Discovery of unexpected deterioration to process equipment can leave process plant operators with seemingly few choices regarding repair or extended shutdown of the equipment. However, with appropriate experience and the use of advanced assessment tools, additional options can be uncovered. For example, pulp mill black liquor evaporators are highly prone to suffer from internal liquor erosion/corrosion, as well as external corrosion under insulation (CUI). Whether falling or rising film, 4th effect evaporator shells and vapor bodies are typically constructed of carbon steel due to the relatively low black liquor solids concentration (~25-30%). The structural integrity and fitness for service of 4th effect evaporators suffering from severe corrosion can be difficult to assess, with varying degrees of localized internal and external corrosion as well as operating conditions of both positive and negative pressures. With the addition of external stiffener rings, domed heads, and internal tubes/plates, an engineering evaluation can be quite complex. CPI assisted two southeastern pulp mills with engineering assessments of their 4th effects. One falling film, plate bundle design suffered from severe external CUI directly above stiffener rings, as well as internal erosion due to high-flow liquor. Detailed finite elemental analysis showed that the addition of several, additional stiffener rings would increase structural integrity to an acceptable level until a new duplex stainless steel evaporator could be installed at the next shutdown. The other evaporator also suffered severe localized CUI above horizontal stiffeners. A Level 2 fitness-for-service assessment (per API 579/ASME FFS-1) of this local thin area proved that the evaporator was still structurally sound and could continue in operation, provided corrosion in this area did not continue. No immediate repairs were necessary, but the area was properly cleaned, coated, and insulation re-installed so as to prevent future CUI.


Service Areas

  • Corrosion and Materials Engineering
    • Corrosion Control/Protection Design
    • Corrosion Analysis and Material Selection Consulting
    • Failure Analysis – Mode and Root Cause Analysis
    • Coatings and Linings Engineering
  • Structural and Mechanical Rehabilitation Services
    • Structural Design Engineering
    • Mechanical Design Engineering
    • Condition Assessment Evaluations
    • Structural Evaluation and Analysis
    • Shop and Field QC Inspection and Support
  • Mechanical Integrity and Inspection Design Services
    • Pressure Vessel and Tank Program Development and Implementation
    • Strategic Inspection Design (SID)
    • Risk-Based Inspection
    • Integrity Evaluation and Analysis
    • Fitness-for-Service Evaluations
    • Welding Consulting and Inspection
  • Project and Quality Management Services
    • Cost Estimating Services for all Construction Disciplines
    • Project Management Services, Including Planning, Scheduling, and Project Controls
    • Quality Control Inspection and Testing Services
    • Quality Assurance Program Development for New and Rehabilitation Construction
    • Quality Assurance Program Auditing and Oversight Services
  • Training Services
    • Alloy Selection for Corrosive Environments
    • Solving Corrosion and Materials Problems for Plant Engineers
    • Welding Essentials for Plant Engineers
    • Brick and Tile-Lined Equipment Inspection and Repair
    • FRP Essentials for Pulp and Paper Mills
    • Concrete Restoration and Protection
    • Quality Assurance for Capital Projects

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