Hi Mr. Karthikeyan
Attached is the extract from PMI spec of one of the oil majors. ± 10% deviation is acceptable . PMI whether it be XRF or Arcmet ( portable Spectroscopy) is highly machine dependent. Minor calibration issues may cause inconsistency of results.
I would advise get the samples tested by the alternative suggested method.
API-578, is the basic document for PMI in oil and gas industries.See the extract from API -578 FYI.
15Mo3 is a C-0.5Mo (P3) steel, while the composition shown below conforms more to P4 material . Based on the results of the alternative test, decide on the acceptance/rejection of the elbows.
Thanks.
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
OIL Major's Spec:-
Methods
· The primary acceptable method is X-ray emission analysis, also known as X-ray fluorescence (XRF) analysis with a calibrated portable instrument. See also API RP 578 Paragraph 5.2.1.
· Because of inherent limitations of XRF, it is not possible to detect all elements. Elements lighter than sulfur (S) can not be detected using portable X-ray fluorescence spectrometers. This technique can't detect carbon (C).
· An optical emission spectrograph (Arcmet/Metorex) may be used to check for all the required elements, including carbon. Any burn damage resulting from the usage of the emission spectograph shall be removed by grinding
Acceptance Criteria--PMI
· For acceptance, it must be demonstrated that materials contain the amounts of alloying elements shown in the material specification. Alloys shall be acceptable if the alloying elements are each within 10% of the specified range of values.
· Welds with consumables that match, or nearly match, the base metal composition shall be within ±12.5% of the ranges allowed in ASME SEC IIC for each element
Rejection Procedures
· If the PMI testing results fall outside the acceptable range using a method described in Section 8(XRF), the Equipment Manufacturer or the Fabricator, as applicable, has the option to conduct a more accurate analysis at his own expense to determine the component acceptance such as obtaining a chemical analysis performed by an independent testing laboratory.
· The alternative test method or independent laboratory must be acceptable .In case of retest-the results of the more accurate test method or independent chemical analysis shall govern .
API-RP-578- Material Verification Program for New and Existing Alloy Piping Systems
Evaluation of PMI Test Results
6.1 MATERIAL ACCEPTANCE METHODS
The owner/user may elect any one of the following methods of material acceptance:
- Materials can be confirmed to contain the nominal amountsof alloying elements specified in the relevant materials specification(e.g. ASME Section II or ASTM specifications)..
- When PMI testing indicates alloying elements are outside the ranges indicated in the material specification, the owner/user may still choose to allow the use of the tested materials in situations where a person knowledgeable of the appropriate damage mechanisms confirms that the material will perform satisfactorily in the service.
- If testing using one of the portable or qualitative analysismethods (see 5.2.1 or 5.2.2) leads to the potential rejection ofa component, a more accurate analysis may be used to determine component acceptance (see 5.2.3).
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of george.dilintas@gr.bureauveritas.com
Sent: Thursday, July 29, 2010 3:09 AM
To: materials-welding
Subject: Re: [MW:6185] Mo and Cr content exceeded in 15Mo3 material-reg
Those two elements are increasing hardness and reduce ductility so on my opinion you should reject them
From: Karthik [karthik6684@yahoo.com]
Sent: 28/07/2010 23:42 MST
To: materials-welding@googlegroups.com
Subject: [MW:6183] Mo and Cr content exceeded in 15Mo3 material-reg
| Dear All, We have received PMI report from our material supplier for 15Mo3 elbow before delivery. We found that Mo and Cr. Contents are higher than the maximum requirement. Please find below the details of Compositions. Matrerial - 15Mo3 Standard Specification (Mo) = 0.25 to 0.35% Actual found (Mo) = 0.50% Standard Specification (Cr) = 0.25 to 0.35% Actual found (Cr) = 0.90% Shall we accept this material, since the Mo and Cr Percentage are exceeded. If it is acceptable, what will be the impact in the actual working conditions? (This material is used for Superheater) Please give us your suggestion Karthikeyan.S Getabec Energy Co.,Ltd. 379,Moo6,Soi8,Nikhomphatana, Rayong-21180, Thailand. Phone: 0066 38 897035-8 (Off) Fax: 0066 38 897034 Hand Phone: 0066 892512282 |
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