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Welding

Mission-critical pipe

By Bill Atkinson, Tri Tool Inc.

July/August 2010- Most industries use fabricated pipe in a wide range of mission-critical roles, whether as structural elements or as a means of fluid transmission. The technology of piping systems and the machinery to build and maintain them has advanced, along with requirements for higher purity and cost-effective logistics for the countless fluids and gasses on which society relies.

Many strategic fluids, such as petroleum-based fuels and petrochemicals, are related to the energy sector. Interrupt the flow of petroleum products, and it would not take long for society to collapse. Global concerns for the environment, heightened by high-impact environmental disasters, have forced society into a love-hate relationship with petroleum products.

Oil-drilling dilemma
On one side of the relationship is society’s growing demand for energy to support economic prosperity and commerce, and on the other are issues of environmental responsibility and the conservation of limited resources. Despite rising demand, the government and consumers alike increasingly are perceiving petroleum-based energy production as an environmental villain.

The petroleum industry is in the national spotlight, and potential moratoriums on drilling operations will have a direct trickle-down effect on jobs and the fabrication of parts and equipment. Fortunately, advanced engineering offers the promise of technical solutions to critical environmental problems.

Engineering and fabricating excellence will play an important role in the struggle to rebuild both national and global economies.

Political and cultural reluctance to develop oil fields on land, where companies can monitor and control operations more closely, will result in driving oil production deeper in the seas, with corresponding operational difficulties. Recent events have shown how difficult it is to deal with problems that arise when catastrophic accidents occur in deep-water petroleum production.

Companies first built pipelines on land. At that time, the flow rates and pressures exerted on the pipelines were reasonable for the fabricating methods used. The ability to explore and operate in deep water eventually brought vast new areas into development.

The pipelines of today move high volumes of oil from countries with oil reserves to consumers far away. These pipelines have larger diameters and can be anywhere from the Arctic Circle to the ocean floor. Flow pressures and forces exerted on the pipeline are extreme. Pipelines in deep water require heavier wall thicknesses and superior welds to connect the sections and durable coating materials to protect the pipe from saltwater.

Because of adverse conditions, oceanic pipeline contractors found it necessary to develop specialized pipeline assembly and laying platforms that are self-propelled and can perform extremely accurate geo-positioning.

New technologies
Pipeline production vessels hoist and store pipeline sections from transport vessels, perform precision weld preparation and orbitally weld sections with amazing accuracy as they deploy them efficiently along the sea floor.

To be economically feasible, pipeline contractors must coordinate welding, inspecting and repairing of defective weld joints, as well as the application of protective coatings. The heavier walls of deep-water pipelines require powerful equipment that can operate continuously, quickly and with an unprecedented level of precision and reliability.

Special equipment design and engineering have provided mechanical solutions the pipeline industry needed to reliably and safely deploy petroleum pipelines in areas deemed impossible before.

Pipe-facing machines can produce excellent weld-prep bevels on heavy-wall pipes in a few minutes instead of taking hours to perform traditionally. This state-of-the-art machinery has had a major impact on the economic feasibility of pipeline fabrication.

Along with weld preparation, alignment systems designed to hold pipe sections in proper orientation for welding have also advanced. Internal lineup clamps can be self-propelled and offer features such as copper shoe weld backing and purge dams to eliminate oxygen from the ID area of the weld. On larger internal alignment clamps, the increased size and strength permit rounding the pipe from the inside bore to compensate for "out-of-round" conditions, producing more consistent, repeatable and accurate weld joints.

Other technologies that facilitate pipe fabrication include laser dimensioning systems that measure and record detailed shape information from pipe ends. A process of "end matching" saves time and performs superior welds by selecting pipe sections to weld that dimensionally match end to end to facilitate the weld joint profile alignment.

High-speed severing systems allow the fabricator to cut out a defective weld while preparing the pipe for re-welding. HSS systems are built on a split-frame lathe platform that separates and mounts in-line around a pipe OD, making them perfect for assemblies with valves or "tees." Another valuable feature of this system is the capability to cut and bevel the outer pipe without disturbing the inner pipe of "pipe in pipe" systems.

The fabricator can ID mount equipment in the open end of pipes and use precision form-tooling or single-point machining for weld prep, flange facing, grooving or counterboring. Other optional mandrel systems allow secure, reliable mounting of portable machining equipment in elbows and fittings. A miter mandrel permits angular offsetting to correct for linear manufacturing or material deviations.

