DS1 vs. NS2 vs. API RP 7G-2

[MalDu]

Hi Everybody,

I need your comments on the aforementioned inspection standards:

1. What are the main difference among the 3 of them?

2. Is API RP 7G-2 the correct equivalent for NS2 & DS1 or is it API RP 7G, or API 7-1? Or DS1 & NS2 contains info from various API standards?

3. My understanding is the following. correct me if I am wrong:

- For manufacturing and inspection of new equipment API RP 7G, NS1, or DS1 (volume 1) are followed
- For inspection of used equipment, API RP 7G-2, NS2, or DS1 volume 3 are followed.

4. Can manufacturing companies get a formal certification of DS1 / NS1 / NS2 the way it can get API certified with an equivalent monogram? If not, why not?

5. Any good online resource you'd recommend where I can know more about these standards?

Thanks
MalDu