3.07.operatingprocedures.magnetic particle inspection of weldsprocesspiping

3.07 WELDING PROCEDURE MANUAL PROCESS PIPING

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OPERATING PROCEDURES

MAGNETIC PARTICLE INSPECTION OF WELDS

04/25/11

HIS SECTION PROVIDES STANDARD PROCEDURES FOR MAGNETIC PARTICLE

INSPECTION of field welds (or base materials) performed on the Company’s process

piping associated with LP Plants. T GENERAL

Pipelines requiring non-destructive testing in accordance with Section 3.02 (“Non-

Destructive Testing Requirements”) of this manual can utilize Magnetic Particle Testing

(MPT) provided another type of more reliable non-destructive testing is not required or

utilized. If another type of non-destructive test is used, MPT may not substitute for its

specific requirements.

NOTE: Although radiography and ultrasonic testing will provide better sub-surface

detection of discontinuities, these types of tests may not be practical due to the

shape or location of the weld. Thus, MPT may present advantages over

radiography in locating tight cracks and surface defects.

This procedure defines the requirements for conducting ultrasonic testing, and is intended to

comply with ASME B31.3 (“Process Piping”) and ASME BPV Section V Article 7 and shall

meet ASTM E709 (“Standard Guide for Magnetic Particle Examination”) requirements.

This process is used to detect discontinuities that extend through the weld surface and only

slightly into the sub-surface, MPT is intended to:

Verify weld integrity

Identify the need for correction of improper welding techniques by indicating recurring

defects

Assist in verifying welder quality in the production weld process

When performing magnetic particle testing, magnetic and metallurgical variations in the weld

may produce indications similar to those produced by imperfections. These are not relevant

to the weld’s acceptability (based on B31.3 or ASME Section V evaluation criteria).

All personnel conducting magnetic particle testing will be qualified as required by SNT-TC-

1A (“Level II for Magnetic Particle Testing”).

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MPT APPLICATION METHOD

Figure 3.07.1

This specification pertains to the use and application of visible and fluorescent, dry or wet magnetic particle (MT) examinations employing direct contact (prod) and indirect contact (yoke) magnetization techniques. These procedures are for the yoke type of magnetization, as it is more widely used in the pipeline industry.

In yoke magnetization, a magnetic field is created by either an AC or DC power source, or even a strong permanent magnet on a piece of ferromagnetic material. The magnetic field is interrupted by discontinuities found in the weld or base material. When the magnetic field is interrupted, lines of flux in the powder or suspended liquid will show variations in the density of those particles. See Figure 3.07.1 for common equipment and supplies used for MPT.

DRY METHOD

The dry method uses finely divided ferromagnetic particles in dry powder form. These are dusted uniformly over the area using a dusting bag, atomizer, or spray gun. Excess powder is then removed with a stream of air just strong enough to carry away particles without disturbing any patterns that develop. It is critical that the surface being tested be free from oil, moisture and dirt. The dry method is easier to use on rough surfaces.

WET METHOD

The wet method uses smaller particles than the dry method. These are suspended in a liquid bath of light petroleum distillates. Because of the smaller size, the wet method is more sensitive than the dry method for fine surface defects but not as sensitive for sub-surface discontinuities. The magnetic particles for liquid suspension are available in either a paste or dry concentrate and may be mixed with oil or water. The water mixture is more sensitive than oil mixtures. However, the oil base may be preferable if working in close proximity to electrical circuits. This material is either flowed onto or sprayed over the surface to be tested. The particles are available in materials that are fluorescent under a black light to further increase the sensitivity of the wet method and will show indications of very small or fine discontinuities.

POST TESTING

After the test is performed, personnel should thoroughly clean the pipe (and if appropriate, demagnetize the area) before coating. Although most weldments do not require demagnetization after MPT, arc welding operations can be affected by strong magnetic fields; see Section 3.13 (“Pipe Magnetization and Correction”) of this manual.

