Subsea Pipeline(DNV) Repair, Maintenance, corrosion prevention method

[UJJ]

Dear All.

I'm writing to inquire about repair methods for long-distance subsea pipelines designed according to the DNV Code.

The pipeline in question is currently covered by protective rock armor, and internal corrosion has been deteced in certain areas based on IP inspection results.
It has been confiemd that theses areas are located more than 2.5 kilometers away from the shore.

Given this situation, it is deemed challenging for personnel to directly access the pipeline for wleding repairs.
Therefore, I would appreciate it if you could provide information on appropriate repair methos and corrosion prevention measures
that coule help extend the service life of the subsea pipeline.

Thanks.

 

[SJones]

1. Has the integrity assessment fully confirmed that a repair intervention is absolutely required?
2. Transported fluid?
3. Pipe diameter and wall thickness?
4. Steel specification and grade?
5. Corrosion is internal, external, both?

DNV-RP-F113 Pipeline subsea repair

This recommended practice (RP) applies to fittings used to repair and tie-in submarine pipelines.

www.dnv.com

 

[UJJ]

1. Has the integrity assessment fully confirmed that a repair intervention is absolutely required?

-> I'm conducting FEA/FFS Analysis. But, according to the average corrosion rate calculated according to the inspection results, it is predicted that many corrosion areas exceeding the MRT in the DNV Code will occur within a few years.

2. Transported fluid?

-> Crude Oil

3. Pipe diameter and wall thickness?

-> 42inch O.D. and Nominal 17.5t

4. Steel specification and grade?

-> API 5L X65 SAW PSL1

5. Corrosion is internal, external, both?

-> Only internal Corossion is dominant at the bottom side of pipeline. It seems that under deposit corrosion has occured.

DNV-RP-F113 Pipeline subsea repair

This recommended practice (RP) applies to fittings used to repair and tie-in submarine pipelines.

www.dnv.com

 

[LittleInch]

Subsea pipelines and similar normally come with a manual which has already looked at tall these issues and determined how to approach different damage or corrosion.

Corrosion prevention is also usually a feature of ongoing maintenece. Corrosion inhibitors are your key tool here.

Is this gas, opil or what?

Amount of corrosion will drive your options. Small isolated then you could probably clamp it. a few hundred metres and you're looking at replacement.

But first do your integrity assessment to DNV or similar integrity assessment methods to see how much life you have left or how much you need to de-rate your pipeline.

But subsea with probably concrete coating and rock armour is horrendously expensive to do repairs. I would start to seriously consider cost of replacement and tie in works.

 

[UJJ]

Subsea pipelines and similar normally come with a manual which has already looked at tall these issues and determined how to approach different damage or corrosion.

Corrosion prevention is also usually a feature of ongoing maintenece. Corrosion inhibitors are your key tool here.

Is this gas, opil or what?

Amount of corrosion will drive your options. Small isolated then you could probably clamp it. a few hundred metres and you're looking at replacement.

But first do your integrity assessment to DNV or similar integrity assessment methods to see how much life you have left or how much you need to de-rate your pipeline.

But subsea with probably concrete coating and rock armour is horrendously expensive to do repairs. I would start to seriously consider cost of replacement and tie in works.

Thank you for your reply. It's for for crude oil buoy system.
I'm doing a Level 3 FFS Assessment (API 579), but Is there other proper integrity assessment method for DNV pipeline?
Actually, there's no designated input factor for DNV designed line at API 579.