Across many forms of merchandise in a selection of industries, the practice of mixing assorted elements from varied sources all over the world is the rule, not the exception. Should this be a concern for a control valve user? For instance, when an end user discovers that several elements are being made in China (Figure 1), should the consumer worry in regards to the quality?
When dealing with a serious valve vendor, the answer is “no.” There shouldn’t be any room for doubt when the seller has a quantity of checks and balances in place focusing on product high quality to ensure management valves operate as designed, need minimal maintenance, perform safely and operate within environmental regulations.
Yet, despite such efforts by the seller, a management valve person may have questions on international sourcing and the nation of origin. This article discusses how one main management valve vendor ensures product quality. Many other control valve distributors comply with the identical or comparable procedures.
Quality specification brings world assurance
Emerson enforces a comprehensive quality specification for its Fisher management valves that have to be met by suppliers of pressure-containing and structural metal castings. The quality specification includes more than a dozen necessities that apply to the following areas:
Supplier qualification
Welding procedures
Marking inspection and testing
Tryout and sample castings
Production castings
Certification of compliance
Supplier qualification — Suppliers bear a rigorous qualification process. The course of thoroughly investigates a possible supplier’s capability to fulfill material specs and applicable worldwide codes and requirements — as properly as particular requirements related to element manufacture. In the case of castings, a foundry is considered “qualified” when it passes a critical analysis by Fisher’s engineers.
The foundry must reveal a record of qualification by a third-party inspection agency and conform to numerous standards, such as ISO 9001:2000, ASME, A2LA, PED and others. It should cross a review of its quality program as well as on-site audits of the foundry’s processes and procedures similar to welding, warmth therapy and non-destructive examination. Additional proof of efficiency is set by evaluation of tryout castings to confirm specifications are met.
Welding procedures — Welding is used in the course of the manufacturing and upgrading of castings, similar to when radiographic examination is required. Welding requirements state that procedures and welder qualifications must meet ASME Section IX (or EN ISO 15614-1 and ISO 9606-1) qualification standards. Similarly, every lot of weld filler must adjust to ASME/AWS chemical evaluation specifications. In Europe, compliance must be to EN499. Weld filler should have actual chemistry.
Marking inspection and testing — Valve physique castings have markings (Figure 2) that determine the foundry that poured the casting and that point out the warmth code. Material identification can also be typically proven on the body casting, corresponding to CC, CF8M, CN7M and others.
Casting checks — Emerson technicians conduct each visual inspections and mechanical exams on pressure-retaining castings.
As-cast exterior and internal surfaces are inspected visually for unacceptable irregularities, together with scorching tears and cracks, shrink, sand inclusions, veining and rat tails. Mechanical testing entails a hydrostatic stress check to verify the leak tightness of a control valve’s pressure-retaining parts, together with the physique and bonnet castings. The take a look at procedure involves a fixture that closes off cavities that may be pressurized in service and then topics the component to the hydrostatic shell check stress appropriate for the valve body material and class.
ASME B16.34 sets out the hydrostatic test pressure to use for steel and alloy valves. It’s calculated by multiplying the working stress by 1.5 and rounding to the next higher 25 psig increment. Any visually detectable weeping or leaking through the stress boundary partitions which may be part of the valve assembly is a mandatory trigger for rejection (Figure 3).
Compliance with these specs should be ensured, as properly as with other necessities concerning supplies.
Figure 2. Markings establish the foundry and materials of the valve physique. These control valve our bodies have been forged at an Emerson-approved foundry in China.
Meeting material necessities
Valve casting integrity and high quality begins with specs that call not just for premium supplies, but additionally for the materials that work finest in the meant purposes. These software necessities embrace strength and ductility in addition to resistance to sure elements, including the makeup of the controlled fluid, working temperature and flow velocity.
For instance, chemical composition should be managed exactly to achieve an alloy’s meant efficiency stage. Carbon metal castings for valves meant for use in oil and gas purposes should meet NACE SP0472 recommendations that chemical composition be managed to lower than zero.43% carbon equivalency. The lower carbon content material improves weldability and reduces the potential for stress cracking by hydrogen sulfide sometimes present in oil and fuel manufacturing and processing purposes.
