QUESTION
Can anyone tell me in which section of ASME B31.3 says that metallic flex hoses can not be used for permanent process piping?
In our company, we don’t have an in-house standard that covers use of flex metallic pipe. I checked two (US) oil & gas major companies and both prohibit the use of flex metallic hoses for permanent process piping.
Yes, I did look at table 326.1 and they list BS 6501, Part 1 as reference standard for flex hoses.
I also found:
“When flex lines are used in critical or hazardous service, the owner should have a high-integrity maintenance system that ensures the flex line is always in good mechanical condition. Flex hoses are more likely to experience catastrophic failure as compared to hard-pipe, and that’s one reason it’s generally unacceptable from a risk perspective to simply run-until-failure. it’s very difficult to implement any type of preventative maintenance testing that will accurately predict the life expectancy of a flex line. Consequently, good maintenance integrity programs typically call for a fixed time period at which the hose needs to be replaced.”
Next question will be : How often should these hoses be replaced? If you tell me to follow manufacturers recommendation, I’ll be changing them every 3 months!!!
REPLIES
moltenmetal
Oil and gas companies prohibit lots of things, some for good reasons related to the LONG design life of their projects, and others for not-so-good reasons. But that’s not the question you asked: you asked whether there were CODE rules preventing their application, and in B31.3 there are not.
Flex hoses, properly implemented, can be real problem solvers and can make piping systems safer. Compare the implementation risk of these against expansion joints of various kinds…But hoses too are often mis-applied, in particular when they are used improperly to replace an axial expansion joint. A hose where the overbraid has been slackened by axial compression is little more than an under-designed expansion joint.
Service life depends greatly on service conditions. Hoses contain thin parts which are highly worked, which makes them vulnerable to corrosion and corrosion-related embrittlement in particular. The nature, direction, magnitude and frequency of flexing is also important.