ML19260D051

Final Deficiency Rept Re Grit Blasting of Fabricated Piping Assemblies.Caused by Operator Sandblasting W/O Diffusers. Straight Nozzle Will Be Locked in Tool Box Under Control of Sandblast Operator

ML19260D051
Person / Time
Site:	Hartsville
Issue date:	01/31/1980
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19260D045	List: ML19260D044 ML19260D051
References
NCR-HNP-A-068, NCR-HNP-A-68, NRC-HNP-A-68, NUDOCS 8002070300
Download: ML19260D051 (2)

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ENCLOSURE HARTSVILLE NUCLEAR PLANT - ALL UNITS GRIT BLASTING OF FABRICATED PIPING ASSEMBLIES 10CFR50.55(e) - REPORT No. 2 (FINAL)

NRC HNP-A-068 On October 19, 1979, TVA notified NRC-OIE Region II, Inspector R. W.

Wright, of a potentially reportable condition under 10CFR50.55(e) regarding removal of excess base metal from elbows of prefabricated piping assemblies due to grit blasting without use of a dif fuser or deflection shields. This is the final report on the subject reportable condition.

Description of Deficiency TVA personnel working in the sandblast shop were cleaning interiors of small diameter (four inches or less) piping assemblies with the diffuser removed from the sandblaster nozzle.

The diffuser redirects the grit f rom straight out the nozzle to an angle roughly perpendicular to the nozzle against the interior wall of the pipe. Removing the diffuser caused the grit to be blown down the pipe and continuously impinged upon any pipe assembly elbow in its path as the blaster nozzle was pulled through the pipe. Continuous blasting of the elbow caused excessive base metal removal in some piping assembly elbows. Attention was directed to the situation when a grit blaster operator blew a hole through a schedule 40 pipe elbow for a nonsafety-related system. As a result, eight QCIR's were initiated.

All of the piping assemblies (165) that were available in the sandblast yard were inspected. No other piping assemblies were found to have wall thicknesses below minimum.

Of the 165 assemblies examined, 48 were grit blasted on the first shift, 59 on the second shift, and 28 on the third shift. The shifts which blasted the 30 remaining assemblies could not be specifically identified.

Of the eight QCIR's involved, two assemblies were blasted on the first shift, four on the second shift, and two on the third shift.

Cause of the Deficiency Sandblaster operators were trying to facilitate their cleaning of small diameter piping assemblies by removing the sandblaster diffusers.

Safety Implications Of the eight QCIR's documenting deficiencies, three deal with safety-related (ASME) piping. Two were in the low pressure injection (LPI) system and one was in the radwaste system. Of those three, one in the LPI system required the replacement of the elbow because the minimum wall thickness was violated. Since this safety-related pipe elbow was damaged beyond acceptable standards, the possibility exists of 1938 078 800207o 3 0 0

having a small pipe break affecting the correct operation of this safety system. Therefore, if this practice had been allowed to continue, multiple occurrences of defective safety-related piping could have been installed, thus degrading plant safety. All safety-related piping has undergone or will undergo testing to above its design pressure in accordance with applicable codes. This will ensure that the piping has sufficient structural integrity to perform its intended safety function.

Corrective Action Eight Quality Control Investigation Reports (QCIR's) have been written to date to document the wall deficiencies resulting from grit blasting.

Of the eight, five were dispositioned to "use as is" because the minimum pipe wall thickness had not been violated. However, three were found to have wall thicknesses below the minimum requirements, one of which was to be part of a safety-related system. The three assemblies which were found to have wall thicknesses below the minimum requirement (including the one with the hole blown in it) have had their piping elbows replaced.

As a result of this deficiency, TVA's Manager of Engineering Design sent a memo to all other TVA plants under construction initiating an investigation into the grit blasting procedures at other plants. All plants reported that no grit blasting was done without the proper diffuser except for a single isolated occurrence at Phipps Bend Nuclear Plant. On that occasion, when the regular sandblast operator was absent, his substitute blasted a hole in an elbow while using a straight nozzle. The damaged elbow was replaced Subsequently, the sandblast shop was instructed to use only a diffuser nozzle when blasting small diameter pipe. Also, the straight nozzle will be locked in a tool box under control of the regular sandblast operator only. No other such occurrences have been encountered at Phipps Bend.

Action Required to Prevent Recurrence Shortly after the deficiency was brought to management's attention, the sandblast shop supervisor was verbally directed to cease sandblasting c' piping four inches and smaller pending further investigations.

Following that action, a memorandum was sent from the construction engineers to the general construction superintendent concerning pre-installation pipe cleaning.

This memorandum directed that no future interior grit blasting of vendor prefabricated piping assemblies would be performed unless approved by construction project engineering and all future grit blasting-would be controlled by a site procedure which was being prepared at that time.

This procedure (SOP 48) has now been approved and issued. It also establishes quality control surveillance requirements to monitor grit blasting practices. All grit blasting personnel have been trained to strictly adhere to this procedure.

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