Carbon Steel X65QS Pipeline Qualification for Extreme Sour Service a Global Approach: Line Pipe, Welding, Eca Methodology and Diyab Pipeline Case Study

In the wake of failures of large diameter pipelines made from plates using the Thermo-Mechanically Controlled Process (TMCP), the suitability of carbon steel material for sour environments where the H2S partial pressure is largely over 1 bar has been questioned. Understanding that seamless quench and tempered material are not prone to the same phenomenon as large diameter TMCP pipes, it has been decided to ensure the integrity of the DIYAB pipeline by qualification using the actual production environment pH=3.5 at 24°C and 6.84 bar H2S plus 6.84 bar CO2. The global approach includes the qualification to sour service resistance under 6.84bar H2S of the base material and the welds without post weld heat treatment. Fracture toughness tests under 6.84bar H2S were also conducted, and the results fed into an Engineering Criticality Assessment (ECA) to define the Non-Destructive Testing (NDT) acceptance criteria. The NDT tools were selected for their ability to detect the critical flaws and validated. The global approach methodology and results are presented.

Study of strain-stress state of flat knives for cutting thin-walled pipes

Cutting of pipes into measured lengths on-line of pipe welding mill by disc saws and by facilities of abrasive cutting requires special measures of safety of personal. Besides, the necessity of frequent change of cutting instrument results in losses of production time. To eliminate the drawbacks, a study was initiated related to creation of shears which could enable to accomplish a quality transverse cutting of thin-walled pipes of small diameter by flat knives with various form of the working edges. A methodology and the results of study of strain-stress state of flat knives with application of physical and mathematical simulation of the process of transverse cutting of thin-walled pipes of small diameter presented. At the physical simulation using a polarization-optical installation, the pictures of deformation centers arising in the lower part of the knife in the zone of contact of its cutting edges with the body of the hollow circular profile being cut by it were obtained. In the experiment, models of three types of knives made of organic glass on a scale of 1:1 were used. Cutting edges of the knives for cutting pipes of 25 mm outer diameter, wall thickness of 2 mm were wedge-shaped, convex semicircular and concave. The data from studies of the loaded state of transparent knife models served as the basis for mathematical simulation of the strain-stress state of the shears cutting tool in the SolidWork application package using a strength analysis module that implements the finite element method in the form of tetrahedrons. The current values of the pipe cutting force used in the mathematical model were preliminarily calculated according to the previously proposed dependence, taking into account the strength of the hollow profile material and the area of the cut layer of its cross section for a given relative displacement of the cutting edges of the knife. The results of mathematical modeling were the pictures of deformations and equivalent stresses of the cutting part of the knife, determined according to the third theory of strength. A qualitative similarity has been established for the distribution patterns of stress fields recorded using the polarization-optical method on knife models and obtained in mathematical modeling for working samples of the shears cutting tool operated under the conditions of pipe welding mills. The proposed mathematical model makes it possible to estimate the values of the maximum equivalent stresses in the working part of a flat knife, taking into account the shape of its cutting edges, as well as the force required for cutting a thin-walled pipe into measured lengths with the corresponding dimensions of its cross-section and the strength of the material.

Effect of welding sequence and welding current on distortion, mechanical properties and metallurgical observations of orbital pipe welding on SS 316L

Orbital pipe welding was often used to manufacture piping systems. In orbital pipe welding, a major challenge is the welding torch’s position during the welding process, so that additional methods are needed to overcome these challenges. This paper discusses the influence of welding sequence and welding current on distortion, mechanical properties and metallurgical observations in orbital pipe welding with SS 316L pipe square butt joints. The variation of the orbital pipe welding parameters used is welding current and welding sequence. The welding current used is 100 A, 110 A, and 120 A, while the welding sequence used is one sequence, two sequences, three sequences, and four sequences. The welding results will be analyzed from distortion measurement, mechanical properties test and metallurgical observations. Distortion measurements are made on the pipe before welding and after welding. Testing of mechanical properties includes tensile tests and microhardness tests, while metallurgical observations include macrostructure and microstructural observations. The results show that maximum axial distortion, transverse distortion, ovality, and taper occurred at a welding current of 120 A with four sequences of 445 µm, 300 µm, 195 µm, and 275 µm, respectively. The decrease in ultimate tensile strength is 51 % compared to the base metal’s ultimate tensile strength. Horizontal and vertical microhardness tests show that welding with one sequence produces the greatest microhardness value, but there is a decrease in the microhardness value using welding with two to four sequences. Orbital pipe welding results in different depths of penetration at each pipe position. The largest and smallest depth of penetration was 4.11 mm and 1.60 mm, respectively

Stainless Steel Pipe Welding With No Backing Gas

For pipe fabrication shops, stainless steel pipe welding typically represents 15%–20% of their business. The pipe materials fabricated in these shops are primarily austenitic stainless 304L and 316L pipe. The quality requirements in stainless pipe fabrication shops are determined by performance requirements for service applications in low temperature, high temperature or corrosive environments. To enable the performance required in these applications, codes, standards and recommended practices for welding are frequently written from a conventional GTAW or SMAW welding paradigm. In addition, for the root pass and the first fill pass made with GTAW, an inert backing gas is always recommended to minimize or eliminate the discoloration or oxidation on the ID surface of the pipe near the root pass. The use of GTAW with inert backing gas adds significant time, complexity and cost to the welding of stainless pipe. In stainless pipe shop fabrication, very few welding practices recognize or encourage the use of GMAW welding solutions for these applications, even though it is known to be a more productive and economical welding process. Moreover, the absence of a consistent and proven GMAW welding solution in terms of either no backing gas GMAW, alternative options for expensive shielding gases, implementing unique welding waveforms etc., proves to be a hindrance in the adoption of GMAW solutions for the welding of stainless pipe. In this paper, we discuss advances that have been made in producing acceptable stainless pipe welds with a 1G GMAW welding solution using an STT® waveform for the root pass and a unique “Rapid X™” waveform for fill passes with no use of backing gas. One goal of this project was to also find a shielding gas mixture to provide acceptable welds from root to cap that takes into account both welding process performance as well as fabrication of defect free welds. Six different shielding gas mixtures with varying amounts of Ar, He, CO2 and N2 were evaluated. Results indicate that STT/RAPID X™ welds made with 97%Ar/2%CO2/1%H2 provide very promising results in terms of weld appearance and other conventional metrics such as radiography, bends and tensile properties. However, assessment of the corrosion performance in comparison to welds made with conventional GTAW requires development of a better test protocol than the ASTM G48 Method A test for it to be relevant and meaningful.

The Defect Analysis of Carbonsteel Pipe Welding Connections Using Non-Destructive Testing with the Penetrant Test Method

In a welding process carried out on metallic materials is sometimes found defects in the material being tested, it is caused by many factors, such as the lack of good materials used and the lack of perfection of the welding process. At testing, it aims to know the surface defects in carbonsteel pipes to know the defects arising after welding. This test is performed with non-destructive tests (NDT) using Dye Penetrant testing method. This test uses 3 types of liquids, including; Cleaner, Penetrant, and developer. The results of these tests will then be observed whether defects occur after welding and what factors affect it. From the test, results there are known 10 locations defects on the surface of the carbonsteel pipe welding with a type of rounded indication of defects that are then followed up by re-welding on indications of such defects.