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MAGNETIC PARTICLE INSPECTION PROCEDURES

These procedures provide the basic steps in performing magnetic particle inspection. They are not intended to cover all details relative to the process and procedures utilized by each non-destructive testing firm.

PREPARING THE EXTERNAL PIPE SURFACE

Surface conditions greatly influence the sensitivity of the inspection process. The surface should be clean, dry, and free from oil, water, excessive weld spatter, or other accumulations that would interfere with efficient inspection. Wire brushing, sandblasting, or other comparable cleaning methods are usually satisfactory for most welds. Surface roughness decreases the sensitivity and tends to distort the magnetic field. It also interferes with the formation of powder patterns.

The Field Inspector is responsible to:

1. Ensure the pipe is essentially clean, dry, and free of contaminants within no less than 1 inch of the test area.

2. Remove any disbonded coating or corrosion products by using power brushing or light abrasive blasting:

A blasting medium of a 3:1 mixture of 12/20 size crushed walnut shells with medium coarse sand (20/50 mesh) may be used

Commercial grit (Black Beauty) may be substituted for sand

3. Use a method that will clean and polish the pipeline without cutting an anchor pattern in the steel; if requested by the non-destructive testing personnel, a power grinder can be utilized to smooth the weld surface provided the weld reinforcement is not cut away beyond the effective weld metal.

MAGNETIC PARTICLE INSPECTION

This process applies to both alternating current (AC) and direct current (DC) yoke style magnetizers, with both dry and wet methods of inspection.

The NDE (Non-Destructive Examination) Service Provider is responsible to:

1. Verify that the AC yoke provides a lifting power of 10 pounds at the maximum pole spacing that will be used. If a DC yoke is used, the lifting power must be at least 40 pounds.

2. Immediately before the magnetic particle examination, clean the prepared surface with a cleaning solvent (if required) and wipe the surface with a dry cloth.

3. Ensure the poles are free of foreign material.

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4. Place the contact poles against the material. It is important that the poles are placed firmly on the test surface before energizing the field to prevent arc flashes. These flashes can arc burn the pipe and may result in a pipe section that must be removed; see Section 3.12 (“Repair of Unacceptable Welds”).

5. Turn on the appropriate magnetization current.

6. For visible dry MT examination, dust the color contrasting magnetic particles lightly upon the examination surface between the poles. If black particles are used, it may be necessary to apply a thin coating of an appropriate background to enhance contrast. For wet MT examination, apply the wet particle bath to the examination surface between the poles.

For visible wet or dry MT examination, the light intensity shall not be less than 100 foot-candles. For wet fluorescent MT examination in a darkened area, the light intensity shall not be exceed 2 foot-candles and have a black light intensity of at least 1000 µW/sq. cm. at the work surface.

For all MT examinations the temperature limitation will be based on the manufacturer’s recommendations.

7. For visible dry MT examination, carefully observe the examination surface for the formation of indications during both application and removal of indicating powder. Remove excess indicating powder in a manner that does not remove lightly held powder patterns. For wet fluorescent examination, carefully observe the examination surface for the formation of indications using the black light.

8. Turn off the magnetizing current.

9. Remove poles.

10. Record and mark any relevant indications. For visible dry MT examination only, remove all indicating powder after the first examination(s) is completed.

11. Analyze the pipe for any discontinuities or cracks. (See “Interpretation” elsewhere in this section.)

12. To maximize crack detection, the handle of the electromagnet connecting the pole pieces should be perpendicular to the crack.

13. Inspect the area twice:

Once with the electromagnet handle oriented circumferentially

Once with the electromagnet handle oriented longitudinally to ensure a thorough inspection.

CAUTION: Mill or other manufacturing related steel surface discontin-uities/defects can be misidentified as SCC.

14. Demagnetize the test area if required.

continued

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15. Document the inspection results:

Ensure the report contains the station location and circumferential position of any SCC or other discontinuities/defects.

Include with the report photographs of magnetic particle indications of SCC and other discontinuities/defects.

