Pipeline Sizing Plate Material

[GregLamberson]

I would like to get some feed back from the forum on the material recommended for pipeline sizing plates. It seems the 2 schools of thought are: 1) mild carbon steel or 2) aluminum. The norm is to size the plate at 95% of ID.

I am a proponent of mild carbon steel for the following 2 basic reasons:

1. it provides a pass or fail test. I have never seen any definitive criteria for evaluating an aluminum sizing plate for damage. For aluminum, there are some obvious failures and the rest seem to be subjective.
2. with a pig tracking device, when the carbons steel sizing plate stops, you know where the defect is, with aluminum, if it comes out damaged????? (of course caliper pigs can be run, but I would like to concentrate on sizing plates)

I have heard arguments that the carbon steel sizing plates can damage the pipe, but that doesn't make much sense to me, mild carbon steel vs an X60 or higher grade pipe. I have seen a mild carbon steel pig body whose pig rubbers disentigrated and came out with 10% of the body ground off. We stripped back 500+ meters and took readings on the pipe WT and there was no degredation, zero. A smart pig baseline survey later also turned up nothing.

So back to the original question - aluminum or carbon steel?

Greg Lamberson
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

Aluminum! So much trouble taken in mill inspection, transport, stacking, slinging without hooks, storing pipe on plastic covered sand berms to protect the coating and keep from scratching the OD, for which the coating is then again inspected for holidays when lowering in should be evidence of the care needed. And that is for areas that can be easily seen and identified. Its not the yield strength of steel that resists scratching, its the hardness. I can easily imagine a steel disk's edge banging around inside a pipe becoming very hard due to cold working the edge. Why risk scratching or gouging the ID where you have no choice but to UT the whole line just in order to know if you did it or not? Risking a serious stress concentration where it can't be found makes no sense to me. I can't imagine a consultant recommending that one. I'd advise against steel.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[GregLamberson]

There are quite a few company's whose specs contain the option of aluminum and mild steel, and leave it up to the contractor to decide.

2 follow up questions - 1) what is the specific criteria for determining if an aluminum plate passes or fails the inspection? and 2) if the aluminum plate fails (severe dent for example), where do you start looking for the anamoly?

Granted the whole question can be solved with a caliper pig, but often company's don't want to go to the expense.


Greg Lamberson
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

Not surprizing. There are quite a few bad specs around.

The Al plate is just an indicator of severe dents. If it gets beat up, it fails and its a judgement call by the engineer in charge. You can get an approximate location in the segment where it took the beating if somebody accurately controls and keeps the plate velocity low and records pressure across the segment's inlet and outlet against time. You may get lucky enough to identify a pressure spike at the time the plate was temporarily stuck and thereby deduce a location, but (fortunately.. and if the construction spec was properly written... ie to define the pass-fail criteria, and NOT define the methods on how to install.) its the contractor's job to find and rectify the problem. All you really need to care about is that the last gaging plate the contractor ran in there... came out intact.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[BigInch]

Correction... Not a judgement call.

B31.4 Par 451.6.2 (probably a similar clause in B31.8, but I didn't look.)

Remove or repair dents that,

1. Affect girth or seam weld.
2. Dents with a scratch gouge or groove
3. exceeding a depth of 1/4" on 4" Diam or less
4. exceeding a depth of 6% of Nominal Diam on NPS 4+
5. Dents containing external corrosion with remaining wall thickness is less than 87.5% needed for design.




BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[GregLamberson]

As far as what needs to be repaired, agreed. And once you determine there are defects, locate them and dig them out, you can take measurements and comapre it with the code (31.8 has the same) and either make the repair or not, - done that hundreds of times. But in every case when using an aluminum plate, we've eventually had to bring in a caliper pig and make the run to find them becasue with aluminum you never know if it's one location or 10.

But the question I have is, when the aluminum plate comes out, what is the criteria to determine if it passes or fails.

Some are obviously failures. But the ones that are not obvious, well, what is the criteria for accepting the plate? For a pipleine weld, 1104 has specific criteria, and while 2 different level II's or III's may disagree on a weld here and there, the criteria is well defined and the result is clear.

I've never seen anything on aluminum sizing plate acceptance and was wondering if there was any out there?



Greg Lamberson
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

Sorry, I have never seen anything specific on that either. I'd make the responsibility for the call lie with the client's engineering rep.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com