Buried SS Piping for High Pressure Water

[jartgo]

I was just reading with interest a post in this forum concerning corrsion of buried stainless piping for hydrogen.

I have an application where I need to convey water from a pressure washer (at 1500 psi) for about 300 feet underground (approx. 5 feet deep), between the pressure washer pump and the point of use. Pressure in the line will fluctuate to the extent that the pump cycles on and off. All power lines in the vicinity are above ground.

The line will run under a concrete slab for about 100 feet, making access after construction very difficult. I had considered placing the SS piping in a casing underneath the slab, but have since decided that's probably overkill for this application.

I had assumed I would specify 316 ss for the carrier pipe. I chose ss because I couldn't find anything that would handle the pressure, if there are other options, please advise.

Any recommendations for reference reading or suggestions of how this construction should be specified? What other questions would I need to answer in developing an acceptable solution?

 

[jartgo]

As additional information on the previous post (I couldn't figure out how to edit the original post), the soils are this site are relatively sandy, and the 5 foot depth may be right at or below the water table for limited times during the year.

 

[metengr]

jthompson;
Based on your original post, I would specify construction of this high pressure water line to ASME B31.1. This is a recognized Piping Code that provides rules for design, fabrication (welding) and inspection.

The line will run under a concrete slab for about 100 feet, making access after construction very difficult. I had considered placing the SS piping in a casing underneath the slab, but have since decided that's probably overkill for this application.

I disagree. If you are going to run this line under concrete and in soil, you need to be sure that exterior corrosion is not a factor due to the cost of trenching to make repairs. I would use a casing to encapsulate the stainless steel water line.

 

[SJones]

NACE SP0169

NFPA 24 might also provide some useful background considerations.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[EdStainless]

People use dual containment systems both for leak protection and piping protection. This is a lot more secure than coating and CP.
In your case a plastic pipe of suitable strength for the ground loads would be fine for the outer pipe. People make plastic 'spiders' that are used to keep the inner pipe centered and not laying against the outer one.
Make sure that there is enough slope that any moisture that collects in the containment pipe will run to one end where you have a way to pump it out.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[jartgo]

Ed,
I'm familiar with the spiders and casing, but only for straight runs in a bore and jack scenario. I'm wondering how to address the bends, which are required to make this pipe run. My first thought is that I could turn the stainless carrier pipe in a manhole, but thought there might be something a little easier or cheaper? Although a manhole would facilitate regular inspection of the piping. Anyone have any other thoughts? This is really outside my area of regular practice. Thanks for the info.

 

[jartgo]

I have a spec for high pressure air piping which references B31.1 throughout. I could almost replace the word air with water in this spec and it sounds pretty good, however, I'd feel more comfortable if I could see a spec for high pressure water piping. Can anyone point me to a reference specification for stainless steel high pressure piping?

 

[SJones]

Select an appropriate piping specification from Process Industry Practices PIP PNCM0002 Piping Material Specifications Line Class Index.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[jartgo]

thanks, I see on the list that it only goes to ASME press. class of 1500. Since my working pressure is 1500, I'd be more comfortable with a higher pressure rating...although I could probably back the pump down a bit to 1200 or so if necessary.

My next question (which I think may be a silly question, but I'm going to ask it anyway), does the bured piping need blocking and restraints for water hammer scenarios? I'm guessing no, since the joints will be welded.

Last question, who should I call for assistance with this type of design? A mechanical engineer? This piping is a very small piece of a larger civil project, but the high pressure piping is not something I'm familiar with. Although I'm getting there.

 

[SJones]

Class 1500 does not mean 1500 psi maximum! At room temperature, the 316 will be rated to 248 bar a.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[metengr]

jthompson;

Last question, who should I call for assistance with this type of design? A mechanical engineer? This piping is a very small piece of a larger civil project, but the high pressure piping is not something I'm familiar with. Although I'm getting there.

Since the last question above was left unanswered, my recommendation is yes, hire the services of a piping engineer or firm that performs this type of engineering practice. Even small aspects of a project can result in overall failure of a project.

 

[jartgo]

Will ASME B31.1 list the various pressure ratings for the various pipe classes and types? I've order what I thought was B31.1, but it turned out to be only the addenda...the spec itself is $315...not a huge problem but I'd like to know what's in it before purchasing it.

 

[jartgo]

After some other conversations and recalling from my previous life building hydraulic hoses at an equipment dealer, I'm just going to use flexible hose which will run in a conduit to the termination point. This will allow them to pull the hose completely out if there's a problem and push a new hose back in with relative ease.