INTERPRETATION

The principle features of discontinuity identification are:

Shape

Sharpness of outline

Width and height to which the particles have built up

The NDE (Non-Destructive Examination) Service Provider will examine for and interpret the following:

TABLE 3.07.1: INTERPRETATION OF DISCONTINUITY IDENTIFICATION FEATURES

CONDITION PATTERN

Surface Cracks Sharply defined, tightly held, and usually built up heavily with powder (the deeper the crack, the heavier the buildup of the indication)

Sub-surface Discontinuity

Indications

Fuzzy appearance, less sharply defined and less tightly adherent

Crater Cracks Small and appearing at the termination of a weld; may be a single line in almost any direction or possibly multiple, or star shaped

Incomplete Fusion Pronounced accumulation of powder at the edge of the weld (the closer to the surface, the sharper the accumulation)

Undercut Less pronounced than incomplete fusion; can normally be detected prior to MPT by visual examination

Sub-surface Porosity Not clearly defined and not as pronounced as other discontinuities, yet readily distinguishable from indications of surface conditions

Slag Inclusion Similar to sub-surface porosity; appears when a high magnetizing field strength is used and slag inclusions are present

MARKING WELDS FOR REPAIR

Welds needing repair as determined by these procedures may be marked in accordance with the suggested process below. Prior to construction or weld inspections, other marking processes may be submitted to the field inspector for review.


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SUGGESTED PROCEDURE FOR MARKING WELDS FOR REPAIR

To mark welds for repair, the authorized representative of the NDE (Non-Destructive Examination) Service Provider will:

1. Paint a 6-inch diameter circle with bright yellow spray paint on the pipe to the left side of the weld near the twelve o’clock position. If more than one repair is required, paint an additional circle adjacent to the first.

2. Indicate the specific defect, its location, and the defective weld area to be repaired, in yellow paint stick or marker inside the circle.

3. After repair(s) have been made and found to be acceptable by appropriate non-destructive testing, paint over the defect and location marks with white spray paint, completely filling in the yellow circle. This signifies the weld is acceptable and ready for protective coating. Only individuals authorized by the NDE (Non-Destructive Examination) Service Provider and approved by the field inspector will use the yellow or white spray paint to mark such indications.

4. If a weld is to be cut out from the pipeline, apply red spray paint along the top of the pipe to the weld for at least 3 inches.

AUTHORIZED REPRESENTATIVE

Only those individuals authorized by the field inspector are permitted to mark welds for repair or acceptance.

EXAMINATION REPORTS

The Field Inspector is responsible to:

1. Verify the person performing the NDE performs the inspection per the requirements of this procedure.

2. Verify a daily report is completed including each weld non-destructively tested and all weld repairs. This sheet will include the person performing the interpretation and their ANST certification level.

3. Verify a status log is maintained daily to ensure all repairs are completed and that only those welds accepted are released for protective coating.

4. Ensure a copy of the report and status logs are turned into the Operating Center for filing for the life of the pipeline.


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PERSONNEL QUALIFICATIONS FOR INSPECTION

All personnel conducting magnetic particle testing will be qualified as required by the latest edition of SNT-TC-1A (“Level II for Magnetic Particle Testing”, latest edition).

The Field Supervisor or Field Inspector is responsible to:

1. Verify personnel or contract personnel performing the magnetic particle inspection meet, at a minimum, ASNT (American Society of Nondestructive Testing) Central Certification Program Level II.

2. Verify this documentation is on file.

3. Verify that personnel have the appropriate Operator Qualifications on file.

ACCEPTANCE STANDARDS

The ASME B31.3 acceptance standards for welds apply to discontinuities located by visual, radiographic, magnetic particle, liquid penetrant and ultrasonic methods which are stated in Section 3.02 (“Non-Destructive Testing Requirements”).

All non-destructive test methods are limited in the information that can be derived for the indications they produce. The Company may, therefore, reject any weld that appears to meet ASME B31.3 acceptance standards if, in the inspector’s opinion, the depth of a discontinuity may be detrimental to the weld.

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