Seal weld

When both components of a threaded joint are of weldable metal, the joint may be seal-welded as shown in Fig. 10-130. Seal welds may be used only to prevent leakage of threaded joints. They are not considered as contributing any strength to the joint. This type of joint is limited to new construction and is not suitable as a repair procedure, since pipe dope in the threads would interfere with welding. This method provides tight joints with a minimum of welding labor. When threaded joints used to join materials with widely dinerent coeffi-... 

Steel forged fittings with screwed ends may be installed without pipe dope in the threads and seal-welded (Fig. 10-130) to secure bubble-tight joints with a minimum of welders labor. They are not subject to deformation by pipe wrenches, and such couplings, bushings, and plugs are often used with the screwed fittings below. 

Screwed joints which are intended to be seal-welded shall be made lip without any thread compound. 

Welded Tube Joints When suitable materials of construc tion are used, the tube ends may be welded to the tube sheets. Welded Joints may be seal-welded Tor additional tightness beyond that of tube rolling or may be strength-welded. Strength-welded Joints have been found satisfactoiw in veiy severe seivdces. Welded Joints may or may not be rolled before or after welding. 

Plugs installed to facilitate pressure testing should be welded in position. However, it is bad practice to seal weld over an ordinary screwed plug. If the thi ead corrodes, the full pressure is applied to the seal, A specially designed plug with a full-strength weld should be used. 

In the Sundyne Canned Motor design, the entire outside of the motor is enclosed in a secondary leakage containment shell or can. Primary leakage protection is provided by corrosion resistant liners which are seal welded and 100% leak checked to assure that pumped fluid does not contact the stator windings or rotor core. There is no shaft protrusion to seal and thus no seals to leak. 

Proper condensate removal is important. An inverted split cup inside the shell, with the upper capped end above the nozzle and the lower open end -in. above the bottom tubesheet, should be used to cover the oudet nozzle. This can be made by splitting a pipe that is one size larger than the condensate oudet down the centerline. In this case, a 2-in. split is adequate. This cup must be fully seal welded (not tack welded) to force condensate down to the -in. clearance above the bottom tubesheet. A common error is to allow 6 in. or more above the tubesheet for the centerline of the condensate oudet. In this case, 6 in. of tube is 10% of the surface. If the cup is not used, add 10% more tubes to correct for the dead liquid space near the bottom. This is in addidon to the 10% safety factor. 

Figures 10-7, 10-7A, 10-7B, and 10-7C illustrate the general arrangements of most manufacturers, although several variations of plate flow pattern designs are available to accomplish specific heat transfer fluids temperature exchanges. Also, the gasket sealing varies, and some styles are seal welded (usually laser) to prevent cross-contamination. Note that Figure 10-7C has no interplate gaskets and is totally accessible on both sides, yet easy to clean.

By eliminating the crevice using the recently developed technique of seal welding the tubes to the back of the tubeplate (Fig. 9.1k). However, this would add markedly to the cost of the unit. 

Packing glands or seals on pumps and compressors Pipe flanges, fittings and valve stems Threaded fittings that are not seal-welded Sample stations with an air break Manways and piping connections to vessels Piping to equipment connections... 

Seal welds shall cover all exposed threads. Seal welding of threaded joints shall not be used for liquid hydrogen service. 

Seal Welding. Seal welding taper-threaded joints should be considered for hydrogen gas inside buildings. Taper-threaded joints shall not be seal welded unless the composition of the metals in the joint is known and proper procedures for those metals are followed. Thread sealants shall not be used and the weld material shall cover the full circumferential length of the thread. 

A333 Piping connections ASSEMBLY C 1 A threaded B socket welded C seal welded Z. other... 

B014 Secondary piping seal welded SEC PI SEW c 1 1 yes (true) 0 no (false)... 

Steel forged fittings with screwed ends may be installed without pipe dope in the threads and seal-welded (Fig. 10-133) to secure bubble-tight joints. 

Eillet weld includes socket and seal welds, and attachment welds for slip-on flanges, branch reinforcement, and supports. 

All joints, including deck plate to structural members, shall be continuously seal-welded to prevent crevice corrosion. Stitch welding, top or bottom, is unacceptable. 

If these ferrules fail, or if the tubesheet overheats, the ends of the tubes will pull away from the tubesheet. The result is called a roll leak. Boiler feedwater will blow out of these roll leaks. Rerolling and seal welding the ends of the tubes, while difficult, is then the only way to stop such leaks. 

Special tests not specified by U.S. regulatory agencies were conducted to simulate expected service conditions. Dummy secondary capsules of the SR-Cf-100 series were subjected to internal and external pressures far in excess of pressures expected under the most adverse industrial service conditions. The special tests that successfully demonstrated the integrity of source construction and the seal welds were ... 

Welding Control. Plugs in the inner and outer capsules for the sales packages and industrial sources are seal-welded with an argon-shielded or helium-shielded tungsten electrode DC arc. The capsule is rotated under the automatically controlled arc to produce a minimum weld penetration of 1.27 mm. Each weld bead is visually inspected by periscope or by Questar telescope, and imperfectly formed welds are rejected. Weld quality is controlled by periodic metallographic examination of dummy capsules welded in the in-cell equipment. 

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