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An Introduction to Coal Silo Failures
September 26, 2019

Summary

Over the past few years, there have been several coal silo failures in power plants in the US and abroad. These failures have dropped as much as 800 tons of coal on the floor below them. To date no injuries have occurred but significant equipment damage has resulted.

The most common cause of failure is occurring in the welds from shell to cone in silos with a C/S shell and SS cone. The failures have occurred primarily at the 40-year mark of operation. Insurance companies are recommending that all silos be inspected at the expected half-life of the power plant (30/2 or fifteen years). The recommendation has been made to almost all coal fired power plants with coal silos.

*Please note some plants have square coal “bins” which are not the same.

Experience

To date, Acuren has inspected silos for several power companies. Our experts have seen everything from no evidence of structural damage to silos with cracks, shell distortion and shell thinning. One client had all C/S cones and silos inspected; no evidence of any cracking was found. At another site, Acuren found cracks in the heat affected zone of the dissimilar metal weld and base material of the cone. Another anomaly that was discovered was a case of severe underfill of the shell to cone weld on the inside of the joint. We verified this using rope access and visual inspection while the silo was out of service. It was determined that the amount of weld deposited was insufficient for the load. The plant is developing a plan for proper repair.

Per Acuren’s experience and collaboration with a mutual insurance company that focuses on the Highly Protected Risk market sector, it has been determined that with higher use of a given silo the more it is prone to cracking. This is the case of the plant with numerous cracks. Plants might run certain silos more often where loading and unloading or cycling leads to greater probability of cracking.

Additionally, plants that had wall degradation used primarily PRB (Powder River Basin) coal. Our technicians have also seen squared coal bins be significantly eroded by the high sulfur content of the PRB coal (water and sulfur creates sulphuric acid).

Solution

It is imperative to have an experienced and dependable inspection company as a partner since all silos are different. Silo construction is not under the jurisdiction of any regulatory codes and no known measures are in place to assure the quality of these welds.

Acuren custom inspection solutions and specific inspection plans are a direct result of interaction with the client’s plant/site engineering team and the design of the silo because every silo is different.

Site drawings/blueprints and a walkdown with our experts are completed to build your inspection plan.

Services

PAUT

Acuren’s inspection of the shell to weld dissimilar metal weld is done primarily with PAUT. Typically, a reference standard is made from the documented joint design with three EDM notches placed at potential crack propagation sites.

This reference standard shows that a plate is welded on the outside of the C/S shell preventing UT from being done from that point. For this particular project, our techs scanned the weld joint from the underside at the crotch of the cone and shell junction with a Cobra probe on the SS cone (angled piece). Acuren experts have also found large amounts of slag in the welds that has not caused cracking. They have seen significant amounts lack of fusion (LOF) at the backside of the joint as well. The significant cracks have been found to open on the inside weld at the HAZ.


Rope Access

Since each silo design is slightly different, many times welds are difficult to access thus Acuren’s rope access solution is a valuable method when inspecting from the inside. Rope access inspection can only be done when the units are out of service. PAUT is available from the outside while the plant is online.

UTT

When clients want to know more about the shell, Acuren uses our UT crawlers proving invaluable in some cases. At times, some silos have so much structure around them that UTT must be done from ropes from the inside of silo.

For a customized plan call our experts today at 1-800-218-7450.

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ACUREN COVID-19 PREPAREDNESS

As the transmission of the COVID-19 virus increases around the world and within our own communities, we want to make our customers aware that, in most jurisdictions, we fall within the essential services exception and we are able to perform the services customers require on their sites. As well we want to take a moment to update you on the measures we continue to implement to ensure business continuity and transmission reduction:

  • We continue to share regular communications with employees to ensure we are providing important news about the status of the virus and the actions taken by the company;
  • The Acuren COVID-19 email address continues to act as a valuable resource to which employees can send questions and concerns, and request other support related to COVID-19;
  • Our single point of contact continues to be a central resource to respond to issues related to the virus and associated company direction;
  • We have responded in real time to take appropriate measures in communities where we are informed of governmental restrictions that have a direct effect on our employees;
  • Alternate work provisions and enhanced infection control practises have been implemented across the business to minimize the potential for spread of the virus in our offices and field work locations;
  • On an almost daily basis we post valuable educational and informational resources on our online portal for the benefit of all North American employees;
  • We regularly remind employees of the critical need to comply with infection prevention and control measures such as frequent hand washing, appropriate respiratory etiquette and instruction to stay home if feeling unwell,
  • We continue to monitor and adjust our inventory of consumables and critical equipment to ensure we are equipped to respond to client needs in the event of a supplier shortage;
  • We have maintained frequent interaction with our leadership team on this matter to ensure we remain fully informed of changing circumstances;
  • We monitor the use of a disclosure form completed prior to employee’s returning to work to identify the presence of any symptoms related to the coronavirus, any personal travel within, or personal contact with travelers to/from, any international location, within the previous 14 days. This has been integrated into our onboarding plan for new projects;
  • We have distributed our Pandemic Plan to address the challenges presented by the current viral spread and to plan for the continuity of our services;
  • We have instituted restrictions on travel that is not business critical and have expanded our use of virtual meeting software.
  • We continue to communicate with our clients regarding the status of our actions, the preparedness of our business, the availability of our workforce, and our express intention to work in partnership to maintain the safety and health of our employees on their sites;
  • We continue to provide instructions related to isolation and quarantine requirements as per the CDC and WHO, and to ensure such requirements are met by affected employees;
  • Where we have employees who test positive for the virus, we have implemented a protocol to ensure all potentially affected parties are notified and proper precautions taken.

Our primary concern is always employee and client safety. To this end, we will continue to add to, or modify, our preparedness program in reaction to this evolving situation. We thank you in advance for all of your efforts in doing the same, and, as always we commit to working with you to ensure a safe worksite for all employees.

Should you have any questions regarding the foregoing, please contact me at (780) 405-5771 or kevin.hill@acuren.com; or Jen Miller at (780) 782-8082 or jen.miller@acuren.com at your earliest convenience.

Best Regards,

Kevin Hill, P.Eng., MBA
Vice President, Commercial
Jen Miller
Director, Human Resources
Acuren Director, COVID-19 Communications
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