Apache Stainless Blog

ASTM (American Society for Materials and Testing) was developed to set standards for chemical, mechanical, physical, and electrical properties of material, as well as testing standards for materials.  ASME (American Society of Mechanical Engineers) includes ASTM standards, AWS (American Welding Society) standards and other nationally and internationally recognized standards as part of a widely adapted design specification for many structures, including pressure vessels.

Apache has substantial capabilities for mechanical and chemical finishing having supplied stainless equipment to hygienic industries for more than four decades.  Passivation, pickle passivation and electropolishing processes and associated ASME testing, and processes are 100% in-house.  
 
Passivation is the removal of excess iron or iron compounds from the surface of stainless steel by means of a chemical, typically an acid based solution. Unlike pickle passivation, no metal is removed from the surface during the process. The process has little effect on the RA values of the stainless material being passivated.

The ASTM A967 is a passivation standard that applies to the cleaning, passivation, and testing of stainless parts. 

Pickle Passivation is the immersion of the metal in a pickling bath or coating the material with pickling solution such as nitric-hydrofluoric acid. The process removes both metallic contamination and heat-treating scales. Pickle passivated stainless steel has a matte appearance. Apache’s tests have confirmed improvements up to 25% in RA readings on material that has been pickle passivated.

The ASTM A380 is a passivation standard that covers cleaning, descaling, and passivating stainless material and parts. Spec A380 may include a variety of treatments, including precleaning, chemical descaling, degreasing and more. 

Electropolishing is an electro-chemical process that removes surface material from stainless steel.  The process includes immersion of the stainless-steel component into a temperature-controlled bath of electrolytes that are charged with a DC power supply. Electrolytes used in electropolishing are concentrated sulfuric and phosphoric acid solutions.  The finish has a mirror appearance. Apache’s before and after tests have shown improvements in RA smoothness up to 50%; results vary depending on stainless material. 

The ASTM B912 specification outlines the electropolishing process for 200, 300 and 400 series alloys.  Spec B912 may include preparatory cleaning procedures, post coating procedures and rinsing protocols.  Final testing is also stated in the specification to evaluate performance of finish.

In Guide to ASTM & ASME Stainless Finishes, learn about the mechanical and chemical finishing processes to meet ASME, ASTM and other compliance requirements. 

Download Guide
 

Depending on the application, processors serving food or other hygienic industries have varying degrees of compliance requirements for custom vessels.  When working with your custom vessel manufacturing partner, it is important to identify the level of sanitary compliance in the pre-engineering discovery phase.

Apache defines three categories of sanitary design to help customers with the type of sanitary specifications for construction and fixtures to meet the vessel’s process goals.

BASE LEVEL

The base level sanitary vessel is cleaned manually. Typical construction fixtures include threaded coupling, threaded dip tubes and ANSI flanges.  Depending on the application, stock vessels may be used or modified. The material is 2B/Mill, or 304 or 316 stainless and is pickle passivated.

Customers use base-level sanitary vessels for waste tanks, hydrocarbon storage, food-grade applications, adhesives, and solvents.

MID-LEVEL

The type of sanitation is also a driver for more complexity in the design of sanitary vessels.  In the mid-level category, components are removed for cleaning or COP (clean out of place).

Mid-Level sanitary vessel designs are constructed with 304 or 316 stainless material and feature mechanical finishing and pickle passivation or nitric passivation.

Sanitary fittings are specified in a mid-level vessel from tri-clamp ferrules and tube connections to NA connects, flush mount outlet valves and sight glasses.

Customers use mid-level sanitary design vessels for material columns, solvent tanks, collection vessels, extraction, expansion chambers, mixing and dispensing.  

HIGH-LEVEL

The highest level of sanitary design vessel is automated to be cleaned-in-place (CIP). A 304 or 316 stainless material is specified for high-level sanitary vessels mechanically finished to less than 32RA (roughness average), with nitric and electropolish chemical finish.

The fixtures in this category are electropolished including tri-clamp ferrules, tube connections, NA connects, sight glasses, j-tubes, dip-tubes, and polished internal coils.

Customers using high-level sanitary vessels are involved in automated processing and manufacturing.  Applications for high-level sanitary designs include WRI tanks, R&D lab equipment, heating, and cooling vessels and nutsche filters. 

Each level of sanitary design can meet ASME UM, ASMEU, FDA, 3-A, CRN, PED, and BPE compliance requirements.

When exploring the project parameters for a custom vessel, our guide, “3 Levels of Sanitary Design Tanks and Vessels” , helps to drive conversations and specifications that will meet the vessel’s application, timing, and compliance requirements.

Apache Stainless Equipment Corporation manufactures stainless equipment for a range of hygienic industries. Apache uploads compliance engineering expertise in beverage, biotechnology, pharmaceutical, cannabinoid, food processing, and life science industries.

Categorizing levels of sanitary design is helpful to professionals new to compliance regulated industries requiring custom vessels because it bridges communications regarding standards and design requirements.

In hygienic applications, stainless equipment requires a sanitary finish which generally refers to a smooth, scratch-free, non-corrosive finish.  The fineness of the finish, which determines its performance, is measured in RA (roughness average). The infographic illustrates the RA of different types of mill, mechanical, and chemical finishes.  The smaller the RA reading in microinches (height in millionths of an inch), the smoother the finish. 

When collaborating to qualify a project, we define a Base Level Finish as a 2B/Mill, 304 or 316 stainless materials that is pickle passivated.  The welds are continuous and crack and crevice-free.  This type of finish is paired with a Base Level Sanitary Design and is cleaned manually. Apache’s standard portable vessel line are an example of the base sanitary design and finish level.

A Mid-Level Finish is also composed of 304 or 316 stainless material and involves a secondary process of mechanical polishing greater than 32RA, with final finishing to include pickle or nitric passivation. The welds are continuous, crack and crevice-free, and are also ground flush and polished smooth to a specific RA.  Sanitary fittings, mechanical polishing, additional passivation processes and a cleanable design with removable components are categorized as Mid-Level Sanitary Design features.

Providing the smoothest RA readings is an electropolished finish after a series of processes, including mechanical finishing to less than 32 RA, passivation, and nitric passivation, which are common for High-Level Finishes.  The base material is 304/316 stainless. The welds are continuous, crack and crevice-free, ground flush and polished smooth to a specific RA designation less than 32RA.  The sanitary fittings are also electropolished.  Vessels with this level of specifications are typically cleaned automatically.

The specifications, construction and finishing of a vessel is often driven by standards and compliance requirements. All three categories, qualify for ASME UM, ASME U, FDA, 3-A, CRN, PED, BPE.

There are other factors that fall in these base, mid and high-level sanitary design categories, including construction features, processing applications and time to delivery.  Download our e-book “Guide to Sanitary Design for Custom Vessels in Hygienic Industries".