Materials Performance

SEP 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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48 SEPTEMBER 2018 W W W.MATERIALSPERFORMANCE.COM CM CORROSION MANAGEMENT As a minimum, thorough reviews of potential damage mechanisms should be conducted in lin e with RBI guidelin es before finalizing inspection and testing plans and scope of work for repair of exist- ing equipment as well as fabrication of new equipment. 5 Using qualitative RBI to develop equip- ment and component risk registers (master risk logs created in the early stages of a project to track issues and address prob- lems as they occur) helps to foresee the individual risks and level of risk; plan the risk mitigation approach; categorize and consolidate inspection efforts for various equipment with similarities in shape and configuration, materials of construction, operating conditions, and service process fluid(s). Risk registers also help to improve bud- geting strategies for routine maintenance as well as turnarounds; avoid rework or procedural revisions; and optimize inspec- tions so they mainly focus on high-risk zones and reduce redundant inspections of l o w - r i s k c o m p o n e n t s . Im p r o v i n g t h e inspection database further helps to pro- vide important input for more detailed RBI (semi-quantitative and quantitative) and predict the future scope of work for replace- ment or repair, and improve personnel skills. Table 1 shows a simplified sample risk register to address various associated damage mechanisms, their probabilities and consequences, and mitigation actions. Another aspect of RBI is to assist when choosing between the options of replace- ment or repair—either proactively or dur- i n g th e re p a i r p h a s e . Th i s w o u l d b e achieved by anticipating the dif ference between repair and replacement costs, the probability of an outage (downtime) for both repair and replacement options, the financial impact of an outage, the probabil- ity of reliable equipment operation until the next planned turnaround (for both repair and replacement), and the financial impact (gain) of reliable operation. 6 Figure 1 shows a simplified decision tree diagram (with arbitrary percentages of probabili- ties) to compare the financial risks and opportunities w h en choosing b etween repair and replacement options. 2,6 Conclusions 1. Undoubt ed ly, c onsultin g th e RBI guidelines as well as API RP 571 3 would have revealed the applicability of ECT for investigating tube thin- ning caused by erosion and corro- sion. Alternate options could have been planned when performing gen- eral ECT on tubes with spiro-vanes TABLE 1. RISK REGISTER Work Description Portion/ Segment Applicable Damage Mechanism Risk Scenario (Qualitative) Proposed Mitigation/ Inspection POF (A) COF (B) Risk Repair and inspection of cryogenic heat exchanger (with welded dished head) Tubes and tube sheet Cooling water corrosion (crevice portions) High High High Internal rotary inspection system (IRIS) monitoring or ECT (based on materials) MIC High Medium Medium Cleaning and inspection cooling water quality checks Erosion/erosion corrosion Medium Medium High Modification of material or process conditions Galvanic corrosion Medium Low Medium Inspections, minimize metal components contacts (isolation) Dished head and shell Carburization of metal during cutting High High High Avoid gouging, cutting, and other sources of carbon ingress; hardness testing prior to and after cutting Thermal distortion of stainless (heavy thickness) during welding High High High Controlled heating and intermittent welding technique Cold cracking of SS welds due to higher residual stresses (cryogenic environment) High High High Hardness testing, appropriate selection and qualification of welding procedures Galvanic corrosion Medium Varying Medium Inspection, minimize metal components contacts (isolation) (A) Probability of failure (B) Consequence of failure

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