Corrosion Growth Rate of a Gas Pipe line
Corrosion Growth Rate of a Gas Pipe line
(OP)
Recently we had our ILI run for our 22" gas pipe line. One of the major out comes of this 2008 ILI run going to be the prediction of corrosion growth rate and our repair plan for the next 5 years. As the vender had done 2003 run as well as 2008 ILI runs they are going to overlay the data for the defects so that , can calculate the growth rate for N number of defects and finally come into a conclusion that corrosion growth rate for each section before having our repair plan.
Appreciate if you could provide me with some information on calculating the corrosion growth rate as I have come across many different approaches and formulas for calculating the corrosion growth rate for buried gas pipe lines
Appreciate if you could provide me with some information on calculating the corrosion growth rate as I have come across many different approaches and formulas for calculating the corrosion growth rate for buried gas pipe lines





RE: Corrosion Growth Rate of a Gas Pipe line
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Corrosion Growth Rate of a Gas Pipe line
You seem to have many questions on pipeline integrity, I guess that is what the forum is for. What I would suggest is you use more than 1 method, complete different scenarios with different methods/rates. The underlying premise to which you suggest you are using 2 ILI runs and calculating a site (or specific corrosion anomaly) rate in my opinion is the way to go. I am not sure about the ILI tool(s), same tool or generation of tool? If they are different generations this can lead to a less accurate correlation. Also, don't be fooled by the ILI vendors statements around accuracy of sizing, most of the runs will have outlyers which are beyond the error bars of the tool, the error bars in reality may be larger than what the tool is specifying. Use your field correlation data you collected, and apply this, not just the ILI data as is. In some cases, this field data may help to narrow the error window and help give a tighter rate. Some companies have data from many different vendor tool field correlations, and have developed their own error bars associated with each tool and apply these. One of the issues around an ILI vendor completing everything is it will be all automated, and perhaps won't have much manual interpretation around anomaly matching. Some of the new methods include an error factor in field measurement as well, they take into account for different methods of measurement (i.e. pit gauge, ultrasonic etc.). I might suggest you use a consultant with experience in this type of analysis rather than 1 ILI vendor. In your analysis on the financial side you want to include some cost calculating on what if you inspect your worst features or some features that can delay the run of an ILI tool a year, or two years etc., based on cost per dig and ILI run. If you are DOT liquid line forced to run every 5 years anyway, this part of the analysis may not be worth (or a detailed analysis may not be worth it) it when the POE will not exceed 5 years in any case. You also must decide what you want to live with, POE on full bore rupture or any leak depending on your company (assuming you go the POE method on top of a determinstic method). Other factors might include class 2 and 3 areas where you might not want to exceed a certain burst pressure etc.
I could go into more details, but your question was very broad and it is dificult to describe methodolgies in full... Perhaps I did not answer what you wanted.
RE: Corrosion Growth Rate of a Gas Pipe line
But as the hi-res ILI result provide identification of SCC or pitting you can secure your conclusion by the operation constrain of water cuts, partial gas, temperature, solid that will not introduce new corrosion mechanisme to your pipeline.
RE: Corrosion Growth Rate of a Gas Pipe line
Fortunately our pipe line hasn't reported any internal corrosion defects as yet. Further we have been carrying out our ILI runs every 5 years. As our pipe line is almost 30 years old , management is happy to continue the ILI runs every 5 years. Like they had done it in the past I prefer to calculate the corrosion growth rate based from past ILI runs. As Brimmer noticed my background of experience was from marine top side piping and not much exposure to buried pipe line industry. Quite rightly Brimmer pointed out that having a forum is all about exchanging our experiences and sharing the views. Appreciate all (S Jones,Brimmer & Abduh) for contributing for this topic.
RE: Corrosion Growth Rate of a Gas Pipe line
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Corrosion Growth Rate of a Gas Pipe line