08282016Sun
Last updateThu, 25 Aug 2016 4pm

i

Valve Basics Training Helps Fill Industry Skills Gap

Valve Basics Training Helps Fill Industry Skills Gap

One of the most keenly felt needs in tod...

An End-User’s Perspective on Valve Selection and Risk

An End-User’s Perspective on Valve Selection and Risk

I am not a valve expert, although I ofte...

New Test Stamp and More Updates on Pressure Vessel Codes

New Test Stamp and More Updates on Pressure Vessel Codes

A new test organization program and stam...

The Role of Valves in HAZOP Studies

The Role of Valves in HAZOP Studies

Process hazard analysis (PHA) is require...

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

Advertisement
i

Industry Headlines

ValvTechnologies Successfully Completes NUPIC Audit

3 DAYS AGO

ValvTechnologies, Inc. recently achieved NUPIC-approved suppliers list status, upon successful completion of the Nuclear Procurement Issues Committee (NUPIC) audit conducted at the Houston facility. NUPIC members include all domestic U.S. nuclear utilities as well as several international members.

Form...

Readmore

GE Oil & Gas Supporting ONGC’s Exploratory Drilling Campaign in India

3 DAYS AGO

GE Oil & Gas has been awarded a multi-million-dollar frame agreement by Oil and Natural Gas Corporation Limited (ONGC), India’s largest exploration and production company. Under the agreement , GE will provide an estimated 55 subsea wellheads (SG5) over next three years for the operator&rsqu...

Readmore

Chemical Activity Barometer Suggests Accelerated Business Activity

4 DAYS AGO

The Chemical Activity Barometer (CAB) expanded 0.4% in August following an upward revision for July. This marks the barometer’s sixth consecutive monthly gain. Accounting for adjustments, the CAB is up 3.2% over this time last year, the strongest year over year growth since January 2015. All d...

Readmore

Innovation Could Lead to Significant Cuts in Chemical Manufacturing Energy Use

4 DAYS AGO

Scientists from ExxonMobil and Georgia Tech have developed a new technology that could significantly reduce the amount of energy and emissions associated with manufacturing plastics. If brought to industrial scale, this breakthrough could reduce industry’s global annual carbon dioxide emissions ...

Readmore

Manufacturing Productivity in U.S. Higher Than Other Nations

2 DAYS AGO

“U.S. productivity unexpectedly declined for a third straight quarter in the three months through June, Labor Department figures showed. On a year-over-year basis, it fell for the first time since 2013,” Bloomberg reports .

But on a more positive note, “the U.S. still blows other natio...

Readmore

Durable Goods Orders Up 4.4%, a Six-Month High

2 DAYS AGO

New orders for manufactured durable goods in July increased $9.7 billion or 4.4% to $228.9 billion, the U.S. Commerce Department announced. This increase, up following two consecutive monthly decreases, followed a 4.2% June decrease. Excluding transportation, new orders increased 1.5%. Excluding def...

Readmore

Choosing the Right Fasteners

materials_q_and_a_graphicQ: What do I need to know to choose the right fasteners for my valves?

A: Choosing the proper fastener alloy is one of the most important considerations for reliable long-term operation of valves and other chemical process equipment. The easy part is choosing a fastener with adequate strength whereas selecting fasteners with the necessary corrosion resistance is somewhat more difficult. Choosing fasteners for their general corrosion resistance is certainly an obvious consideration, but it is sometimes even more important to use and specify fastener materials that will be resistant to the various forms of environmental stress corrosion cracking (SCC). Therefore, in certain environments it may be necessary to choose a bolt material that will experience some general corrosion but will provide adequate resistance to stress corrosion cracking. The logic behind this practice is that general corrosion is visually evident and with proper preventative maintenance, general corrosion can be seen and fasteners replaced as necessary. On the other hand, stress corrosion cracking is rarely visually apparent and often occurs without warning. When it does, then a serious valve failure is likely.

There are several forms of stress corrosion cracking that we need to be aware of such as chloride SCC, hydrogen sulfide HSSC, caustic embrittlement and liquid metal embrittlement. Because austenitic stainless-steel fasteners like ASTM A193 grade B8 provide good general corrosion resistance, they are commonly requested. However, one must exercise care as to their use if there is reason to believe that chloride SCC may be an issue. Chlorides as well as other halogens such as fluorides may be present in many CPI plants, and they can be the catalyst for SCC of austenitic stainless steels like 304 or 316. Chlorides are also present in the environment of seacoast plants. Because marine environments are very corrosive to carbon steels, many plants request stainless-steel fasteners but this may lead to the potential for a serious failure due to chloride SCC. Therefore, for marine environments or other chloride-containing services, alloy steel fasteners are preferred. In order to reduce their susceptibility to general corrosion, alloy steel fasteners like grade B7 are usually provided with some type of protective coating such as zinc or cadmium plating. Unfortunately, this can lead to another form of environmental stress cracking known as liquid metal embrittlement (LME), or a related failure mode, solid metal induced embrittlement (SMIE).

Zinc and cadmium plating are commonly used to provide galvanic protection to carbon steel fasteners so they will have an acceptable general corrosion rate. This is a useful practice for moderate temperatures but at elevated temperatures either LME or SMIE may occur. LME is the brittle failure of a normally ductile metal when in contact with a thin film of liquid metal and stressed in tension. The source of the thin film of liquid metal is the cadmium or zinc used for galvanic protection of steel from general corrosion. Cadmium and zinc have relatively low melting points so when plated fasteners are used near or above their melting point LME is possible. SMIE is similar, but occurs below the melting point of the embrittling metal. Prevention of LME and SMIE can be accomplished by avoiding plated fasteners above certain maximum temperatures. According to the available literature, this temperature is 370º F (188º C) for cadmium and 489º F (254º C) for zinc-plated alloy steel. Due to other environmental concerns, cadmium is not used much today but it is still available so you need to be sure of what type of plated fasteners you are getting from your supplier. I know of one case where zinc-plated fasteners were ordered but the supplier substituted some cadmium-plated fasteners by mistake. Since the service temperature was above 370° F (188° C), an LME/SMIE failure resulted.

Another common concern about fastener selection is hydrogen sulfide stress cracking, HSSC. Most metals are susceptible to stress cracking if exposed to hydrogen sulfide, and fasteners that are high strength and highly stressed are very susceptible to HSSC. Therefore, the NACE specifications, MR0103 and ISO 15156, which deal with hydrogen sulfide services, state that if fasteners are exposed to hydrogen sulfide they need to be made of certain alloys. For MR0103 those are ASTM A193 grades B7M or B8MA class 1A and A320 grade L7M. For ISO 15156 the recommend fasteners are A193 grade B7M or A320 grade L7M.

Some other services that can cause SCC with certain fasteners are caustic compounds and hydrofluoric acid. Fortunately, most atmospheric environments do not contain the stress cracking agents discussed here but if there is any chance of exposure, give careful consideration to the selection of fasteners. Choosing the right fastener is rather complex so use a fastener supplier that understands these issues or consult with a corrosion engineer.

Thomas Spence is director of materials engineering for Flowserve Corp. (www.flowserve.com), Dayton, OH. Reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association