PMI accpetance criteria

Date 04-05-2008 10:13

With regards to Positive Material Identification (PMI) inspections, ASME section II A/B/C shows the chemical composition value of an alloying element which states the minimum and maximum values permitted.

For example Chromium requirements as per ASME sect. II A/B/C is 19.5-22.0 for ER 308 electrode. Project specification's acceptance criterion allows the chromium requirements minimum of 17.55 and maximum of 24.00.

Is it possible to override the requirements of ASME section II if the project specification we undertake requires additional ± 10% of the amount specified on the standard?

By chall

Date 04-05-2008 12:38

As I see this, there are two concerns:

1) Compliance with the Code
2) Compliance with your WPS

Looking at item 1 first: Unless you are working on a component within the Jurisdictional Boundary of the State you are working in or where the component will be installed, the code (any part of it) may be overruled by the owner. (Note - excluded from my comments is any reference to work involving the nuclear industry.)

Generally, the hierarchy of controlling documents (listed somewhere in the contract technical clarifications) lists the precedence. It will typically say something like, if a disparity between the code of construction and these specifications is identified, the contract specifications shall be followed. It's their right to make that call, but you should point the situation out. This could be an error on the part of the engineer and they may change it if it is pointed out to them.

Item 2: The requirements for filler metal classification / F & A numbers must be adhered to in accordance with your qualified WPS. If the component is within the Jurisdictional Boundary (ASME Section I: Boiler Proper or Boiler External Piping; or ASME Section VIII: Pressure Vessel), you have to comply with the code. This may require that you qualify an "unassigned" filler metal specifically for the application (ie - base metal welded with a filler metal that does not conform to the F or A number rules of Section IX.

I hope I haven't confused the issue. It's clear to me, but I know things don't come out the way we think them sometimes.

Charles.

By MBSims

Date 04-05-2008 17:37 Edited 04-05-2008 17:40

Portable PMI instruments are usually used to check materials before they are installed to make sure a mix-up has not occurred, to check already installed materials to confirm them prior to welding, to check minimum specified chemistry for cladding, or similar applications. They are usually not accurate enough to verify conformance to a material specification, although some types are very good, so a plus or minus would be appropriate in that application. I would not consider this "overriding" the material spec, just recognizing the limitations of in-situ measurement methods. If compliance to a material spec is being checked, then laboratory testing methods are required.

By js55

Date 04-07-2008 14:46

Charles hit the nail on the head. This isn't a code issue (other than Section IX). It's a WPS issue. Section II don't care, nor any code of construction, what filler metal chemistry you end up with. Thats an issue for design.
Although, as Charles said you have to comply with your WPS. You can generally drop the filler metal classification without requal, but you have to comply with the A No. which ASME Section IX says Cr can be as low as 14.5 and still be A 8.