Regarding the material of the gauge pressure leads and the flanges of the main pipeline: whether electrochemical corrosion can occur, and how to prevent it

Carbon steel pipes are used before the valve, while stainless steel pipes are used after the valve.

Carbon steel pipes are used before the valve, while stainless steel pipes are used after the valve.

Whether two different materials can form a welded joint directly depends on the strength of the interactions between the atoms or molecules that make up those materials. The interaction between two elements is determined by factors such as their electron shell structure, number of valence electrons, atomic size, electronegativity, as well as the crystal lattice and lattice constants. For the welding of dissimilar metal materials, one can consider the similarities in the main factors present in the two alloys. Generally, good-quality welded joints can be easily formed between two metals that are infinitely miscible in both liquid and solid states. Two metals that are infinitely miscible in the liquid state but only partially miscible in the solid state can form weldable joints regardless of whether they have an eutectic or peritectic phase diagram structure; however, their properties depend on the degree of structural transition between the two metals. The two alloys that form intermetallic or interstitial compound intermediates can also be welded together, and the performance of their joints is largely influenced by the properties of such compounds. If two metals are completely immiscible in both liquid and solid states, or if their solubility is extremely low, then a true welded joint cannot be formed; at best, only a weak adhesion between them will occur ； Such a joint will only possess a certain degree of strength when the mating surfaces are highly interlocked to the point where they interlock with each other; essentially, this type of connection can be considered merely a mechanical joint. If these two metals are to be firmly welded together, a third metal can be used to achieve that. Of course, the phase diagram structure of binary alloys ultimately stems from the physicochemical properties of the aforementioned elements. (1) Form brittle compounds. During the welding of dissimilar metals, due to the diversity and complexity of the chemical composition of the weld metal, various non-metals or intermetallic compounds can precipitate, in addition to the formation of various carbides and nitrides. In addition to their inherent brittleness, these non-metallic compounds have a significant impact on the mechanical properties of welded joints; they often reduce the plasticity and toughness of the weld metal, and can even increase the tendency for cracking, thereby becoming important factors that lead to brittle fracture of the welded joints. (2) Welded joints have difficulty achieving properties comparable to those of the base metal. Typically, when two different metals are combined, they form a corrosion cell, resulting in corrosion resistance that is lower than that of either metal alone; this is a difficult problem to resolve. Furthermore, in order to achieve welding of dissimilar metals, welding materials with good plasticity are often selected – WeChat official account: hcsteel – to prevent cracking or embrittlement of the weld metal, but this may reduce the strength of the welded joint. Therefore, in order to ensure that welded joints of dissimilar metals possess good overall performance, it is often necessary to compromise on or reduce certain requirements regarding secondary performance indicators; this is an inevitable issue when welding dissimilar metals. It is evident that there are many issues to address when welding dissimilar metals, and the welding process is quite challenging. Only by selecting appropriate welding methods and materials, formulating a proper welding procedure, and taking certain special measures can high-quality welds between dissimilar metals be achieved.

Made of stainless steel, with a long service life

If the materials are different, padding is definitely necessary; not only for the main pipes, but also for the clamps used to secure the pressure transfer pipes, as well as items like angle irons, all of which require rubber pads.

If it can’t be separated, create a transition section

Isolating the valve once; using a pad can solve the problem

Carbon steel is used in front of the manual valve, while stainless steel is used behind it; if possible, PTFE gaskets should be used behind the valve.