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Stainless Steel Pipe Fittings Ensure The Quality Of Its Selection, Material, Manufacture, Installation And Inspection
Nov 01, 2017

Stainless steel fittings, especially tee, elbow and size are used more and more in the Stainless Steel Pipe Fittingsconstruction process, this is mainly because of its good forming, pressure-resistant ability, welding form simple and so on, in order to ensure the pressure capacity of the Stainless Steel Pipe Fittings, so in the process piping engineering, especially in the petrochemical and other high-temperature high-pressure and flammable explosive Stainless Steel Pipe Fittings, The reasonable use of Stainless Steel Pipe Fittings nd the quality of the Stainless Steel Pipe Fittings itself directly play an important role.

Because of this, in the Stainless Steel Pipe Fittings design, installation process, especially in the petrochemical industry high temperature and high pressure and inflammable and explosive Stainless Steel Pipe Fittings engineering, no matter from the design selection or manufacturing, until the construction of the installation and inspection of each link, design and manufacture and installation unit personnel to strictly check, to ensure its selection, use of materials, manufacturing, installation and inspection quality, Otherwise in the plant construction and production process will cause difficult SI loss.

From the construction process, we found that the quality of the Stainless Steel Pipe Fittings  are mainly the following problems:

I. Uneven wall thickness of Stainless Steel Pipe Fittings

The thickness of Stainless Steel Pipe Fittings is mainly occurred in the most deformation parts. such as the wall thickness of the elbow on the back of the other parts; Provisions in relevant national standards. The thickness of the wall thickness of the tube should not exceed the maximum of 1 2, 5, but in situ measurements found that some of the wall thickness reduction reached 2o items. Inspection of such problems, with the general caliper and other measuring tools are often difficult to find, at this time only using ultrasonic thickness gauge can be measured.

Second, the hardness exceeded

The problem of hardness exceeding the standard is mainly due to the process of heat treatment after forming, the solution is to use the correct heat treatment process again. This problem can be solved in general

III. Defects in materials and processes

This kind of problem is the most harmful to the safety of the device. It's more trouble to check it out. The factors that produce defects are more complicated, which have defects of the material itself, the process of manufacturing and the improper heat treatment process. So why do they have a safety hazard, and how to avoid such problems? Now take tee as an example to do an analysis.

1. Problems of raw materials

We know that for high temperature and high pressure and inflammable and explosive media fittings. The quality of raw materials, directly affect the quality of Stainless Steel Pipe Fittings  used to manufacture such Stainless Steel Pipe Fittings, for carbon steel Stainless Steel Pipe Fittings, most of the use of GB531 0-85 "high-pressure boiler seamless steel tube", gb6479-86 "fertilizer equipment with high-pressure seamless steel tube" gb9448-88 "petroleum cracking seamless steel Stainless Steel Pipe Fittings" As well as GB81 63-87{transmission fluid with seamless steel Stainless Steel Pipe Fittings "standard material. For this kind of steel Stainless Steel Pipe Fittings, the steel mill should carry on the water pressure test by root. For large and medium-sized steel, often using eddy current or ultrasonic crossing inspection (UT) instead of water pressure, such as strictly according to national and relevant standards to test, the quality of tubes can be guaranteed. But sometimes there will be missed, false inspection, and even more because of the Stainless Steel Pipe Fittings stock channels mixed, some of the raw materials have not been tested into the circulation, therefore, after the arrival of Stainless Steel Pipe Fittings, especially in batches from the steel Stainless Steel Pipe Fittings factory directly purchased materials. In addition to a comprehensive re-examination according to the standard, but also to increase the rate of retest, or even root check but. From the extensive survey of the size of Stainless Steel Pipe Fittings We have contacted, many factories on the purchase of the Stainless Steel Pipe Fittings to check the inspection is not strict, blindly letter to the quality of the factory certificate (it is noteworthy that some of the factory quality certificate is the authenticity of the problem), and only the appearance of the two-pier Stainless Steel Pipe Fittings made of these unqualified Stainless Steel Pipe Fittings, Its quality is difficult to be guaranteed. In addition to the current many manufacturers of testing methods are neither advanced nor perfect, so some unqualified Stainless Steel Pipe Fittings are very easy as qualified products factory.

2. Processing technology

At present, the processing of domestic manufacturers are generally using the following methods:

(1) cold stamping forming;

(2) hot stamping forming;

(3) Oil pressure forming

The common problems in the quality of Stainless Steel Pipe Fittings in construction and the solving methods

Three-way internal and external wall surface metallographic structure for larger diameter, thick wall thickness of the tee, the use of the following two forming methods, and these two methods of forming time generally takes 1-2 minutes, or even some up to 3 minutes. In these few minutes, how to maintain the relative stability of the temperature, for the quality of Stainless Steel Pipe Fittings is the key problem, such as the temperature difference is too large, will result in steel fibrous flow imbalance, especially for the larger parts of deformation. Because of its large plastic deformation, such as low temperature will cause cold hardening phenomenon and produce brittle damage.

3. Heat treatment after forming

The final heat treatment after the tee forming can remarkably improve the mechanical properties of the steel. Especially for the three-way factory with less advanced processing method, it is especially important to choose the correct heat treatment system and process. In the gb12459-90 "Steel butt welded seamless Stainless Steel Pipe Fittings," R cold formed carbon steel Stainless Steel Pipe Fittings parts to be fire or annealing hot treatment. So what kind of heat treatment is chosen, especially which annealing system is good, the standard does not have the choice or description, which depends on the manufacturing process to determine. The author thinks that whichever kind of heat treatment system is chosen is to improve the mechanical properties of the Stainless Steel Pipe Fittings and increase its strength. In the process of cold extrusion forming, the microstructure of steel will change greatly due to its large plastic deformation, such as the obvious banded structure, coarse grain, dislocation of grains boundary, slip of interface and so on. These organizational changes have a great impact on the cutting process and performance of steels. To overcome these adverse changes should be through heat treatment to completely change the structure of these changes, so that its grain refinement, uniform tissue. To achieve this, it is necessary to use a complete annealing process in normalizing or annealing. Many Stainless Steel Pipe Fittingsmanufacturers are not fully aware of this point. For some reason, they only carried out the annealing heat treatment which was designed to remove the stress, and the annealing did not fundamentally change the microstructure and properties of the tube, and it was difficult to ensure the quality of the tube.