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Sealing Technology for Caustic Service – Chemical Engineering

Mish Boyka

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Sealing Technology for Caustic Service - Chemical Engineering

This overview compares various sealing technologies, and points out advantages and disadvantages of applying different mechanical-sealing designs for caustic fluids

Caustic applications in chemical plants can play havoc on the mechanical seals of rotating equipment. These applications can be difficult to seal because of the caustic chemical properties in both solution and dehydrated states. Caustic solutions form harmful crystals as the liquid evaporates and the concentration increases past the solubility point. As the solution becomes hotter or more concentrated (or both), it becomes more corrosive, further impacting mechanical seal reliability.

Each caustic application presents unique complications due to different concentrations, desired purity levels and pump design. As a result, seal manufacturers have developed seal designs and support systems to ensure that the seal will survive the harsh demands placed on them by the pump, the process and the operating conditions. Among these new seal designs is the dynamic lift up-stream pumping (USP) technology.

Understanding these seal design options and arrangements for caustic applications, along with their benefits and shortcomings, will help chemical operations avoid costly mechanical failures, equipment damage, impacts to the environment and personnel exposure to hazardous materials.

sealing technology

 

An overview of sealing technologies

Single seals. Single seals, defined in API 682 “Pumps — Shaft Sealing Systems for Centrifugal and Rotary Pumps” as Arrangement 1 (Figure 1), are the simplest and least expensive method of achieving a seal for any pump. The mechanical seal faces are lubricated by the process fluid. In the case of applications such as caustic, normal seal leakage across the seal faces can result in plating and atmospheric side deposits that can contribute to seal component hang-up. For this reason, conventional piping plans, such as API Plan 11 are less desirable in these services.

Figure 1. A typical API Flush Plan 32 is diagrammed here

For sealing caustic applications, an API 682 Plan 32 flush is often recommended. This system injects clean liquid from an external source into the seal chamber (also known as the stuffing box) at a pressure slightly higher than the chamber itself. Because the external fluid flow needs to be high enough to prevent ingress of the caustic fluid, the costs associated with the flush can prove prohibitive.

Dual unpressurized seals. Dual unpressurized seals defined in API 682 as Arrangement 2 (Figure 2), utilize an unpressurized buffer fluid between two pairs of seal faces. The inner seal faces are lubricated by the process fluid. Any leakage across the inner seal is added to the buffer fluid.

Figure 2. Shown here is a typical dual unpressurized seal pressure arrangement

In caustic applications, this arrangement leads to contamination of the buffer fluid from inner seal leakage. To combat this, an API Plan 32 is recommended for a dual unpressurized seal, with the same drawbacks as a single seal for added fluid initial expenditure, but with the additional costs of circulating another fluid and the associated support system cost, monitoring, and maintenance requirements.

Dual pressurized seals. Dual pressurized seals defined in API 682 as Arrangement 3 (Figure 3), utilize a barrier fluid pressurized above the process pressure. The seal faces are lubricated by a clean barrier fluid. Any leakage across the inner seal face will therefore be from the barrier fluid into the process fluid.

Figure 3. This diagram shows a typical dual pressurized seal arrangement

Because the leakage across the inner seal faces is clean barrier fluid, abrasive particles from the caustic fluid are isolated from the seal face area.

The initial cost of this option is the most expensive, due to the complications of providing a pressurized barrier-fluid system. However, this option generally offers better reliability than the other two arrangements since seal performance is not dependent on the process fluid for lubrication.

 

Dynamic-lift USP technology

A conventional mechanical seal operates by utilizing the higher pressure fluid as a film between two precision-lapped seal faces. The hydrodynamic action of the seal allows a film to form of usually less than 1µm that lubricates, cools and minimizes mechanical contact. Any leakage across the seal faces occurs from a higher pressure fluid into a lower pressure region.

