Materials Performance

APR 2017

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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52 APRIL 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 4 CHEMICAL TREATMENT ever, Table 2 presents the sessile bacteria population density obtained from coupon scrapings from the export gas line in 2015. While the sulfate-reducing bacteria (SRB) population density was above the operator maximum limit (>100 counts/cm 2 ) one time, the population densities of acid-pro- ducing general aerobic bacteria (GAB) and general anaerobic bacteria (GAnB) were above the maximum limit in the majority of the observations. The data, therefore, sup- port the earlier observations. 3-4 The severity of corrosion conditions in the export gas line was confirmed by the results of chemical analysis from samples of the accumulated organics, water, salts, corrosion products, and scales obtained by maintenance pigging during 2012 to 2016. Soluble iron ref lects active corrosion tak- ing place in the pipelines. The sulfate con- tent was higher than that present in pro- duced water, suggesting supplementar y oxidation of H 2 S to sulfate, 5-6 a by-product of a corrosion reaction. The observed total iron and manganese levels, as well as their compounds of oxides, sulfides, and car - bonates, were presumed to be due to cor- rosion of carbon steel (CS). When linked to the fact that sulfides, carbonates, iron, cal- cium, and manganese are the key constitu- ents of black powder deposits, presented in Table 3, it is convincing that all the in- gredients exist for the export gas pipeline to be a prime location for black powder formation. Black Powder Formation Considering the documented dew point data in Table 1, if the dew point of the out- let gas is 10 °C less than the prevailing tem- perature of the export gas handling system, the f lowing gas is considered dry. During the summer months, the ambient tempera- ture is normally above 30 °C and condensa- tion is unlikely. However, in winter months, subzero temperatures in Kuwait are condu- cive to the condensation of water vapor, especially in the desert areas where most of the pipelines are located. Any accumulated condensed water or carryover water/glycol mixture would cause corrosion, and the re- sulting corrosion products are the key in- gredients for black powder formation, par- ticularly in the presence of acid gases (H 2 S and CO 2 ) together or individually in the presence of oxygen. In addition, the presence of moisture, organics, chlorides, and soluble salts in the export gas line is indicative of production water carryover through the dehydration unit, as discussed earlier. Indeed, the liquid carryover level is estimated to be ~10.4 m 3 per day, which represents a liquid concen- tration of 12,137 ppmw (1.2% wt). This, as well as the following facts, illustrates the reduced efficiency of the glycol absorber : • The glycol absorber is designed for handling a certain level of moisture content in the gas. Variations in pro- cess conditions, accompanied by additional carr yover of moisture, periodically overwhelm the system. • Improp er op eration of upstream facilities results in increased liquid carryover and reduced dehydration TABLE 2. SESSILE BACTERIA POPULATION DENSITY IN EXPORT GAS LINES Counts/cm 2 Vessel No./ Line No. Location Description Installed Date Sampling Date SRB GAB GAnB HP-029 HP gas line from GMW-1 to Shuaiba-1 24-May-15 2-Sep-15 0 380 38 HP-030 HP gas from manifold GMW-1 to Shuaiba (13 km away from GMW-1) 1-Jun-15 2-Sep-15 3,800 3,800 380 HP-061 HP gas pipe line from TP-1 M/F to MAA 19-Jan-15 14-Jul-15 38 38 38 HP gas pipe line from TP-1 M/F to MAA 19-Jan-15 14-Jul-15 0 38 0 HP gas pipe line from TP-1 M/F to MAA 31-May-15 6-Sep-15 0 380 380 HP gas pipe line from TP-1 M/F to MAA 14-Jul-15 6-Sep-15 0 380 38 HP gas pipe line from TP-1 M/F to MAA 6-Sep-15 17-Dec-15 0 3,800 3,800 TABLE 3. CHEMICAL ANALYSIS OF BLACK POWDER DEPOSITS S/N Equipment No. Description Physical Characteristics Chemical Analysis of Water Solubles Chemical Analysis of Acid Solubles Color and Appearance Loss on Drying (LOD) % (100 °C) LOD % (500 °C) Carbonates % (as LOD at 900 °C) pH Total Water Solubles (ppm) Cl – (ppm) S – -(Qualitative) Fe (ppm) Mn (ppm) Fe (%) Mn (%) Ca (%) Mg (%) Acid Insoluble (%) 1 569 Glycol tower demister pad deposit Black solid powder 6.1 35.9 4.5 4.1 12,310 423 +Ve 4,852 61 3.3 0.01 3.6 0.24 32 2 575A After scrubber deposit Black damp solid 23.8 21.9 3.8 4.3 46,037 153 +Ve 17,647 281 8.8 0.04 0.4 0.15 30

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