Understanding end user valve approvals - Part 11b: Castings

Understanding end user valve approvals. Part 11b - Castings

Barrie Kirkman - 29 October 2015

The previous article began to tackle the difficult task of end user assessment of castings and casting qualities. The first model discussed was The Valve Manufacturer using only third party foundries (i.e. the most common). This is where the end user has to use his experience and judgment of the castings seen in the valve manufacture factory. I will from an end user view point continue to indicate those areas that they look out for when visiting valve manufacturers.

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

Valve manufacturer and foundries

We have discussed the valve manufacturer’s control of these foundries and documentation requirements. The goods-in area inspection and variable interpretation in “casting surface review” to ANSI/ MSS SP55 “Quality Standard for Steel Castings for Valves, Flanges, Fittings, and Other Piping Components - Visual Method for Evaluation of Surface Irregularities” was identified. The castings are then either released into production or put in a rejection area for further action.

Rejection areas

The rejection areas can be most interesting. A small area is selected in a corner of the shop to be an exclusion area with a rectangular painted red line. So is this area ever used? If so what is the timeline to follow nonconformance reporting? I have seen rejected castings that have just been in the rejection area for months with evidence of “dust” on the casting surface. Dare I say these are just for “show”? Also the rejection area has often been empty…. where in fact if the valve manufacturer had followed their procedures, the area would be far too small! The end user observes this practice and often mentally notes the actual process. Confidence in the valve manufacturer begins to waver.

Production areas – casting machining

Gasket Machining – Gasket Surface Repairs

The castings will go through pre-machining and machining activities to achieve the final component for seat welding, assembly and testing. The machining activity will give a very good insight into the “internal quality” of the casting. For years I have witnessed many, many castings that completed this process without any issues such as slag inclusion, cracking etc. and need for weld repair. Today machining opens up internal defects on gasket surfaces and often on the flange extremes.

Depending on the material such repairs are permitted and the defects are qualified “minor” and “major repairs”. Such guide lines are given in the ASTM standards with various “interpretations” from manufacturer to manufacturer. The “visual” experience of seeing “no weld repairs” to “a rash of repairs” can cause the end user to accept or reject the casting. Repairs are witnessed to ensure they are in accordance to the WPS etc. Is the welder appropriately qualified? Removal of defect by chipping and grinding often is missed. The record of the defect is very rarely done as “they are qualified as minor”. Crack surface detection is often omitted. The flange gasket surface repair does give rise to concern. These repairs will not be heat treated and therefore will result in hard areas for the gasket to seal against. For certain gaskets this will be no problem but there is a probability that they may give an issue in the field. I have seen some manufacturers attempting to locally heat the weld repair areas with gas torches but in reality their effect is not ensured.

Gasket Machining – Gasket Surface Repairs

Being an auditor you can stand back and look at the castings to identify “common issues” in defects and repairs. Repair patterns and trends are very obvious. As quality data is not collected, correlated nor subject to improvement, “poor practices” continue unabated. When the valve manufacturer is challenged answers vary. “It’s acceptable to the client”, “It meets the standards”, “It’s always been done like this”, “It’s too costly to correct”.

This has been seen on carbon steel, low alloys and stainless steels……even Duplex. Discussion always occurs on allowable weld repair percentages and again reflects type of materials. At the lower end for carbon steel minor repairs could be 40% and major 15%. When the valve is assembled and painted the end user has no knowledge of what weld repair has been done. The responsibility to have this information supplied on the casting lies with “The Purchaser” as they have to state this requirement on the purchase order. How many know this and if they do have actually implemented?

Conversation with end users reveals they really believe that the brand they are using has zero or minimal repairs. They qualify this as they state they have visited the manufacturer. I keep quiet. As I have moved around the manufacturing supply chain I have seen “welders and their weld bays cleaned up and removed from the shop floor” to give the impression “no weld repairs”.

I observed one manufacturer placing a welder and mobile equipment in the machine shop that just repaired casting machining defects without any control. When an end user toured the factory the welder was removed. In another example a manufacturer removed all welding stubs and equipment from areas of the plant in preparation for an end user visit. I was in the factory before, during and after the end user visit. The welding practices were back in operation immediately after the visit. Dare I say it was a little difficult to approve such a practice?

Where “reputable” manufacturers are audited they do have good controls on casting quality and require foundry improvements. Unsuitable foundries are removed from the supplier list. The auditor has no problem in accepting.

Conclusion

 Valve manufacturer and foundries

When an auditor witnesses the above casting machining and repairs, acceptance of the valve manufacturer’s sub-supplier foundry maybe unlikely. It may also jeopardize approval of the valve manufacturer? The series will continue with the next article when the auditor observes the castings through 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. They are most welcome.



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