Piping exposed

For pipe exposed to wind velocities other than calm, use Figure 10-171 to determine a value for h, which can he much greater than the calm values of 1.8-2.1 Btu/(hr) (fT)(°F). 

Find the tensile load capacity of 5-in., nominal weight 19.5-lb/ft, steel grade E, premium class drill pipe exposed to internal drill pipe pressure = 3,000 psi and rotary torque T = 15,000 ft-lb. 

It should be noted that it is extremely difficult to predict service lives of buried pipelines from the results of controlled trials with small specimens, whether in the laboratory or in the field. For example a study on the comparative corrosion resistances of ductile and grey iron pipes carried out jointly by European pipemakers in 1964-1973 indicated a mean pitting rate of 0 -35 mm/y for uncoated ductile iron pipe exposed in a typical heavy Essex clay of 500-900 ohm cm resistivity for 9 years. This is clearly at odds with the rate of 1 mm/y normally found on a corroded service pipe from such a soil. The discrepancy appears to be due to the use of specimens that were only a third of a pipe length each and were buried separately. It may reflect the contribution of the total surface area of the pipe as a cathode to the corrosion current at the anodic area at the pitting site. 

To presume that thermal insulation is always necessary is false. For example, when cryogenic fluids arc transported from a supply suurce to a vessel, even in bright sunshine, it is usually most economical not to insulate the line at all. The reason for this Is twofold (I) lor the short time of transport the area of the pipe exposed to the surt is much smaller than the area that would be exposed if it were insulated and (2i the heat that would be in the insulation when the transport starts would have to be removed by the cryogenic fluid. The combination of these two factors often makes the use of insulation undesirable for this type of cold fluid transport system. Moreover, the rapid formation of ice crystals front moisture in the air constitutes a thermal insulation. 

Two different approaches for lifetime prediction are presented. The underlying lifetime limiting processes have been identified in two cases. Mathematical expressions of chemical/physical relevance were used for the lifetime predictions for PE hot-water pipes and cables insulated with plasticized PVC. Accelerated testing, extrapolation and validation of the extrapolation by assessment of the remaining lifetime of objects aged during service conditions for 25 years were successfully applied to cables insulated with chlorosulfonated polyethylene. Polyolefin pipes exposed to chlorinated water showed a very complex deterioration scenario and it was only possible to find a method suitable for predicting the time for the depletion of the stabilizer system. 

Fig. 2 presents the analysis based on OIT data and the linear extrapolation of these data to longer times. The time to reach depletion of the antioxidant system can thus be predicted even after relatively short testing times (see insert figure in Fig. 2). Data by Hassinen et al. (//) for the antioxidant concentration profiles taken from high-density polyethylene pipes exposed to chlorinated water (3 ppm chlorine) at different temperatures between 25 and 105°C followed the Arrhenius equation with an activation energy of 85 kJ mol (0-0.1 mm beneath inner wall surface) and 80 kJ mol (0.35-0.45 mm beneath the inner wall surface). It is thus possible to make predictions about the time for antioxidant depletion at service temperatures (20-40°C) by extrapolation of high temperature data. However, there is currently not a sufficient set of data to reveal the kinetics of polymer degradation and crack growth that would allow reliable extrapolation to room temperature.

An insulated cylindrical pipe exposed to convection from the outer surface and the thermal resistance network associated with it. 

C Consider an insulated pipe exposed to the atmosphere. Will the critical tadiiis of insulation be greater on calm days or on windy days Why ... 

The nature of interaction of magnetic fields with scale formation on solid surfaces (e.g. pipes) exposed to liquid flow is not understood fully at present. Retardation of scaling, reported by various experimenters [e.g. 54, 55, 121-123], has not been explained by a... 

For polypropylene at 130 °C, y = 0.1mm. At the higher temperatures in melt processing, y decreases, because the activation energy for oxidation is higher than that for diffusion. Consequently, the inside wall of a polyolefin pipe, exposed to air while the melt cools, only oxidises to a depth of about 10 pm if insufficient antioxidant is present. 

