Excavating around in-service pipeline for rehabilitation project 3

[siavash1111]

We have 15 KM in service oil pipeline coating rehabilitation project to replace old coating with a new .we do excavating around the pipeline with excavator to expose pipeline . We have many problems during excavating . Such as human error , surface damage to a pipeline caused by contact of excavator tooth (dent , gouge , … etc ) .
Can anyone advise whether there is a machine that can dig around the pipeline without any damage?
In practical field how many is maximum span for 8” in service oil pipeline? is there any standard for temporary support and span ?

 

[zdas04]

You are replacing the exterior coating on 15 km of pipeline? If I was a betting man I would bet long odds that there is no way you are going to dig it up with "excavator" equipment without a major leak.

If I got stuck with that horrible job, I would use a track hoe to dig to within 12-18 inches of the pipe and use a HydroVac to actually uncover the pipe. SLOW work, but safe.

An 8-inch line full of oil is pretty heavy. A stress analysis would probably limit you to about a joint of pipe suspended at a time. I hope you are using shrink sleeves instead of tape (you don't have to underdig as far to slip a sleeve under the pipe). I'd also dump the HydroVac truck back into the ditch to try to get some flow support and leave fewer voids under the pipe.

Good luck with this.

David

 

[BigInch]

Working on "in service" line with excavation equipment. OMG!
At least reduce pressure and get the hydrovac zdas recommends, or do manual excavation of the last 0.5 m

What would you be doing, if you knew that you could not fail?

 

[brimmer]

I can't see how you would complete 15 km of coating rehab without taking the line out of service in any kind of reasonable time frame, it would take you years. You would have to have an incredible number of back hoes, hydrovacs, etc. essentially excavating one joint at a time. I have been involved in large scale projects like this, 30 miles, but the lines were always taken out of service, pulled from the ground and everytihng done in-line (coating removal, blasting and recoating). I also have been involved in projects where 1/4 mile sections were done in service and it takes a couple months. And yes, it was done with a live line and excavating equipment, yes there was a pressure reduction and detailed excavation procedures (no hydrovac, some hand digging in close proximity to pipe). We certainly did not use shrink sleeves to recoat for this, I can't imagine how many shrink sleeves it would take, how many would be applied incorrectly and how long it would take. A far better option for coating larger sections of pipe is 2 part epoxy, spray grade.
As far as span, there are guidelines in one of the API codes, I just can't remember which one. Typically I have seen 1 joint length done at a time (approx 40 ft) in these types of projects. You could get skids and use them as you wish for pipe support, and simply move and come back and coat the areas where these were sitting at the time of coating before backfill, not a big deal.
When we looked at cost comparisons, it was cheaper to build a new pipeline than do coating rehab projects if it was smaller diameter, the pay off came for larger diameters, say 36 inch and greater, that these types of large scale projects were cost feasible.