NDT Inspection on pipeline 2

[cpewhf]

Recently, I take part in a project and come across a problem on the NDT inspection. Usually, the 10% random RT for the buried pipeline is enough, but in this project, the 100% RT is required and it is mandatory. Who can enlight me to persuade them to convince that 10% RT is enouth.

Your valuable reply will be highly appreciated.

 

[ndeguy]

Your post is not so clear, but as you are posting on the API board then I assume this is a new construction line being built to API standards. What is your role?

API 1104 makes the extent of inspection a contractual issue, 8.1. Rights of Inspection "The frequency of inspection shall be a specified by the company" the "Company" being defined as the pipeline owner perhaps acting through an inspector or authorised representative. So read your contract and if you are contracted to 100% inspection then that is what you do.

Has a crawler RT company been contracted for the inspection?. If yes, then RollPac film will be wrapped around the circumference of the pipe and 100% panoramic inspection will give 100% coverage at one exposure (SWSI = Single wall, single image). Cycle time for crawler panoramic can be as low as a few minutes.

If this an in-service inspection of a buried pipeline, then RT is not feasible and you need to contact a pigging company for the inspection options - ultrasonic, magnetic flux leakage, guided wave.

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[cpewhf]

ndeguy, thank you so much for your quickly and valuable point. I am a designer for a buried crude oil transmittion pipeline. And puzzled to select how much percentage shall be applied to inspect the welding point. Because in my opinion the 100% RT is more expensive than 10% RT, and require more manpower. Concluding from your post, I think it have been taken account in the bidding.

Thank you again.

 

[BigInch]

100% is not unreasonable for pipelines in critical service, passing highly populated areas, environmentally sensitive areas, (many offshore pipelines require 100%) and whenever there is a belief that welding quality control is of high importance. 100% radiographing is more common than you think.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[theo1960]

I am also working on a big construction projec.

Approach is as follows.

10% RT testing has been specified. But under the condition there is adequate confidence.

Confidence:

Initially the constrcution contractor will need to apply a higher percentage wih a maximum of 100 %. Which after good experience can be gradually reduced to 10%.

If "10% + occasional random spot checks" from then onwards does not result in any rejections, then there is no reason for increasing above 10 %, else...

 

[ndeguy]

For such long-enduring and generally very profitable structures as pipelines, I dont understand the 10% philosophy. If a crew puts together 100 joints a day on a cross-coountry pipeline, thats 10 welds (unless 10% of EACH weld is specified). Who selects those 10 welds and more importantly neglects the other 90 welds? It will take a good bombing crew maybe actually 2 hours maximum to bomb 10 adjacent welds. What if its on a remote site, do they chill-out for the rest of the day? OK some poorboys as well maybe, but for the minimal extra cost of having 100% when the mobilization and equipment call-out charges have already been paid.

If the automated UT route is chosen there is better quicker feedback on the trend of weld quality and more likelihood of finding detrimental through-thickness defects such as stacked LOSWF rather than the relatively harmless slag and porosity that radiography is good at picking up.

Either way - RT or AUT, a permanent fingerprint of the weld is held for comparison with later pigging results which report "girth weld anomalies". If the AUT strip chart or radiograph is available it can be reviewed and perhaps an idea of the anomaly obtained prior to expensive digging.

The fact that the original contract specification is clearly 100% probably means the pipelien construction code requires it based on stress analysis, pie amterial and wall thickness. And whilst the cost difference between 100% and 10% is certainly not 10:1 (unless multiple rejpairs are entailed) the increase in confidence in the durability at least of the welded joints must be greater than 10:1.

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[BigInch]

No argument... that's why many do use 100% anyway... Except for the required by code bit. Its not a design code or stress issue, only a construction spec QA/QC thing.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[GregLamberson]

Do the 100%. If it is a domestic job, the travel time from the NDT crews going back and forth to shoot the 10% will probably offset the crew costs of them staying out all day and you only have consumibles which are a minor cost component.

If you are on a camp job it's a no brainer, the crew is there anyway.

I personally don't see the advantage in 10% and would only consider it in very specific cases and then only with some criteria such as what theo1960 pointed out. What minor savings you might get is more than offset by the risk. The most critical part of your pipeline are the joints (both welding and coating). It comes down to cost versus value and the 100% NDT easily provides the value.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy

Website:

http://www.oil-gas-consulting.com

 

[BigInch]

10% allowance for tie-ins at road crossings etc.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com