Failing Brine Piping Replaced at World`s Largest Ion Exchange Membrane Plant

0

Courtesy of Fabricated Plastics Limited

Fabricated Plastics Limited is headquartered in Maple, Ontario, located on the northern outskirts of Toronto. One of North America's largest custom composite and dual laminate fabrication companies. Fabricated Plastics is dynamic, energetic, creative and resourceful. Engineering design, problem solving and fabrication are world class with the result that Fabricated Plastics is frequently invited to tender on many global projects.

The most valuable compliment that any commercial enterprise can be paid is when a company, having experienced a successful completion to a previous job, is invited back to supply another project. This is an example of just such a case.

Some years ago Fabricated Plastics designed, engineered and fabricated and shipped the components for an enormous petrochemical complex in the Far East. Each aspect of the work was highly problematic: size, specific materials, the logistical nightmare of shipping such huge equipment half way round the world, the time parameters etc. Fabricated Plastics completed the project perfectly, on time and on budget. Notably, this project was given to Fabricated Plastics based on a previous difficult and successfully completed assignment for the same company.

So now, a third assignment was offered to Fabricated Plastics.

The petrochemical complex includes a plant for producing Poly Vinyl Chloride (PVC) located in Taiwan.

Within the huge manufacturing area is the world's largest IEM Plant. (Ion Exchange Membrane Plant). This modern plant processes a treated Brine solution and through an electrolysis process it produces three distinct products, Chlorine, Caustic (Na OH) and Hydrogen gas. The resultant Chlorine is an ingredient in PVC production.

Specifically, the project requirement was to replace corroding metal piping that was used to draw salt water from the ocean to the brine treatment area where the salt water solution is further treated to create a saturated brine solution that is fed to the IEM plant and back to the brine treatment area. The total length of the brine piping was approximately 10 km - 5 km each way. The pipe was sized to be 22' (560 mm) diameter to accommodate the plant's current and anticipated future needs. The entry pipe starts at the ocean. Sea water is pumped to a brine treatment area near the oceanside where it is prepared in accordance with the IEM's requirements, heated to between 60 degrees and 70 degrees C, and then the treated Brine Solution is piped 5 km to the IEM plant. There it is electrolyzed, creating Chlorine, Caustic (NaOH) and Hydrogen. Finally the remaining solution of depleted Brine is return pumped to the Brine treatment area to close the process loop.

The original construction used mild steel. This works well with sea water providing a special epoxy type of coating is applied to the pipe.

However, as plant processes changed after initial start-up it had not been taken into consideration that heating the brine solution to 60 or 70 degrees C produces very high corrosive levels. As a result the pipe started leaking at welded joint areas with increasing frequency after a year or so. Almost every 90 degree elbow fitting was leaking and was being patched externally to keep the line running. The condition of the pipeline was rapidly deteriorating, and threatened the production capability of the IEM plant and the other downstream plants relying on the IEM's feedstock of Chlorine, NaOH and Hydrogen gas.

One bright spot that gave the plant operations people a little more time was provided by a resourceful process engineer in the IEM's operations management. The ingress pipe was carrying the 60 - 70 degree C liquid Brine solution and was subject to correspondingly high corrosive attack. The egress pipe carried a much cooler Spent Brine solution and had correspondingly less corrosion. So, by simply switching the line, this process engineering hero provided a little more breathing space but the urgency was still there.

Most engineering work can be categorized as problem to solution thinking.

In this case the oustanding challenges were:

  1. Speedy repair /replacement. The leaking pipe work created a serious production capacity shortfall.
  2. The sheer length of the piping presented a problem as FRP pipe expands and contracts 3 times as much as steel.
  3. Insistence on the client's behalf that the work was to have a 4 year warranty. All joints had to be extra carefully wrapped.
  4. The retrofitting work was to be done using a completely different material (FRP) from the original (mild steel). The racks that supported the piping had span criteria based on steel. As the support spans could not be changed, the pipes had to be designed to accomodate the existing support spans.

The challenges in design were also extremely demanding. Using a specific piping stress analysis software program, the design engineer at Fabricated Plastics had to make many more calculations than usual as the client required the total system to be designed. In essence this required calculating where the supports should be sliding, fixed and anchored, the force loads exerted at each and every joint and every directional change - simply stated, the calculations had to satisfy every criteria for every possible occurrence in the whole pipeline.

In a typical FRP pipeline, supports are placed at every 3.5 - 4.2 meters. However, the existing pipe bridge supports were 5 meters and even up to 6 meters apart, modifications of the existing bridge support to allow shorter spans was not feasible. Consequently, the longer spans in combination with the additional axial loads, created the need for a stress analysis at 220 elbow fittings required for the piping system. (In fact, the analysis was made on the 110 elbows of the incoming pipe, and then duplicated for the outgoing pipe). The required internal operating pressure for the brine pipe system was 12 bar (approximately 160 psi).

The client's desire to have a 4 year warranty required a change in thinking on Fabricated Plastics' part. There would be no problem in a 4 year warranty for work that Fabricated Plastics had total control over. But, as in many projects, the engineers and fabricators do exactly that - engineer and fabricate. The actual installation, fitting and finishing of some components is frequently performed by a variety of people not under Fabricated Plastics control. If any of these uncontrolled operations is performed incorrectly, it can have a serious impact on longevity and thus on warranty of any length of time.

To accomodate these unforseen but possible errors, Fabricated Plastics created a 4 point fool proof program.

  1. Fabricated Plastics established a training program for the second installation contractor.
  2. All joints had the required glass pre-cut to the exact width, length, with the exact number of layers and placed in a sealed plastic bag. Apart from protecting the contents from external moisture or dirt, this 'control kit' removed any guesswork as to the number of layers required by the installer.
  3. On the job site, the contractor has to cap the cut end of a pipe with a corrosion liner. This can be difficult as the inside of the pipe is inaccessible due to the size limitations of the bore. Fabricated Plastics' unique end capping procedure, 'Resin Rich Corrosion Capping' removes this difficulty and ensures an efficient joint seal.
  4. The last procedure introduced to ensure top quality work at the site, was to stencil each joint with pertinent information: The name of the person who made the joint, the date it was made, the temperature on that day, and the signature of a QA inspector.

In addition Fabricated Plastics coordinated site requirements and worked very closely with the excellent installation contractor to insure timely logistics and overall support of field activity to accomodate the IEM plant's requirements.

What seemed like an impossible task was finished successfully and in rapid time to allow the IEM to keep producing.

The piping system has now operated for 5 years without any issue, it is inspected regularly and demonstrates again that superior design, quality fabrication and controlled installation procedures will result in long lasting trouble free equipment.

Customer comments

No comments were found for Failing Brine Piping Replaced at World's Largest Ion Exchange Membrane Plant. Be the first to comment!