API 5L-X70 steel tube,
Diameter: 48 in (1219 mm)
Line wall pipe thickness: 21 mm.
Operating pressure: 72 bar
Gas temperature: 40-44oC
Gas flow rate: 1,265,000 KNm3/h
Linear pitting corrosion throughout the perimeter of the tube at an average distance of 200-300 mm from the original pipe welded joint.
This corrosion is presumably due to a defect in the bonding of the original tube liner with the local coating of the pipe bonding weld area.
|The optimum pre-heating and interpass temperature was previously established by qualification of the welding procedure. Several tests were carried out to study the variation between the welding temperature and the toughness of the Weld Heat Affected Zone. It was therefore essential to achieve and maintain a temperature between 90 and 100oC during the entire welding operation. Achieving 90-100ºC was made possible by the studied induction heating procedure developed by SOLYSOL during the repair process.||
Procurement of material for making the half-cylinders that will form the jacketed to cover the damaged area, of the same characteristics of the steel of the original tube: API 5L-X70, thickness 25.4 mm (1″).
Cutting and bending of semi-cylinders to wrap the damaged section of the original tube.
SOLYSOL subcontracted this phase of the project to ANGEL RUIZ E HIJOS, S.L.,for its capacity and experience in this type of materials.
For the Qualification of Welding Procedures, tube of the same material was cut and curved as the jacketing semi-cylinders. This ensured that the mechanical properties obtained in the tests would indicate the exact behavior of the welded cylinders in service.
The essential variables of qualifications were defined on the basis of the ASME, Sections VIII and IX Code,because it is a very high pressure gas conduction and because it is this code that brings the most experience in the behavior of these types of components: The choice of code and project requirements are essential. In the absence of requirements on the part of the customer, except for the integrity of the pipe and the realization of the repairs keeping the tube in full load, the SCWI defined this code as the safest for elaboration of the WPSs of the project.
Welders were also approved during the execution of the PQRs. All Solysol welders who participated in the project are experts in carrying out high-responsibility work. Our welder instructor, Fernando Sánchez Deza, in addition to performing most of the repair, acted as a welding coordinator during the entire project. Welders José Pinto and Braulio Condori did an excellent job. No weld performed throughout the entire project required any repair. And, in particular, they worked aware of the responsibility and risk of welding on a high pressure and flow gas-fired tube, traversing the corrosion zone with the proper procedure to ensure the integrity of the tube and their own lives.
The customer’s trenching and handling staff in Morocco proved essential for the repair project as well.
Choosing an excellent electrode ensures the mechanical properties of welds and helps welders to make each bead flawless, with easy-to-clean surface slag that is not trapped at the edges of the beveled joints. ESAB FILARC 98S electrode, with the same mechanical properties as the base metal, provided excellent tensile yield & strength, and toughness at -20oC.
The necessary tests and control of the weld execution is performed by a CWI, Certified Welding Inspector by the American Welding Society (AWS). All work is scheduled, supervised and approved by a SCWI (Senior Certified Welding Inspector),Angela Lazaro.
The staff dedicated to repairs of great responsibility, as in this work, has a great experience, qualification and certification. In addition, their continuous training and study and their passion for the work they do are an excellent guarantee for customers who have this type of needs.
3.1 Jacketing (semi-cylinders) Preparation: Beveling and Inserting Steel Backing
3.2 PREHEATING of the area to be welded
3.3. Welding the circumferential Buttering at both sides of the seat of the cylinder
Preparation of the edges of the semi-cylinders with S460 steel plate to insert a secure backing into both longitudinal joints to conform the tubular jacket.
Solysol supplied welding, induction heating and auxiliary equipment for the project:
A small but very powerful and robust welding equipment: the ESAB RENEGADE,held hours of work at temperature above 40oC, sandstorms, non-stop welding of basic high yield strength electrodes, FILARC 98S, up to 4 mm diameter.
Performing “buttering” or surfacing welding on both sides of the tubular jacket to provide the right support for the fillet welding around the full perimeter of the joint from the jacket to the original tube.
Control of the preheating and interpass temperature is essential, throughout the whole perimeter.
Heating with SOLYSOL induction equipment enabled a constant temperature of 90-100oC throughout the entire welding process.
3.4 Placing semi-cylinders to wrap the tube
Placing the semi-cylinders to form the jacketing in the area to be repaired of the tube in service.
3.5 Preheating Longitudinal Weld Joints
3.6 Longitudinal welds on both sides of the tube were carried simultaneously
Performing the longitudinal welds on both sides for the closure of the tube casing.
3.7 Preheating Gaskets Circumferential Welds
3.8 Fillet overlap circumferential welds
Performing circumferential welds for joining and sealing the perimeter of the tube and its casing, on the surfacing or “buttering” of safely previously applied on the tube.
3.9 Continuous temperature control throughout the perimeter of the tube: WARRANTY OF TOUGHNESS OF WELDS AND HEAT AFFECTED ZONES.
Continuous control of the preheating temperature and maintenance in the entire perimeter and longitudinal areas of the areas adjacent to the weld.
Hardness control in these affected areas, to ensure the toughness of the welded areas.
One of the most important challenges was the maintenance of this temperature throughout the entire welding process, in each one of the repairs: During buttering, longitudinal groove welds and circumferential fillet welds. The gas circulating through the tube at a temperature of 40-44oC, at pressure of 72 bar and flow rate of 1,265,000 KNm3/h acts as an instant cooler of any heating that we try to apply from the outside of the tube.
The development of the heating procedure was one of the great achievements during the project to repair this pipeline in service. This ensures the toughness of both the welded casing and the original tube on which it sits, and therefore the integrity of the repair to provide a complete warranty of service, as original.
3.10 Work Planning and Quality Control by an SCWI
3.11 Continuous Visual Inspection of each bead and NDT at the end of each weld.
Repair executed in record time, once the minimum safety conditions and guarantee of the integrity of the pipeline and personnel at the compression station and in the execution of repairs were established.
Execution of four (4) repairs in different sectors of the same pipeline.
Maintenance of pipeline service conditions throughout the entire process.
Remark of the history of this pipeline: Angela Lazaro also participated in the beginnings of the construction of this pipeline, in the elaboration of the Welding Procedures and in the research to solve the problems that posed the API 5L-X70 steel welding at the time. Welding with cellulosic electrodes, widely extended for pipeline welding had to be redefined to ensure mechanical properties of welded joints. Exquisite cleaning of each weld bead, preheating and maintenance of temperatures and control of the Heat Input, were decisive to achieve the desired results. The use of other welding processes was extended from then, to avoid the limitations of cellulosic electrodes in these high yield limit steels.