ther­mal dif­fu­sion — parts are cov­ered with a lay­er of zinc, which is after heat­ing to 2500 degrees. in a vapor state, it is used for pro­cess­ing small parts in large quan­ti­ties — screws, bolts, nuts, wash­ers that require high adhe­sion of zinc to met­al.

Parameters of zinc coated steel pipes

The main tech­ni­cal para­me­ters of zinc coat­ed steel pipes are:

  • out­er diam­e­ter (10.2 — 165 mm);
  • weight of 1 m of pipe (0.4 — 22 kg);
  • con­di­tion­al pas­sage (6 — 150 mm);
  • wall thick­ness (1.8 — 5.5 m);
  • length (4 — 12 m).

As with ordi­nary pipes, the walls of gal­va­nized prod­ucts can be light, rein­forced or stan­dard, the accu­ra­cy of exe­cu­tion is assigned to ordi­nary or increased.

Impor­tant! A pro­tec­tive zinc coat­ing should be applied to the entire sur­face of the prod­uct and have a thick­ness of 30 microns. Peel­ing of the pro­tec­tive lay­er, peel­ing and swelling on it are not allowed (“Steel water and gas pipes”, Spec­i­fi­ca­tions, GOST 3262–75, rev. No. 4.6).

Advantages and disadvantages

Most of the char­ac­ter­is­tics of gal­va­nized VGP pipes, both pos­i­tive and neg­a­tive, coin­cide with the para­me­ters of black steel prod­ucts, but there are also indi­vid­ual qual­i­ties.

Advantages

  • Strength (espe­cial­ly ten­sile strength).
  • Fire resis­tance.
  • Low coef­fi­cient of ther­mal elon­ga­tion.
  • Absolute tight­ness.
  • Impact resis­tant.
  • Dura­bil­i­ty.
  • Pos­si­bil­i­ty of use as a heat exchang­er.
  • Pos­si­bil­i­ty of instal­la­tion, includ­ing ongo­ing repairs, with your own hands.
  • Two assem­bly meth­ods (weld­ing, thread­ed con­nec­tion).
  • Ease of dis­pos­al.

The fact that the exter­nal lay­ing of the gas pipeline from the main to con­sumers is only allowed from steel mate­r­i­al speaks in favor of steel GWP pipes.

Flaws

  • Sig­nif­i­cant share.
  • Elec­tri­cal con­duc­tiv­i­ty.
  • High ther­mal con­duc­tiv­i­ty (the need to insu­late pipes in heat­ing and hot water sys­tems).
  • Sus­cep­ti­bil­i­ty to cor­ro­sion if the zinc pro­tec­tion is dam­aged.

Mounting and assembly methods

Gal­va­nized pipes that form a heat­ing or hot water sys­tem are mount­ed in three ways:

  • weld­ing;
  • flange con­nec­tion;
  • thread­ed con­nec­tion;
  • sol­der­ing.

Each of the above meth­ods has its pros and cons. Con­sid­er these instal­la­tion meth­ods and the nuances asso­ci­at­ed with them.

Welding of galvanized pipes

Zinc-coat­ed water and gas pipes can be con­nect­ed by elec­tric or gas weld­ing — both types of instal­la­tion are con­ve­nient because they take lit­tle time. But there is one neg­a­tive fac­tor, the effect of which must be min­i­mized, since it can­not be com­plete­ly elim­i­nat­ed.

The fact is that the tem­per­a­ture of the weld reach­es 1200 degrees, and zinc boils at 906 degrees and begins to evap­o­rate from heat­ing dur­ing the weld­ing process. In doing so, the fol­low­ing hap­pens:

  • the harm­ful effects of zinc vapor on the welder, up to the onset of suf­fo­ca­tion, as they are poi­so­nous;
  • evap­o­rat­ing zinc expos­es steel and makes it vul­ner­a­ble to cor­ro­sion;
  • zinc vapor con­tributes to the for­ma­tion of pores and cracks in the weld, reduc­ing the strength of the joint.

