Hyperbaric welding

Hyperbaric welding is the process of welding at elevated pressures, normally underwater. Hyperbaric welding can either take place wet in the water itself or dry inside a specially constructed positive pressure enclosure and hence a 'dry' environment. It is predominantly referred to as "Hyperbaric Welding" when used in a dry environment, and "Underwater Welding" when in a wet environment. The applications of hyperbaric welding are diverse — it is often used to repair ships, offshore oil platforms, and pipelines. Steel is the most common material welded.

Dry hyperbaric welding is used in preference to wet underwater welding when high quality welds are required because of the increased control over conditions which can be exerted, such as through application of prior and post weld heat treatments. This improved environmental control leads directly to improved process performance and a generally much higher quality weld than a comparative wet weld. Thus, when a very high quality weld is required, dry hyperbaric welding is normally utilized. Research into using dry hyperbaric welding at depths of up to 1000 m is ongoing. In general, assuring the integrity of underwater welds can be difficult (but is possible using various nondestructive testing applications), especially for wet underwater welds, because defects are difficult to detect if the defects are beneath the surface of the weld.

Dry hyperbaric welding involves the weld being performed at the prevailing pressure in a chamber filled with a gas mixture sealed around the structure being welded.

Most welding processes SMAW, FCAW, GTAW, GMAW, PAW could be operated at hyperbaric pressures, but all suffer as the pressure increases. Gas tungsten arc welding is most commonly used. The degradation is associated with physical changes of the arc behaviour as the gas flow regime around the arc changes and the arc roots contract and become more mobile. Of note is a dramatic increase in arc voltage which is associated with the increase in pressure. Overall degradation in capability and efficiency results as the pressure increases.

Заведующий кафедрой

общеобразовательных дисциплин

____________ В.П. Павлов

Уфимский государственный Кафедра общеобразовательных

авиационный технический дисциплин

университет

ЭКЗАМЕНАЦИОННЫЙ БИЛЕТ № 11

Факультет: АТС (СП) Вопрос: 2

Equipment

• The two types of lasers commonly used in are solid-state lasers and gas lasers (especially carbon dioxide lasers and Nd:YAG lasers).

• The first type uses one of several solid media, including synthetic ruby and chromium in aluminum oxide, neodymium in glass (Nd:glass), and the most common type, crystal composed of yttrium aluminum garnet doped with neodymium (Nd:YAG).

• Gas lasers use mixtures of gases like helium, nitrogen, and carbon dioxide (C02 laser) as a medium.

• Regardless of type, however, when the medium is excited, it emits photons and forms the laser beam.

Solid state laser

Solid-state lasers operate at wavelengths on the order of 1 micrometer, much shorter than gas lasers, and as a result require that operators wear special eyewear or use special screens to prevent retina damage. Nd:YAG lasers can operate in both pulsed and continuous mode, but the other types are limited to pulsed mode. The original and still popular solid-state design is a single crystal shaped as a rod approximately 20 mm in diameter and 200 mm long, and the ends are ground flat. This rod is surrounded by a flash tube containing xenon or krypton. When flashed, a pulse of light lasting about two milliseconds is emitted by the laser. Disk shaped crystals are growing in popularity in the industry, and flashlamps are giving way to diodes due to their high efficiency. Typical power output for ruby lasers is 10-20 W, while the Nd:YAG laser outputs between 0.04-6,000 W. To deliver the laser beam to the weld area, fiber optics are usually employed.

Gas laser

Gas lasers use high-voltage, low-current power sources to supply the energy needed to excite the gas mixture used as a lasing medium. These lasers can operate in both continuous and pulsed mode, and the wavelength of the laser beam is 10.6 urn. Fiber optic cable absorbs and is destroyed by this wavelength, so a rigid lens and mirror delivery system is used. Power outputs for gas lasers can be much higher than solid-state lasers, reaching 25 kW.

Заведующий кафедрой

общеобразовательных дисциплин

____________ В.П. Павлов

Уфимский государственный Кафедра общеобразовательных

авиационный технический дисциплин

университет

ЭКЗАМЕНАЦИОННЫЙ БИЛЕТ № 12

Факультет: АТС (СП) Вопрос: 1