Threadless connection of steel pipes


The for­ma­tion of the pipeline involves the con­nec­tion of pipes. for this, thread­ed and thread­less meth­ods are used. Which option is cho­sen depends on the pur­pose, loca­tion, mate­r­i­al of the con­nect­ed ele­ments. But if thread­ing is dif­fi­cult, a thread­less weld­ed or fit­ting con­nec­tion of steel pipes is used.

Types of pipe con­nec­tion

Threadless Connection Classification

Con­di­tion­al­ly sep­a­rate two meth­ods:

  • by weld­ing. Accord­ing to the con­di­tions of the work, fusion weld­ing and pres­sure weld­ing are dis­tin­guished;
  • using con­nect­ing fit­tings. In this capac­i­ty, cou­plings, flanges act.

Pros and cons of welding

This method gives a strong, air­tight con­nec­tion. Its advan­tages also include:

  • there is no weight­ing of the sys­tem with addi­tion­al details;
  • process automa­tion;
  • for weld­ing, there is no need to spe­cial­ly lev­el the edge of the cut;
  • suit­able for sys­tems of non-stan­dard sec­tion ele­ments: square. rec­tan­gu­lar, oval. The con­nec­tion of non-cir­cu­lar steel pipes on the thread is not pos­si­ble.

Weld­ing work is usu­al­ly per­formed by a spe­cial­ist and requires spe­cial equip­ment. Resid­ual stress­es aris­ing at the joints can lead to depres­sur­iza­tion of the joints under mechan­i­cal loads, vibra­tions. If repair is nec­es­sary, weld­ed parts can only be cut off. It is tech­no­log­i­cal­ly dif­fi­cult to weld dif­fer­ent met­als (steel/cast iron), and it is impos­si­ble to weld dif­fer­ent mate­ri­als (steel/PVC). It is impos­si­ble to con­nect steel pipes with cop­per, alu­minum by weld­ing.

Work­ing with a weld­ing machine

Pros and cons of a fitting connection


The fit­ting con­nec­tion pro­vides a num­ber of advan­tages with­out chang­ing the require­ments for joint tight­ness:

  • all dock­ing nodes are easy and quick to change;
  • you can make changes to the sys­tem your­self by chang­ing the type of fit­ting;
  • if the pipeline breaks, fit­tings can be reused;
  • no expen­sive spe­cial equip­ment is required;
  • You can con­nect pipes from dif­fer­ent mate­ri­als.

Of the minus­es, the impos­si­bil­i­ty of con­nect­ing slices with an angu­lar sec­tion, the weight­ing of the sys­tem with addi­tion­al ele­ments are dis­tin­guished. Such a con­nec­tion will serve for a long time with strict adher­ence to the instal­la­tion tech­nol­o­gy.

Welding technology

Weld­ing work is car­ried out using weld­ing machines. In addi­tion, trans­form­ers (rec­ti­fiers), a set of elec­trodes are used in elec­tric weld­ing. Be sure to work only in pro­tec­tive equip­ment.

For all types of weld­ing, pipe sec­tions are pre­lim­i­nar­i­ly pre­pared for weld­ed seams: they are cleaned, the flange is cut, degreased, rust and paint are removed.

Fur­ther, the process depends on the weld­ing method:

  • The gas method involves the use of weld­ing wire, with which the seam is filled in one go. In order to imme­di­ate­ly get a high-qual­i­ty result, you need to have spe­cial train­ing. If, for tech­no­log­i­cal rea­sons, the out­er seam does not pro­vide the nec­es­sary tight­ness, an inter­nal seam is per­formed in front of it. Opti­mal for pipes with wall thick­ness up to 4 mm;
  • The elec­tric arc method requires cen­ter­ing, instal­la­tion of pipeline ele­ments in tacks. This is due to the fact that the work is done in parts. The seam is formed lay­er by lay­er. For each stage, an elec­trode of a larg­er diam­e­ter is tak­en. The method is applied to thick-walled pipes;
  • Shield­ed weld­ing is the most effi­cient way. The pro­tec­tion is a mix­ture of gas­es: argon, oxy­gen, car­bon diox­ide. The seam is neat and durable.

After weld­ing in any way, the seam is cleaned of slag deposits, its tight­ness is checked. Weld­ed joints are durable, aes­thet­ic.


