Castings

Understanding end user valve approvals. Part 11a - Castings

Barrie Kirkman - 1 October 2015

There is much discussion in the market with regards to castings, casting quality and in-field performance. In this article I will “attempt”, from an end user viewpoint, to indicate those areas that they look out for when visiting valve manufacturers. Depending on their findings end users may also visit foundries.

About the author

Mr Barrie Kirkman
Barrie Kirkman, BSc CEng MIMechE, writes a regular column for Valve World, bringing his own personal views from inside the valve business.
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Valve manufacturer & foundries

Valve manufacturer and foundries

There are typically four models that end users see. They are listed below.

  1. The valve manufacturer uses only third party foundries (i.e. the most common).
  2. The valve manufacturer has a “Joint Venture Foundry”.
  3. The valve manufacturer is vertically integrated with their own foundry and also use other third party foundries.
  4. The valve manufacturer is vertically integrated with their own foundry and use no other foundries.

The valve manufacturer uses only third party foundries (i.e. the most common)

This is the most challenging for end users /auditors to assess. Some valve manufacturers operate their own approval methods restricting to a few foundries. These have been shared at several Valve World conferences and are very good. Others are less strict to the other extreme that the foundries are chosen based on ISO 9001 certification and commercial reasons. The auditor is faced with numerous foundries of which the quality varies considerably between them. The auditor begins to tackle the difficult task to assess the castings seen in the valve manufacturing plant. Remember the auditor’s time and his casting knowledge maybe limited?

  • Questions typically asked by the auditor cover the foundry history, qualification, selection, design methods, pattern design, acceptance criteria and monitoring. ANSI B16.34 levels 1 to 5 should be discussed together with required surface finish, reject / weld repair data. An understanding of various material qualifications should be obtained.

For example the pattern design with the runners / downcomers should be explained and their design basis established. Are the patterns supplied by the valve manufacturer or the foundry? Is it by “experience” or “analysis”? Often for commodity valves with “excess” design this area is not questioned. Beware though when producing low alloys / high end materials as such assumptions are very risky. I have seen WCB prototype extrapolated for alloy materials with disastrous results.

  • The auditor also should ask to see at least the following documentation from the foundries:
    • ISO Certification.
    • Valve manufacturer assessment data of the foundry, including pilot and casting production quality monitoring.
    • Heat treatment specification to review heating / cooling rates etc.
    • Review heat treatment charts against the specification.
    • Production casting analysis of defects / failures and continuous improvement.
    • The valve manufacturer QA/QC control of the foundry.
    • Last but not least – ask to see an original foundry material certificate.

Answers vary from comprehensive to nil. The auditor “relaxes” or “has concerns to follow through”. Dare I say “production casting analysis of defects / failures and continuous improvement” are often lacking. Amazingly, reviewing the above information often does reveal discrepancies such as heating rates, hold temperatures for the actual thickness, etc. In one example I reviewed some 29 heat treatment charts to identify the hold temperature shown for WCB was 880°C rather than 920°C. Neither the foundry nor the valve manufacturer had identified this through their normal QA/QC control. Sadly the western OEM had also not identified this……the valves are in the supply chain somewhere…maybe HSE “roll of the dice” on the operation plant?

The materials goods-in area at the valve manufacturer

Typical MSS SP55 information

The auditor looks for clear definitive hold areas for castings awaiting inspection and an effective process that shows inspection has been successfully completed. As the auditor walks through the plant he sees castings in process of manufacturer and arrives at the goods-in hold area. Within minutes you can judge whether the castings are acceptable or doubtful. As an auditor, I always ask the goods-in inspector:

  • To run through precisely the acceptance criteria they follow. Are they familiar with ANSI/ MSS SP55 “Quality Standard for Steel Castings for Valves, Flanges, Fittings, and Other Piping Components - Visual Method for Evaluation of Surface Irregularities”.
  • Are any castings rejected? If so for what reason and for which foundry?
  • Is any statistical analysis of rejects etc. undertaken?

 

The castings should have already been through due control at the foundry such that rejects should be very low indeed at the valve manufacturer. Actually zero but often they are not. Goods-in is used to control the casting quality which is most ineffective. It’s common practice in some parts of the world. Visibly the goods-in area looks impressive with copies of MSS SP55 displayed on the walls to give guidance to inspectors on surface finishes. This to me is a warning bell as the inspectors should have been suitably trained to MSS SP55. Also sample inspection is employed with no process to increase inspection levels when castings are rejected.

Typical surface finish

Too often poor castings are accepted that are clearly not meeting the surface requirements. Poor weld repairs seen with visible surface defects / cracks. Why? The foundry itself has no chance of meeting these requirements. Also the inspector advises that the casting is urgently required for production so they are accepted. So the inspector “accepts the castings”. Colour markings, hard stamp or simple paper acceptance are used. Where the hard stamp is used correctly quality control tends to be good. Identification of the inspector gives ownership and full traceability. In one instance the specification clearly stated the hard stamp to be used but on the shop floor it was not. As a “rule of thumb”, if the visual inspection of the casting reveals unacceptable surfaces / defects / high level of weld repairs then the quality of the casting internally would be suspect. Machining of flange surfaces often

Conclusion

Whenever an Auditor experiences any of the above findings then qualification of the valve manufacturer’s sub supplier foundry is highly unlikely. It may also jeopardize approval of the valve manufacturer?

I would like to qualify what I mean by “end users”. I refer to those end users that are top quartile in the end user community. There are end users that do accept the above casting quality which causes much confusion within the industry. I do not have to state those in the top quartile…you know who they are. Dare I say there are 3 levels of end users which I will attempt to define later.

The article will continue in the next magazine issue when the auditor observes the castings through the machining, NDT and hydrotesting processes. Discussions will develop into the three other valve manufacturer and foundry models. Thank you for your continued support. Please contact me if you have any questions or different views. If you wish a specific topic to be covered please do not hesitate to contact me and I will try to accommodate.

Barrie Kirkman, BSc CEng MIMechE, writes a regular column for Valve World, bringing his own personal views from inside the valve business.

Barrie can be reached on: barriekirkman@ntlworld.com.

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