Figure 4. A typical up-stream pumping arrangement is shown here

How it works. Dynamic lift technology uses grooves on one of the seal faces to generate pressure between the seal rings so that they physically separate and operate in non-contacting mode (Figures 4 and 5). The most well-known use of this is for dry gas seals, where a barrier gas at a higher pressure than the sealed pressure is used to separate the faces.

Figure 5. This diagram shows the pressure generation in a USP seal

Dynamic lift USP utilizes specially optimized spiral grooves on one of the seal faces to create a pumping effect. The face design generates a positive pressure across the seal face from inside diameter to outside diameter — that is, from the lower-pressure buffer fluid to the higher-pressure process fluid in the seal chamber. This has the effect of raising the pressure of the fluid film between the seal faces to above that of the process (Figure 5). The pumping mechanism creates a controlled flow of buffer fluid from low-pressure into the higher-pressure process fluid. The seal acts like a pressurized dual seal without the need to pressurize a barrier fluid. The low-pressure buffer fluid is sealed by a containment seal typically operating at the pre-set buffer-fluid pressure, but capable of containing the seal chamber pressure in the event of an inner seal failure.

Advantages. Dynamic-lift up-stream pumping technology offers many advantages over the traditional dual-seal approach, including the following:

 

    • The technology is “non-contacting” and therefore the usual pressure-velocity limitations imposed by contacting seals, and the resultant wear, do not apply

 

    • The power consumed is significantly lower than a dual-pressurized or unpressurized seal arrangement

 

    • Compared to a dual unpressurized seal, a USP seal has the advantages of clean fluid lubrication and non-contacting operation

 

    • Compared to a dual unpressurized seal, a USP seal requires a much simpler support system

 

    • The process fluid is on the outside diameter of the seal faces — solids suspended in the process fluid are centrifuged away from the seal faces and secondary seal area

 

    • Buffer fluid leakage to atmosphere is significantly reduced when compared to a pressurized dual seal, where the outer seal can often operate with a considerable pressure differential

 

    • The concept allows a simple upgrade of single- or multiple-seal services where process changes have rendered the process fluid a poor seal lubricant

 

    • In services where the process pressure is variable, or where pressure spikes are likely, the spiral groove constantly regulates against this varying pressure, maintaining a sealing gap at all times

 

    • The flush requirement for dual pressurized or unpressurized arrangements is often unnecessary with USP due to low heat generation, reducing water usage

 

    • Increased mean time between repair (MTBR)

 

Developing the high-pressure USP seal. The first high-pressure USP seal was designed and validated back in 2003. The initial design focused on an emulsification of oil and water contaminated with varying concentrations of sand.

Figure 6. This cutaway shows the first high-pressure USP sealing arrangement

The 75-mm seal design shown in Figure 6 was tested under the following operating conditions:

 

    • Shaft speed: 3,600 rpm

 

    • Seal chamber pressure: 5 to 40 barg

 

    • Seal chamber temperature: 70–80°C

 

    • Process fluid: water, water/oil/sand (20 wt.% sand)

 

    • Buffer fluid: seawater

 

Simplified seal-support systems. By nature of the design and operation of dynamic-lift USP mechanical seals, the required support system complexity is greatly reduced compared to that used with a conventional dual pressurized seal.

For example, due to a lack of cooling requirement for many designs, the system requirement is simply an elevated tank with an optional automatic fluid top-up system. Figures 7 and 8 show examples of a basic support system.

Figure 7. This schematic shows a typical piping plan arrangement

Figure 8. A typical piping plan arrangement with a USP seal in operation

Two case studies

This final section presents two applications of the mechanical seal using dynamic-lift technology.

Case 1. Improving MTBR at a chemical plant. Recently, a chemical plant in the eastern U.S. experienced a high seal-failure rate on one of its proprietary single-pump processes. Over the course of one year, the traditional mechanical seal required repair or replacement at least 17 times.

