High Strength Pipes
High Strength Pipes are widely used in the oil and gas industry for transporting crude, natural gas and petroleum products.
They must be able to withstand high pressures and temperatures as well as corrosive elements. API 5L X52, X 65, X70 and X80 are some of the most popular varieties of High Strength Pipes used in pipelines around the world.
All of these offer excellent performance characteristics such as higher yield strength values than standard grade pipes; enhanced resistance against corrosion; improved weldability; increased toughness; better wear resistance; superior dimensional stability over time; and excellent stress crack resistance.
API 5L X52 is known for its excellent weldability properties that make it suitable for use across a wide range of applications including utility pipelines and offshore structures.
It has a tensile strength range of 52000 – 65600 PSI (359 – 460 MPa). API 5L X65 pipes have higher yield strength up to 75200 PSI (517 MPa) with good resistance against sour systems due to their low carbon content.
Common API5L Pipes Grades
The API 5L pipe grades are commonly used in the oil and gas industry. The most common API 5L pipe grades are X42, X46, X52, X60, X 65, X70 and X80.
These grade specifications indicate the minimum yield strength of each grade in megapascals (MPA). Grade 42 has a minimum yield strength of 42 Mpa while Grade 80 has a minimum yield strength of 80 Mpa.
Each grade is suitable for different applications with varying levels of resistance to corrosion or abrasion. For instance, Grade 70 is often used in high-pressure applications due to its greater load-bearing capacity.
|Tensile strength (Ksi)||60||63||66||71||75||77||82||90-120|
|Yield strength (Ksi)||42||46||52||56||60||65||70||80|
The most important factor to consider when selecting an appropriate grade is its application requirements.
The strength of steel can be increased in several ways – including the addition of additional chemical elements, microalloying and cold pipe pulling in the manufacture in the pipe plant.
In the case of high-strength steel grades, cold pulling and microalloying are often used to keep the carbon and manganese content low and thereby reduce the hardness of the material in the thermal impact zone and reduce – although not completely eliminate – the problems associated with diffusion hydrogen in the deposition metal.
For example, modern steels of strength classes X70 and X80 have a carbon content of less than 0.05%. Some grades of steel of the X80 class at the same time have a Pcm value of less than 0.20.
Welding of API 5L High strength Pipes
first stage of pipe welding is the welding high quality root run. For several reasons, it can be called the most important.
First, this pass is the most difficult to perform. It requires the operator to have extensive experience with manual stick welding, precise control of the welding process and the position of the torch.
Automatic processes require welders to have high technical skills and the use of advanced auxiliary and positioning systems.
To date, the preferred process of automatic welding is welding with a stick welding electrode in a protective gas environment (GMAW), which is usually used using an internal copper support ring or, in the case of a sufficiently large pipe diameter, an internal welding system.
Both of these methods further complicate the welding process and impose certain restrictions on the use of traditional methods of metal transfer in the GMAW mode.
Speaking of root welding, you also need to remember the speed of welding. The speed of laying pipelines largely depends on how quickly you can make a root passage.
Welding can be somewhat accelerated if it is conducted by several operators at once, but this method is often too impractical.
Therefore, the speed of welding is of critical importance – high speed will allow the project to be completed on time and thereby reduce the cost of renting equipment.
Welding electrode selection chart for API 5L X42, X46, X52, X60, X 65, X70 and X80
The selection of a welding electrode for any task requires careful consideration and research into the properties of the material being welded.
When it comes to welding pipes in accordance with the American Petroleum Institute (API) standards, the most commonly used materials are API 5L X42, X46, X52, X60, X65, X70 and X80.
For example, if you are working with an API 5L pipe grade such as X60 or higher then you would need to use a high-strength low-alloy electrode.
Alternatively, if you were working with an API 5L pipe grade less than or equal to Grade 42 then you could opt for a standard carbon steel electrode.
The recommended welding electrodes for API 5L X42, X46, X52, X60, X65, X70 and X80 grade pipes are given in the below table:
API 1104 Guidelines for High strength pipeline welding
API 1104 code is used to establish quality standards for the welding of pipelines and related facilities.
API 1104 covers many aspects of welding procedures and practices including joint preparation, preheating and post-weld heat treatment requirements.
It also provides detailed specifications on materials to be used in construction as well as acceptable levels of discontinuities within welds.
Welding electrodes and wires grouping as per API 1104 standard is given in the below table:
There are total of 8 groups for welding electrodes and filler wires as specified in API 1104 table 1.