For max­i­mum local­iza­tion of these process­es, before start­ing weld­ing, apart from the manda­to­ry device for effec­tive ven­ti­la­tion of the room, it is nec­es­sary to per­form the fol­low­ing actions.

  • pre­pare the joint edges, that is, make an exter­nal cham­fer on them and remove the zinc coat­ing by 25–30 mm on both sides of the joint;
  • weld the joint with sub­se­quent clean­ing of the weld from slag and coat­ing the bare sec­tion of the pipe with zinc-con­tain­ing paint (zinc dust con­tent — 94%, binder — 6%) — cold gal­va­niz­ing.

To pre­vent the zinc lay­er from boil­ing, it is pos­si­ble to treat the junc­tion with hydrochlo­ric acid 5 cm in both direc­tions, but in this case, acid fumes will form dur­ing weld­ing.

Impor­tant! Accord­ing to para­graph 4.6 of SP (Build­ing Rules) 73.13330.2012, the device of weld­ed joints on pipelines made of gal­va­nized steel is not allowed, since zinc is not removed from the inner sur­face of the pipe before weld­ing, and zinc fumes, the for­ma­tion of which can­not be avoid­ed, cause the for­ma­tion in the seam pores and shells. But this doc­u­ment is of vol­un­tary use, and if the project does not con­tain a ref­er­ence to the manda­to­ry use of this para­graph, then the instal­la­tion of gal­va­nized pipes by weld­ing is per­mis­si­ble.

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In order to min­i­mize the impact of zinc on the qual­i­ty of elec­tric weld­ing, instal­la­tion must be car­ried out in accor­dance with the fol­low­ing rec­om­men­da­tions:

  • per­form weld­ing at low speed, but avoid­ing burn­ing the pipe, and with an increased cur­rent strength;
  • use elec­trodes with rutile coat­ing (elec­trode com­po­si­tion con­tains tita­ni­um oxide).

Elec­tric weld­ing of zinc-coat­ed pipes requires cer­tain skills from the welder. In addi­tion to the com­po­si­tion of the out­er coat­ing of the elec­trode, the qual­i­ty of the weld is affect­ed by the thick­ness of its rod, which deter­mines the pow­er of the arc — an exces­sive­ly thick elec­trode will burn through the wall, and a thin one will not pro­vide the nec­es­sary strength of the weld­ed joint. For weld­ing gal­va­nized pipes with a wall thick­ness of 1.5 — 5 mm, elec­trodes with a diam­e­ter of 2–3 mm are used.

Flange connection of galvanized pipes

This method is based on bolt­ing togeth­er frag­ments of pipes, at the ends of which flanges are weld­ed — steel rings with an inner diam­e­ter equal to the out­er diam­e­ter of the pipe, and holes around the perime­ter for mount­ing bolts. Two flanges of dif­fer­ent frag­ments are applied to each oth­er using an inter­me­di­ate seal­ing gas­ket and tight­ened with bolt nuts or studs.

In this method of instal­la­tion, there is the same neg­a­tive fac­tor as in the weld­ed joint — in the process of weld­ing the flanges to the pipes, zinc boils and the pro­tec­tive lay­er in the area of ​​the weld is destroyed. There­fore, it is also nec­es­sary to take mea­sures to local­ize the tem­per­a­ture effect on the zinc lay­er, and after weld­ing, clean the seam and apply an anti-cor­ro­sion zinc-con­tain­ing coat­ing (cold gal­va­niz­ing) on ​​it.

The flange con­nec­tion is not com­pact, there­fore it is used in most cas­es when lay­ing pipelines in util­i­ty rooms or out­side. On the mat­ing side of the flange there is an annu­lar area called a mir­ror. Between the two mir­rors of the joined flanges, before tight­en­ing them, a paronite gas­ket with a hole is installed, the diam­e­ter of which must match the inner diam­e­ter of the pipe. The out­er diam­e­ter of the gas­ket is equal to the dis­tance between the oppo­site fix­ing bolts.

Threaded connection

This instal­la­tion method elim­i­nates the need for ther­mal con­nec­tion meth­ods and is per­formed using var­i­ous types of fit­tings designed to con­nect indi­vid­ual pipeline frag­ments after thread­ing them.

