Overview
From perspective of cleanliness grade, stainless steel tubes can be classified into AP tubes, BA tubes & EP tubes. This article will focus on the meanings of each tube category and the differences among them.
The Meanings of AP, BA & EP Stainless Steel Tubes
When we talk about tube cleanliness grade AP, BA & EP, we are referring to stainless steel seamless tubes. Stainless steel welded tubes are seldom expressed in this way, because they are either as-weld in 2B or No.1 finish, pickled finish (for industrial use) or mechanically polished (MP) to the required finish for decoration applications. MP (mechanically polished) is also applicable to stainless steel seamless tubes, but not as common. That’s why it is not listed for comparison.
AP Stainless Steel Tubes
AP is abbreviated from Annealed and Pickled. AP tubes can be the most common stainless steel seamless tubes, whether for small diameter or for larger diameter. Multiple grades, durability and affordable price render AP tubes desirable for most industrial applications, represented by boiler, superheater, and heat exchanger tubes produced per ASTM A213.
BA Stainless Steel Tube
BA stands for Bright Annealed. Unlike traditional annealing during which process stainless steel tubes become oxidized into black finish throughout, BA tubes get annealed under the protection of pure hydrogen. With this, BA stainless steel tubes are imaginably bright without color changing, uniformly bright inside and outside tube wall after annealing.
BA tubes feature smooth and bright finish, free from surface imperfections such as water spots, over-pickling which can occasionally happen to small-diameter AP tubes. For tube OD below 18mm, BA tube is advisably selected over AP tube for clean and smooth inner wall when budget is sufficient. Stainless steel BA tubes are produced per ASTM A269.
Clean BA Stainless Steel Tubes
BA tubes are generally below 0.45μm in terms of roughness. Clean BA can achieve below 0.38μm at CIVMATS. It is more than roughness. To meet cleanliness applications such as transportation of high-purity gas, extra processes like ultrasonic cleaning and packaging at clean room are necessary.
EP Stainless Steel Tubes
EP means electro polished. EP tubes feature the highest finish cleanliness grade among the three. Roughness can be measured below 0.25μm.
The uniform bright finish of EP tubes is acquired through chemical polishing. Specifically, stainless steel tubes are put into a sink filled with electrolyte solution and then get electrically charged. The charged solution will dissolve all the imperfections and remove any contamination attached on the tubes and passivate them, left EP tubes with smooth and shiny finish as well as enhanced corrosion resistance.
To produce qualified EP tubes, ISO certified (ISO 1 to ISO 9) clean room must be equipped to make sure the tubes will be packaged free from any contamination. Each tube will be purged with ultra-high purity (UHP) nitrogen, capped and double bagged in clean room. EP tubes are produced per ASTM A269 & A262 E Method & ASTM A632.
EP tubes are typically used in pharmaceutical industry, biotechnology and semiconductor industry where tube cleanliness and corrosion resistance can directly impact product functionality. For instance, any tiny impurity can interfere with semiconductor fabrication.
Differences Among AP, BA & EP Stainless Steel Tubes
From the finish, we can judge the right one among AP, BA & EP stainless steel tubes intuitively. There are still other differences as below listed.
- • Grade Options: AP > BA > EP
- • Surface Roughness (High to Low): AP < BA < EP
- • Application-Wide: AP > BA > EP
- • Price (Low to High): AP < BA < EP
Stainless Steel Tubes at CIVMATS China
Whether you are in the market for stainless steel AP tubes, BA tubes, or EP tubes, CIVMATS, will always be your best possible stainless steel tube choice from China.
Every order will be executed strictly per standard at CIVMATS. Unqualified product will be picked out from the bulk for sake of 100% quality warrantee, making sure the products you will receive live up to your expectation and trust. Welcome for your stainless steel enquiry and purchasing.
