The following appeared in the November 2014 issue of World Pipelines, in response to industry questions about pipe welding trends.

What are the best methods for welding oil/gas pipes in the field?
As the industry is evolving and the integrity of the weld joint becomes more important than ever before, it is crucial that we evolve our welding methods.  Moving to a more efficient and lower hydrogen process is key to obtaining a better overall weld. Companies can gain those benefits by using a solid or metal-cored wire with a modified short circuit welding process (e.g. Miller Regulated Metal Deposition or RMD®); the process helps ensure contractors get the proper root reinforcement, excellent side wall penetration and a low hydrogen weld deposit. The computer feedback during the weld compensates for welder mistakes, making it a more forgiving root welding process for less skilled welders. There are several methods available for the fill and cap passes that would prove to be excellent choices for welding oil/gas pipe in the field. Fill and cap welding with a metal-cored wire using a pulse program such as the Miller Pulse allows welding operators to weld in either the vertical up or down progression with a low hydrogen weld deposit and provides an option to weld root to cap with one wire. A second option would be gas-shielded flux-cored wire. These products provide excellent weldabillity and robust properties; are welded in the vertical up progression; and can also be utilized with mechanized welding equipment. Specially designed self-shielded flux-cored wires have also been created for welding on oil/gas pipe. These products have great weldability, are designed to weld in the vertical down progression; are extremely resistant to wind; and offer very robust mechanical properties.  These are an excellent choice when welding in windy conditions; contractors don’t have to worry about hauling and moving gas bottles.    

How important is testing of welds? Which methods are used?
The first step will be testing the filler metal. A procedure is carried out to ensure that the filler metal will meet all mechanical properties required to ensure a sound weld in the environmental conditions in which it will be placed.  What mechanical properties are tested will vary depending on the code followed, but typically it includes transvers tensile, root bends, face bends, side bends, Charpy impact tests, nick break tests and some form of NDT testing (radiograph or AUT automated ultrasonic testing). For in-service welds or new construction, the most common type of weld testing is Radiograph or AUT.  This is done to ensure that the weld going into service is free of any defects that could cause weld failures. If a defect is found and it is larger than the code allow, then that weld must be re worked to ensure that the defect has been removed.    

What role does automatic welding have in the pipeline industry?
Automatic welding is taking a larger role in the pipeline industry especially for the welding of transmission pipelines.  Automation requires very consistent control of variables such as fit-up and roundness, but automatic welding allows for greater productivity while minimizing human error.

Why do companies carry out low hydrogen welds?
The presence of hydrogen in a finished weld increases the opportunity for cracking. Hydrogen is quite mobile when introduced into the liquid weld pool, especially at elevated temperatures, and much of it is able to diffuse out into the atmosphere. Once the weld has cooled, however, it is more difficult for hydrogen to escape and the element tends to collect in the grain boundaries and the heat affected zone (HAZ) — the area of base metal just beyond the weld deposit. Over time, hydrogen collects in these areas and builds stress that, in some cases, is high enough that hydrogen-induced cracking occurs. The amount of hydrogen in the weld can be controlled by using low hydrogen filler metals and proper heating processes. Taking precautions to protect the weld from the atmospheric pick up of hydrogen (e.g. induction heating) and using low hydrogen filler metals is important to preventing these cracking issues. 

How can you prevent weld defects?
Proper welding practices, including using the right travel and work angle can help to prevent issues like undercut, overlap, convexity, concavity or underfill. Running the proper travel and work angle can also help prevent slag inclusions or silicon inclusions. Running the proper parameters is also important to help prevent issues like spatter, porosity, poor bead appearance and improper bead sizing.  Proper preheating, interpass temperatures and post heating, along with utilizing lower hydrogen filler metal, can help prevent cracking issues in the weld. It is also important to follow the welding procedures. These help monitor what welding parameters, preheat temperature, interpass heat, post heat and other important factors that minimize the opportunity for weld defects.   

How do you tackle the problem of human error in welding operations?
Equipment and filler metal manufacturers have been working to help reduce human error by creating equipment matched with filler metal that is easier to use and operate.  High tech welding power sources with welding processes such as Regulated Metal Deposition or RMD® and Pulse have computer controlled feedback that compensate for human error. Thousands of times per second the machine monitors the power being required versus that being used and makes slight adjustments. These adjustments help less skilled welding operators perform higher quality welds.  Additionally, when this high tech equipment is matched with filler metals that have been developed for greater weldability (e.g. less spatter, easier control of the puddle, greater deposition), the system is easier for the welding operator to run.

How can you best address the issue of safety in the welding environment?
Induction heating is a much safer and efficient alternative to open flame heating for preheating.   With an induction heating system, heat is created electromagnetically in the part rather than by surface heating. Heat is induced in the part by placing it in an alternating magnetic field created by liquid- or air-cooled induction heating cables. The induction cables are wrapped around the pipe and only metal to be welded gets hot.  The process is safer, faster and easier to use than other heating methods and provides uniform heating throughout the part. It generates fewer fumes, too, making it a safer, more comfortable process for welding operators. The added benefit is that it is also less expensive in the long term.

What advances in welding technologies and methods will prove to be most successful in the next few decades?
Advancements in equipment and filler metal will continue to move forward as safety, weld quality and productivity demands continue to grow.  New equipment will continue to be designed to be easier to use, but still provide more advanced technology features and benefits.  Filler metal products will continue to evolve and grow as more stringent requirements and more robust mechanical properties are also required. The combination of these will assist greatly in producing high quality welds as the number of less skilled welding operators continues to grow.  Through these advancements, it’s possible that there will also be an increase and advances in automation and mechanized welding.   

Which certifications and standards are the most helpful for the pipeline welding industry?
The most common codes and standards for pipeline wilding industry are API 1104; ASME Section 9 B31.3 – Process Piping; ASME Section 9 B31.4 – Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids; and ASME Section 9 B31.8 – Gas transmission and distribution piping systems.