Minimum Pipe Wall Thickness

From the standpoint of mechanical strength, impact resistance, and corrosion resistance, some operators prefer to establish a minimum wall thickness of approximately 0.20 in. Thus, they establish the following minimum 

ANSI B 31.3 requires threaded pipe that is IM in. and smaller be at least Sch 80 and that 2 in. and larger be at lea.st Sch 40. 

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The specifications give the minimum pipe wall thickness, the pipe schedule and insulation requirements. 

Forged Steel Fittings, Socket-Welding and Threaded, requires that the wall thickness of the socket must be equal to or greater than 1.25 times the minimum pipe wall. 

For simplicity, the condition considers the conservative case where the pipe acts simply as a support. The normal practice is to solve all these equations simultaneously, then determine the minimum wall thickness that has strains equal to or less than the allowable design strain. Thus, the minimum structural wall thickness is dictated by the longitudinal tensile load. 

T = pipe wall thickness (measured or minimum per purchase specification) t — pressure design thickness, as calculated in accordance with para. IP-3.2.1 for internal pressure or as determined in accordance with para. IP-3.2.2 for external pressure tm — minimum required thickness, including mechanical, corrosion, and erosion allowances W = weld joint strength reduction factor per para. IP-2.2.10... 

T Pipe wall thickness (measured or minimum per purchase specification) mm in. 

For straight metal pipe under internal pressure the formula for minimum required wall thickness is applicable for ... 

Minimum Practical Wall Thickness for Thin Wall Pipe. 110... 

For straight metal pipe under internal pressure the formula for minimum required wall thickness is applicable for Do/t ratios greater than 6. The more conservative Barlow and Lam equations may also be used. Equation (10-92) includes a factor Y varying with material and temperature to account for the redistribution of circumferential stress which occurs under steady-state creep at high temperature and permits slightly lesser thickness at this range. 

Hubs have no minimum limit for h and go, but values of go < 1.5 tn and h < go are not recommended. For slip-on flanges as a first trial, use gi = 2 times pipe wall thickness. 

Decision criteria relates to the safety critical deterioration level. It is necessary to determine this level to be able to make appropriate decisions regarding further action. Usually a first basic intervention level is defined according to relevant codes, standards or internal company requirements. A minimum required wall thickness is usually determined due to a stress criterion and depends on allowable stress, design pressure, pipe dimensions and material strength. When deterioration beyond this basic intervention level is revealed through inspection, further actions must he decided. When the basic intervention level is reached, there may... 

The wall thicknesses of thermoset pipe are not defined in the same way as for thermoplastic pipe because key properties such as strength and stiffness depend not only on material but also on exact wall construction, which can vary not only among manufacturers but even with pipe diameter. The resultant pipe wall thickness will generally be set by the performance requirements of the pipe. Some standards set minimum values for wall thickness. Thermosetting pipe may not be field-threaded. If the pipe is to be joined by threading, it is available with factory-apphed molded threads. Threaded adapters are also available. 

An optimum layout is arrived at, based on the requirement of flexibility to accommodate thermal expansion and the availability of space in the cold pool and compactness. The optimized layout consists of a short straight portion connected to a single curvature bend having a radius equal to 945 mm (1.5 times diameter). Stress analysis has been carried out for an internal pressure of 0.8 MPa and seismic loads imposed at the nozzle in the horizontal direction (peak value of 20 t under SSE). Analysis shows that the maximum Pm and (Pm+Pb) values are 76 and 80 Mpa, respectively, for the pipe wall thickness of 8 mm. These values are less than the primary stress limits of RCC-MR, 104 and 156 Mpa respectively. Considering the possible wall thinning during fabrication of the pipe bend, a plate thickness of 10 mm is used for the manufacture of the pipes, ensuring the minimum requirement of the wall thickness of 8 mm after fabrication. 

A number of sensitivity studies have been performed which investigate the effects of changing piping wall thickness, secondary support stiffness, and structure material and temperature on the ASME primary and primary plus secondary stress limits discussed above. A summary of the cases run is listed In Table 9-32. The primary stresses are only evaluated for the wall thickness study, because the primary stresses are not dependent on the other parameters studied. For all of the results tables, the minimum, average, and maximum stress values refer to the minimum, average, and maximum stress Intensity values at all of the element nodes evaluated in the model. It is presented in this form to better comprehend the distribution of stress values. 

In Eqn (11.1), Puve is the internal pressure in the pipe at the time of the repair application, Ec and Eg are the composite and the steel module of elasticity, is the remaining pipe wall thickness, tmin is the minimum required thickness of the composite layer, D is the pipe diameter, P is the design pressure and finally is the composite allowable strain. The only difference between the two codes is the definition of s—ASME PCC-2 identifies it as the specific minimum yield stress while ISO 24,817 recognizes it as the pipe allowable stress. 

The wall thickness selected varies with the service and material. Carbon steel coils are often made from schedule 80 or heavier pipe to allow for corrosion. When stainless-steel or other high-aUoy coils are not subject to corrosion or excessive pressure, they mav be of schedule 5 or 10 pipe to keep costs at a minimum, altliougli high-quahty welding is required for these thin walls to assure trouble-free seiwice. 

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