Mlng Scw Cmp

Topics: Water, Corrosion, Chlorine Pages: 6 (1994 words) Published: March 3, 2013
07 JULY 2012

A. CORROSION GROUP DATA Corrosion Group ID Corrosion Group Name Process Service Material of Construction Corrosion Group Description 4CG-5235 Sea Cooling Water Sea Cooling Water Piping(CS,cement,U.G/A.G);Tube(Al Br),Channel(Cu) The group consist of sea cooling water supplied to all sea cooling water exchanger in Module 4. Unit 5200: Sea cooling water to various heat exchangers with temperature range between 30 to 50 degC and pressure 3barg Sea Cooling Water (SCW) exchangers provide cooling medium for process and utilities units. The source of SCW is located at Terminal SCW intake system. This SCW is pumped to the modules via four SCW pumps. Mechanical and chemical treatment of the seawater is required because of debris and marine life presence. The intake station contains a series of screening facilities (bucket sieve screens and rotating drum screens to remove floating solids from the seawater. Sodium hypochlorite is also added to the seawater to prevent multiplication of marine organisms in the system. Sodium hypochlorite is produced electrolytically from seawater by the electrochlorinaton units. The free residual chlorine (FRC) is maintained between 0.5-0.7 ppm at the SCW pumps discharge header and between 0.2-0.5 ppm at the SCW outfall channel. The purpose of having excess FRC is to ensure enough chlorine is dosed to prevent the marine growth. SCW enters the module at ambient temperature while the exit temperature is controlled not to exceed DOE requirement of 40°C.

Process Description


Damage Mechanism Summary

Tube (Al-Br) and Channel (Cu) Internal Corrosion: 1. Erosion-Corr: At tube ends; due to high velocity. Erosion corrosion can occur in flowing liquid-solid streams or in gas-solid streams. Erosional velocity limits are as follows: a) Al-Br: 2.4 m/s b) 90-10 Cu-Ni: 3.0 m/s c) 70-30 Cu-Ni: 3.7 m/s 2. P-Erosion: Carry-over of sand, silt, debris in combination with velocity. Occur due to mechanical interaction between the solid particle and wall surface. Installation of strainer/mesh size reduces the severity of this degradation. 3. O2-Corr: Of heat exchangers and piping; if AILs are exceeded and at areas of low flow. 4. MIC: Of heat exchangers and piping; If MIC count exceeds AIL (>10, 10,000 High Risk). Occur at 6 o'clock position i.e. Low flow, stagnant areas, dead leg and end caps. 5. Ammonia-SCC: Of Copper alloy tubes in aqueous NH3 environment with traces of O2, pH>8.5, residual stresses and at any temperature. The probability for this mechanism to occur on tube internal depends on quality of seawater at intake when ammonia is detected. 6. Dealloying: Selective leaching of alloying components (Primarily copper alloys and cast iron) leading to dark patches and porosity of areas attack due to the following alloys in sea water system: a) Brass: De-zincification b) 70-30 Cu-Ni: De-nickelification The component may fail due to reduction in mechanical properties. 7. General Corrosion: To be selected where actual corrosion rate of equipment is the same as design corrosion rate. Presence of contaminants such as Chloride, sulphur, sulphide and ammonia may accelerate corrosion rate of pipework and equipment of the SCW system. Piping Corrosion (CS,cement,U.G/A.G): 1. Ext-Atm-Corr: Can occur if painting starts to degrade when expose to marine environment 2. Ext-Crevice-Corr: Can occur underneath the pipe support 3. VI-Cracking: To check if piping vibration has been observed anywhere (not for equipment) 4. Deadlegs/NNF: To be identified jointly; Mitigation involves execution of Deadlegs and NNF inspection programs. 5. Galvanic-Corr: At junction of dissimilar material; in presence of aqueous environment Pump Corrosion: 1. Cavitation: At pump (pump is not addressed in P-RBI)

Parameters Design Pressure (barg) Operating Pressure (barg)

Minimum 3.50 0.00

Maximum 22.50 0.00


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