Steel braiding is used to reinforce flexible hoses that are intended for elevate

Question

Steel braiding is used to reinforce flexible hoses that are intended for elevated temperature and pressure environments, particularly for domestic and industrial hot water washing applications. The braiding covers an elastomeric tubing and provides the rigidity needed to contain 0.5 - 0.7 MPa of water pressure, yet maintain the flexibility needed for the activity. The elastomeric tubing is not designed to maintain the pressure boundary, but it is needed to provide the elastic properties required for the many washing endeavours. A number of unexpected failures of your flexible tubing product have been reported and the customers are expecting compensation for failed hoses that caused flooding of their facilities and the resulting damage to their infrastructure. The customers expected a 15 a lifetime for the hoses, the industry standard, not the 15 months they have experienced. Your product engineer has determined that the reported failures coincided with the start of a new roll of braided sheath. She also reported that the material met the quality control requirements and this was confirmed by an independent laboratory using a random sample from the roll. She has recommended that a failure analyst be contracted to identify the root cause of the failure and to recommend a path forward. All the failures occurred for hot-water washing applications. The temperature of the water was between 40 degree C and 60 degree C, and commercial detergents were used. The hoses were not immersed in the hot water baths, but were handled by wet and soapy hands. Before failure, the clients noted the hoses "felt" rough. The failures often occurred near the couplings. Upon removing the braiding an orange-brown stain was noted on both the braiding and the tubing. The tubing showed evidence of the stain several centimeters from the rupture, in the direction of the lowest point of the hose when it was in its resting position. The results of the investigation are reported in this document. You have been hired to assess the corrosion - determine the cause of the incident, explain the corrosion mechanism, and provide recommendations to prevent a reoccurrence. You are expected to deliver a 5-8 page report. The owner is busy and will reject any report with more than 8 pages of text. The report is to follow standard company guidelines (available in the Blackboard Content folder under Projects).

Explanation / Answer

Causes of Failure of flexible hoses : either improper component selection, incorrect assembly procedure, poor installation.The hose may be not inserted properly in the shell of the fitting during assembly. All the grips in the shell are used to hold the fitting the hose.The hose was exposed beyond maximum heaing temperature . The plasticizers in the elastomer that give the hose its flexibility may have broken down or hardened. Aerated oils cause oxidation to occur in the inner tube of the hose, which can cause the hose to harden. oxygen and heat can accelerate the hardening of the inner tube. Cavitation also may create the same effect.The hose may have exceeded its service life, as a result of a high number of pressure cycles or a continuous flexing of the hose in one area.

Recommendation to prevent a reoccurrence : Replace the hose assembly. Mark the cover of the new hose according to the catalog before inserting it into the fitting, then push the hose into the fitting until the end of the shell lines up with the mark. Reduce temperature of the fluid or replace the hose with one that has a higher qualified temperature rating. For ambient heat , install heat guards or shields and replace the hose assembly. Forhigh fluid temperature, evaluate the system design to improve its efficiency, or install a heat exchanger to reduce fluid temperature.Replace the hose assembly. Check for proper fitting usage and review instructions of the crimping machine being used including the proper tooling.

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