A New Casting Standard

Transcription

1 By: Greg Johnson 1

2 A New Casting Standard Who, What, Where, When & Most importantly -Why?

3 Casting Quality is Scrutinized More Today New foundries in New Countries

4 Casting Quality is Scrutinized More Today New foundries in New Countries A much higher A much higher percentage of recent casting failures and rejections

5 Casting Quality is Scrutinized More Today New foundries in New Countries A much higher percentage of recent casting failures and rejections Casting problems Some real and some perceived Perception (of quality) is reality End-user s under much more pressure from management & government entities

6 Increased Pressure on Casting Suppliers Most casting suppliers are in China Culture is a issue Commitment to western requirements is still an issue

7 Culture & Commitment Many Chinese foundries are not firmly rooted in western quality expectations nor do they understand the western manufacturing approach Chinese NDE personnel, techniques and equipment are still not universally equal to western standards nor do they fully understand western NDE requirements & specifications The culture in China requires buyers to have boots on the ground and eyes on the processes Lack of repeatability is still a big issue

8 Additional Guidance for Commodity Casting Quality will Help

9 Standard Class or Commodity Valve Castings Have Few Requirements Must meet ASTM material specifications Must not leak under hydrotest Must pass MSS SP-55 visual examination

10 Visual Examination Doesn t Reveal Everything

11 Oops is not an Excuse

12 Were those Old Castings Really Better?

13 The Short Answer is We Think So However there was not much radiography done on commodity valves years ago. There were not even any acceptance criteria until MSS SP-54 in 1959 The requirements for SP-54 were voluntary and not mandatory But Designs were robust and wall thickness much greater than today.

14 The Short Answer is, "we think So Was it a case of no one scrutinized the castings, or were they all very good? Catastrophic casting failures were almost unheard of.

15 The Short Answer is, "we think So Domestic foundries had been pouring quality steel since the early 1900 s There was a lot of pride and art in the casting process

16 What are the guidelines for valve castings today? Unless a specific casting quality level is specified via NDE, valve castings must only meet MSS SP-55 visual inspection criteria and not leak under hydrotest

17 API 598 & MSS SP-55 API 598, Para : A visual examination shall be performed by the valve manufacturer on all castings of bodies, bonnets, covers and closure elements to assure conformance with MSS SP- 55.

18 What Higher Casting Quality Levels are Requested? Most common is- Special Class in accordance with ASME B16.34 Highly critical applications such as Hydrogen and nuclear service require much better castings

19 What is Special Class? Radiographic acceptance criteria in accordance with B16.34

20 What is Special Class? Critical areas per B16.34

21 Commodity or Standard Castings Commodity is a commercial term, not a technical term The vast majority of steel valve castings are not special How is their quality assessed? What acceptance criteria is there? MSS SP-55 and no leakage!

22 End-users and OEM s want guidelines Castings are evaluated today when API RP591 testing is requested. Users originally wanted all evaluated valves to meet special class Latest revision of RP591 has loosened the radiographic acceptance criteria by one level This has established a quality expectation for standard class valves

23 Some Requirements of RP591 are 100% of pressure boundary must be radiographed Microstructural examination at 100X More extensive chemical analysis Now Tougher

24 The Proposed MSS Casting Standard Who-The Manufacturers Standardization Society (MSS) What- Quality Standard for Steel Castings Used in Standard Class Steel Valves-Sampling Method for Evaluating Casting Quality When- Under development now Where-Under the auspices of MSS Com. 304, Quality Standards

25 Scope This standard practice provides minimum requirements for pressure containing steel castings used in the manufacture of ASME B16.34 Standard Class, cast steel valves. It covers castings made by both the green sand and investment casting methods. Acceptance standards, which provide for a minimum quality level for Standard Class cast steel valve castings, are detailed within this document. Materials covered by this standard include ASTM A216, grades WCA, WCB & WCC and ASTM A217 grades WC6, WC9, C5 & C12. This Standard can also be utilized for other materials such as stainless steel etc.

