Crack Arrestors - long running brittle fractures

[tickle]

All

I would be grateful for advice on the use / availability of crack arrestors to arrest long running brittle fractures in a pipeline.

The pipeline of interest is old, transports natural gas, and is made from X42 steel with a low toughness and high ductile brittle transition temperature. I am trying to identify crack arrestors that would arrest long running brittle fractures. These arrestors would ideally be fitted to the outside of the pipeline (without welding - but beggars cannot be choosers). I am aware that clock springs, and others, are suitable for ductile fractures where the pipe wall deforms, but have not identified any suitable for brittle fractures.

Any assistance would be gratefully received.

Regards

Tickle

 

[C2it]

Are you suggesting that a propagating crack of any kind in your gas pipeline might be acceptable ?
Sounds like a disaster in the making to me.

 

[brimmer]

No C2it, I think tickle is suggesting that if there is a crack that fails by brittle mechanism on the line, there has to be a way to stop it rather than potentially let miles of pipe fail.

I would re-visit clocksprings, or other newer composite sleeves, as they were originally designed as crack arrestors (not sleeves to put over corrosion) to prevent what you are referring to. Others are tight fitting metal sleeves (with grouting), such as compression sleeves, which don't require welding to the pipe, but still two halves of the sleeve need to be welded together. I believe iron clamps may have been used as well, not sure of there effectiveness though.

 

[saplanti]

I think this and other kind of protections need to be planned during the design/construction stage, otherwise will be very costly or impossible. The brittle and ductile fracture needs to be considered in the design stage for the material selection of the high pressure gas pipelines Unfortunately other than Australian Standard AS 2885, the other pipeline standards do not directly ask this in the design. This requirement is hidden in ASME B31.4S, other local requirements and risk assessments, and mostly forgotten.

https://www.icheme.org/~/media/Docu...vention/Hazards Archive/XXI/XXI-Paper-046.pdf

Protection against external damage also needs to be thought. This will effect the the required toughness on the selected material and the acceptable/controlled ductile fracture length.

So covering one side of the problems will not reduce the risk as expected. Most of the damages are from the external machinery damages. In case the pipeline length is too long and the pipeline is running in the cities, putting new pipeline with new material with adequate toughness properties are much better solution.

I know this is not the answer that you would like to see here. In case you want to concentrate on your side application there are some references in British HSE guidelines:

http://www.hse.gov.uk/research/otopdf/2001/oto01038.pdf

http://www.hse.gov.uk/pipelines/resources/pipelinestandards.htm

 

[saplanti]

In my previous comment ASME B31.4S should be read as ASME B31.8S. It is my typing error.

 

[saplanti]

Please read the following document for critical defect length which is related to the toughness of the material:

http://www.igem.org.uk/media/220015/igem-td-2 draft for comment (igem-tsp-12-156).pdf

 

[saplanti]

http://www.penspen.com/wp-content/uploads/2014/09/comparison-of-risk-levels.pdf

 

[saplanti]

This is another one:

http://www.penspen.com/wp-content/uploads/2014/09/emergency-repair-system.pdf

 

[tickle]

Thank you to Saplanti and Brimmer for your helpful comments. You have both hit the nail on the head of the knowledge we have and what we are trying to achieve. There is always some possibility of an incident, and there is a need to reduce the consequence to reduce the residual risk.

Unfortunately, in my case, the knowledge on which the standards are based has developed over the last 40 years, whereas the steel of our pipeline has not (rather rude of it I suppose). Considering a failure (third party or otherwise) that leads to a rupture (as opposed to leak), the pipeline code requires the resulting crack be arrested within one or five pipe lengths depending on location. This gives a maximum length of pipeline failure and the potential damage.

As Saplanti suggests for an existing pipeline, we are trying to identify the residual risk to ensure that it is ALARP, and obviously one solution is to install a new pipe with new steel. Other solutions are in the installation of a crack arrestor. Clock springs look like they need further investigation and I will continue my questions with the company on their suitability for long running brittle fractures

Thank you once again.

 

[saplanti]

API 5L has been changed a lot on the fracture side with the latest versions. And standards and risk assessment procedures are asking for brittle and ductile fracture properties on the pipeline materials against possible incidents which may results with fatal explosion. I do not think the old piping material for the high pressure gas application will be risk free. Even if you provide crack arrestors this will not stop piping fracture against the external mechanical damages.

In long term you will see the benefit of replacing the pipeline with the new designed pipeline with suitable material.

 

[SJones]

40 years ago would have put the pipe in a period when the phenomenon had received attention and specifications adjusted accordingly. Can you evaluate, by fracture mechanics, at what size imperfections become unstable to assess whether you have a fighting chance of detecting them by inspection before they initiate a failure? Such an assessment might help to avoid frequent ILI and/or hydrotesting. In essence, is there actually a brittle fracture problem that requires fixing, and will ductile fracture considerations be necessary too?

Steve Jones
Corrosion Management Consultant

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

All answers are personal opinions only and are in no way connected with any employer.

 

[saplanti]

The following might help to understand the phenomena:

http://www.jfe-steel.co.jp/en/research/report/018/pdf/018-06.pdf

There are many discussions/articles available on Google about brittle and ductile fracture:

https://www.google.com.au/search?q=ductile+fracture+failure+on+

[ipelines&ie=utf-8&oe=utf-8&gws_rd=cr&ei=Cv4BV_i8JsbBmAXBgbjQBA#q=ductile+fracture+failure+on+pipelines&start=0

The material with right toughness is selected it is easy to control the defect (critical defect length)and the damage on the gas pipeline. Gas can leak but the fracture on the pipeline will be within the critical defect length, not be in a long distance and fatal, so it is manageable to repair easily.

 

[saplanti]

Additionally you can look at this article for the vintage pipeline:

http://primis.phmsa.dot.gov/gasimp/docs/integritycharacteristicsofvintagepipelineslbcover.pdf

My discussion point is on the high pressure gas pipeline. These pipelines are mainly with thin wall thickness and the stress is above %70 SMYS. However if the pipe hoop stress is around %20-30 SMYS on the pipeline your risk assessment approach might be different. The article above may give reasonable information on the vintage pipeline and their failure.