It has to be paid a special attention to welding in chemical and petroleum industries. The matter is that them (as well as Food, Pharmaceutical and Electronics Industries, etc.) deal with various thin-walled metal constructions which often work in the so-called singular conditions and simultaneously belong to precision structures. Among them are different vessels (for manufacturing, cleaning and storage of varied solid, liquid and gaseous substances), filters (including membranes), fuel elements and catalytic reactors and many others. It is very difficult to show all possible applications of the above mentioned equipment and technologies for these industries' needs. We shall cover some of them in this rubric, applied for the two industries mentioned earlier.

Perhaps out of the two given below subrubrics (thin-walled vessels, filters, fuel elements and catalytic reactors), the second one is the most complicated in our site. Refering only to one document C-046N with the name "The Membrane Microfiltration Market", written by Susan Hanift and published in March 2006 (www.bccresearch.com), we can see a lot of membrane filters applications in Food Processing, Biotechnology/Pharmaceuticals, Technical Chemicals, Medical, Oil and Gas Processing (oil/water,air/gas manufacturers). The document considers Gas Separation, Applications for Gas Separation Membranes, Gas Filtration and Purification. It gives information about Manufacturers of Membranes for the Semiconductor Idustry, Catalytic Membrane Reactors, etc.

The market of Hydrogen Purification is estimated in millions of dollars. So, indeed, this subrubric looks quite realistic and relevant.

Since we have much experience in welding of membrane hydrogen (diffusion) filters and catalytic reactors [see, please, N.N. (2),(7), (9), (10), (14 -19), (26), (23) of www.pogrebis-temp.com/main-works.html], here such structures peculiarities and the proper welding problems will be described in more detail.

Among the main consumers of hydrogen there could be named: chemical industy, oil recast and petroleum production, metallurgy, electronics and food industry, etc. Various methods allow the acheivement of different kinds of hydrogen purification : up to 96,6% - membrane method based on synthetic fibre using; up to 97,5% - cryogenic; up to 99,4% - short-cycle method. If to use cryogenic and short-cycle methods repeatedly or some complex methods combinations, it is possible to reach the level of hydrogen refinement of nearly 99,999%. Really cleaning only by "lattice elements", also called the diffusion filters, gives possibilities to reach the hydrogen purification > 99,9999%. Such hydrogen is extra pure and it is extremely useful : in the production of the semiconductor materials (Ge,Si,etc.); in light tempering of transformer, dynamic steels and tubes (pipes) made from stainless steel; in preparation of metal powder materials, food margarine, medical products and other substances.

Two welded membranes devided by a remote mesh-grid.

Usually a capillary tube or a foil of 0,02-0,1 mm thick of palladium based alloys is used as a material for the filtering membrane. There is a tendency to obtain such membrane by palladium alloys deposition at the porous support - like a very thin (but compact) layer which has to be hermetically fixed to a gas-impenetrable body of the filter. However, it is still not used in industrial scales. Independent on the Pd-based membrane's structure, if from one its side we have a hydrogen-containing gas mixture, only hydrogen can penetrate through the membrane to its opposite side (as a rule, under specific conditions - high temperature and pressure). And (according to the existing hypothesis) the crystalline grill of the named membrane carries out the role of a filter for hydrogen, which penetrates through it in an "atomic", more exactly - in a "proton" mode - because before this penetration an electron had to leave each atom of hydrogen and to go to the opposite side of the membrane (due to its electoconduction). Before, of course, every hydrogen molecule had to dissociate on two atoms and each of their temporary parts with their own electrons, forming two protons. Only after "personal tunneling" through the mentioned grill a proton can reunite with an electron, giving an atom of hydrogen which is much more active than its molecule, that appears later - after association of a pair of hydrogen atoms.

Various filters and reactors as well as fuel elements now are still in the focus of scientific research in the USA , Russia, Japan, Germany, etc. For example, at the 14-th annual U.S.Hydrogen Conference in Washington more than 500 engineers and researchers took participation. President George W.Bush proposed spending $1,2 billion over 5 years on hydrogen-powered vehicle research. This problem became much more relevant now when sotimes the prices for oil have a fantastic level.

As our site readers may see, we have been successful in microplasma welding of very thin components made from noble metals. For example, due to exclusive properties of the modular-inverter AMC-1 welder, it became possible to weld thin Pd-based membranes, devided by a remote mesh-grid (see our unique innovations the USSR inventon 869108 - "Diffusion element") without using a filler material - picture.

Perhaps, due to a certain lack of our work exposure, similar problems still remain actual today. For instance, not so long ago the Italian specialists developed Method of diffusion bonding thin foils, made of metal alloys, selectively permeable to hydrogen, particularly providing membrane devices, and apparatus for carrying out the same job. This method is based on conducting hot diffusion bonding in "an oven under controlled temperature conditions and in a mixture of argon and 5% hydrogen at a pressure of 1 atm. An alumina rigid support is used to keep the edges of the foils to be joined in the correct position. A pressure blade is used to press evenly over the length of the welding seam. The pressure exerted by the pressure blade is adjusted by set screws. The method is particularly suitable for joining thin foils of palladium-silver alloys to make tubes for production of ultra-pure hydrogen". (European Patent Application 1 184 125 A1. Filed: 12 July 2001 - Italy RM200412, 25 July 2000 - Publ: 6 Mar.2002). Without criticing this invention, we would only remind that the applicability of argon-hydrogen mixtures for welding of palladium and its alloys we had offered much earlier (3).

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