Stress Engineering Services combines their experience with the latest engineering software tools and materials engineering knowledge to provide "Health Monitoring Technology" for fixed equipment. This assists plant personnel to solve daily engineering problems in an effort to improve plant integrity, safety and profitability
Stress Engineering now provides an unprecedented opportunity to operators of Delayed Cokers to monitor and improve the "Health" and economics of reliable coke drum operation.
Our Coke Drum experience has evolved into an organized approach described as a "Health Monitoring System". As cycles of drum operations are collected, the tools to assimilate and evaluate large volumes of data efficiently has been named SESDrumBeat.
Coke Drum Operators can improve the reliability of their existing and new coke drums by having SES install strain gages to monitor the vessels structural performance versus daily operation. Both the cylindrical shell and the supporting skirt can be protected through improved knowledge of consequence resulting from operation of the drum. SES can tie directly into local DCS making it easier for the operator to evaluate, control and improve operation.
High stress and cracking happens in all drums sooner or later. The question is "can we learn to improve the way we operate the drums to reduce the rate of damage?".
Stress range (max to min) varies from cycle to cycle, Some are higher than yield strength of the steel, and others are much lower. This is likely caused by variations in the flow channels developed near the inside wall due to operation and process changes. Local water/steam channels cause local relative cooling placing the shell in local hoop and axial tensions.
Stress ranges measured for each cycle are used to provide a probabilistic summation of fatigue damage. This information is used to assess and predict the progression of cracking and to evaluate the effects of modified operating practices.
Changes to drum operation are intended to not only "move the histogram to the left" shifting to a lower stressed operation, but are also intended to reduce the likelihood of the "bell ringing bingos" that create the most damage. The histogram shows frequency of occurence for a stress range and the cumulative damage associated with frequency of each stress using a Miner?s Rule for Unit Damage or Usage Factor (x one million). Notice that the higher stress values create much more damage per cycle than lower stress values.
By measuring actual drum stress at strategic locations, we can estimate the rate of damage accumulation from low cycle fatigue for the skirt and shell. There have been many discussions over the past decade as to the actual cause of the fatigue stress and bulge formation. These discussions focus on the role of the hardened coke inside the drum, and how steam and water flow through it to cool the hot mass: strength and permeability are functions of feedstock and process batch procedures. Regardless of the cause of stress, we are measuring the surface stress range on the outside of the drum.
Consequently, the result is difficult to predict from analysis alone. Measurement and interpretation is essential for low cycle fatigue and fracture mechanics assessments.
High stress happens in nearly all drums sooner or later, creating ratcheting fatigue and crack growth propagation. What are you doing as an operator to damage the drums that you can change or improve? Our goal is to help you understand what you are doing or not doing that hurts you and provide recommendations to improve the operation.