Stainless Steel Elbow Fitting

In stainless-steel piping system, stainless steel elbow fitting is used to change the flow direction in the pipe. According to its angle, the most commonly-used ones are 45°, 90° and 180°. And in some engineering projects, 60° elbow or other unconventional angle elbow are also required. Except for stainless steel, the materials of elbow also include cast iron, alloy steel, malleable iron, carbon steel, non-ferrous metals and plastics.

The forging process of stainless steel elbow fitting
In order to be able to create stainless steel elbow fitting that comply with the regulations and quality requirements requested by customers, controlled production processes following the best procedures deriving from both study and experience in the field.
In particular, the forging process assumes considerable importance. This operation allows the transformation of stainless steel by bringing it to high temperatures and plastically deforming it to obtain a semi-finished product. The correct choice of the parameters to be set for the process is fundamental, in addition to the continuous maintenance of the systems, both to avoid subsequent damage during operation and not to produce an excessive number of rejects which represents damage from an economic point of view.
Among these are:

• Temperature of the starting steel;
• Form of the starting material;
• Type of material and chemical composition;
• Presence and intensity of tensions;
• Type of forging operation carried out;
• Type of lubricant used in the process.

Welding of stainless steel elbow fitting
Welding stainless steels is not as simple as for other typical materials of the hydraulic world. In fact, stainless steel usually has a characteristic oxide layer (suitable, for example, for protection against the phenomenon of corrosion) which tends to make the process difficult and requires some precautions:

• Preparation for caulking: It is important to remove the oxide layer in correspondence with the welding area by means of mechanical abrasion;
• Use of appropriate filler material: This addition improves the characteristics of the area, avoiding resistance problems that can arise in correspondence with the welded or heat-altered area.
• Use of austenitic stainless steels: They have better weldability than other stainless steels, reducing the upstream problem.
• For the latter reason, austenitic stainless steels such as those previously mentioned in the appropriate paragraph are chosen for this type of application.
• Certainly following these indications represents a good starting point but it is not sufficient to achieve a work of art welding. In fact, the welder must be adequately trained and must know the importance of each characteristic parameter of welding such as, for example, the depth and the speed of the pass. If the welding is not carried out correctly, it will bring with it numerous problems from a resistance and structural point of view which can act as areas of weakness for the system once the stainless steel elbow fitting have been put into operation.

The characteristic dimensions of the elbows and their design
Given the regulations, the types and methods of connection, it is necessary to shift attention to the design phase of the stainless steel elbow fitting and to the characteristic dimensions that act as a cornerstone both for the choice and for the realization.
In particular:
External diameter: Whether in inches or mm, it represents the main characteristic for the choice as it must be made on the basis of the system in which it will operate.
Thickness: It is essential for the structural resistance of the system as it guarantees certain resistance characteristics. For this reason it must be made uniform along the entire section.
Distance between the entrance section and the axis of the other entrance: It is an important dimensional characteristic and valid only for 90° elbows;
Distance between the entry section and the center of the elbow: It is an important dimensional characteristic and valid only for 45° elbows;
Elbow weight: It may be necessary to estimate the loads and inertias during operation.
The role of the designer, while adhering to the stringent rules highlighted above, is to understand the main possible "failure modes" and anticipate them in the design phase, preventing them from occurring. Furthermore, it must be able to provide support to the customer regarding the specific application of the stainless steel elbow fitting, highlighting the advantages and criticalities in order to carry out a complete service that allows the interconnection between the manufacturer and the customer, improving the final yield of the system.