主要演講

Flow Accelerated Corrosion Failures in Refineries

Among various deterioration modes in steam/condensate services flow accelerated corrosion (FAC) is established as the chief failure mechanism. This article focuses on various aspects of FAC from the standpoint of reliability and safety. It discusses areas susceptible to FAC, effects of different factors of FAC like flow velocity, water chemistry, material of construction, effect of dissolved oxygen etc., and possible solutions in terms of water chemistry control, use of specific inspection program, selection and upgrading to suitable metallurgy and limiting flow velocity by proper design.

M Y Bhave
DGM (M&I)
INDIAN OIL CORPORATION

Prevention of Chloride Stress Corrosion Cracking (CSCC) using Thermally Sprayed Coating (TSC)

Austenitic Stainless Steel Columns subjected to cyclic temperatures have traditionally been externally coated on the shell side with an Amine Cured Phenolic Epoxy. The epoxy coatings have prematurely delaminated on these columns due to the stresses created by the temperature swings, but went undetected for some time due to the insulation covering the external of the shell. Such exposed surfaces in presence of moisture & chlorides from the atmosphere can develop Chloride Stress corrosion cracks on the surface. Such cracks propagate over time through to the inner wall of the shell, leading to the leak of process gas outside & resulting in a subsequent plant shutdown.

In order to prevent premature failure of such equipment, it was recommended to replace the ineffective Phenolic Epoxy with a more robust & sacrificially active thermally sprayed Coating (Aluminium, Grade 1350) and to replace the existing insulation material i.e. chloride contaminated Mineral wool, hygroscopic insulation, with the inert Cellular Glass insulation.

The application of the TSC was required to be carried out under controlled conditions, controlling the level of moisture in the vicinity of the column surface, including the requirement of a chloride free environment. This was achieved using a flameproof habitat constructed around the work site & by dehumidifying the air inside using A/C units.

The TSC was also required to be carried out during a plant shutdown/turnaround to ensure a stable surface to apply the TSC on to. The job was also required to be done within this short period of time to ensure minimal disruption to plant production.

Being a confined space activity, the job was to fulfill all safety requirements, with a goal of no incident or accident. Maintaining adequate Oxygen levels, good visibility, safe operations of blasting equipment, effective arc spray units were paramount to a successful application as well.

The paper discusses the TSC design and methodology adopted to mitigate CSCC on SS columns, the job requirements, job planning incorporating industry best practices, QA/QC regime followed , and the actual execution process, and subsequent lessons learnt, considering the fact that the job was completed 48 hours in advance of actual planned completion without any recorded LTI.

The paper will conclude on the merits of utilizing experienced personnel with effective work management processes to ensure optimal results.

Rehan Ahmed**
Senior Corrosion Engineer
RASGAS, QATAR