26 Purpose The purpose of this standard practice is to provide evaluation methods and nondestructive acceptance criteria for non- Special Class, steel valve castings. The document additionally provides procedures for developing and qualifying Standard Class pilot castings.

27 Some Key Definitions Standard Class steel casting-a valve casting designed for Standard Class in accordance with ASME B16.34 and not requiring any additional acceptance criteria for Limited Class or Special Class. Pilot Casting(s)-A casting(s) made and examined as part of the initiation and development of the production method, e.g., the first casting(s) from a new or modified pattern using the identical foundry practice, i.e., risering, gating, chilling, coring and molding as the produc-tion castings it is intended to represent. Production Casting(s) -A casting(s) produced as part of a standard product run using normal production processes, practices and examinations as defined by the manufacturer.

28 Mandatory Requirements for Pilot Castings All pilot castings shall be evaluated without weld repairs All accessible external and internal surfaces shall be dye penetrant (PT) inspected in accordance with MSS SP-93. All accessible external and internal surfaces shall be magnetic particle (MT) inspected in accordance with MSS SP-53. Critical areas as defined by ASME B16.34 are radiographed (RT) in accordance with MSS SP-54

29 Requirements for Production Castings Each production casting shall have all external and accessible internal areas of the casting visually inspected to the requirements of MSS SP-55 Standard production, pressure containing castings shall be randomly selected based on the sampling plan specified in Annex A The randomly selected casting(s) shall be radiographed and shall meet the radiographic quality levels as listed in Tables 1, 2 & 3, as applicable for critical areas as designated in ASME B16.34

30 Recommended Sample Plan- Gate Valves Pressure Class NPS % 1% 2% 5% 5% % 1% 5% 5% 5% % 2% 5% 10% 10% >24 5% 5% 10% 10% 10%

31 Recommended Sample Plan- Globe Valves Pressure Class NPS % 5% 5% 5% 5% % 5% 5% 5% 10% % 10% 10% 10%

32 Recommended Sample Plan- Check Valves Pressure Class NPS % 1% 2% 5% 10% % 1% 5% 5% 10% % 2% 5% 10% 10% >24 5% 5% 10% 10%

33 RT Acceptance Criteria Discontinuity Type Category B16.34 Special Class RP591 & MSS Document Gas A A2 A3 Sand B B3 B4 Shrink, Type 1 C CA2 CA3 Shrink, Type 2 C CB3 CB4 Shrink, Type 3 C CC3 CC4 Shrink, Type 4 C CD3 CD4 Hot Tears and cracks D & E none none Inserts (chills & chaplets) F none none

34 End-users Casting Quality Needs are Varied Not every plant requirement calls for high integrity castings which do cost more to produce

35 An Additional Solution Create three classes of valves, all based upon NDE performed and acceptance criteria applied Would create an opportunity for the best manufacturers and the average ones as well Class 1, Class 2, Class 3

36 Class 1 Valves Pressure envelope radiographed with acceptance criteria in accordance ASME B16.34 for special class Castings magnetic particle (MT) or dye penetrant (PT) examined in accordance with MSS SP-53 & SP-93 Castings visually examined in accordance to MSS SP-55 Finished valves hydrostatically tested in accordance with API 598

37 Could Reduce the Cost of Expensive Casting Upgrades

38 Class 2 Valves Castings evaluated in accordance with the proposed MSS document Visually examined in accordance with MSS SP-55 Valves hydrostatically tested in accordance with API 598

39 Class 3 Valves Castings visually examined in accordance with MSS SP55 Finished valves hydrostatically tested in accordance with API 598

40 Review Casting quality is still a concern Standard class valves have no real inspection criteria MSS is creating a casting document for specifying standard class castings RT Acceptance criteria A detailed sampling plan

41 Thanks