Piping, Internal corrosion

Pipelines—oil, gas, water, wastewater Internal corrosion primarily at the bottom (6 00) position Dead ends and stagnant areas Low points in long-distance pipes Waste pipes—internal corrosion at the liquid/air interface Buried pipelines—on the exterior of the pipe, especially in wet clay environments under disbonded coating Aerobic and anaerobic acid producers, SRB, manganese and iron-oxidizing bacteria, sulfur-oxidizing bacteria... 

The required pipe internal diameter can be calculated based on the volumetric flow rate and a maximum velocity. The maximum velocity may be the erosional velocity or a limiting value based on noise or inability to use corrosion inhibitors. In gas lines it is recommended that the maximum... 

Borehole waters are generally very hard and cast iron pipes are still used because of the low internal corrosion rates permitted by the scaling which occurs naturally. Acidic waters cause graphitic attack on cast irons. 

The ends of pipe specimens should be closed to prevent internal corrosion. 

What if pipe ruptures due to internal corrosion, defective materials, or poor... 

Corrosion of the pipe wall can occur either internally or externally. Internal corrosion occurs when corrosive fluids or condensates are transported through the pipelines. Depending on the nature of corrosive liquid and the transport velocity, different forms of corrosion may occur, namely, uniform corrosion, pitting/crevice corrosion, and erosion-corrosion. Figure 3.8 shows an example of internal corrosion that occurred in a crude oil pipeline because of high levels of salt water and carbon dioxide (CO2). 

A large percentage of mains (57%) and services (46%) are metallic systems (steel/cast iron/copper), and corrosion is a major problem. For distribution pipe, external corrosion is the primary problem and internal corrosion has also been observed in some instances. The methods of corrosion monitoring on cathodically protected piping are similar to the methods used in the case of transmission pipelines... 

Major internal corrosion can occur in pipes made of cast iron, ductile iron, steel, galvanized steel, and cement-based materials. Table 3.3 summarizes the types of corrosion occurring in different piping materials and the possible tap water quality problems caused by them, as described by the AWWA Research Foundation in 1996 in a reference book on internal corrosion of water distribution systems (17). 

A large percentage (57%) of mains and services (46%) is metal (steel, cast iron or copper), and corrosion is a major issue. For distribution pipe, external corrosion is of primary importance, although internal corrosion has been noted in some cases. The methods of monitoring corrosion on cathodically protected pipe are similar to those in the transmission pipeline sector, including pipe-to-soil potential and coating surveys. One difference is that in distribution systems, leak detection is an acceptable method of monitoring for these pipelines without CP (nearly 15% of the steel mains). 

The most common failure modes of these pipes are uniform corrosion (both external and internal), graphitization, and pitting under unprotected corrosion scales. Loose tubercles may cause blockage of pipes. The corrosion control of loose particles is by the addition of corrosion inhibitors, which protect the inside pipe walls or internal lining of the pipe. Other protective linings are specialty cement mortars, epoxies, polyethylene, and polyurethane. 

The mechanism of material degradation in sewer pipes is similar to potable water systems. The internal corrosion may be more severe than in potable water because the wastewater is not clean. The winterizing treatments of roads are a source of chloride, which comes into contact with the pipe. Cement-based pipe experiences corrosion of reinforced steel. The corrosion control method consists of using thicker pipe walls, which provide for larger corrosion tolerance and a longer design life. 

Metal pipe Small leak Multiple leaks Large leak/rupture Internal corrosion External corrosion Clap or sleeve aronnd pipe or replace small pipe section Replace pipe section Replace pipe section Apply cement lining. Insert PVC tubing in pipe Evalnate structural integrity. If fit for service, then apply coating to protect metal and/or apply cathodic protection to rednce corrosion rate... 

Flow Lines Pipe and Internal Corrosion Duplex Stainless Steel Alloy... 

Visual examination and the metal ion content of the water samples shows internal corrosion of pipe in various locations in the hot water distribution system that compromises the quality of hot water. The internal pipe corrosion is because of the following factors or a combination of the factors. 

Interconnecting pits were observed inside the pipe in the ruptured area. The pits showed striations and undercutting features that are associated with microbial corrosion. A pit profile showed the chloride in the pits increased steadily from top to bottom. Sulfate-reducing, acid producing, general aerobic, and anaerobic bacteria were present in the deposits taken from two pit areas in the piece of line where internal corrosion was noted after the accident 630 m downstream of the rupture site. 

The RTR pipe structure is shown in Figure 8.5 where the glass fibers are filament wounded at a helix angle that is at 55° to 65° to the horizontal to maximize hoop and longitudinal stress efficiency. Glass fiber content is at a minimum of 45wt%. An internal corrosion resistant leak proof barrier liner is usually included that is not included in the stress analysis. 

Formation of black powder (BP) is one of the reasons of internal corrosion in pipelines. BP resnlts from chemical reactions between components of the transported gas (HjS and COj) and primarily the iron (Fe) portion of ferrous pipe alloys. In some cases, microbial action exacerbates the ongoing chemical process. The presence of water is key to supporting biological and certain chemical corrosion phenomena leading to BP. The formation of BP in pipelines may be mitigated by the following ... 

Internal corrosion in a gas pipeline may be detected by sophisticated methods such as intelligent pigging, which travels inside the pipe with the flow of the fluid and measures all information such as thickness loss, pitting, and other types of corrosion. 

FIG U RE 19.17 Equivalent current flow loop for internal corrosion protection of a pipe, where = anode potential (V vs. Ag/AgCl) Eq = potential on the pipe surface (cathode) (V versus Ag/AgCl) = anode resistance ( 2) Rs = resistance for current flow in seawater inside the pipe ( 2) Rc = resistance for current entering the pipe surface = resistance for current flowing in the pipe metal ( 2) and = total protection current in the loop (A) [5]. 

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