Inquiry 9

[Abeerj]

Hello,

I want to know when we use welded valves or flanged valves with underground pipeline , what standards guide me to what is suitable.

Thanks in advance

 

[pennpiper]

Rule #1 - Never put Valves underground
Rule #2 - If your commodity is Fire Water then use Extended Stem Valves
Rule #3 - If your commodity is anything other than water place the valve above ground or in a valve box (so it can be inspected for leaks and repaired)
Rule #4 - If your Pipeline will be Pigged then place your valves above ground with 'Pig Sigs' before and after the Valves
Rule #5 - Remember Rule #1


Sometimes its possible to do all the right things and still get bad results

 

[BigInch]

Pipeline rules.
1) Always put valves underground, or under water.
2) If the valve has a flange, use a flange protection kit.
3) Don't use a valve box. It just gets full of water, snakes or rats. If it leaks it's full of gasoline or natural gas.
3) Pig sigs have extensions, which are also available for valves when you put them underground.
4) If you connect to an underground pipeline that has an existing flange, use a flange too.
5) Remember rule 1


you must get smarter than the software you're using.

 

[Abeerj]

Thanks a lot for your answers.
I should have mentioned that the pipeline is for petroleum products ( Gas-oil,gasoline ...).
API 6D didn't mentioned any rules ...
I'm in need of any Standard.
Thanks again

 

[BigInch]

ASME B31.4 This code (as do most) only tell you what you must do. Anything else you can do safely, or otherwise demonstrate is safe in your particular situation, by test, calculation, by experience, or however else you can justify, is allowed.

Buried valves, or flanges are not prohibited.
Valve boxes, or vaults, are not prohibited. Many companies prohibit valve vaults in their standards and some require them.
If you believe it is safe to bury your pipeline, valves and flanges included, it is not prohibited.


you must get smarter than the software you're using.

 

[TD2K]

< I'm in need of any Standard >

Standards are not design cookbooks, they are minimum technical requirements. You have to decide what makes sense in your case. Design guidelines will give you issues to consider but you still need to evaluate what makes sense in your case.

Pennpiper is quite right that for a plant you really want to avoid buried valves and I don't even like buried piping. Sometimes you can't avoid it such as firewater main isolation valves or main cooling water lines, oily water sewers, etc. IN those cases, you need to evaluate the pros and cons of installation options and decides which makes sense for your installation.

BigInch is also correct that for pipelines, a different set of "rules" is common.

At the end of the day it's your responsibility what you decide to do. You can't just say "well, standard/practice/xxxx told me to do that it way" and that covers your butt.

 

[Abeerj]

Thanks all for your answers.

 

[OffshoreTrevelyan]

Hi,

With an MSC in Pipeline Eng, plus 15 years of working on pipelines. BigInch is correct (mostly) use ASME B31.4 (liquids) or B31.8 (gas). Block valves above ground outside controlled areas are a significant risk. In regards to valve pits depends on the carrier fluid (big no for heavier than air gases) and the natural environment, you'll need to use engineering judgement.

 

[LittleInch]

Not unsurprisingly I agree with BI, but to answer the actual question from the OP - many people now look at the location and product when deciding whether to use welded valves in place of flanged valves.

Underground, not in a pit (quite normal) use welded connections preferentially - the corrosion risk from flanges is too big. Even if in a pit, welded is better to prevent any leaks in a confined area. To maintain or replace this valve you'll need to blowdown or drain the pipeline anyway so flanging it doesn't really help.

Above ground - first valve, especially if it's gas - welded. Any leak on the flange needs the entire pipeline to be blown down to fix it. Sometime this is welded one side and flanged on the plant side.

Most other A/G valves - mainly flanged just because it is easier to remove unless you've got something quite nasty in there that you really really don't want any fugitive leaks from.

There will be company specifications and personal preferences that guide your decision, but no specific code or standards AFAIK.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

There's hundreds of flanged, tee-type, blinded, future tie-ins left out there laying on the Gulf of Mexico mud. We used to leave one almost every couple of blocks when routing around, near or through a hot play. When connecting a new platform, we seldom had to go more than 5 miles to find one. Flange bands; corrosion protectors; lots of heavy grease.

Actually a bit more like 35 years.
300 ft was deep water back when I started this.
I see pipelines in my sleep now.
Even dream catchers don't work.

 

[BigInch]

BTW I've got hundreds of stations and main line block valves located on Google Earth.
All you can see is the handwheels and blowdown stacks.
Compressor stations, pump stations, all gas valves and piping .... buried.

 

[BigInch]

BTW I do (mostly) agree with Pennpiper, for non-pipeline work ... and for above ground pipelines.

 

[LittleInch]

I agree that buried and submerged flanged connections abound in the pipeline world and in many cases are fully justified, but on a risk basis and if there is a free choice, then welded is better for buried applications.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way