Thread­ed assem­bly also has its draw­backs:

  • the process of thread­ing is labo­ri­ous and time con­sum­ing;
  • a cut­ting tool (die) when cut­ting a thread removes a lay­er of steel of a cer­tain thick­ness along with a pro­tec­tive zinc coat­ing.
  • the tight­ness of the thread­ed con­nec­tion is ensured by wrap­ping the thread with FUM tape, seal­ing paste or tow with paint applied, which lose their prop­er­ties over time and require replace­ment.

Soldering galvanized pipes

To mount a heat­ing or hot water sys­tem from gal­va­nized pipes with­out dam­ag­ing the zinc lay­er, sol­der­ing is used, which is per­formed in the fol­low­ing sequence:

  • the con­nect­ed ends of the pipe are fac­ing and, if the wall thick­ness is more than 3 mm, a cham­fer is made on the out­er edges;
  • the joints are degreased by heat­ing, after which the flux (HLS‑B com­po­si­tion) also heat­ed to plas­tic­i­ty is applied in a thick lay­er to the sur­face adja­cent to the planned joint;
  • the ends are arranged with a gap of 2–3 m;
  • the burn­er flame is set to excess oxy­gen.

The size of the burn­er is select­ed depend­ing on the diam­e­ter and wall thick­ness of the gal­va­nized pipe:

For high-qual­i­ty sol­der­ing of a gal­va­nized pipe, it is nec­es­sary to fol­low the rule: the size of the burn­er must be one unit small­er than when weld­ing pipes of the same dimen­sions with­out zinc coat­ing. Dur­ing the sol­der­ing process, the flame must be con­cen­trat­ed on the edges to be joined and the joint gap in order to exclude heat­ing and evap­o­ra­tion of zinc from under the flux lay­er.

The con­nect­ing seams of well-made sol­der­ing of gal­va­nized pipes do not need addi­tion­al anti-cor­ro­sion pro­tec­tion, but apply­ing zinc-con­tain­ing paint as an insur­ing oper­a­tion will not be super­flu­ous.

The specifics of the use of galvanized pipes in heating and hot water systems

Zinc-coat­ed pipes in heat­ing sys­tems and water pipes are used tak­ing into account oper­at­ing con­di­tions.

If the coolant tem­per­a­ture does not exceed 65 degrees, then the zinc coat­ing suc­cess­ful­ly per­forms its func­tions. In the north­ern regions, where this para­me­ter is much high­er, the inner zinc lay­er reacts with water under the influ­ence of high tem­per­a­ture:

Zn + H2O = ZnO + H2.

Both sub­stances result­ing from such an inter­ac­tion are neg­a­tive fac­tors:

  • ZnO is flakes that pre­cip­i­tate and clog the lumen of small diam­e­ter pipelines;
  • H2 is hydro­gen, which, when mixed with air in a cer­tain pro­por­tion, is explo­sive or at least forms plugs in the sys­tem.

There­fore, in hot water and heat­ing sys­tems with a coolant tem­per­a­ture above 60 degrees, it is allowed to use pipes that have only an exter­nal pro­tec­tive zinc coat­ing, which will pro­tect the pipeline from cor­ro­sion dur­ing peri­ods of down­time. How­ev­er, when water gets on the sur­face of a hot pipe, the zinc shell begins to peel off from the base, there­fore, in order to avoid this, it is nec­es­sary to paint such pipelines over zinc, which will lead to an even greater increase in the cost of the sys­tem.

Con­clu­sion: the use of pipes gal­va­nized on the out­side in hot water and heat­ing sys­tems with a coolant tem­per­a­ture above 60 degrees is unrea­son­ably expen­sive, and gal­va­nized on the inside is harm­ful and dan­ger­ous.

Conclusion

A gal­va­nized water and gas steel pipe is a mate­r­i­al in demand today, but it must be used and installed tak­ing into account the char­ac­ter­is­tics of the pro­tec­tive coat­ing, so that the advan­tages of zinc are used ratio­nal­ly, and do not become a fac­tor that only increas­es the cost of work.

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