During recent decades, automated welding procedures have made major advances. Frequently the equipment is very performing, precise, and adaptable.
The welding parameters can be adjusted during the welding cycle. Some of them offer even real time interpretation of the images captured by camera.
Nevertheless, we often notice that all the steps of the tube preparation before welding is often neglected. There is not an orbital welding machine, even the most performing, that can comply with a bad preparation.
The final weld result cannot be of good quality if all the previous steps have not been considered.
Here you will find some basic information to be considered in order to obtain the best possible welding result.
#1 Choice of the workpieces
Let us start with the tubes and pipes, as well as all the accessories such as bends, fittings, T-pieces to mention just a few.
These parts are classified according to geometrical and metallurgical characteristics. The compliance with these standards and characteristics is a very important issue when it comes to comparing purchase prices.
These workpieces can be very expensive and high quality products are mainly used in high added-value applications, as for example in the semiconductor industry and the pharmaceutical applications.
Other standards such as ISO, DIN, ISO, SMS are less stringent and the tolerances are larger. This is a fact you will have to comply with if these pieces have to be welded.
In many cases the purchase department will decide about the choice of the parts by means of price comparison. It is in fact very difficult to consider the whole value chain starting with the purchase of the pieces, which goes beyond the simple purchasing price.
If you consider the complete process, you might reconsider buying better quality workpieces, as the production will be faster and easier to handle. Thanks to the repeatability of the process the number of defects diminish. If you invest more (for purchasing), you will save on the other hand (productivity). But this is not easy to quantify.
What is the use of buying high performance welding equipment if the workpieces are of bad quality?
#2 Preparation of the edges before welding
Before assembling the pieces the edges of the working pieces must be prepared. We can say that intelligent machines are on the market for tube preparation: cutting – squaring – bevelling.
The different machines have to comply with some nuances when it comes to work with thicker wall and larger diameters.
There are quite a few machines that can put into compliance tubes and pipes. Some of them even can adjust geometrical defaults by profile monitoring or counterboring for example.
#3 Accessories and a perfect tube preparation before welding
The most common accessories are bends and T-pieces, so we wish to take these two examples to explain the issue.
The production techniques for bends and T-pieces induce some defects such as ovalization of the edges and variations of the wall thicknesses, and particularly at the edges.
These defects have to be correlated with those of the tubes to which they have to be fitted.
The smaller the faults and their control, the easier will be the tacking and the welding process. Unfortunately price cutting are often made at this stage, which will complicate the progress of tube preparation and welding!
#4 Beveling and pipe preparation
Let us take the example of an accessory (T,elbow, flange…) with a wall thickness of more than 4mm that will need a specific preparation (bevel).
- V-Bevel: 95% of the produced volumes of accessories are made with a V-bevel, which means that in automated welding we will choose a V-J bevel configuration. J is the abbreviation of a tulip bevel on a pipe, a compulsory process in case of orbital welding. It is quite difficult to make a V-J welding with regards to the preparation process. Only few companies are able today to master this kind of welding, even if there is a high demand on the market. This process needs a skilled welder with a long and high level of experience.
>> V or J bevel? How to choose?
- J-Bevel: You can find in Austria a producer of bends who realizes a J-preparation. This means that the welding will use a J-J configuration, which is easier to handle. As a result, you will have less scrap at the end of the production. But the main obstacle is the purchase price, which is 20 to 40 % higher for bends or T-pieces compared to traditional bends (with V-bevel).
This is the main reason why only few companies buy these kinds of accessories, as most of them look at the purchase price and neglect the whole process!
The extra cost of these pieces is quickly compensated by a higher productivity and lower scrap rates. The price for “no quality” is considerably reduced.
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