Tube sheet corner joints and tube sheet fillet welds – such a pain; it’s impossible to figure them out or get them to work properly!

What you wrote is a bit messy..... When it comes to welding issues, one must first learn to distinguish between joints and welds (see GB 3375-1994). Joints generally include butt joints, T-joints, lap joints, corner joints, etc., and they are classified mainly based on the shape of the combined structure of the parts being welded； There are 5 types of welds, and the most common ones in our pressure-bearing equipment are butt welds and fillet welds; their definitions are shown in the figure below. Simply put, the weld area at the groove is a butt weld, while the area outside the groove is a fillet weld; see my other structural diagram. As for the welding procedure qualification, according to NB/T 47014, the evaluation of butt welds can cover fillet welded structures; therefore, it is sufficient to conduct the qualification using butt weld test pieces. According to the TSG Z6002 regulations for welder examinations, there is a qualification requirement for FG welding on tube sheet corner joint specimens. At present, this FG qualification cannot overlap with the G qualification for welding pipe butt joints; the FG qualification refers to plug-type corner joints, which are typically combination welds of butt joints and fillet welds.

For a detailed understanding, you can refer to the explanations provided by the standard committee; the older JB4708 standards and the explanations related to welder examination rules can also help you understand. I uploaded it to the forum; it can be found there.

The tube is inserted into the plate, with neither the tube nor the plate requiring beveling; this type of weld is called a tube-plate fillet weld. The joint itself is not referred to as a tube-plate corner joint, right? That’s because there is only a fillet weld of type F, no butt weld of type G.

What was said above is correct: a joint with grooves is called a fillet joint, which consists of a butt weld plus fillet welds; a joint without grooves is called a fillet weld, denoted as F. Regarding weld evaluation, it mainly assesses the performance of the weld under specified process conditions, focusing on the weld itself, regardless of the type of joint. Therefore, weld assessments are generally conducted on butt welds, not fillet welds. Unless, for those types of heat exchangers, the fillet welds at the tube sheet require a different assessment method.

A joint refers to the structural form； A weld refers to the jointed area; in everyday language, a weld actually denotes the weld zone.

TSG 21 and GB150 use either welded joints or welds in terms of inspection and testing, but neither of them refers to the welds specified in GB3375.

This post was last edited by Buddha and Orchid on 2026-6-21 at 15:59. Within the standard system for pressure equipment, one should never attempt to identify a term that is applicable in all contexts, as the members responsible for drafting these standards and regulations are not the same people in each case, and each group has its own way of describing things. Corner joints in the context of weld evaluation: It depends solely on whether a groove is used; those with grooves are evaluated as butt welds, while those without grooves are considered fillet welds ； Fillet joints in the context of welder examinations: Only fillet welds and combined welds are distinguished; a combined weld is what is known as a \"tube sheet fillet joint.\" A tube sheet fillet joint has one very distinct feature – the piece that is inserted always has a bevel, while those without a bevel are fillet welds. Additionally, the fixed-type fitting, which involves grooving on the pipe, features a butt weld. Corner joints in normal contexts: joints where the plates, or a plate and a tube (cylinder), or tubes (cylinders) are at right angles to each other along their axes. Therefore, the joint between the heat exchange tube and the tube sheet is, in a conventional context, an angled joint; however, whether it constitutes an angled joint of the tube sheet as defined in welder certification exams depends on whether bevels are provided on the tube sheet.

Standards have temporary conflicts but no permanent ones, because corrections will eventually be made. A weld is a weld, a joint is a joint, and a weld zone is a weld zone; it should not be difficult to understand the difference between them.