Q:  Hello I am researching titanium and C276 hardware for a submerged application in a high chloride (20,000 mg/L) elevated temperature environment (125F). Corrosion resistance is more important than shear or tensile strength in this application.

A: Titanium screws should be a good choice for your application especially Grade 2 if the strength is not an issue. Hastelloy C276 fasteners may also be a good choice as well if your forming a lot of HCl.  In terms of galling, whenever you have similar fasteners tightened on each other there is the possibility for galling. However there are a few great ways to minimize galling depending on your application needs (See the Blog Post:  https://www.extreme-bolt.com/blog/thread-galling-what-is-it-how-to-prevent-it/).

Fasteners for CHLORIDE CORROSION
Fighting chloride corrosion is one of the most common issues that face industrial processes. From industrial process in water treatment to pulp & paper as well as seawater applications, chlorides are very common and menace to industry. This brief newsletter shares insight into which materials for fasteners work best to defend against chloride corrosion to protect your equipment.

TITANIUM: Premium Chloride Protection
Titanium fasteners offer unparalleled resistance to chloride including chloride solutions, hypochlorites, chlorates, perchlorates, sodium chlorite, and chlorine dioxide. In addition, Titanium grade 5 fasteners also offer high strength of 148ksi UTS in addition to excellent chloride resistance. The only drawback is titanium cannot be used with dry chlorides or it will rapidly corrode.

DUPLEX STEEL: Localized Corrosion
Duplex fasteners offer an economic solution for high strength chloride resistance, especially for localized corrosion such as crevice and pitting, as well as stress corrosion cracking. Available in Duplex 2205 and Super Duplex 2507 for added strength.

AL6XN: Chloride & Reasonable General Corrosion Resistance
AL6XN bolts offers a high level of chloride resistance combined with high temperature usability (1000F), as well as moderate general corrosion resistance to other chemicals.

ALLOY 20: Chloride + Good General Corrosion Resistance
Alloy 20 fasteners are a good mid-range corrosion resistant alloy. They offer decent resistance to chloride but also good resistance to other chemicals such as sulfuric acid. They are also usable to 1000˚F

Titanium is an amazing material offering strength, lightness of weight, and corrosion resistance but there are also instances that titanium should not be used. This brief newsletter covers the do’s and don’ts of titanium screws.

Do Use for Saltwater & Chloride Resistance
One of the most noteworthy uses of titanium screws is in saltwater environments.  Naval as well as industries like desalination and offshore oil rely on titanium for their unparalleled resistance to saltwater. Titanium fasteners are resistant to both rapid moving and stagnant seawater up to a mile deep – even at temperatures of up to 500°F.

Like seawater, titanium screws are also almost inert to all chloride and chlorine solutions. This is due to titanium’s ability to rapidly regenerate its protective passive layer in the presence of oxygen. Titanium fasteners are also resistant to::
•  Chlorite
•  Hypochlorite (Bleach)
•  Chlorate
•  Perchlorate
•  Chlorine dioxide

Do Use for Strength and Lightness
Titanium grade 5 offers industry impressive strength: 148 ksi UTS and 138 ksi yield.  What
makes titanium’s strength truly unique is that it is also extraordinarily light. Grade 5
fasteners are 4 times stronger than 316 stainless steel at nearly half the weight.  (Grade 2 titanium is approximately 2 times stronger.) This unparalleled strength-to-weight ratio make titanium ideal for medical, aerospace, and military applications.

Don’t Use in Acids
Titanium fasteners offer excellent corrosion resistance to salt water and chlorides but NOT strong acids. When exposed to acids like sulfuric (H2SO4), hydrochloric (HCl), their protective passive layer is attacked and can rapidly corrode in the right concentrations and temperatures.

Don’t Use in Dry Chlorine
Though titanium screws are ideal for almost all chloride and chlorine applications they cannot be used in the absence of water. Dry chlorine and chlorine gases will make them rapidly corrode and even ignite. Typically 1% moisture (at room temperature) and 1.5% (at high temperature) is sufficient for titanium to regenerate its passive layer and remain resistant.

Q: Since Monel is resistant to NaCl does that mean it can handle a strong chloride situation?

A: Monel is resistant to chlorides but, for strong chlorides your best bet is to use Titanium screws. Titanium fasteners are almost inert to all chlorine and chloride environments due to the fact that it can rapidly regenerate its protective passive layer in the presence of oxygen. However, be careful NOT to use titanium in dry chlorine gas environments unless there is at least 1-1.5% water present. Alone, titanium screws can rapidly corrode and even ignite in the presence of chlorine gas due to the fact that it has no oxygen to regenerate its passive layer.