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Apr-2013

Industrial gases support the natural gas production chain

The contribution of industrial gases across the petrochemical processing spectrum is crucial to performance and safety

STEPHEN HARRISON and ERNST MIKLOS
Linde Gases

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Article Summary

For decades, industrial gas companies have assisted producers in the petrochemical landscape to ensure they are able to deliver the levels of product quality and operational safety demanded by changing legislation, environmental regulations and customer requirements.

Industrial gases come into play from the very earliest upstream stage, where offshore exploration equipment is manufactured from steel and special metal alloys. These materials need to be cut, heated, welded and coated with the aid of industrial gases. In particular, many applications associated with drilling equipment now demand the use of higher performance materials. These materials are a world away from what was being used as recently as 10 years ago and, as modern material specifications evolve, metal fabrication companies need to adapt their gases to suit the latest welding processes.

Offshore exploration equipment is often situated in some of the roughest and most inhospitable seas, and has to be able to withstand enormous loads from huge waves and swells and highly corrosive conditions. High-quality steel and the most up-to-date production methods are necessary for exploration operations under such harsh conditions. In this context, welding becomes particularly important, as the huge steel towers and support stilts are manufactured from many individual steel segments. A faulty weld seam on a single component can have catastrophic consequences. Cracks or dangerous salt-water corrosion could lead to a rupture in one or more of the steel components. Performance standards for exploration equipment components, particularly those operating offshore, therefore confront manufacturers with tough challenges.

As more high-strength steels are being specified to manufacture increasingly tough drilling equipment, this has resulted in an extra preheating stage prior to welding in order to safeguard the metallurgical properties of the steel. Preheating prevents failures, such as hydrogen-induced cracking, as well as common failures in the heat-affected zone. As more fine-grained structural steels are being used to construct apparatus and equipment for the oil and gas industry, the importance of preheating prior to the welding process is becoming a focal point.

Welding in this application is a complicated affair. To begin with, the thick metal pieces need to be preheated. If this is not done, the large, cold steel plates will lose heat too quickly and the metal will not be completely melted in the welding zone, making a secure connection impossible. Preheating will also prevent the build-up of cold cracks, which can occur due to hydrogen exposure or internal stress in the component.

This is particularly important when treating high-strength steels. After the weld, these materials must be post-heated for around two to three hours to diffuse any rogue hydrogen atoms in the weld seam. For manufacturers that have to maintain a fast production speed, it is vital that they quickly reach a preheated temperature of greater than 100°C.

In response, special burners for preheating steel before welding are required. Linde has engineered a Lindoflamm acetylene burners for preheating steel before welding takes place. Acetylene provides high heat intensity in the primary flame, establishing a focused flame, so that preheating occurs only in the weld area. This results in an increase in the speed at which the weld area is heated — as much as two-thirds faster than that achieved by other fuel gases — plus significant savings on total process cost.

As opposed to a propane gas flame, acetylene gas burns with a very precise, pointed “primary flame cone”, which drives the heat directly into the metal. Additionally, flame temperatures that can be reached with the associated acetylene-compressed air torch — approximately 2400°C — are significantly higher than those achievable using other fuel gases in combination with air (see Figures 1 and 2).

Prolonging the lifespan of these offshore assets is another important factor, since equipment lifespan impacts the price of the final product. This issue has led to the development of special coating technologies that lengthen the lifetime of offshore installations. Linde Gases Division has recently developed a state-of-the-art cathodic protection technology as a first line of defence against metal corrosion.

Traditional arc spraying processes involve the use of air to coat metals. However, the enhanced Linspray arc spraying process employs a mixture of nitrogen and hydrogen to avoid oxidation of the applied coating. The new technique provides “active” protection, meaning the coating materials will actively repair the surface as it detects corrosion. Results show it can improve the lifetime of heavy exploration and processing equipment by up to 50%. This is a significant step forward in reducing the number of maintenance intervals required and the associated costs involved.

A critical application of speciality gases within the gas extraction and processing industry is the testing of gas leakage detectors on offshore drilling platforms. With tonnes of natural gas being handled via the platform each day, any leakage could build up rapidly into an explosive atmosphere. Offshore platforms, therefore, have permanent monitors in operation, sniffing for gas seepage, and these gas detectors need continual testing and calibration with speciality gas mixtures.

Human element
During the natural gas exploration phase, a lot of the work takes place under the surface of the ocean, as specialised technical divers undertake oil and gas pipeline construction and maintenance, or maintenance of oil rigs and valves, and so on. Underwater, these divers breathe a range of different gases, depending on the depth at which they need to work.

Recreational divers breathe air, but commercial divers plunging to depths of up to 50 m need specialised mixtures of oxygen and nitrogen in varying concentrations. When divers are required to go down to between 50 and 200 m, helium is introduced into a “tri-mix” with oxygen and nitrogen, or as heliox, which is helium mixed with low concentrations of oxygen.


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