Example Above ground piping, exposed to direct sunlight in Houston, Texas)... 

While many requests deal with supply water heated by nearby industrial processes or pipes exposed to the... 

The simultaneous action of erosive wear and corrosion is called erosion corrosion. Erosion corrosion is often encountered in pumps and pipes exposed to turbulent flow in the presence of suspended particles. It also occurs in other situations, for example in incinerators due to ash particles that are entrained by the exhaust gas. The damage caused by the combined effect of the impingement of a liquid and of corrosion is sometimes referred to as impingement corrosion or impingement attack. 

The failures by SCC of welded Type 304 piping exposed to water at 289 C with 0.2-8 ppm of oxygen on boiling water nuclear power plants created a demand for a nondestructive method for detecting quantitatively the degrees of sensitization in these pipes. A nondestructive method was needed so that measurements could be made directly on the heat-affected zones of pipes on the plants. For this purpose, Clarke et al. [20] selected and applied the electrochemical potentiokinetic reactivation (EPR) technique. A cell was designed that could be attached to pipes. 

Excavate a 10-ft (3-m) section of pipe, exposing the entire circumference of the pipe so that the entire pipe can be reached for examination. 

Carbon steel piping exposed to low-pH water with SO2 or SO3 present is also subject to pitting. This has been noted on several sulfuric acid alkylation units. Type 316 stainless is recommended to resist pitting in this service. 

Hydrogen sulfide attacks steel rapidly and it can be assumed that bare or galvanized steel will not endure in outdoor ambient conditions where hydrogen sulfide is present. The use of galvanized or bare steel should therefore be limited. Steel structural materials or piping exposed to the atmosphere should be coated with suitable coatings for nearly aU exposures. 

Tests at Miami, Florida have exposed identical specimens by continuous total immersion and by intermittent immersion during high tide. The continuously immersed specimens tended to develop fewer but deeper sites of corrosion. Tests on pilings and pipe exposed above and below water have shown that increased pitting sometimes occurs at the waterline and in the splash zone. This most likely is the result of increased oxygen content near the surface, plus concentration effects due to partial drying in the splash zone. 

A common occurrence of surface film cell is found in older distribution piping systems where a section of pipe has been replaced because of corrosion damage. The new piece of pipe, exposed to the... 

A reduction in stabilizer concentration can take place in pipes as a protection mechanism against oxidation, migration, and extraction by water. The concentration profile of PE-MD pipe exposed to water internally and to air externally becomes asymmetric due to exposure. Figure 5.262 left. Maximum concentration shifts toward the pipe outer wall, because stabilizer reduction caused by extraction is higher on the inner pipe wall than reduction caused by oxidation on the outer pipe wall. If the same pipe is loaded both internally and externally by air, the concentration profile remains symmetric. Figure 5.262 right. A PB pipe exhibits a symmetric profile even under internal load by water and external load by air however, stabilizer concentration also decreases [191]. 

Figure 5.287 shows that the profiles for the viscosity index and the oxidation induction time i.e., degradation, of pipes in internal pressure creep tests is independent of internal pressure. One of two pipes exposed to 4 N/mm broke after 8,208 h, while the other one broke after 1,442 h, 3,720 h, and 13,690 h in the second case, the pipe was reinstalled and reloaded at 4 N/mm after elimination of the failure area [181]. 

BLEVEs (Boiling Liquid Expanding Vapor Explosions) A pressurized tank of VCM or associated piping exposed to an external fire may fail due to metallurgical weakening. Such failure may result in a catastrophic tank failure, a fireball and the potential for rocketing fragments. Relief valve overpressure protection will not prevent a BLEVE. 

Since parts subject to both tensile and compressive loading are frequently found in practice, a section of plastics pipe exposed to vertex loading will be studied by way of example below. Figure 7 shows the areas of the part subjected to primarily compressive and tensile stress for a relative pipe vertex drawdown of 6%. On the basis of the FEA model it can be seen that there are areas of the part that are subject to tensile stress and areas that are subject to compressive stress. 

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