Stainless steels pipeline

Fig. 3. Operating pressure and mass of solids entering and leaving conveying pipeline for unstable flow of poly granules through 21.7 m long and 60 mm ID stainless steel pipeline.

As in the case of corrosion at the insulating connection due to different potentials caused by cathodic protection of the pipeline, there is a danger if the insulating connection is fitted between two sections of a pipeline with different materials, e.g., mild and stainless steel. The difference between the external pipe/soil potential is changed by cell currents so that the difference between the internal pipe/ medium potential has the same value, i.e., both potential differences become equal. If the latter is lower than the former for the case of free corrosion, the part of the pipe with the material that has the more positive rest potential in the soil is polarized anodically on the inner surface. The danger increases with external cathodic protection in the part of the pipeline made of mild steel. 

Recently in some types of refuelling stations, corrosion-resistant materials have been used between the filter-water separator and the outlet pipeline and valves, usually stainless steel, rarely aluminum. If these are buried, they must have good insulating coating and be electrically separated from other tank installations by insulating couplings. 

Propeller/paddle mixers are used to blend or agitate liquid mixtures in tanks, pipelines, or vessels. Figure 38.1 illustrates a typical top-entering propeller/paddle mixer. This unit consists of an electric motor, a mounting bracket, an extended shaft, and one or more impeller(s) or pro-peller(s). Materials of construction range from bronze to stainless steel, which are selected based on the particular requirements of the application. 

Two 4 1 cylindrical glass(QVF) vessels with stainless steel end plates, serve as reservoirs(Figure 1) for surfactant solution(B) and water(9). Facility is available to evacuate these vessels as required by means of a rotary vacuum pump with glass cold trap in line to minimise water vapour. Another pipeline permits supply of pure nitrogen, or other gas, at low pressure, to the vessels, to provide a blanket, as desired. Proper operation and safety from over pressure is ensured by a pressure relief valve(10 in Figure 1) and the pressure gauge(P in Figure 1). 

Find the most economical diameter of sch 40 commercial steel pipe that would be needed to transport a petroleum fraction with a viscosity of 60 cP and SG of 1.3 at a rate of 1500gpm. The economic life of the pipeline is 30 yr, the cost of energy is 0.08/kWh, and the pump efficiency is 60%. The cost of pipe is 20 per ft length per inch ID. What would be the most economical diameter to use if the pipe is stainless steel, at a cost of 85 per (ft in. ID), all other things being equal ... 

The most complete set of overpressure measurements was obtained by Enger and Hartman in the Shell Pipeline study. The data were collected using a spill tank 1.5 m deep and 2.1 m in diameter. The tank was made of 6.3-mm mild steel plate with 12-mm-diameter circumferential reinforcing rods spot-welded to the exterior. The capacity was 5.3 m, but during the tests the water depth was held constant at 1 m (3.8 m ). The LNG was contained in a 0.13-m Dewar made from 6.3-mm mild steel with a stainless steel inner liner. The annulus was evacuated. When spilling, the Dewar lip was about 0.75 m above the water surface. 

Fittings, pumps, and pipelines can be made of certain types of stainless steels which can be allowed to remain in contact with hydrogen peroxide for relatively short periods, i.e. a few days. 

Pipelines for the transmission of water for manufacturing or final rinse and other liquid components shall be constructed of welded stainless steel (nonrusting grade) equipped for sterilization with steam, except that sanitary stainless steel lines with fittings capable of disassembly may be immediately adjacent to the equipment or valves that must be removed from the lines for servicing and replacement. 

Starches often contain a substantial amount of salt (sodium chloride or sodium sulfate) as a residue from the modification process. Small quantities of salt in a hot starch dispersion will attack low-grade stainless steel and can cause severe corrosion of tanks, pipelines and coating application equipment. The salt content should not exceed 0.2% or 2000 ppm chloride. 

The petroleum feedstocks that contain sulfur as an impurity are handled under ambient conditions in carbon-steel tanks and pipelines where the corrosion attack by sulfur is less severe. In the desulfurization step, vaporized feedstock is processed at 400°C in the presence of hydrogen sulfide (H2S) and carbonyl sulfide (COS) - both of which are highly corrosive. Stainless Steels (SS) 304, 316 or 321 (for the fired heater) are used as the material of construction for various pieces of process equipment in this section of the plant. Equipment failures occur because of external corrosion and thinning of fired-heater coils and interior deposition of carbon from coking which leads to overheating. Fuel-gas lines, that contain hydrocarbon vapors and H2S, should be constructed of SS 304 and heat traced to avoid condensation88. 

The corrosivity of soils also depends upon the oxidation-reduction potential as classified by Booth et al.15 The classification scheme of the corrosivity of soils is given in Table 4.4b. Macrogalvanic cells are formed in underground pipelines due to foreign structure the combination of new and old pipe dissimilar metals (stainless steel and carbon steel) differential aeration dissimilar soils and stray currents. All these lead to localized corrosion of underground pipelines. 

The damage caused by corrosion is of two general kinds aesthetic and engineering. An example of the former is the development of rust spots on so-called stainless steel cutlery. Although rust, which is just a mixture of oxides of iron, is not harmful in any way, one would not like to eat with a rusted fork or spoon. Examples of engineering damage due to corrosion are countless. From car bodies to pipelines to electronic components almost everything must be protected and... 

Hydrochloric add Nitric add Dissolves most water scales and corrosion products Dissolves most water scales and corrosion products On boilers, heat exchangers, pipelines, etc. On stainless steel and aluminum Corrosive to steel temperature must be below 175T Cannot be used on copper and ferrous alloys... 

Pipeline transportation of liquid hydrogen is realized on a small scale and short range. Stainless steel is usually taken for the inner line with low heat conduction spacers as a support in the vacuum jacket. The Kennedy Space Center in Florida uses an LH2 and LOX pipeline of 500 m length with an irmer pipe diameter of 0.15 m. Flow rates achieved are up to 250 LH2 per minute and 100 m LOX per minute, respectively [12]. Transfer is realized by applying pressure, no pumps. Major concerns besides heat leakage is the mechanical stress imposed on the irmer line due to contraction / expansion, pressure oscillations upon cooldown, or two-phase flow. 

Engineering Design Features. Equipment such as pumps and motors have been designed for outdoor exposure pipelines are well insulated and weatherproofed, jacketed or steam-traced to take care of widely fluctuating temperatures. Weather-resistant metals, materials, and finishes (stainless steel, plastic coatings, impregnated wood, etc.) are significant factors. 

Sample probe for removing a representative sample from the pipeline. Usually the probe is a length of 1/ 4 stainless steel tubing extending into the pipe approximately 1/3 of the pipe diameter. By sampling from... 

---