1

Progress Energy’s

Experiences with Quality

Issues on Cast C12A Valve

Bodies

2

Background

As part of the construction of the Richmond County 5 Combined Cycle Unit, large bore C12A valves had been ordered for HP and HRH steam lines

4 – 24” HRH valves and 2 – 16” HP steam valves were ordered.

Early indications of problems

During routine correspondence with the design company it was noticed that numerous base metal repairs had been performed on the valve bodies at the valve manufacturer.

As a result, Progress requested weld documentation including, filler metal chemistries, PWHT charts and hardness data.

The fabricator was unable to supply the data.

3

Emerging Problems

A shop visit was performed to audit the fabricators compliance with the Progress Energy Grade 91 specification.

It was discovered that the fabricator was unaware of the spec even though it had been provided with the contract.

As a result, none of the requirements of spec had been met.

4

Deficiencies discovered

The valves had been processed according to the fabricators standard practices.

The following deficiencies were noted:

Failure to adhere to Ni+Mn content in the filler metals

Inappropriate preheat practices

No moisture control between welding and PWHT

Minimal control of PWHT process

No formal hardness testing procedures

5

Follow up testing

Since the requirements of the spec had not been adhered to, follow up testing was performed.

MT surface examination was performed to ensure no surface cracking from SCC.

Random hardness testing was performed in areas where welds were supposedly performed. Some soft areas were identified.

6

Recovery Plan

Since the delivery schedule was being impacted, the fabricator decided to disassemble the valves, renormalize and temper.

To account for oxidation during heat treatment, the weld prep areas and areas on the bonnet were built up with weld metal.

7

Renormalization and Tempering

Initial attempts at renormalizing the HP valves was unsuccessful due to slow cooling rates.

8

Renormalizing and Tempering

It was also discovered that the standard method of temperature control was with a single TC located at the top of the furnace.

No base metal thermocouples were attached.

Comparisons of temperature trends showed up to 90 minutes of lag time.

After the challenges with N&T, there was also the unanticipated departure of the QC Manager.

9

Further casting problems

After N&T was completed, machining of the valves was started.

As the weld preps were being machined, cracking was found in the areas that were built up.

The cracking was oriented both circumferentially and longitudinally.

10

Crack Locations

11

Crack Locations

12

Crack repairs

The cracks were mostly machined out and those that extended in the base metal were ground and welded.

To ensure there was no further subsurface cracking, Progress requested RT of the bodies.

The RT’s showed no further cracking but revealed extensive casting and shrinkage voids in the 24” valves but not the 16” valves.

All valve bodies were 100% RT’d. 13

Voids

The voids discovered in the 24” valves ranged in size but some were quite extensive.

The voids were compared to reference radiographs to determine acceptability.

3 to 4 areas on each valve body were found to be unacceptable and required repair.

All unacceptable voids were ground out and repaired. Some extended almost through wall.

14

Example of excavations

15

Excavated Voids

16

Void Radiographs

17

Valve Completion

Finally, all valve repairs were completed and the assembled valves were shipped to the site for installation.

As precaution, Mr. Jeff Henry with Structural Integrity was contracted to review all of the QC documentation to ensure that the valves were fit for service.

All valves were found to be fit but numerous concerns had been raised that may need to be addressed at a code level.

18

Issues raised

Handling and processing of C12A cast material is problematic. Foundries and valve fabricators are clearly not up to speed on the proper procedures.

Little to no filler metal chemistry control

Poor preheat practices

Moisture control between welding and PWHT.

Poor PWHT practices, especially in furnace PWHT.

19

Issues continued

No requirement for volumetric examination unless specified by the customer (see A217 supplementary requirements).

QC documentation is not adequately retained. Especially dealing with base metal repairs at the foundry and the fabricator.

This is not an isolated occurrance. Similar issues were found at other fabricators although not to the same extent.

20

Other concerns

Follow up visits to the foundries uncovered other issues such as:

Sequence of heat treatment (N&T then weld repair then PWHT)

Adequacy of temperature monitoring during furnace heat treatment.

No volumetric examination requirements.

21

Now What?

Immediately revise the fabrication specification to include the following items:

Mandatory full volumetric examinations of all castings using radiography

Require thermocouples to be placed directly on the casting bodies at prescribed locations during normalizing, tempering and PWHT.

Require valve manufacturers to communicate requirements to foundries.

22

Existing Equipment

With the issues identified, what is the status of cast valves in the field?

A plan of action was developed to address the status of valves in service.

Review of fabrication documentation.

Development of NDE procedures to identify welds in existing valves.

23

Documentation Review

A review of existing valve fabrication documentation was initiated.

As expected, most of the relevant information did not exist. There was no standard practice for foundries to document weld repairs.

No N&T or PWHT charts were provided from the foundries.

Conclusions: No way to verify that valves were fabricated correctly.

24

NDE Development

Without documentation, the valves would

have to be evaluated individually.

Progress Energy NDE Services began research on how to detect weld repairs in existing valves.

A technique was developed using Eddy Current testing to detect changes in permeability.

This technique has now been used successfully in the field to detect repairs.

25

ASME Code Changes

As a result of the problems encountered, a presentation was made to the ASME Section II/IX Task Group on CSEF Steels.

Changes were proposed to Code Case 2192 to include:

Full volumetric examination

Renormalizing after major repairs

Requirement for attaching TC’s to base metal

Mapping of weld repairs

26

ASME Code Changes

Revised Code Case 2192-7 was passed by ASME Section I at the August Code meetings and was sent to letter ballot.

Next step: Submit the same proposal to ASME B31.1 for action.

27

Questions ?

28