The toll plant, specializing in intermediates, polymers and colorants used by a diverse customer base around the world, relied primarily on a manual operation, leading to repeated production errors. The low seal mean time between repair (MTBR) hit the company’s bottom line in production and maintenance costs.

A thorough review of the operation and a comprehensive failure GFN revealed that employees would manually dump improper levels of crystal particles into a conical-bottom process tank. Because there was no way to measure the proper particle-to-water ratio — only employee judgment — incorrect levels were applied, often in chunks. As the volatile mixture recirculated in the tank, the seal and pump would not only starve at the start, but would also deadhead at the end of the process. This caused the seal to overheat and cook the O-rings until they resembled “charcoal.” Engineers consided a proven recirculating seal-support-system technology that would accommodate the manual process.

After the pump was rebuilt, the plant agreed to a six-month trial that replaced the existing mechanical seal with a 1.750-in. T5620 USP seal. The seal was chosen for the operation because it is designed to handle the inconsistent and caustic mixtures of the plant’s manual-dissolution process. Inboard seal faces, comprised of silicon carbide material, combined with the dynamic-lift USP face pattern.

Following the six-month trial, plant engineers said they “were ecstatic” with the performance of the T5620 USP seal. The USP seal racked up an impressive three-year MTBR, a significant improvement over the previous MTBR performance. Immediately following the installation of the USP seal, the plant eliminated the frequent half-day production interruptions, saving the company untold sales revenue. Pulling technicians away from other duties, oftentimes for four to six hours to work on the pump and seal, came to an end. The plant saved nearly $25,000 in seal-repair costs over three years after the USP was installed.

Case 2: Saving water at a chemical-processing plant. Engineers at a large chemical manufacturing plant on the east coast of the U.S. were concerned about how much water it used to process lithium hydroxide. Packing on a water pump used in the process caused significant water loss, requiring constant adjustments by plant technicians.

When the water/lithium hydroxide slurry seeped into the red clay under the plant, the reaction caused significant concrete floor heaves. The U.S. Environmental Protection Agency (EPA; www.epa.gov) required the plant to curtail the water and lithium hydroxide losses and adhere to regulations. The 24/7 chemical-manufacturing plant needed a cost-effective solution to stop the leakage to reduce costs, stop damage to the floor and conform to EPA requirements.

The company sought a solution to the problem on an open-vane, recirculating propeller pump. After careful review, it was determined that the lithium-hydroxide process was losing nearly 1.8-million gallons of water annually. Because of the water leakage, the plant’s floor would heave approximately 1.25 in./yr at the site of the process. Some areas of the floor rose 6 in. higher than other spots, creating trip hazards and costly pump, piping and infrastructure adjustments. Because of the thick and volatile nature of the slurry, traditional seals had not worked to correct the problem in the past.

Plant engineers agreed to discard the existing pump packing and replace it with engineered USP non-contacting face and filtered water-buffer-fluid seal technology. The pump was reconditioned and a 2-in. T5620 USP seal standard double-seal was installed.

The USP seal performed for six years of uninterrupted operation, eliminating constant attention from plant service personnel to service the pump packing. Annual planned packing replacement was eliminated. Excessive water consumption and associated costs were immediately halted, allowing the plant to cut water usage by up to 1.8 million gal/yr. EPA concerns regarding the water leakage into the clay soil were addressed. Leaks into the ground from the lithium-hydroxide process no longer caused the floor to heave.

        Edited by Gerald Ondrey

 

Author

Brian Kalfrin is a senior regional engineering manager with John Crane Inc. (4001 Fair Dr., Pasadena, TX 77507; Phone: 1-281-474-1700; Email: bkalfrin@johncrane.com), with over 19 years of experience with mechanical seals and related systems. He is responsible for engineering expertise within the North America Region for John Crane, encompassing the U.S. and Canada. His duties include design engineering oversight, GFN, and recommendation formulation to address challenging problem applications, along with design evaluation of existing and proposed mechanical seals. He is also responsible for training both customers and John Crane personnel in both mechanical seal application and troubleshooting. Kalfrin is a member of the Texas A&M International Pump Users Symposium Advisory Committee, the API 682 Task Force currently working on the 5th Edition. He holds a B.S.M.E. degree from Drexel University in Philadelphia, Pa.

