Methods for distinguishing high and low quality stainless steel pipes
It is well known that stainless steel pipe fittings are a hygienic and healthy metal material and are widely used in food processing and transportation pipelines. This is because the stainless steel pipe has excellent material properties, which can effectively reduce transportation costs, and can keep the inner wall smooth and clean during long-term use, reducing transportation energy consumption, and is very cost-effective.
So how to identify the quality of stainless steel pipe fittings? Let’s talk about the next two methods.
The first is the nitric acid point test. An obvious feature of stainless steel pipes is that they have good corrosion resistance against concentrated nitric acid and dilute nitric acid. This property allows it to be easily distinguished from most other metals or alloys. However, high-carbon 420 and 440 stainless steel are susceptible to slight corrosion when subjected to nitric acid point tests, and non-ferrous metals will be corroded immediately when exposed to concentrated nitric acid. Dilute nitric acid is very corrosive to carbon steel.
The second is physical testing. Magnetic testing is the most convenient method to identify annealed austenitic stainless steel and ferritic stainless steel. Stainless steel elbow Austenitic stainless steel is non-magnetic steel, but it will become slightly magnetic after cold working under high pressure, and pure chromium steel and low alloy steel are both highly magnetic stainless steel.
Comparing the tooth front and tooth spacing of stainless steel pipes, standard pipes can be seen with the naked eye that the tooth edges are sharp, the tooth spacing is uniform and bright, because this type of stainless steel pipe has been mechanically treated before leaving the factory, and there are no inclusions on the surface. Its feel also shows that the tooth edges are smooth, the processing depth is standardized, the core is even and the walls are smooth, and the flow parts are smooth. Judging from the degree of rough manufacturing, inferior stainless steel pipes have unfavorable and thick tooth edges, irregular tooth spacing, frequent tooth edge damage, and easy leakage. They have high carbon content, are not resistant to corrosion, and have poor toughness and tensile strength.
The installation of stainless steel pipe fittings also requires skills. When lifting stainless steel pipe materials, they must not be in direct contact with other metals, and non-metallic materials such as wooden boards or rubber sheets need to be added. Secondly, the inside of the weld of stainless steel pipes and fittings should be protected by argon filling during position welding. In addition, ordinary grinding wheels cannot be used when cutting pipes. Stainless steel special grinding wheels or plasma cutting must be used. The pipe uses arc starting and arc closing when welding. The arc starting uses the reflow method, and the arc crater must be filled in during arc closing. Arcing must be completed within the groove, and arcing and arcing cannot be performed on the surface of the base material of pipes and pipe fittings. If defects such as pores and cracks are found in the arc starting and closing areas, they must be dealt with quickly.
In addition, the hydraulic pressure test of stainless steel pipe fittings has certain requirements for water temperature and water quality. The water temperature cannot be lower than 5 degrees Celsius, and the chloride ion content in the water cannot be higher than 25Pmm.
When connecting stainless steel pipes and pipe fittings and stainless steel pipes and pipe fittings to non-stainless steel pipes and pipe fittings, the pipe and cavity should be filled with argon gas for protection before welding the butt joint, before tungsten argon arc welding can be performed. The welds at the connection joints of stainless steel pipes must be pickled and passivated after welding. It should be noted that the arc starting and closing points of multi-pass and multi-layer welding should be staggered from each other.
