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Should API replace ASME on certain offshore tools?

The offshore oil and gas industry is governed by strict standards and approvals to ensure not only the performance, reliability and interchangeability of different manufactured products, but also to minimize the health and safety risks on platforms.

These standards are crucial, as without them it would not be possible for different elements of a system to work together; products need to be standardized so that all manufacturers can have guidelines with which to produce products. This simplifies the specification process and ensures oil and gas operators can be confident that a fully matched system is put in place.

There are thousands of standards and approvals dictating the manufacture of all products used within offshore systems from pipelines and pressure gauges through to gaskets and valves, with many published by ASME (American Society of Mechanical Engineers) and API (American Petroleum Institute). These standards cover all aspects of design, functionality, inspection and testing, but with so many different codes and standards available for similar products, it can make the specification and procurement of products quite complex.

If a particular standard is chosen, all products from the varying manufacturers need to be constructed in accordance with that standard to ensure complete compatibility; this can limit the options available in terms of both the chosen manufacturer and the product. Therefore, it is vital to work to the right standard.

Today there are options available to platform operators in the selection of valve products. More than 90% of valves have traditionally been manufactured to ASME B16.34--specification for steel buttwelded and flanged valves. This is a long-standing standard that was first introduced when oil could be found easily on the surface. While it has provided an effective solution over the last 30 years, it no longer caters for the diverse needs of tomorrow's oil and gas platforms.

As oil and gas becomes more difficult to extract, the exploration operations need to drill deeper, meaning the pressure requirements of the associated pipelines and products increases. This is where ASME's options are limited; valves manufactured to ASME B16.34, can only operate in working pressures of up to 6,250 psi.

As an alternative, the specification for valves manufactured in accordance with API 6A--Specification for Wellhead and Christmas Tree Equipment--is similar in its dimensions; taking a typical size, the ASME B16.34 valve is manufactured as a 10-inch x 8-inch class 25,000-lb. valve, while the API 6A version is 11-inch x 7 1/16-inch class 5,000 lb., but this is where the similarities end.

The API 6A standard has been specifically written to cater to the increased pressures faced by the industry today and offers a working pressure of up to 15,000 psi, more than double that of the ASME solution.

The ASME B16.34 standard has become a habit within the industry as it was the only option for so long, but there are additional benefits that API 6A can offer, even for pressures below 6,250 psi.

Valves manufactured to API 6A offer significant cost savings for platform owners due to the construction; the ASME valve uses three times the amount of bolting and double the wall thickness of the API version, which all adds to the weight of the valve. This is an established standard, which needed to include this amount of bolting and wall thickness at the time it was written to ensure the performance and safety of the system.

However, despite many amendments being made through the years, it has not been updated to take into account the technological developments and advanced material characteristics available today. This has resulted in an over-engineered valve, which is not necessary in today's applications, being installed at an extra cost.

The increased bolting and wall thickness sees a typical 10-inch ASME B16.34 valve weigh 3 1/2 tons, while its equivalent API 6A valve weighs just 1 1/2 tons, providing a weight saving of two tons. This equates to a cost saving of more than 30%; not only are less material and parts needed to manufacture the API 6A product, but the lifting equipment required to transport a 1 1/2-ton valve is significantly less than that of a product two tons heavier.

While the topside platforms have not yet realized the full benefits of the API specification, the sub-sea industry adopted this standard over a decade ago when it was first introduced. Valves lying on the sea bed inevitably deal with higher working pressures than topside valves, so the API standard offers immediate performance benefits.

Weight is also an issue as valves need to be lifted into place and the cost of industrial ROVs to transport such products is considerable, so the weight saving of the API version equates to huge cost savings for sub-sea contractors.

All existing platforms will continue to use ASME B16.34-approved products for refurbishments on existing rigs and while it is a more than adequate standard for new platforms dealing with pressures below 6,250 psi, oil and gas operators need to be considering more cost-effective options if they want to compete for tomorrow's business.

By Craig Furnival, Engineering Director, Oliver Twinsafe Valves, Cheshire, England
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Title Annotation:American Society of Mechanical Engineers; American Petroleum Institute
Comment:Should API replace ASME on certain offshore tools?(American Society of Mechanical Engineers)(American Petroleum Institute)
Author:Furnival, Craig
Publication:Pipeline & Gas Journal
Geographic Code:1USA
Date:Dec 1, 2008
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