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Technical Discussions
thanh
university, Vietnam, Joined Mar 2019, 2

thanh

university,
Vietnam,
Joined Mar 2019
2
10:37 Apr-19-2019
DNV-OS-F101

Dear colleague !
I have a question need your help. In OFFSHORE STANDARD DNV-OS-F101 (2013), APP E (H600 test welds) AUT Qualification sample. In Table E-2 Number of deliberate flaws for GMAW J prep welds. in defects type group Root & HP/radius regulated Specifically 29 defects per one but just beside is (7*). please show me what is "7". My identify in 601 "However,
EDM notch technique may substitute 70% of the total number of flaws in each flaw group.....Hence a minimum of 30% natural flaws shall be part of the data population". So, 7* is number of natural defect shall be induced in qualification sample ? 22 defects rest may substitute by EDM notch ? it right ?

    
 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1252

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1252
14:56 Apr-19-2019
Re: DNV-OS-F101
In Reply to thanh at 10:37 Apr-19-2019 (Opening).

In my copy of OS-F101-2013, the HP/radius category in Table E-2 requires 29 flaws but in brackets it states (*6)...not *7 as you are stating. The comment column suggesting combining the 2 zones is only applicable when the zones are combined. The new edition of the standard is also significantly different in the requirements for a project-specific validation, requiring less than 29 observations.

Firstly, a note on the applicable standard. DNV-OS-F101 has been replaced by DNVGL-ST-F101 (https://rules.dnvgl.com/docs/pdf/dnvgl/st/2017-12/DNVGL-ST-F101.pdf). There is a significant change relating to the use of EDM notches in the latest edition.

The asterisk plainly defines the number at the bottom of Tables E-2, E-3 and E-4. There you read:
* Number of defects for project specific AUT procedure validation.
So your assumption is incorrect! *7 is NOT the number of natural defects.

Project specific AUT Procedure validations are detailed in the next section (Section I) of Appendix E of the 2013 edition and apply only to previously qualified systems/procedures.

For the initial qualification you will still need to conform to the larger number of flaws in each column of the Tables E-2, E-3 and E-4.

I pointed out that the old 2013 edition has been replaced by the 2017 edition because there is a very important sentence added with regards to the EDM notches. Also, the 3 tables are now grouped into a single table.

In the new standard you read in Appendix E 8.7.2 "... Machined imperfection techniques shall not be used to produce ID and OD surface breaking imperfections due to the similarity to the reference reflector for these channels."

Therefore the only place that EDM notches can be used in the fabrication of the qualification test welds is to prepare simulations of subsurface nonfusion flaws.

From personal experience I suggest you make quite a few more flaws in the test coupons than you see listed in the Tables in the DNV standard. EDM notches are often melted away as you make subsequent welding passes. So even though you measured the EDM notch after it was made and it was 15mm long and 3mm high, it may be only 5mm long and 0,5mm high (or not exist at all) after welding.
You are also to avoid flaws being too closely spaced along the length of the weld and also avoid stacked flaws.
Since you must eventually slice, polish and macro-photograph each flaw used for the POD qualification, you may find that you have introduced unwanted flaws that are too close to the flaws you had intended. As a result, your ultrasonic responses may be distorted and the detection and sizing analysis will not be suitable for the requirements of DNV.
Unsuitable defect-indications are to be removed from the data set. Therefore, you had best ensure that you have other suitable candidates to choose from.
Ed





    
 
 

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