TIG Welding tip

"Tungsten Inert Gas" welding or "GTAW" for Gas Tungsten Arc Welding is an arc welding process that uses an arc between a tungsten electrode (non consumable) and the weld pool. And in this oportunity I would like to share a very important tip for the preparation of the tungsten tip. As is well known this has to be sharpened at one end and in the video shared in this post it is shown the right way to do it. It has to be grinded along the axis of the electrode, please pay attention to the video wich is a courtesy of Lincol Electric.-

Safety in welding

Now available the AWS safety code to be freely downloaded at: http://www.aws.org/safety/ 

Weld inspection.

The owner of a project has the right to designate an inspection company to verify the quality of the weldings during it´s construction, and this area is covered in section 6 of the code AWS D1.1/D1.1M Structural  Welding Code - Steel. In the video above we can see a CPJ, (Complete Penetration Joint) in a pipe and in this case the welders are performing a NDT, ( Non Destructive Test) with Liquid Penetrant to verify the quality of the weld, in this case all pipe joints were checked with this system and this is covered in section 6.10 of the code after the first pass of the weld..-

As the readers can apreciate, the joint of the pipes has a "V" beveled joint as aproved in the prequalified joints in Figure 3.4 and they have a geometry as shown below:

 In this drawing we can see the main parts of this kind of joints:

1. Root opening "R" 

2. Roof penetration "f"

3. Angle of the bevel 

More aspects will be covered later.

Petroleum tank welding

So what about API tank welding, this are ruled by API 650, (American Petroleum Institute); Welded Steel Tanks for Oil Storage (API 650). Tanks have 3 main parts, bottom, shell and roof; also it´s very important the piping connected to it. And this code starts by ruling materials, plates and sheets used for it´s  construction in part  2.1, and in part 2.2.1.3 it states:
"All plates shall be manufactured by the openhearth, electric-furnace, or basic oxygen process. Steels produced by the thermo-mechanical control process (TMCP) may be used, provided that the combination of chemical composition and integrated controls of the steel manufacturing i mutually acceptable to the purchaser and the manufacturer, and provided that the specified mechanical properties in the required plate thicknesses are achieved. Copper-bearing steel shall be used if specified by the purchaser. Also in part 2.2.1.4 we read:
"Shell plates are limited to a maximum thickness of 45 mm (1.75 in.) unless a lesser thickness is stated in this
standard or in the plate specification. Plates used as inserts or flanges may be thicker than 45 mm (1.75 in.). Plates thicker than 40 mm (1.5 in.) shall be normalized or quench tempered, killed, made to fine-grain practice, and impact tested."
This is very important from the beggining of the design of an API tank, we notice here that the thickness of the shell is limited, something that is not stated in other materials.-
And as for welding, the electrodes to be used are ruled here:

"2.8 WELDING ELECTRODES
2.8.1 For the welding of materials with a minimum tensile strength less than 550 MPa (80 ksi), the manual arc-welding electrodes shall conform to the E60 and E70 classification series (suitable for the electric current characteristics, the position of welding, and other conditions of intended use) in AWS A5.1 and shall conform to 5.2.1.10 as applicable. 2.8.2 For the welding of materials with a minimum tensile strength of 550 through 585 MPa (80 through 85 ksi), the manual arc-welding electrodes shall conform to the E80XXCX
classification series in AWS A5.5."
And as you should have seen in the abobe video, it´s very important and hard to comply with is the shell´s dimensional tolerance, one welder was checking the roundness with a piece of wood, tis part is stated in part 5.5, Dimensional tolerances.

Other standards

Depending on the project where you will weld parts, there are special standards to be applied in the design and construction of the project, as an example in petroleum tanks the standard is Welded Steel Tanks for Oil Storage (API 650), from the American Petroleum Institute, and there are also standards for petroleum pipes, like Code Clinic for Study of API 1104 Welding of Pipelines and Related Facilities (American Welding Society), and for pipes we have ASME B31.8 for gas transportation and ASME B31.4 for liquid hydrocarbons. For painting there is  SSPC: Steel Structures Painting Manual (2 Volume Set) (Hardcover) and of course we cant´forget about security, it´s first in every project! for that we have to work acording to OSHA Standards for the Construction Industry as of 01/2011.-

And here I post a new video on a petroleum tank farm construction:
http://www.youtube.com/watch?v=Tz3ZFUw_rng 

Type of welds

There are basically 2 kind of welds, groove and fillet; this are aproved in AWS D1.1 in section 2.3. Groove welds are shown below:

From the site "Weldguru".

And this joint can also be divided in two cathegories, complete penetration (CJP) and partial penetration (PJP) . PJP is standarized in part 2.3.3.1 of the code and CJP in part 2.3.4. The difference between them is the penetration, wich is well understood in the words complete and partial.- 

Fillet welds are standirezed in section 2.4 of the code and they look like this:

From Unified Eng. Inc.

And below we can see a recent picture taken at a petroleum tank farm construction.

Below we can apreciate a preparation for a fillet weld for the floor of a tank acording to API.-

And a very important aspect of fillet welds can be to determine the maximum size of it, this can be found in 2.4.5 and figure 2.1 as seen below:

Details for Prequalified Fillet Welds. (See 2.4.5)

Welding symbols

Acording to AWS D1.1 section 2.2.4.1, it is recommended that contract design drawings show complete joint penetration or partial joint penetration grove weld requirements without specifying the grove weld dimensions.

A welding symbol consists of 3 basic elements: Reference line, Arrow and Tail as shown below:

From metallicfusion.com 

Reference Line must always be horizontal,

Arrow points to the line or lines on drawing which clearly identify the proposed joint or weld area. The tail of the welding symbol is used to indicate the welding or cutting processes, as well as the welding specification, procedures, or the supplementary information to be used in making the weld.