Couplings and their installation

In the thread­less method, com­pres­sion iron, met­al-plas­tic, steel cou­plings, Gebo com­pres­sion cou­plings are used.

Com­pres­sion cou­plings have a seal­ing ring, a union nut. They do not pro­vide com­plete reli­a­bil­i­ty of fas­ten­ing: with mechan­i­cal force, the pipe can be pulled out of the cou­pling. They are installed either as a tem­po­rary option at the repair stage, or where exter­nal influ­ence is not expect­ed.

Gebo com­pres­sion cou­plings have three rings:

  • clamp­ing;
  • seal­ing;
  • clamp­ing.

All ele­ments are placed in a met­al case, and with a clamp­ing nut they form a com­mon device. Such a cou­pling is effec­tive when con­nect­ing steel struc­tures with plas­tic, PVC pipelines. Scope of appli­ca­tion: water sup­ply, sew­er­age and gas sys­tems where the pres­sure does not exceed 0.4 MPa. The pos­i­tive aspects of using the Gebo cou­pling include:

  • ver­sa­til­i­ty of use;
  • not sub­ject to elas­tic defor­ma­tions;
  • the declared war­ran­ty peri­od of use is more than 10 years;
  • con­nec­tion qual­i­ty devi­a­tion of 30 does not affect;
  • no inter­nal stress­es;
  • no met­al fatigue.

Orig­i­nal Gebo cou­plings are sold with a pass­port.

Cou­pling con­nec­tion


Mounting the compression sleeve

  1. Cut two pipes.
  2. Con­nect the slices and cen­ter them.
  3. Make marks for the loca­tion of the cou­pling.
  4. Lubri­cate the inside of the cou­pling and the out­er pipe with sealants.
  5. Put the cou­pling on the marked place and let it hard­en on the sealant.

Installation of the Gebo-coupling

  1. A clamp­ing nut is fixed on one of the parts of the pipeline.
  2. Going to fit­ting start­ing.
  3. The nut is tight­ened onto the parts, the rings are clamped inside.
  4. Then every­thing is done for the sec­ond slice. The joint is sealed.

Flanges and their installation

The scope of the flange con­nec­tion is fit­tings with a diam­e­ter of 50 mm. Flanges for pipes of small­er diam­e­ters are rare and are used only in excep­tion­al cas­es.

Flange fit­ting design:

  • met­al ring with flanges locat­ed on both sides;
  • seal­ing rings locat­ed inside the hous­ing;
  • fix­ing bolts.

The con­nec­tion is reli­able, easy to install, but the design has a sig­nif­i­cant weight and dimen­sions.



Flange mount­ing

  1. Deter­mine the con­nec­tion points and clean them of any plaque.
  2. Put a flange on each con­nect­ed ele­ment.
  3. Instal­la­tion of gas­kets so that they extend beyond the edge of the pipe.
  4. Bolt the flanges togeth­er. Inter­nal seals will ensure the tight­ness of the joint.

In high-pres­sure pipelines, bolts are fixed by weld­ing. If the fas­ten­er is tight­ened, care must be tak­en that it does not burst.

In order for dock­ing to com­ply with reg­u­la­to­ry require­ments, it is nec­es­sary to con­sid­er:

  • the type of gas­ket is select­ed depend­ing on the pur­pose of the pipeline. for plumb­ing — porous card­board impreg­nat­ed with oil, for heat­ing sys­tems — asbestos card­board;
  • it is not advis­able to install more than one gas­ket;
  • gas­kets must not come into con­tact with bolts. Their size is select­ed slight­ly larg­er than the diam­e­ter of the pipes;
  • to even­ly tight­en the bolts, this is done in pairs, and not one after the oth­er.

Installing a flange on a pipe is effec­tive both for the method of thread­less con­nec­tion of steel pipes, and for elim­i­nat­ing leaks in emer­gency sit­u­a­tions.

Mount­ing order

The use of fit­tings, cou­plings allows you to weld the pipe with­out thread­ing and weld­ing. But all con­nec­tion meth­ods are equal. Their choice depends on the spe­cif­ic instal­la­tion con­di­tions, pipe mate­r­i­al, avail­abil­i­ty of tools.


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