Welding pressure dependence

Radiographic tests are made on pipeline welds, pressure vessels, nuclear fuel rods, and other critical materials and components that may contain three-dimensional voids, inclusions, gaps or cracks that are aligned so that the critical areas are parallel to the x-ray beam. Since penetrating radiation tests depend upon the absorption properties of materials on x-ray photons, the tests can reveal changes in thickness and density and the presence of inclusions in the material. 

Caution. Crimp welds cannot dependably withstand the necessary pressures. A steel or Inconel tube furnace liner is recommended as partial protection against possible explosion hazard. It also serves to smooth out temperature gradients. 

Resistance to microfissuring is strongly affected by plate structure it is excellent in a plate with fine and fibrous structure, as shown in Fig. 1. Because of severe safety requirements for LNG storage tanks, the quality of the majority of welds is specified to be monitored by ultrasonic inspection. The accuracy of ultrasonic inspection of weld defects depends mainly on the ultrasonic characteristics of the base metal, in which noises and attenuations are important. Distance amplitude correction curves, obtained in accordance with Section VIII of the ASME Boiler and Pressure Vessel Code and NV Rules, are shown in Fig. 1. Since the evaluation level is 20% of the reference level (R.L.), it is difficult to detect defects unless the noise level is below 20% of R.L. at every node. Noises and attenuations of ultrasonic responses increase with coarsened plate structure, and in plates with very... 

The overall injection profile divides into two distinct sections the injection and the packing (holding pressure) sections. The injection section is primarily speed-dependent, and packing is pressure-dependent. The point in the overall cycle at which the change is made from the one to the other can often be critical, as we saw in the case of the spool-end moulding in forming satisfactory welds at the outer rim of the product. 

Weld lines occur when plastic melt flowing from two different directions join together. Such is the case if the material has to flow around a metal insert in the cavity (for moulding a hole) and join on the other side. The strength of the weld line depends upon the melt temperature and pressure at that point. Since the melt pressure in the SF process is very low the weld could be of low strength especially if the melt has to flow a long distance in the cavity and consequently cooling somewhat. A weld line in a... 

Weld line Weld or knit fines where two parts of a melt join while flowing into the mold cavity can result in problems. The quality of the weld depends on the temperature of the material at the weld point and the pressure present in the melt after flowing from the gate. The higher the temperature and pressure, the more complete the weld and the better the product performance and appearance. Bringing the material to the weld point at a higher temperature and pressure requires rapid filling of the mold cavity (Chapter 3, BASIC FEATURE, Weld Line). 

The correct form to use for a given joint will depend on the material, the method of welding (machine or hand), the plate thickness, and the service conditions. Double-sided V- or U-sections are used for thick plates, and single V- or U-profiles for thin plates. A backing strip is used where it is not possible to weld from both sides. Lap joints are seldom used for pressure vessels construction, but are used for atmospheric pressure storage tanks. 

These recent tests were conducted at applied stress levels similar to those that might be experienced by ASME Section Vm, Division 2 vessels. Test exposure times exceeded 50,000 hours depending on applied stress and temperature. The test specimens were from weldments of thick section plates and represented base metal, weld metal, and heat-affected zone. Detrimental effects of hydrogen were found down to the Figure 1 limit of 850°F (454°C) at 2000 pounds per square inch absolute (14 megapascals) and 3000 pounds per square inch absolute (21 megapascals) hydrogen partial pressure. 

The amount of hydrogen partial pressure reduction depends upon the materials and the relative thickness of the cladding/ weld overlay and the base metal—the thicker the stainless barrier is relative to the base metal the better.32 Archakov and Grebeshkova33 mathematically considered how stainless steel corrosion barrier layers increase resistance of carbon and low alloy steels to high temperature hydrogen attack. 

---