December 2023, Vol. 250, No. 12
Features
Oxygen Corrosion Control for Multiphase, Gas Phase Pipelines
By Geeta Rana, Caleb Clark, Jeremy Moloney and Henry Garlick, ChampionX
(P&GJ) — The oil and gas industry is committed to driving greater production and transportation from existing infrastructure, and ensuring effective asset integrity and flow assurance is essential to this objective.
Challenges such as oxygen ingress, scale deposition, corrosion and hydrate formation can substantially hinder flow and jeopardize the efficiency and safety of both upstream and midstream operations.
In particular, the presence of even small amounts of oxygen can pose a severe threat to the integrity of oil and gas pipelines, and it can contribute to sharp increases in corrosion rates and metal loss in gas pipelines. It can also impede the formation of a protective layer of iron carbonate on assets, which increases the corrosion rate of steel and causes pitting and under-deposit corrosion.
While many operators prefer to use chemical control for mitigating oxygen corrosion, commercially available oilfield corrosion inhibitors do not always provide adequate corrosion protection under elevated levels of oxygen.
Produced fluids in the oil and gas sector do not generally contain oxygen, but ingress of the gas can occur at various locations, such as vapor space in tanks, injection pumps or gas lift operations and pipelines that are not properly purged of oxygen during commissioning operations. Contamination of oxygen in sweet/sour systems can lead to oxygen-induced corrosion and cause high general and pitting corrosion rates and failures.
Oxygen scavengers are commonly applied as an economical method to inhibit oxygen-induced corrosion. However, they often require higher concentrations for treatment and may require higher temperatures for enough reactivity. They are also not suitable for gas systems and treatment in hydrocarbon fluids.
Using its experience supporting operators with complex corrosion issues, ChampionX — a provider of chemistry solutions and technologies — recently changed the status quo by developing and qualifying a corrosion inhibitor that provides effective protection in gas and multi-phase applications, where oxygen can be a major concern.
Effective Development
ChampionX conducted a range of testing procedures from its Sugar Land, Texas, facility, including rotating cylinder electrode (RCE), rotating cylinder autoclave (RCA) and top-of-line (TOL) corrosion RCE assessments, as part of the development process.
To understand how the chemical would react in pipeline conditions, tests were conducted to represent realistic pipeline scenarios, where water can separate out due to low velocity of fluids. Temperature, pressure and flow parameters were set to represent the environment of liquid transport pipelines, and 100% brine was utilized, to represent a worst-case scenario.
The tests were conducted at a low pH of 4.5 to 6.5, which is a normal range for pipelines. The inhibitor was added at 200 parts per million (ppm) to the test fluids, after an initial two hours of pre-corrosion, for a total duration of 18 hours.
The tests were carried out with a continuous purge of oxygen, representing the continuous flow of oxygen in a pipeline, which is a very aggressive scenario. However, the product provided adequate percent protection in these sets of hostile conditions.
Field application to determine efficacy
Following successful lab results, the ChampionX chemical was deployed for a field trial. A midstream operator had asked for internal corrosion inhibition technology, for treating a sour natural gas pipeline where oxygen ingress was a frequent issue.
The oxygen contamination — in tandem with water and acid gases, like carbon dioxide (CO2) and hydrogen sulfide (H2S) — was causing corrosion rates (MPY) to exceed the operator’s corrosion KPI, averaging 2.3 MPY.
In addition, the oxygen ingress was peaking at hundreds of ppm, creating elevated safety concerns from the risk of pipeline failure. Solids and dark condensate were also being collected in pig returns.
The study was conducted in a 16-inch diameter line, which was nine miles long with oxygen analyzers installed to allow direct, in-line measurements of oxygen levels. In each phase of the trial, a 1 mil film batch of a corrosion inhibitor was applied at the beginning, then the new oxygen corrosion inhibitor chemistry was applied continuously.
Coupons remained in the system for 28-40 days, until the end of the phase, at which point they were removed and analyzed for corrosion rate. Key metrics were selected to track internal corrosion in a challenging oxygenated environment. These included:
- Coupon corrosion rates
- Visual presence of solids in pig return condensate
- Average in-line oxygen levels in each phase
- Number of discrete oxygen ingress events (starting when oxygen levels rose above 25 ppm and ending when levels returned below 1 ppm)
The graph below displays the corrosion rate, average oxygen level and oxygen ingress event frequency during the trial. Bars within the blue rectangle (Figure 1) indicate the corrosion rate of the new chemistry during the trial. As compared to the incumbent, lower corrosion rates were observed, even though the oxygen levels and ingress event frequency were much higher during this phase.
Even with elevated oxygen levels, the new oxygen corrosion inhibitor delivered consistent improvement in every metric. The corrosion rate was reduced month-over-month and condensate clarity was improved in consecutive pig runs, indicating reduced corrosion, corrosion byproducts and solids.
These results were achieved with reduced chemical dosage, which required only an application rate corresponding to 1 mil thickness of the new inhibitor chemistry, rather than the up to 2 mil thickness required for the incumbent products.
Effective protection was achieved, even though more than 200 oxygen ingress events occurred and 60 hours total elapsed, with oxygen levels above 25 ppm. The final product is a proprietary blend, which forms an effective barrier layer on the metals surface and can be applied in batches — or continuously — depending on operational conditions.
Gas Applications
Following successful laboratory development and field implementation, the new oxygen corrosion inhibitor was qualified as an effective solution for mitigating oxygen corrosion. The application not only reduced corrosion rates, but it also increased project safety and profitability.
The solution is designed with broad system compatibility, including wet gas gathering and transmission lines, crude pipelines and topside production environments. It has the ability to perform in a range of velocity and shear conditions — including gas lift applications beyond 200 degrees F — with very low emulsions and foaming tendency.
The development of new chemical technologies is increasingly important to the oil and gas sector, as operators realize the benefits they can deliver to performance. By actively targeting specific challenges — such as oxygen corrosion — substantial gains can be garnered from innovative research and development (R&D). As the industry remains focused on improving oil recovery to meet global energy demands, chemical applications support this drive.
The development of such chemistries is a clear advancement in ensuring the longevity and integrity of infrastructure within the oil and gas industry. By increasing flow assurance and minimizing risk to assets, these chemistries help protect vital pipelines and equipment, underlining the commitment to sustainable practices and the protection of vital assets, to ensure a more efficient and resilient energy sector for the future.
© AMPP 2023, used with permission
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