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Vermont Health Connect had 10 data breaches last winter

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Vermont Health Connect had 10 data breaches last winter
Vermont Health Connect has set up a special enrollment period in response to the coronavirus outbreak. VHC photo

In mid-December, a Vermont Health Connect user was logging in when the names of two strangers popped up in the newly created account.

The individual, who was trying to sign up for health insurance, deleted the information that had suddenly appeared.

“It was super unsettling to think that someone is filing in my account with my information,” the person, whose name is redacted in records, wrote in a complaint to the Department of Vermont Health Access. “Just seems like the whole thing needs a big overhaul.”

It was one of 10 instances between November and February when Vermont Health Connect users reported logging to find someone else’s information on their account.

The data breaches included names of other applicants and, in some cases, their children’s names, birth dates, citizenship information, annual income, health care plans, and once, the last four digits of a Social Security number, according to nearly 900 pages of public records obtained by VTDigger. On Dec. 22, the department’s staff shut down the site to try to diagnose the problem.

While officials say the glitches have been resolved, it’s the most recent mishap for a system that has historically been plagued by security and technical issues. The breaches could be even more widespread: Administrators of Vermont Health Connect can’t tell if other, similar breaches went unreported.

“We don’t know what we don’t know,” said Jon Rajewski, a managing director at the cybersecurity response company Stroz Friedberg. Regardless of whether there are legal ramifications for the incidents, they should be taken “very seriously,” he said.

“If my data was being stored on a website that was personal, — maybe it contains names or my Social Security number, like my status of insurance… — I would expect that website to secure it and keep it safe,” he said.

“I wouldn’t want someone else to access my personal information.”

Andrea De La Bruere, executive director of the Agency of Human Services, called the data breaches “unfortunate.” But she downplayed the severity of the issues. Between November and December, 75,000 people visited the Vermont Health Connect website for a total of 330,000 page views, she said. The 10 incidents? “It’s a very uncommon thing to have happen,” she said.

De La Bruere said the issue was fixed on Feb. 17, and users had reported no similar problems since. The information that was shared was not protected health information, she added, and the breaches didn’t violate the Health Insurance Portability and Accountability Act, or HIPAA.

“No matter what the law says technically, whether it’s HIPAA-related or just one’s personal information, it’s really concerning,” said Health Care Advocate Mike Fisher.

The timing of the issue is less than ideal, he added. Thousands of Vermonters will be logging into Vermont Health Connect in the coming weeks to take advantage of discounts granted by the American Rescue Plan. “It’s super important that people can access the system, and that it’s safe and secure,” Fisher said.

A ‘major issue

The issues first arose on Nov, 12, when at least two Vermonters logged in and found information about another user, according to records obtained by VTDigger.

Department of Vermont Health Access workers flagged it as a “major issue” for their boss, Kristine Fortier, a business application support specialist for the department.

Similar incidents also occurred on Nov. 17 and 18, and later on multiple days in December.

Department of Vermont Health Access staff members appeared alarmed at the issues, and IT staff escalated the tickets to “URGENT.”

“YIKES,” wrote a staff member Brittney Richardson. While the people affected were notified, the data breaches were never made public.

State workers pressed OptumInsights, a national health care tech company that hosts and manages Vermont Health Connect, for answers. The state has contracted with the company since 2014. It has paid about $11 million a year for the past four years for maintenance and operations, with more added in “discretionary funds.”

Optum appeared unable to figure out the glitch. “It is hard to find root cause of issue,” wrote Yogi Singh, service delivery manager for Optum on Dec. 10. Optum representatives referred comments on the issues to the state.

