Gauging Plate Diameter

[perruolo]

Good Morning to All

We are right now close to achieve the mechanical completion of a 4" Butane Gas Pipeline among others. We are cleaning the line and then passing the gauging plate. Calculations taking into consideration the positive tolerance (Thickness) and negative tolerance (diameter) to get the minimum acceptable pipe diameter in conjunction with project specification that state the gauging plate must be 95% of the minimum internal pipe diameter give us a final gauging plate diameter of 95.7 mm.

Minimum Pipe Diameter= 100.7 mm
Gauging Plate Diameter = 95.7
Difference = 5.03 mm

Now, API 1104 specified a maximum of 1.6 mm root weld penetration which will be 3.2 mm (diameter)

Final difference = 5.03 - 3.2 = 1.8 mm (0.9 mm each side)

3 gauging plates already passed thorough the pipeline came out with several scratches. Client is demanding a deep investigation of possible causes.

Our position is that with such minimum tolerance is almost impossible to get a clean and smooth gauging plate. It always will suffer some scratches. Your comments are highly

 

[LittleInch]

It sounds like your client is an arse who clearly hasn't seen any gauging plates before??

You appear to have done all the right things.

What does the construction or testing specification say about the gauging plate? That's what you need to base any response to the client on to say you've done all the right things and this is what you get.

Now for a 4" pipe you're going to get some nicks and grooves because the plate is never dead centred and the actual gap between edge of plate and pipe is very small compared to say a 12" pipe.

Can you post a photo of the discs?

A gauging disc is a pretty crude tool and intended only to demonstrate that there are no internal dents or restrictions less than 95% of the ID. So basically if the petals are not bent out of shape then it's passed. Any grooves or scratches are welding protrusions.

The only way to do a "deep investigation" is to run a caliper gauging tool. If you didn't include for it or it wasn't stated as a scope of work item then give the client the costs and the schedule impact and see what he says.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[perruolo]

 

[LittleInch]

Absolutely nothing wrong with that plate. The pig has clearly sat down a little at the back as evidenced by the wear on the rubbers hence why the scratches are concentrated on one section. Hence you could be within your penetration limits for the weld but the plate is just not centered exactly.

Those nicks and scratches are what you expect when you slide a soft metal plate over a harder one for several hundred metres.

That's all perfectly normal.

Now how you convince your client I'm not so sure. ...

Good luck and let us know the outcome.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.