Brant Pfantz, global supply chain strategy manager at Emerson Automation Solutions in Marshalltown, Iowa, writes that control valve users can be concerned when they learn certain valve components are not made in the U.S. or Europe, but elsewhere. In his article, Valve Sourcing Goes Global in the August 2019 issue of Processing magazine, he shows how Emerson goes to great lengths to ensure that valve components from all suppliers worldwide meet its strict requirements for quality.
When an end user discovers that several components are being made in China, should the user worry about the quality? When dealing with a major valve vendor, the answer is “no.” There shouldn’t be any room for doubt when the vendor has multiple checks and balances in place focusing on product quality to ensure control valves operate as designed, need minimal maintenance, perform safely and operate within environmental regulations.
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Control valve components from China and other countries are perfectly acceptable if manufacturing processes are certified and approved by major valve vendors.
Quality Specification Brings Global Assurance
Emerson enforces a comprehensive quality specification for its Fisher control valves that must be met by suppliers of pressure-containing and structural metal castings. The quality specification includes more than a dozen requirements applying to:
Pfantz says suppliers undergo a rigorous qualification process.
The foundry must demonstrate a record of qualification by a third-party inspection agency and conform to various standards, such as ISO 9001:2000, ASME, A2LA, PED and others. It must pass a review of its quality program as well as on-site audits of the foundry’s processes and procedures such as welding, heat treatment and non-destructive examination.
Markings identify the foundry and materials of the valve body. These control valve bodies were cast at an Emerson-approved foundry in China.
Emerson technicians conduct both visual inspections and mechanical tests on pressure-retaining castings, Pfantz explains:
As-cast external and internal surfaces are inspected visually for unacceptable irregularities, including hot tears and cracks, shrink, sand inclusions, veining and rat tails. Mechanical testing involves a hydrostatic pressure test to confirm the leak tightness of a control valve’s pressure-retaining parts, including the body and bonnet castings. The test procedure involves a fixture that closes off cavities that would be pressurized in service and then subjects the component to the hydrostatic shell test pressure appropriate for the valve body material and class.
Any visually detectable weeping or leaking through the pressure boundary walls that are part of the valve assembly is a mandatory cause for rejection.
Pressure-retaining components of a valve are subjected to hydrostatic testing to evaluate the parts’ integrity. Visible leakage or seepage through a casting means automatic rejection.
Valve casting integrity and quality begins with specifications that call not only for premium materials, but also for the materials that work best in the intended applications. These application requirements include strength and ductility as well as resistance to certain factors, including the makeup of the controlled fluid, operating temperature and flow velocity, says Pfantz:
For instance, chemical composition must be controlled precisely to achieve an alloy’s intended performance level. Carbon steel castings for valves intended for use in oil and gas applications must meet NACE SP0472 recommendations that chemical composition be controlled to less than 0.43% carbon equivalency.
In the past, Emerson has supplemented conventional ASTM and ASME specifications to achieve and verify the enhanced corrosion-resistance levels and high temperature capabilities provided by high-nickel alloys. This enhancement is now addressed by the new ASTM specification A990, which addresses both material composition and quality.
Qualifying a Foundry
As part of a prospective foundry’s qualification, Emerson inspects and tests Fisher valve castings. Non-destructive testing radiography is used as a monitoring tool. Also, the foundry must cast a high-nickel test plate that meets ASTM Material Specification A990, says Pfantz.
Test bars (3/8-inch thick) are cut from the plate and bent over a 1½-inch mandrel per ASTM A990 into a U-shape. The bars are examined closely for cracking along the weld heat-affected zone, casting grain boundaries or dendrite boundaries. Failure to meet quality standards will result in the disqualification of the foundry from further consideration.
In a foundry evaluation, a casting is filled with weld filler, then sliced to yield a bar for bend testing.
A Qualified Foundry
Pfantz says Emerson has used a Chinese foundry to cast Fisher valve bodies for more than a decade.
After an exploratory visit by procurement and manufacturing specialists, followed by an extensive qualification process, the foundry was approved and has been delivering high-quality valve body and bonnet castings to Fisher valve manufacturing sites.
The foundry has been awarded Gold Medals three times consecutively in the Beijing International Casting, Forging and Industrial Boiler Expo. It has twice received an Excellent Supplier award from Emerson.
Summary
Control valve purchasers might can be concerned when they learn certain valve components are not made in the U.S. or Europe. But Pfantz says if the valve parts are being supplied to a major control valve vendor that has gone to great lengths to qualify the foundry or supplier, then users can be assured the valves meet all specifications.