By Dec. 14, Grant Steffens, IT manager for the department, raised the alarm. “I’m concerned on the growing number of these reports,” he wrote in an email to Optum.

The company halted the creation of new accounts on Dec, 14, and shut down the site entirely on Dec, 22 to install a temporary fix. “It’s a very complex interplay of many many pieces of software on the back end,” said Darin Prail, agency director of digital services. The complexity made it challenging to identify the problem, and to fix it without introducing any new issues, he said.

In spite of the fixes, a caller reported a similar incident on Jan. 13.

On Feb. 8, a mother logged in to find that she could see her daughter’s information. When she logged into her daughter’s account, the insurance information had been replaced by her own.

“Very weird,” the mother wrote in an emailed complaint.

Optum completed a permanent fix on Feb. 17, according to Prail. Vermont Health Connect has not had a problem since, he said.

Prail said the state had reported the issues to the Centers for Medicaid and Medicare Services as required, and had undergone a regular audit in February that had no findings. The state “persistently pressured Optum to determine the root cause and correct the issue expeditiously but at the same time, cautiously, so as to not introduce additional issues/problems,” he wrote in an email to VTDigger.

“We take reported issues like this very seriously,” he said.

A history of glitches

The state’s health exchange has been replete with problems, including significant security issues and privacy violations, since it was built in 2012 at a cost of $200 million.

The state fired its first contractor, CGI Technology Systems, in 2014. A subcontractor, Exeter, went out of business in 2015. Optum took over for CGI, and continued to provide maintenance and tech support for the system.

Don Turner
Don Turner, right, then the House minority leader, speaks in 2016 about the need to fix the state’s glitch-ridden Vermont Health Connect website. With him are Phil Scott, left, then the lieutenant governor, and Sen. Joe Benning. Photo by Erin Mansfield/VTDigger

In 2018, when Vermont Health Connect was less than 6 years old, a report dubbed the exchange outdated and “obsolete.”

Officials reported similar privacy breaches in 2013, when Vermonters saw other people’s information.

An auditor’s report in 2016 found a slew of cybersecurity flaws, and officials raised concerns again during a  2018 email breach.

It wasn’t the first time that Vermont Health Connect users had been able to view other people’s personal information. Three times since October 2019, individuals had logged in to see another individual’s insurance documents. Prail attributed those incidents to human error, not to system glitch; a staff member uploaded documents to the wrong site, he said.

In spite of the issues, Prail said he and other state officials have been happy with Optum. After years of technical challenges with Vermont Health Connect, “Optum has really picked up the ball and improved it and been running it pretty well,” he said.

Glitches are inevitable, he added, and Optum has addressed them quickly. “They took a really difficult-to-manage site and made it work pretty well,” he said. “Optum is generally quite responsive to any issues we have.”

“I find any privacy breach to be concerning,” said Scott Carbee, chief information security officer for the state. He noted that the state uses “hundreds of software systems.” “While the scope of the breaches can be mitigated, true prevention is a difficult task,” he wrote in an email to VTDigger.

Optum spokesperson Gwen Moore Holliday referred comments to the state, but said the company was “honored” to work with Vermont Health Connect “to support the health care needs of Vermont residents.”

Prail said the Agency of Human Services had no plans to halt its contract with the company. “I don’t have a complaint about Optum,” he said. “They took a really difficult-to-manage site and made it work pretty well.”

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Health Care

Tags: data breaches, Optum, Vermont Health Connect

Katie Jickling

About Katie

Katie Jickling covers health care for VTDigger. She previously reported on Burlington city politics for Seven Days. She has freelanced and interned for half a dozen news organizations, including Vermont Public Radio, the Valley News, Northern Woodlands, Eating Well magazine and the Herald of Randolph. She is a graduate of Hamilton College and a native of Brookfield.