These highly advanced fabrication machines can incorporate miniature video cameras and/or remote controls to operate in hazardous environments, underwater or down pipe. When combined with orbital welding systems, it’s possible to get extremely reliable and durable welds. Machinery capable of generating deep counterbores is mandatory for certain nondestructive testing, such as X-ray inspection of critical weld joints.

Of prime importance to any company that works with pipe is the ability of equipment manufacturers to provide specialized equipment design and manufacturing to address special requirements beyond the scope of conventional machinery.

Special equipment applications
Special-application engineering offers three advantages. One is economy. If a fabricator has high volumes of repeated machining processes or high quantities of fabricated products, special tooling or machinery can provide rapid cycle time and ensure precision. This offers significant labor savings through fewer rejects that dramatically increase production costs. Custom-designed mounting systems and custom tool bits also offer fabricators time-saving alternatives with lower production costs.

Safety is the second advantage. Machinery designed for specific applications can be built for maximum operator safety by reducing the possibility of mistakes through human error, and remotely controlled machinery can be designed for applications in which operator safety is compromised or impossible.

The third advantage is equipment can be designed to perform specific operations in environmentally sensitive situations. An example is the Alaska pipeline. A major valve required replacing, but the remote location meant everything had to go smoothly and without environmental impact.

Because of the stresses present in long runs of pipeline, cutting by saw blades was virtually impossible. As workers cut the pipe section, stresses would cause both sides of the pipe to creep and bind on a saw blade, halting the cut.

This was an in-line operation, so machine designers selected a split-frame lathe platform because it could be separated, placed on either side of the pipe and reassembled. After careful mounting, two hydraulic milling heads mounted 180 degrees apart cut the pipe from either side. By using milling bits, any creep of the pipe would be absorbed into the cut. This approach allowed the project to be completed without oil or hazardous levels of toxic fumes impacting the environment and with minimal downtime.

Unique platform
Another example of an engineering solution successfully implemented for the offshore industry is the fabrication of tendon legs that are critical to a more-efficient and stable offshore platform. The Extended Tension Leg Platform provides stability at significant cost savings over other platform types. The ETLP tendon legs are fabricated onshore from 40-ft. pipe sections that are joined into 240-ft.-long "legs."

These legs have a threaded male connector on one end and a threaded female connector on the other. A ship transports the 240-ft.-long assemblies.

The modular system permits operators to use as many sections necessary to extend down from pontoons at the base of the platform to anchoring assemblies on the sea floor.

Tension legs have to flex with ocean currents and tides. The problem was each weld was a mechanical "stress collector," and traditional weld joints would have resulted in broken legs from the weld joints’ flexing and separating. Project supervisors working with an OEM needed to get much more strength out of each weld joint.

After the individual pipe sections had been assembled into the long leg assemblies in a fabrication yard, custom machines performed profile facing on the weld joints’ ID and OD surfaces. The smooth surface of the profiled weld joint meant mechanical forces could be transferred across the joint with increased strength.

Testing showed the resulting structures were up to three times as strong. This met the critical design criteria for the project and ensured the tension legs, although constructed with numerous welds, would provide the material strength requirement for safe and durable offshore platform support.

Special engineering can play a role in contingency planning for companies operating in remote or difficult environments. Physical simulation modeling allows today’s engineers to test structures and machinery in virtual space and to predict with reliability the damaging effects of forces on those structures.

Contingency planning is important to developing policies and procedures to deal with emergency outages or equipment and structural failures. Once a company completes engineering studies, it can build machinery and place it into storage or use it in training programs for specialized personnel. Even if the actual equipment is not built and tested at the time of equipment design, a company can implement it more efficiently if a need arises if the design engineering is completed in advance.

Special equipment design and manufacturing can help reduce costs, increase operator safety and maintain environmental responsibility. Contingency planning and advanced engineering design can provide real cost savings when compared with unnecessary and/or unexpected liability and massive environmental cleanup costs and fines.

Corporate management and project safety and maintenance managers need to evaluate and consider existing and planned projects and maintenance schedules to seek appropriate opportunities where specialized equipment could ensure project success or result in substantial cost savings.

The term "addicted to oil" is unfair and misapplied to the national situation, but it’s clear the United States has a substance dependency that will remain until technological advancements make alternative-energy sources economically viable.

Until then, society will continue to depend on petroleum, and the safe, clean and cost-effective transfer of petroleum products will be of ever-increasing importance to companies around the world. FFJ

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Sources

  • Tri Tool Inc.
    Rancho Cordova, Calif.
    phone: 916/288-6100
    fax: 916/288-6160
    www.tritool.com

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