Plumbing steel pipes: options, pros and cons, standards
Should I use a steel pipe when installing water and heating systems? What is the best way to seal her connections? What are the advantages and disadvantages of traditional material? Does he have modern counterparts that are not inferior in consumer qualities? In the article we have to find answers to these and some other questions.
What they are
In the houses of different years of construction, three types of steel pipes can now be found.
- VGP (water pipeline) pipe GOST 3262-75. These pipes were massively used in construction from the 70s of the last century to about 2000.
- Galvanized AIV pipe produced in our time according to the same standard. It was she who was applied to black steel products; it can be found in houses built in the 30s – 60s. The transition to pipes without a zinc layer was associated with attempts to reduce the cost of construction.
Curiously, the heating and water supply systems were assembled from galvanized exclusively on threads, with cast iron fittings. SNiPs of that time quite reasonably forbade welding: it breaks the protective zinc layer, making the pipeline unprotected against corrosion.
- Corrugated stainless steel pipe has become widespread in the past few years. Of modern materials, it is most resistant to extreme conditions: the nominal operating temperature reaches 130 degrees, and the operating pressure is 25 atmospheres.
Key features
What should you know about the listed types of steel pipes?
Black steel
From the plumbing point of view, these products are the quintessence of world evil. The use of VGP pipes is to some extent justified only in heating systems - and then only if the systems are not discharged for the summer.
Otherwise, Her Majesty Corrosion takes up the job: first of all the threaded connections, and then the smooth-wall sections of the risers and liners begin to remind of themselves with fistulas.
By the way: according to GOST 3262-75, all VGP pipes are electrowelded. The longitudinal seam remains a vulnerable place not only for corrosion, but also for pressure surges during hydraulic shocks.
The most terrible horror among professionals is caused by the houses of the end of the 80s. The transition to market relations has forced contractors to save on everything that was not explicitly spelled out in contracts; as a result, lightweight (thin-walled) pipes were massively used during installation. The thickness of their walls on the threads was 0.5 - 0.8 mm, the service life before the appearance of the first leaks - 5-8 years.
Galvanized
Despite the production of a single standard with our previous nominee, the impressions of these materials are diametrically opposite. The zinc layer reliably protects the steel from corrosion; no characteristic lime deposits in the aqueducts either. After the half-century (!) Of operation, the risers of the heat that the author opened appeared to have been collected yesterday.
Recently, in the thematic forums there was a fair amount of references to the fact that the de-zinc layer rapidly degraded during reactions with water, therefore galvanizing cannot be used on heating. How many professionals, so many opinions, so we will not argue; let's say this: the author’s entire experience disproves this statement.
The only drawback of galvanizing is time-consuming installation with the need to manufacture sgons and nozzles.
Stainless steel
Corrugated stainless steel water pipes - a rare case when it is difficult to name at least some of the shortcomings of the solution. Oh yes, the price: for pipes DU15 it is about 170 rubles per meter.
But the other properties only please.
- Exceptional strength already mentioned. Heat resistance due to fittings with silicone seals is higher than that of black steel and galvanized: organic winding on the threads burns out in one or two seasons already at 95-100С, silicone also keeps the declared 130 for an unlimited time.
- The pipeline can bend with a minimum radius, which greatly simplifies installation.
- Fittings require for assembly only a pair of adjustable or rozhkov keys. The assembly is so simple that it can be done even by a child.
- Pipeline is aesthetic, does not need painting and retains its appearance indefinitely.
Thread sealing
If fittings do not need special comments, then thread sealing will cause eternal questions for beginners. How and how to thread the thread?
Option 1
Reliable and durable combination - flax with paint. In the notorious stalinkas, threads were assembled on linen underwrap with iron red lead, however, it can be replaced with any loss of reliability with any nitro, alkyd or oil enamel. Instead of missing paint, you can even use silicone pipe sealant.
Instructions for assembling the connection with their own hands is no different complexity.
- A little dye or sealant is applied to the thread ridges.
- From above along the thread, a thin strand of flax is wound in several turns.
- A bit of sealant or paint is worn over it.
- The thread is screwed into the sleeve, a corner or tightened by a locknut.
Option 2
A very favorable impression on the author was made by polymer sealing threads (Tangit and its analogs). The thread is simply wound on the nipple or the thread; unlike tape FUM, it does not leak with a slight reverse course of the thread.
Regulations
What are the requirements for VGP pipes? What are the diameters of steel water pipes can offer domestic industry?
Refer to the already mentioned by us GOST 3262 - 75.
Products are delivered in lengths from 4 to 12 meters.
They can be:
- Measured length;
- Length, multiple dimensional, with an allowance of 5 mm per cut;
- Unmeasured length.
Curvature should not exceed:
- With a nominal diameter of 20 mm - 2 mm / linear meter;
- When UD 20 mm and above - 1.5 mm / linear meter.
What are the size limits?
| The size | Maximum deviations | |
| Normal accuracy | Increased accuracy | |
| Outer diameter at DD up to 40 mm | +0.4 mm, -0.5 mm | +0.4 mm, -0.4 mm |
| Outer diameter at UD over 40 mm | +0.8%, -1.0% | +0.8%, -0.8% |
| Wall thickness | -15 % | -ten % |
And what can be the dimensions of a water steel pipe according to GOST?
| Nominal diameter | Outer diameter, mm | Wall thickness mm | ||
| Lungs | Ordinary | Reinforced | ||
| 15 | 21.3 | 2.5 | 2.8 | 3.2 |
| 20 | 26,8 | 2.5 | 2.8 | 3.2 |
| 25 | 33.5 | 2.8 | 3.2 | 4.0 |
| 32 | 42.3 | 2.8 | 3.2 | 4.0 |
| 40 | 48.0 | 3.0 | 3.5 | 4.0 |
| 50 | 60.0 | 3.0 | 3.5 | 4.5 |
| 65 | 75.5 | 3.2 | 4.0 | 4.5 |
| 80 | 88.5 | 3.5 | 4.0 | 4.5 |
| 100 | 114.0 | 4.0 | 4.5 | 5.0 |
| 125 | 140.0 | 4.0 | 4.5 | 5.5 |
| 150 | 165.0 | 4.0 | 4.5 | 5.5 |
How to read the notation of products described by the standard?
His text gives several examples.
- 20Х2,8 GOST 3262-75 - conditional passage of 20 mm with a wall thickness of 2.8 mm.
- R-20x2.8 - 4000 GOST 3262-75 - the same, measuring length of 4 meters with thread.
- Ц-Р-20х2,8 - 4000 GOST 3262-75 - measuring length of 4 meters with thread and zinc coating.
What is the maximum pressure for the products manufactured in accordance with GOST?
- Ordinary and light pipes - 25 kgf / cm2 (atmospheres).
- Reinforced - 32 kgf / cm2.
It is curious: during normal operation of water supply and heating, the pressure in the systems does not exceed 8-10 atmospheres. Safety factor is necessary due to the weakening of the walls of the threads and the likelihood of water hammer at start.
Conclusion
We hope that our material will help the reader to make a choice on the eve of repair or construction and save him from annoying mistakes. As usual, the video in this article will offer him more information. Successes!