Another instance of supplies tied to a particular utility embody those for upstream oil and gasoline manufacturing. Many of these purposes occur in the arctic regions of Russia and Canada. For this service, castings are ASME SA 352 Grade LCC, while forgings should meet ASME SA 350 Grade LF2.
Many merchandise with global use now comply with twin materials specifications to meet ASME and European standards. For instance, steel castings are specified and licensed to both ASME SA216 Grade WCC and EN 10213 Grade 1.0619. Emerson often adds its personal stringent necessities corresponding to the heat treating of high nickel alloys, more demanding chemical composition or special welding procedures.
In the previous, Emerson has supplemented conventional ASTM and ASME specifications to attain the improved corrosion-resistance ranges and excessive temperature capabilities offered by high-nickel alloys. This is now completed by the model new ASTM specification A990, which addresses both material composition and quality.
Figure 3. Pressure-retaining components of a valve are subjected to hydrostatic testing to evaluate the parts’ integrity. Visible leakage or seepage by way of a casting means automatic rejection.
Qualifying a foundry
As a part of a prospective foundry’s qualification, Emerson inspects and checks Fisher valve castings. Non-destructive testing radiography is used as a monitoring device. ASTM A990 Class C requires radiography of the primary casting of each sample. The acceptance criterion is Level three for categories A, B and C. For categories D via G, no cracking, sizzling tears or inserts are allowed as specified in ASTM A990.
High-nickel alloy castings provide improved performance in corrosive providers and elevated temperatures. However, if high-nickel castings are improperly ready, they’ll pose main issues, including poor integrity, poor weldability and lower-than-expected corrosion resistance. A systematic foundry qualification course of could be adopted to avoid these casting difficulties.
เกจวัดแรงดันออกซิเจนราคา must cast a 1-inch thick high-nickel test plate (Figure 4) that meets ASTM Material Specification A990. It’s troublesome to cast because of the distinction in cross-section between the base of the weld cavity (in the center) and the general 1-inch thickness of the plate. The cavity of the poured plate is then crammed with a matching composition weld material. The welder and process for this step must meet the standards outlined in Section IX of the ASME Boiler and Pressure Vessel Code. Test bars (3/8-inch thick) are cut from the plate and bent over a 1½-inch mandrel per ASTM A990 right into a U-shape.
The bars are examined closely for cracking alongside the weld heat-affected zone, casting grain boundaries or dendrite boundaries. Failure to fulfill quality standards will result within the disqualification of the foundry from additional consideration. Casting patterns have to be dedicated solely to high-nickel alloy service. Use of carbon steel or a stainless-steel sample is unacceptable because of differences in solidification properties.
Shrinkage rates for gates, risers and different equipment can vary considerably. Once the dedicated sample tools for every of those components has been secured, try-out castings are poured for each pattern-alloy combination. The castings are then radiographed.
The intent is to reveal any inherent casting defects — similar to shrinkage — that must be eradicated by modifying the pattern rigging.
Figure four. In a foundry evaluation, a casting is filled with weld filler, then sliced to yield a bar for bend testing.
A certified foundry
Emerson has used a Chinese foundry (Figure 5) to forged Fisher valve our bodies for more than a decade. After an exploratory visit by procurement and manufacturing specialists, followed by an extensive qualification process, the foundry was accredited and has been delivering high-quality valve body and bonnet castings to Fisher valve manufacturing websites.
To assist guarantee the standard of the castings it produces, the Chinese foundry has carried out international standards and has obtained certifications for German TUV and CE, Norway DNV, German Lloyd’s and American ABS, and has passed worldwide high quality system certifications of ISO 9001 and QS -9000.
The foundry has been awarded Gold Medals 3 times consecutively in the Beijing International Casting, Forging and Industrial Boiler Expo. It has twice obtained an Excellent Supplier award from Emerson.
Figure 5. This Chinese foundry meets all specs for casting valve our bodies.
Control valve customers could be involved once they learn certain valve components usually are not made in the us or Europe, but elsewhere. Perhaps their concern stems from expertise with different inferior merchandise, similar to appliances, garments or electronics made in those nations and sold on-line. But if the valve parts are being provided to a major management valve vendor that has gone to nice lengths to qualify the foundry or provider, then users may be assured the valves meet all specifications.