The penstock is an intake structure that is used in hydro-electrical power plants to control the water flow through the turbines. The shape of penstock is like an enclosed pipe. Penstocks fabrication and welding should be reliable and efficient to prevent failure that could result in loss of life and property.
There are different materials from which penstock can be manufactured; but steel suits best due to its strength and flexibility that can bear pressure fluctuations during the turbine operation.
A penstock is fabricated by welding the pieces of rolled plates. If the welded joint quality of the plate is poor, then it can also cause failure of the penstock.
Penstock structure is hundreds of feet in length. The diameter and length is penstock is such a huge that even a 20-foot length has a very large weight. Due to that reason, the short sections of penstock are first fabricated in a welding shop, and the subsequent welding structure is fabricated by welding together those short sections in a field.
Welding Techniques of Penstock
Short joints of penstock are usually welded with semi-automatic or automatic welding machines in the welding shop; while infield, the sections of penstock are manually welded. In shop welding, after rolling of plates, they are tack welded into pipe courses, and then welded by automatic machines. Submerged arc welding (SMAW) is used to make the welding joints.
While installation of penstock in a tunnel, there might not be sufficient clearance between penstock and tunnel walls to back-weld field girth joints from the outside. In such cases, welding is done from the inside using an outside backing strip. Penstock sections that are embedded in the dam are placed in position on temporary structural steel supports and welded into the line.
Nondestructive Inspection of Penstock Welds
After the completion of welding, the butt-welded joints of penstock are examined using the radiography technique to detect welding defects. Welding defects may include undercutting, incomplete fusion, and cracks.
The inspection may also be performed using the X-rays technique. Equipment for radiography examination is usually portable. For field use, small compact inspection units are also available. Radioactive isotopes are contained in metal capsules, which are stored in a portable lead container.
Preheating and Post weld Heat Treatment (PWTH) of Penstock Welds
The purpose of preheating and PWTH of penstock is performed for heavier plates and for steels of high carbon content. Penstocks that are fabricated from plates with thickness greater than 1 inch are preheated before welding.
We are specialized in the fabrication and welding of penstock based on the standard methods as discussed above. Our welding process is highly customizable and can be configured to create a wide range of steel penstock of different sizes. Our penstock is created from the best carbon steel and tested from severe inspection procedures before shipment to our clients.
Our expert welding team follows recognized standards such as AWS D1.1 for the welding of the penstock. Our quality control division ensures that the penstock successfully meets the requirements of your job site.