API 579 FFS - Allowable Minimum Measured Thickness of Pipe

[Mamacint]

Hello,

I have a question about API 579, will pipe always fail Level 1 and 2 assessments and require a Level 3 analysis if there is a minimum thickness measurement below 2.5mm/0.1"? (Per Table 4.4)

If it's B31.3 and the supplemental loads are neglible such that you can perform a Level 1 analysis, must it still pass the tmm >= 0.1"? 4.4.2.1 d) seems to suggest this. How does this effect small D pipe especially 5S where tnom is less than 0.1" up to size 4"?

Thanks in advance for any help.

 

[LSThill]

Mamacint (Mechanical)

have you read the API 579 & A S M E FFS 2 (2009) Fitness for Service Example Problem?

 

[Mamacint]

I have looked there and didn't see any applicable problem. It seems like API 579 is much better written for pressure vessels where I'm working with small pipe w/ only several RT readings. I'm trying to be conservative by using the lowest reading but it does seem like for smaller sizes w/ low pressure that the 2.5mm requirement seems excessive yet I don't see any exceptions to this.

 

[Duwe6]

Don't try to force piping into a Vessel Evaluation "Recommended Practice". Get a copy of API-570 -- it is a Standard, not a "Recommended Practice" and thus much more mature. And it specifically addresses pipe.

8"NPS Sch 5S = .109" 2.8mm Sch 10S = .148" 3.8mm

3"NPS Sch 5S = .083 2.1mm Sch 10S = .120 3.1mm

It is impossible for brand new pipe that is at the nominal wall thickness to be deemed as below necessary thickness. You are in the wrong book.

 

[Mamacint]

Thanks for you response.

I'm somewhat confused as API-579 does include piping and API-570 specifically refers to API-579. There is a specific requirement for piping components that minimum measured t >= 2.5mm in Table 4.4 of API579.

I agree that this requirement doesn't make sense, and the RP seems much better written for vessels and piping, however, that acceptability criteria is still there for piping.

Has anyone run into this before or received clarification? It seems unnecessary to jump to a Level 3 assessment when you're confident it's already acceptable.

 

[Mamacint]

* sorry, meant to say "RP seems much better written for vessels than piping" instead of "vessels and piping"

OT: I don't see any means to edit my post.

 

[Duwe6]

Since 570 does not have that rediciouls requirement, I just ignore 579 in favor of 570.

When you calculate the pressure-based minimum thickness of pipe, the numbers are usually at or below 2.5mm. So the limiting condition is Span. Thus the evaluation becomes "Is the existing wall thickness sufficient for the weight of the unsupported span?"

And yes, the answer usually arrived at is that 2.5mm or more is needed to span the gap between hangers. The point is that "one size fits all" is no more applicable in piping than it is in underwear. When you approach 2.5mm, evaluate your condition. Do not automatically reject it without an evaluation.

 

[LSThill]

Mamacint (Mechanical)

HAVE YOU READ Overview of Process Plant Piping System Maintenance
and Repair AND THE 3 EXAMPLES

http://files.asme.org/asmeorg/Governance/Volunteer/CareerSeries/9654.pdf