there is on the market cheap alternatives to swagelok and parket fittings and conector for steel tubing . can somebody do comments.

Several manufacturers offer knockoffs of the Swagelok and Parker fitting dimensions.  The noticeable observation is that knockoffs lack the pretty finish of Swagelok.  More subtle and serious issues may also exist.  Swagelok uses a special carborization technique for stainless that hardens the ferrules.  I can look for the details but it could take some time.  If the knockoff fittings lack the polished finish, surely they also lack the metallurgical techniques too.

I am less familiar with any special metallurgical issues with Parker.  Even the major hydrocarbon processing companies consider the knockoffs for air supply tubing etc.  Few use knockoffs for analyzer tubing.

Compression fittings are a wonderful option for line sizes below 3/4" pipe, if properly designed and installed.

There is more than one company claiming to have two-ferrule compression fittings which are interchangeable and intermixable with Swagelok.  Gyrolok (Hoke) is not one of them as they have a different ferrule geometry, but there are numerous others, some of whom are quite large operations with very significant sales volumes and a very broad product line of associated valves(globle valve), filters etc.  Numerous major (multinational) end-user companies have accepted the fittings supplied by some of these knock-off suppliers as functionally equivalent to Swagelok.

Swagelok's patents expired many, many years ago.  They have a well established brand, a very broad and quite complete product line, a good reputation in the marketplace, lots of stock of common items, and often very helpful sales reps- some of whom provide a very valuble service in educating thousands of students, lab techs and fitters in the proper use of the product.  They tend to be conservative in rating their product, and to stand behind its quality if any problems are discovered.  

You pay for all of that in a price premium for their product.  That price premium can be minor to substantial depending on what you're comparing it against.

I look forward to the day when there's an MSS-type standard for these fittings, such that we can get REAL competition going and drive the prices down on these items to the commodity level where they belong.  Until then it's a matter of comparing how much you'll save in purchasing the knock-offs versus the potential cost in labour and damage (physical and to your reputation) of a potentially defective product.  For 15% savings in the bare cost of the fittings, it's probably not worth the risk.  For 50% or more, maybe it is- depending on the hazards associated with the services where you're using the product.

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