Successfully transforming today’s hydrocarbon discoveries into prolific producers will partly rely on solving materials problems, including tackling corrosion issues in HP/HT and high-velocity environments.

This, according to panelists speaking during Teledyne’s Technology Focus Day, involves making informed material selections for HP/HT applications and conducting the most appropriate tests under the right conditions when evaluating possible materials. Failure to address such issues could lead to damaging consequences.

“We’ve seen in the last few years many failures related to high-velocity fluid flows. We call it high voltage, too. Corrosion can play a major or secondary role in failures,” Dr. Binder Singh, principle integrity engineer for Genesis Oil & Gas, said before citing a few examples including the 1988 Piper Alpha explosion in the North Sea that left more than 160 people dead. “When we look at the report we find that the latent or hidden problems behind the failure were major corrosion issues on the platform.”

Evidence of corrosion problems were present years prior to the deadly event, but maintenance was deferred, he said, noting that the tragedy led to major regulatory changes in the U.K.

Hundreds of people gathered in Houston for the event to learn about and discuss new technologies and processes as well as challenges facing certain aspects of the business. The Nov. 12 event took place one day before DNV GL announced the formation of a joint industry project to develop guidelines concerning corrosion assessment and integrity management of aging wells. The focus comes as old wells get older and operators look for ways to safely extend their lifespans while also venturing into new frontiers and deeper into mature ones in search of more oil and gas to meet growing future demands.

The projects are reaching depths of 914 m (3,000 ft) with high pressures of between 4,000 psi and 15,000 psi along with temperatures greater than 121 C (250 F) at a velocity of about 9 m/sec (30 ft/sec), creating conditions that are ripe for crevice, fatigue, microbial and stress-induced corrosion among other types of corrosion. In the Gulf of Mexico—the site of major developments such as Appomattox, Shenandoah and Cascade—humidity adds to the challenge and in some cases causes fasteners and valves to break down in just a few years, he said. Here, CO2 and H2S localized corrosion has also become an issue.

“This is a major threat, certainly in the Gulf of Mexico, and probably worldwide,” Singh said. “Whenever we have any upsets or excursions ,whether it’s the surface metallurgy or fluid flows or physical conditions, including pressure, temperature, velocity or stress, [these] could lead to very unpredictable localized corrosion.”

Corrosion related to pressure on topsides resting on beams is one problem for which the industry has found a solution—thermoplastic inserts. The beauty of this simple design is that the contact point is semicircular, which allows the water to drain off and eliminate the crevice, Singh said.

Progress is also being made in the area of coatings, including some that are invisible—a positive when it comes to detecting weeping in flanges and crevices as an indicator of corrosion.

“Corrosion under insulation is probably one of the biggest threats worldwide, most operators would agree,” he added. “In high humidity environments, it’s a very big deal. The problem is what to do.”

Besides removing the insulation, methods to alleviate the problem include guided wave technology, described by DNV as long-range ultrasonic testing that allows for “tens of meters of pipeline to be simultaneously assessed for internal and external corrosion, in either direction, from a single location achieving complete coverage of the pipe wall” without having to remove insulation or coating. Other nondestructive methods include radiographic and ultrasonic testing as well as thermography.

More recently, Sindh added, people have been using electrochemical noise sensors to detect corrosion.

Dr. Janet Davis, principle material scientist for Teledyne Scientific Co., said operating in extreme environments with higher pressures and higher temperatures will likely cause a paradigm shift in terms of materials and products.

“Incremental improvements aren’t going to get us there. What we need to do is develop a methodology to determine how material selection can be done in an efficient way,” she said.

As a material scientist, Davis’ challenge is to determine the best way to simulate complex environments for studies to determine the best material solution for any given application.

“We have to define the key performance parameters for the product we’re trying to develop then relate those to the properties of the materials that we’re going to need to incorporate in that product. The materials that satisfy the requirements define our design space, and within that space we can rate materials based on the relative performance parameters,” Davis said. “What materials selection is not is a substitute for is qualification testing. … The reason that this methodology is important for HP/HT [is because] we are moving beyond the regime or legacy material. We need to start with a clean sheet to really address the new environment that we are trying to build solutions for. This process can reduce development time, and it can also improve your reliability.”

She stressed the importance of considering every possible material, including emerging materials, and then quickly eliminating those deemed unsuitable. Adding constraints for the HP/HT environment can further eliminate materials to narrow the list, while cost could be another constraint, she said.

“If several options still exist, then we need to generate more data that allow us to be more discerning,” she added, noting the data could include the end-of-life properties of materials. “We subject materials to a simulated-use environment as close to the actual-use conditions as we can get and measure properties. … This allows us to rank materials and eliminate those that are less promising.”

This type of testing is repeated with increasing stress levels to determine the maximum accelerating factor and to generate enough data to determine the end-of-life performance for materials, better capturing the functional properties of material tested for the application.

Davis also noted that attention should be given to the fluid environment, considering materials age differently in water under certain conditions than they do in completion brines or hydrate inhibitors, for example.

Luis Garfias, materials and testing consultant for Wood Group Kenny, spoke about the use of the ripple strain rate test for simulating corrosion and mechanical failure conditions of strain-based design components in sour environments. As part of a test aimed at finding suitable materials and processes for use in the oil and gas sector, an autoclave was loaded with high H2S concentrations to test the performance of the HCRA UNS N06625 overly material applied to carbon steel. The results were compared to those obtained during the critical pitting temperature and critical crevice temperature—the material proved to be corrosion-resistant.

Following this test, another study was conducted at HP/HT in sour environments with H2S and CO2, using a mini-autoclave. “The idea was to show that you can have pitting in some materials,” he said, later adding, “It turns out that in sour environments—H2S, H2L, CO2—and high-temperature/high-pressure, those events are etching event.”

Garfias stressed the importance of selecting the correct test and mimicking real environments.

“There are a lot of programs that are very focused on getting the right material for the right application. … The industry is looking at the polymer seals and things like that,” he said. But “one of the things that is extremely is important is to make sure you measure correctly your reservoir conditions.”

Contact the author, Velda Addison, at vaddison@hartenergy.com.

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