Home - TripleNine Stainless - specialists in stainless steel fabrication, orbital tube and pipe welding

ORBITAL WELDING

Orbital welding of piping and critical tubing is essential and of greatest importance for industries such as Biopharmaceutical, Food, Beverage, Dairy and semi-conductor. Microbiologically cleanliness and particle control is of and absolute necessary in several industrial fields e.g.; Semiconductor manufacturing, pharmaceutical manufacturing and biotechnology. The demand on process cleanliness with regards to analysis and process gases, water for injection (WFI), chemicals and products within these industries has played a major role.

Available Equipment

We have three fully equipped orbital tube and pipe welding machines, including our latest “ 307” AMI Orbital weld machine that allows us to computerise and maintain an electronic record of welds for QA documentation on the welds carried out. The machines are capable of welding 6mm – 100mm diameters, using fully enclosed weld heads and unlimited (using an) open framed head with or without wire feed. For quality assurance purposes, every welds is traceable and documented in accordance with the code of GMP

Welding Capabilities

Our orbital welding procedures are set up to only produce 5% ferrite, no one else in the industry can guarantee such a low percentage of ferrite.

PVDF Welding
Duplex

Welding

The weld abilities of the various grades of stainless steels vary considerably. Nearly all can be welded, and the austenitic grades are some of the most readily welded of all metals. In general the stainless steels have weld abilities, which depend upon the family to which they belong. Australian Standard AS 1554.6 covers structural welding of stainless steels, and gives a number of pre-qualified conditions for welding. Pre-qualified welding consumables for welding of same-metal and mixed-metal welding are given in Table 4.5.1 of AS 1554.6. This excellent standard also enables specification of welding procedures appropriate to each particular application.

Austenitic Stainless Steels
The austenitic grades are all very readily welded (with the exception of the free-machining grade 303 noted elsewhere). All the usual electric welding processes can be used. A full range of welding consumables is readily available and standard equipment can be used.
The use of low carbon content grades (304L and 316L) or stabilised grades (321 or 347) needs to be considered for heavy section product, which is to be welded. This overcomes the problem of "sensitisation" and intergranular corrosion. As the sensitisation problem is time/temperature dependent, so thin materials, which are welded quickly, are not usually a problem. It should be noted that if a fabrication has become sensitised during welding the effect can be reversed and the material restored to full corrosion resistance by a full solution treatment.
The free-machining grade 303 is not recommended for welded applications as it is subject to hot cracking; the Ugima improved machinability grades, Ugima 304 and Ugima 316, offer a much better combination of reasonable machinability with excellent weld ability.

Duplex Stainless Steels
Duplex stainless steels also have good weld ability, albeit not quite as good as that of the austenitics. Again all the usual processes can be used, and a range of consumables is available. For the most common duplex grade 2205 the standard consumable is a 2209 - the higher nickel content ensures the correct 50/50 ferrite/austenite structure in the weld deposit, thus maintaining strength, ductility and corrosion resistance. One of the advantages of duplex stainless steels over austenitics is their comparatively low coefficient of thermal expansion. This closely matches that of carbon steels, as shown in the table in the section of this handbook on high temperature properties of stainless steels.

Martensitic Stainless Steels
Martensitic stainless steels can be welded (again with the high sulphur free machining grade 416 being not recommended) but caution needs to be exercised, as they will produce a very hard and brittle zone adjacent to the weld. Cracking in this zone can occur unless much care is taken with pre-heating and with post weld heat treatment. These steels are often welded with austenitic filler rods to increase the ductility of the deposit.

Ferritic Stainless Steels
The ferritic grades again do not possess good welding properties. The three major problems encountered are excessive grain growth, sensitisation and lack of ductility. Some of these problems can be minimised by post-weld heat treatment. Filler metal can be of either a similar composition or alternatively an austenitic grade (e.g. Grades 308L, 309, 316L or 310) which is helpful in improving weld toughness. The excessive grain growth problem is difficult to overcome, so most grades are only welded in thin gauges. Stabilised ferritic grades include 409 and 430Ti. These possess considerably better weld ability compared to the unstabilised alternatives such as 430. These grades can be welded, but certainly not as readily as the austenitic grades
3CR12 is a proprietary ferritic (actually dual-phase ferritic plus some martensite) grade, which has a very low carbon content and has the remaining composition and the mill-processing route balanced to enable welding. 3CR12 is quite readily welded even in heavy section plate. As for other ferritic grades it is normal to use austenitic stainless steel fillers.

Welding Dissimilar Metals
Welding together of different metals, such as of Grade 304 to Grade 430 or a stainless steel to a mild steel, can be carried out, although some extra precautions need to be taken. It is usually recommended that over-alloyed austenitic welding rods, such as Grade 309, be used to minimise dilution effects on the stainless steel component. The composition of the weld deposit resulting from dissimilar grade welding is shown in the Schaeffler diagram or its successors by De Long and more recently the WRC. AS 1554.6 contains a table giving the pre-qualified consumables for each combination of dissimilar metal welds

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