Dear all,

I have some doubts using the API 579 section in CodeCalc. I want to perform an analysis of the Fitness for Service of a vessel subject to external pressure (1 barg) with Local Thin Areas due to a bad fabrication process.

Searching in ASME section VIII Div 1 & 2, I have found nothing except the cited to API 579/ASME FFS-1, which was released in 2007.

I have the latest version of Codecalc, but i am not sure if it is using API 579 (from 2001)instead the new released code version. The problem is that i guess that API is not very suitable for External Pressure, isn`t it? I would be very pleased if someone could give me clarifications of this.

Besides, if someone has valuable experience in how to decide between Local or General Metal Loss (Is there any way or limit to calculate the maximum length which allows to consider the flaws as local?)

Last point, I haven't the API 579 ASME FFS-1 Code, but to my mind, if the flaw is "local", there is no too much problem with external pressure. The problem should be if the vessel is subjected to Internal Pressure. Any has the Code? Is there any requeriments for local flaws when External pressure?

Thanks,

Ignacio

Dear Ignacio,

You might refer to criterion for evaluating out of roundness, which is a concern for external pressure. This is also given in ASME Sec. VIII Div. 1 (I think UG-84).

CodeCalc includes, API 579 (from 2001). It is good for thinned areas, pitting and grooves. This API std. includes the criterion for local or general metal loss. Their name indicates what they mean.

In a quick look in those section (4,5) in the FFS std. I could not find external pressure. But, I believe that I have seen the out of roundness criterion in 579 document as well.

Dear Mandeep,

Thanks for your answer, but to my mind, you are wrong.The UG-80 about Out-of-roundness is not valid for Local Thin Areas.

There is a new version of API 579: API 579-1/ASME FFS-1(2007), which may be used (see VIII Div2 points 4.4.10 and 4.14.2) to qualify the design of components that have a LTA.

I guess that if the version implemented in CodeCalc 2008 is from 2001, and knowing that API standards are not very suitable for external pressure, i can't use it in the assesment. So, I encourage you to actualizate Codecalc to the new standard asap.

Thanks

What I meant was that if you have dent on the outside of the vessel and you are concerned about external pressure case (vacuum) then you can use out of roundness.