DISADVANTAGES OF OTHER SHROUDING METHODS

REMOVABLE METAL SHROUD / METAL LINE

• Requires couplings at each bend to allow assembly (excessive number of parts and leak paths).

• Requires large bends and large shroud diameter.

• Line and shroud are only grounded to bulkhead, not to each other.

• Difficult to provide support to inner line.

RUBBER SHROUD / METAL LINE

• Shrouds are prone to damage (mishandling, dropped tools, slipped screwdriver).

• Small leaks are difficult to isolate.

• Shroud can be clamped or collapsed around line, blocking drainage.

• Climb and descent pressure cycling fatigues and cracks shrouds.

• Shrouds can not be used above operating pressures of 30 psi.

METAL OR RUBBER SHROUD / FLEXIBLE LINE

• Requires very large bends.

• Very heavy.

METAL SHROUD WELDED OVER METAL LINE

• High cost and labor intensive.

• Requires 100% x-ray inspection.

• High scrap rate.

• Welds are inherently less reliable.

METAL SHROUD / METAL LINE (FORMED WITH HOT WAX, CERROBEND, SAND OR SHOT FILLER)

• Difficult to keep tubes concentric when filling and bending.

• Impractical to manufacture long tubes with many bends as scrap rates become intolerable.

• Difficult to remove filler material completely, creating a line contamination risk.

• Labor intensive to place spacers between the tubes for support after filler is removed.

• Risk of being burned by hot wax and Cerrobend (metal alloy) fillers.

• Metal alloy fillers contain lead and cadmium (serious health risk).

• Can't be used for tight bends without increasing wall thickness and/or using softer tube material
  (fillers do not flow and maintain their integrity well on the stretched side of the bend).

DISADVANTAGES COMMON TO MOST OTHER METHODS

• Require more time consuming, difficult and costly assembly in aircraft.

• Greater risk of damaging parts when assembling in tight or limited spaces.

• Require customized detail part design and manufacture from outside suppliers.

• Longer, more expensive design cycle time.