Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Are Underground flanges allowed per 31.3?
- Thread starter RNGtrw
- Start date
LittleInch
Petroleum
Your title says B 31.3, but the post says B 31.1. Which is it?
Either way I can't find any reference to a specific code requirement not to bury flanges, but there are many construction specifications or company guidance documents which don't permit this.
If you could provide some reference to the "posts" where this was seen then we might stand a chance of replying better.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Either way I can't find any reference to a specific code requirement not to bury flanges, but there are many construction specifications or company guidance documents which don't permit this.
If you could provide some reference to the "posts" where this was seen then we might stand a chance of replying better.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
I would not if the trench backfilled due to the restraining effect on the high temperature piping and difficulties in corrosion prevention.
Similar things can be considered for the plastic piping. In non-metallic piping flange connections you still need to use metal bolts and metal backing ring which may be effected by corrosion. The flange connections engages space in radial direction and this will be uncontrolled restraining location which is a bit unknown and may cause fracture due to stress concentration.
Having said these you may be able to use an undisturbed cavity (flange house similar to valve house) for the flange connection, this is acceptable. But you need to have attention in details which may cause more problem. I would not put any B31.1 piping in compacted trenches since the difficulties in operation and maintenance.
Similar things can be considered for the plastic piping. In non-metallic piping flange connections you still need to use metal bolts and metal backing ring which may be effected by corrosion. The flange connections engages space in radial direction and this will be uncontrolled restraining location which is a bit unknown and may cause fracture due to stress concentration.
Having said these you may be able to use an undisturbed cavity (flange house similar to valve house) for the flange connection, this is acceptable. But you need to have attention in details which may cause more problem. I would not put any B31.1 piping in compacted trenches since the difficulties in operation and maintenance.
LittleInch
Petroleum
The key question is whether and how the flange is protected from corrosion and damage when buried.
Flanges are a weak point in the piping system and burial makes it hard to spot any leaks. Protecting the sealing faces and bolts from corrosion is also very difficult over a long period of time.
But the codes are not design manuals or construction specifications. They tell you how to do something in a manner which works and provides a safe enough design without excessive cost.
They tend ot avoid saying don't do this or that as they can't cover every possible combination of circumstances.
There are millions of buried, bolted connections in existence worldwide. The vast majority work.
But dig one up and try and repair it or remove it and most of the time you need to cut it out or cut the bolts off.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Flanges are a weak point in the piping system and burial makes it hard to spot any leaks. Protecting the sealing faces and bolts from corrosion is also very difficult over a long period of time.
But the codes are not design manuals or construction specifications. They tell you how to do something in a manner which works and provides a safe enough design without excessive cost.
They tend ot avoid saying don't do this or that as they can't cover every possible combination of circumstances.
There are millions of buried, bolted connections in existence worldwide. The vast majority work.
But dig one up and try and repair it or remove it and most of the time you need to cut it out or cut the bolts off.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
goutam_freelance
Mechanical
I did not find any restriction on use of flanged joints in UG piping in ANSI/ASME but loads and stresses will be imposed on UG piping due to thermal expansion, soil weight and pressure forces etc. ANSI/ASME B31.1 Nonmandatory Appendix VII provides guidelines for calculation of such forces and stresses. The important force which is friction force with soil is calculated in ANSI using welded pipe joints. The forces and stresses will be more severe if you use flanged joints.
Therefore it will be prudent not to use flanged joints in UG piping if there is significant thermal expansion/contraction, e.g. for moderately high temperature piping.
In addition, the following are drawbacks for UG flanged joints:
1. Unless properly coated or otherwise protected flanges and bolts will be corroded
2. Bolts may loosen after some time due to thermal cycles etc. There is no way to check leakage (and so tighten the bolts).
3. Possibility of groundwater contamination from leaking joints.
Engineers, think what we have done to the environment !
Therefore it will be prudent not to use flanged joints in UG piping if there is significant thermal expansion/contraction, e.g. for moderately high temperature piping.
In addition, the following are drawbacks for UG flanged joints:
1. Unless properly coated or otherwise protected flanges and bolts will be corroded
2. Bolts may loosen after some time due to thermal cycles etc. There is no way to check leakage (and so tighten the bolts).
3. Possibility of groundwater contamination from leaking joints.
Engineers, think what we have done to the environment !
Why do you want to put flanged joints underground (in intimate contact with the soil) if you can avoid it ???
Explain why a concrete vault at the flanged joint is not acceptable
Why MUST you have a mechanical joint where it cannot be inspected or tested AND the potential for leakage is much higher than an all-welded system ?
What kind of service does the piping system perform ?..... What are the Design Temperatures and pressures ?
Explain why a tried-and-true proven underground mechanical system, like the MEGALUG Ductile Iron joining system will not work for you ?
MJCronin
Sr. Process Engineer
Explain why a concrete vault at the flanged joint is not acceptable
Why MUST you have a mechanical joint where it cannot be inspected or tested AND the potential for leakage is much higher than an all-welded system ?
What kind of service does the piping system perform ?..... What are the Design Temperatures and pressures ?
Explain why a tried-and-true proven underground mechanical system, like the MEGALUG Ductile Iron joining system will not work for you ?
MJCronin
Sr. Process Engineer
- Status
Similar threads
- Question
- Locked
- Question
- Question
- Locked
- Question