PetroStreet

i want to know that whats criteria to evaluate the repair rate of any project and what is the acceptance limit for it

i have heard its about 2.5 - 3%

Evaluating overall repair rate is a subject which becomes very controversial sometimes between a contractor and client. Contractor is always interested that the repair rate must be calculated in linear inch (repair length of weld / total length radiographed) and client is of the view that the weld having even one repair no matter what how many repairs and what the length is must be treated as rejected (total rejected welds / total welds radiographed).

Now the appropriate method of measuring repair rate is decided between a contractor and client before the start of welding works at site. For all the piping, normally for size above 24" (or any decided between contractor and client), repair is taken in linear form as total linear rejected length / total welded length radiographed done and for piping below this size is taken as total rejected welds / total welds radiographed. For tanks, it is always taken as linear rejected length / total welding length made.

For acceptable repair rate, you are right. On large construction projects anything below 4% is considered to be good and the insurance auditor also feel happy.

in our case we force contractor to evaluate on film basis
i.e
repair film/ total required films

but contractor emphasis on formula mentioned by ARCPO
so ARCPO will u please quote any reference of formula that u mentioned as if i go via your mentioned formula then repair rate will become in points that is not more than 1%

and is there any reference of acceptable limit of repair rate

Dear fellow member,
I have edited my above post, with total weld length made I mean total welding length inspected with radiography or ultrasonically tested and with total welds made means total welds radiographed and ultrasonically tested.
Now if you have any question, you many ask please.

We are in the construction stage of a new fertilizer plant and the strategy we adopted at our site for repair rate is as follows:
1. For all the weld joints below 40" NPS, the scheme was to calculate the repair rate as number of welds rejected / total welds radiographed. We consider a weld as rejected even having a single repair.
2. For weld joints > 40" NPS, we consider repair rate as linear that is rejected linear weld length / total linear weld length radiographed

Now initially for all piping sizes we were adopting the scheme as mentioned in para 1 but for some pipeline welds above 40" NPS, we increased the RT% from 5% to 100% (hydrostatic test was not to be conducted for those lines that's why increased the RT examination to 100%). In this case, repair rate starts touching a very high number and Contractor came to us and requested to consider the scheme as mentioned in para 2 and with mutual consent we changed our strategy for piping in sizes above 40" NPS.

We have set our acceptable repair rate as 5% being realistic due to many factors but generally anything below 4% is a good figure.

thanks for reply

what about criteria for the tank constructed on API 620?
now we have three formulas to evaluate the repair rate

1. rejected linear weld length / total linear weld length radiographed
2.welds rejected / total welds radiographed
3.repair film/ total required films

and no body quoted me any reference of this formulas yet....

You would not be finding any internationally accepted code or standard reference regarding calculation of repair rate and the acceptable value.
Both method and the acceptable repair rate is decided between the client and the construction contractor. Normally, method (2) is the most common and the direct one but if you want to be more specific with your weld repair rate which must also reflect the amount of re-work, go either for (1) or (3) which are almost the same.
For all the tanks, repair rate is only calculated with method (1) or (3).

Hope this helps.

To me the repair rate which is normally taken as the formulas you mentioned is only a measure of re-work which is being done at a site. In order to monitor, welding works at your site the actual going in position is different. You have to collect the data welder wise, each and every welder working at your site must be monitored closely on his individual repair rate so that the welding job on lines not being radiographed 100% shall also be in good condition.

mechcolor,
Would you please elaborate methodology to be adopted for welding works inspection?

The methodology is very simple and easy going. Let the contractor introduce welders like 50 initially, you just keep the track of each welder. Examination should be made and recorded welder wise. On a big chart against every welder's name, repair rate and classification of repair must be registered on per day basis. This chart would allow you to make quick decision in order to improve the condition of welding at your location like replacement of welder, understanding welding problems being faced by welders, identification of good welders and the most common type of repair.
You may use colors just to differentiate the performance of your welders. Now, when starting welding of critical class piping, choose the best welders of the lot as the chart would be depicting. This chart will also make welders feel good or bad about their performance as they would be in a position of comparison.

Remember, control on welders will automatically control overall welding works at your site.