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Valves in a Cement Slurry Line

Valves in a Cement Slurry Line

Basically everywhere you look in modern ...

Triple Offset Butterfly Valves

Triple Offset Butterfly Valves

Since their introduction to the market m...

Digital Valve Control Leads to Increased Plant Availability

Digital Valve Control Leads to Increased Plant Availability

Surge is characterized by fast flow reve...

Cast vs. Forged: The Ongoing Debate Takes a New Direction

Cast vs. Forged: The Ongoing Debate Takes a New Direction

In the valve industry, the cast versus f...

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VMA Members Among Plant Engineering 2016 Product of the Year Finalists

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Several VMA members are among this year’s Plant Engineering Product of the Year finalists. Emerson has products nominated in four different categories, while Siemens has several products nominated in a total of three different categories. Chesterton and Hunt Valve have products up for awards the...

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MSS Publishes Revised American National Standard for Steel Pipeline Flanges and Receives ANSI Approval

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The Manufacturers Standardization Society (MSS) announces that the substantially revised Standard Practice, SP-44-2016, Steel Pipeline Flanges, has been approved by the American National Standards Institute (ANSI) as a Revised American National Standard (ANS).

The first edition of MSS SP-44 was publish...

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U.S. Chemical Industry Remains Optimistic for 2017

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Hydraulic Institute Celebrates Centennial with New Logo

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Hydraulic Institute Celebrates Centennial with New Logo

The Hydraulic Institute (HI) will celebrate its centennial in 2017 with a new logo as part of a larger initiative to position HI for the next 100 years of service to the pump industry. The new logo is a key element of HI’s overall brand refresh and redesign process.

The logo includes a hidden &ld...

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U.S. Adds 178,000 Jobs, Unemployment Rate at 4.6%

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The unemployment rate declined 0.3% to 4.6% in November, and total nonfarm payroll employment increased by 178,000, the Department of Labor reported today. Employment gains occurred in professional and business services and in health care.

Employment in construction continued on its recent upward trend...

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Third Quarter GDP Revised Up to 3.2% Growth

2 DAYS AGO

Gross domestic product (GDP) in the U.S. increased at an annual rate of 3.2% in the third quarter of 2016, according to the second estimate released by the Department of Commerce. In the second quarter, real GDP increased 1.4%.

This new GDP estimate is based on more complete source data than were avail...

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Testing High-Nickel Alloy Castings in Refineries

vmspr12_nickel_1

Refiners today are increasingly dealing with more corrosive feedstocks that present new demands on valves in the process. However, maintenance personnel can detect problems before they become major issues by using different testing methods.

In 2009, a Minnesota-located refinery was experiencing through-wall leakage with several Class 300 rotary valves tasked with controlling crude unit vacuum prefractionator charge heaters. Maintenance personnel removed insulation from the valves and noted coke residue on the surface of the valve bodies, which identified for them where the leaks were occurring (Figure 1).

vmspr12_nickel_fig1Figure 1. Removing insulation from around the ball valve in question revealed leakage locations.Fortunately, this particular situation did not result in a safety event or a fire. Instead, it illustrates how the refining industry’s use of increasingly corrosive feedstocks can combine with unknown casting defects to cause potential valve problems.


THE INVESTIGATION/ EVALUATION

Five valve body castings, all grade CW2M (cast alloy C), were returned from the refinery to the manufacturer for evaluation using both nondestructive and destructive tests.

The nondestructive tests performed on the returned castings included visual examination, pressure testing and liquid penetrant (LP) examination.

Visual examination did not reveal any signs of corrosion on the wetted casting surfaces of the returned valves, which included both as-cast and machined surfaces.

The pressure testing used water at 1125 psig (7.76 megapascals or MPa) followed by helium at 150 psig (1.0 MPa). LP testing was performed to the requirements of ASTM A903 Level III, which considers linear and rounded indications exceeding 3/16 inch (4.8 millimeters) to be relevant. The helium and hydrostatic water tests revealed no leaks. Apparently, the hydrocarbon or potential coking sealed the leak paths once the valves were brought down to ambient temperature and removed from service.

LP testing of the castings revealed indications on the exterior surface—a lesser number of indications were on the interior, cored surfaces. These indications were on both as-cast and machined surfaces. Most of the LP indications were shallow [<0.02 inch (0.5 millimeters)] and removed with minor grinding. However, on the neck area of some castings, grinding did not remove the indications. The defect progressed through the wall of the casting and could represent a leak path. (Note that all of the returned valves had through-wall leaks in the neck area.)

Destructive testing, including metallographic examination, scanning electron microscopy (SEM) and energy dispersive spectrographic analyses, was performed on several of the returned castings.

vmspr12_nickel_fig2Figure 2. Opened defect showing three zones of fracture. Original magnification 11x. For example, corrosion testing was done on one valve body casting to compare results to maximum acceptance values previously set for this material grade. The test environment was boiling ferric sulfate-sulfuric acid per ASTM G28 Practice A. Although this standard is intended for wrought product forms, the practice A test method is also useful for castings. The corrosion rate was 140 milli-inches per year or mpy (3.5 millimeters/year or mm/y) compared to the manufacturer’s acceptance criteria of 360 mpy (9.1 mm/y) maximum. The grain boundaries were visible, which is typical for this grade. Of importance to this issue is the fact that this is a very severe test that does not represent actual applications for CW2M but does detect susceptibility of weld metal and heat-affected zone to intergranular corrosion attack.

vmspr12_nickel_fig3Figure 3. Rounded dendrite fingers indicating a shrinkage defect. Original magnification 600x.Fracture surfaces from the neck area of the same valve body were examined using SEM (Figure 2). The first zone examined was an outer layer that was approximately 0.03 to 0.06 inch (0.8 to 1.5 millimeters) thick. This chill layer solidifies rapidly when the molten metal first contacts the mold surface.

The second layer or zone 2 of the fracture has a dendritic pattern. This pattern represents columnar grains that grew perpendicular from the chill layer during the balance of the solidification process. The neck was cast solid so all the grain growth was from the outer diameter to the center. The center of the neck was then bored out during machining of the casting.

Zone 3 was ductile, dimple shear. This is the fracture mode seen on any mechanical break produced in the lab.

Within the dendritic zone of some of the fractures were rounded dendrite arms (Figure 3). The rounding indicates a shrinkage defect caused by an isolated area of liquid that was frozen off from the riser system because it was not properly fed. When the liquid was consumed during solidification, the dendrite arms could not continue to grow, leaving the blunted tips. Dark areas, which were identified as oxide films formed from exposure to air during casting solidification or heat treatment, were also found on the lab fractures. This proves the fractures were present before the casting went into service.

vmspr12_nickel_fig4Figure 4. Photomicrograph showing the leak path and the continuation of the grain boundary. Original magnification 500x.Inclusions and porosity also were visible. The inclusions were mold sand, slag and oxides. The grains were very large compared to wrought product forms—about 1/4 to over 1/2 inch (6 to 13 millimeters). The grain boundaries were the intersection of the dendrites formed during solidification. One leak path was cross-sectioned (the photomicrograph in Figure 4 shows the continuation along a grain boundary).

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